AM Radio Design Log

[M. Hamed]

#1
---

Ok, now that I got some encouragement, I am going to start here. This is inspired by fitness forums where people post a training log to chart their progress and get guidance (Needless to say I no longer follow these fitness forums since I was bitten by the radio bug).

Similarly, this is a design log of me building an AM radio receiver and most of the steps I have to go through. Some of that stuff will be laughable to plenty of people here due to my extreme electronics inexperience. I am an electronics and RF newbie (I have posted about that before), and I am trying to learn.

There will be another one later for FM radio. The goal is not AM or FM radio. It's the amplifiers, oscillators, mixers, noise figures, detectors, etc etc. I have chosen AM and FM because they are guaranteed to be always there, and the goal seems to be pretty well defined. Amateur bands will come later. I only got my license about a week ago and I don't have experience operating. With amateur bands you also really need a transmitter most of the time and transmitters are still further down my list.

With respect to AM radio, I am fully aware of Ron Quan's popular book (and own it), but I promised myself I will not touch that book until I have gotten my hands dirty enough with personal experimentation. I want to commit some serious errors before I look into a ready-built project book :)

------------------------------------------------------------
First step is to understand about Mixers. I was told these are the most complicated parts of the radio and have very specific requirement. At this point I don't have any spec for the signals that will be at the mixer ports (Jeff Liebermann are you staring at me?)

So I thought I'd first build a two tone module with a variable output level then build the mixer and find the best performance the mixer can give. From this I can go backward to the Antenna and try amplifying the signal coming from the Antenna to the level established by my experiments with the Mixer.
---------------------------------------------------------------
Two Tone generator:

For the AM band build two oscillators one at 550 KHz, another at 1600KHz. Sum those two signals then using an attenuator, control the level going into the Mixer.

My choice of oscillator was arbitrary. Just pick the first oscillator design from "Experimental Methods" which happened to be a JFET Hartley oscillator. Seems like an overkill for a 2MHz oscillator but I don't care at this point. I'm sure I'll learn a thing or two.

I decided to choose L much larger than C presumably because this improves the Q. I picked a value of C around 600pF. 1. Because I found some in my junk box 2. Because I found variable caps online in the pF range which makes it easier for me to change the design to use variable caps in case I wanted to build a VFO.

@580pF + 550KHz -> L = 144uH. This was worked out to about 17 turns on an FT50-43 toroid

@595pF + 1600KHz -> L = 16uH. This was worked out to about 15 turns on an FT50-61 toroid

Still not sure whether the relatively small number of turns would hurt the Q or not.

I have a few Toroids on order from eBay.
------------------------------------------------------------

Summing amplifier:

Once the two oscillators are working (hopefully) I would like to combine them together to form something resembling the AM band. For AM I should then probably insert a filter before the mixer.

I looked into ways of combining signal and I found the concept of the Hybrid Combiner. I feel this is probably more usable at higher frequency.

I decided I should be Ok just using an OpAmp. With an OpAmp I could sum the two signals and possibly easily control the output impedance seen by the filter or mixer. I could also amplify or attenuate the signal coming from the oscillator.

I am convinced that I can use the same approach even when I start working with the FM band. I suspect that nowadays using an OpAmp to sum two signals in the 100 MHz range should be a piece of cake for modern OpAmps provided you pick the right OpAmp with good frequency response.

------------------------------------------------------------
Takeaway:

- Generate two tones using some arbitrary Hartley Oscillator
- Choices of L and C may not be appropriate. Unsure about whether 15 turns on a toroid should be good for Q and oscillation.
- Sum two signals using an OpAmp

------------------------------------------------------------

Next steps:

- Once the toroids arrive I will start building the oscillators on perfboards and check their output then I'll throw in the OpAmp and see what I get. I'll then add a filter/amplifier before the mixer.

[Jan Panteltje]

On a sunny day (Mon, 15 Jul 2013 20:20:27 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<28099ff6-a9bd-42cc...@googlegroups.com>:

>#1

I admire your step by step approach.

Remember the simplest way to _add_ 2 signals is with 2 resistors, cheap too.

As to mixer, it is _hard_ to find something that is 100% linear,
so most things will mix (will multiply, are non linear),
from a simple diode to nice little ring diode mixers, (I like those),
balanced mixers, JFETs, dual gate MOSFETS (I like those too,
RF in one gate and LO on the other, just play with gate2 bias for max non-linearity),
or a good old non-biased transistor with RF on the base and LO on the emitter... etc etc..

As to Q, LC ratio and bandwidth, it may be worth it to run that in LTspice,
and use small signal mode and sweep a couple of octaves, you may find that a bigger C may help sometimes.
Using bigger values for C also means you can hang your scope probe on the coil and tune for maximum,
while with C values if in the few pF range the probe capacitance will de-tune things, just a practical consideration.

[M. Hamed]

On Tuesday, July 16, 2013 1:06:37 AM UTC-7, Jan Panteltje wrote:

>
> I admire your step by step approach.
>
>

Thanks!

>
> Remember the simplest way to _add_ 2 signals is with 2 resistors, cheap too.
>

Two resistors to sum voltages, wow, why didn't I think of that! It seems to me for this to work I'll need to make sure the input impedance of the next stage is much higher.

> As to Q, LC ratio and bandwidth, it may be worth it to run that in LTspice,
>

Thanks for the tips on L's and C's. Now to actually figure it out using LTSpice, wouldn't I need to know the unloaded Q of the inductors for the simulation to be any useful?

[josephkk]

Oh my goodness. Are you designing a fixed frequency receiver or a
tunable receiver? Two oscillators at fixed frequencies does not give you
a tunable receiver without some serious DSP or FPGA components.

Are you designing a direct conversion receiver or a superhetrodyne
receiver?

There seems to be some serious misconceptions here.

Please read a primer on basic receiver types and the principles that they
work on.

?-)

[M. Hamed]

On Tuesday, July 16, 2013 7:22:20 PM UTC-7, josephkk wrote:
> Oh my goodness. Are you designing a fixed frequency receiver or a
> tunable receiver? Two oscillators at fixed frequencies does not give you
> a tunable receiver without some serious DSP or FPGA components.
>
> Are you designing a direct conversion receiver or a superhetrodyne
> receiver?
>
> There seems to be some serious misconceptions here.
>
> Please read a primer on basic receiver types and the principles that they
> work on.
>

Neither. The two fixed oscillators are not for the final receiver. They are just for testing purposes and experimenting with mixers and filters. The final receiver should be a superhet.

[Robert Baer]

The way i understand his approach, is that initially, those questions
are in the future of experimentation.
I see it as: step 1 use 2 ARBITRARY frequencies and try various
amplitudes, (linear) summing methods, and (nonlinear) multiplier/mixer
methods. Document results, make notes one what works and how well it
works/does not work.
Fundamental groundwork for next step.
I see absolutely NO "misconceptions here".
I see a rather rigorous investigation of a well-known technology
using scientific analysis.
The approach is admirable.

Boil no water without pot or fire.

[Phil Allison]

"Robert Bore"

>> There seems to be some serious misconceptions here.
>>
>> Please read a primer on basic receiver types and the principles that they
>> work on.
>>

> I see absolutely NO "misconceptions here".

** I see nothing else but misconceptions - too many to count.

> I see a rather rigorous investigation of a well-known technology using
> scientific analysis.

** You on drugs ??


> The approach is admirable.

** Hamed's approach is patently absurd - nothing more than the day dreams
of a bored code monkey.



... Phil

[Jan Panteltje]

On a sunny day (Tue, 16 Jul 2013 15:49:53 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<e03a80a4-66ae-43c0...@googlegroups.com>:

>On Tuesday, July 16, 2013 1:06:37 AM UTC-7, Jan Panteltje wrote:
>
>>
>> I admire your step by step approach.
>>
>>
>
>Thanks!
>
>>
>> Remember the simplest way to _add_ 2 signals is with 2 resistors, cheap too.
>>
>
>Two resistors to sum voltages, wow, why didn't I think of that! It seems to me for this to work I'll need to make sure the input
>impedance of the next stage is much higher.

Actually no,
you can drive it into a zero ohm inverting opamp input and it will still work.
Or, if that eludes you, into a 1 Ohm resistor, try it in spice.

>> As to Q, LC ratio and bandwidth, it may be worth it to run that in LTspice,
>>
>
>Thanks for the tips on L's and C's. Now to actually figure it out using LTSpice, wouldn't I need to know the unloaded Q of the
>inductors for the simulation to be any useful?

'Q' is a very vague thing, others may disagree, but what you probably really want is bandwidth.
As I was mentioning resistors, you can make your own Q with a simple parallel or series resistor,
and if you know what bandwidth you want, work out that resistor (and Q).

You can see me do that here:
http://panteltje.com/panteltje/raspberry_pi_dvb-s_transmitter/raspberry_pi_datv_transmitter_circuit_diagram_IMG_3943.JPG

Note the two 2k2 resistors, bottom right QPSK modulator, and the LC, (actually L is 184 nH, not uH).
I started with the required attenuation for the mirror frequency after the mixer,
say you mix 25 MHz with 1 GHz, you get (when carrier is suppressed in a ring modulator) 1GHz + 25 MHz +- sidebands,
and 1 GHz - 25 MHz +- sidebands.
When not filtering the 25 MHz enough, then the sidebands (in this digital setup) will extend from zero to eeeeh Ferry Much.
You want some real attenuation so the LO + 25 spectrum and LO - 25 spectrum do not overlap, as then receiver gets confused.
(so it does not work then).
So couple of MHz and at least some decent deebees at the other side is required, you start with BANDWIDTH.
From the bandwidth the Q follows, and from the LC ratio AND that Q you can get the attenuation.
I actually did try it in LT spice, although I already knew 220 pF is a good value for about 30 MHz (analog TV IF I designed in the past).
But I ran the spice for a smaller C too and that sucked, just to make sure.
The 2 2k2 SUM the signal, and in these case work into a VARIABLE impedance (parallel LC impedance is high in resonance),
and gets SHORTED at other frequencies, there is a non-linear! load from the ring diode mixer too.
And man does it work!

To get rid of the mirror I may add a Ghz or there about 25 MHz wide SAW filer, 10 for 5 dollar on ebay...

Well, maybe my way of designing is not conventional, but it always works and nothing goes phut for me,
so I am doing something right.

Should not be writing this...
LOL

PS
LTpsice is actually easy, even I could use it, easy enough for me to use to decide not to write my own,
something I sometimes do when a program's learning curve takes more time than writing my own version.
But I use it just to test small sub-circuits, never a complete setup, that would not work likely,
in the real world there are such things as parasitic capacitance and inductance, coupling between tracks (magnetic too),
track impedances, you need a lot of experience making peeseebees or special RF software (microwave) for that.
Wavelength is the keyword..
It is fun..

[Don Kuenz]

Jan Panteltje <pNaonSt...@yahoo.com> wrote:
> On a sunny day (Tue, 16 Jul 2013 15:49:53 -0700 (PDT)) it happened "M. Hamed"
> <mhdp...@gmail.com> wrote in
> <e03a80a4-66ae-43c0...@googlegroups.com>:
>
>>On Tuesday, July 16, 2013 1:06:37 AM UTC-7, Jan Panteltje wrote:
>>
>>>
>>> I admire your step by step approach.
>>>
>>>
>>
>>Thanks!
>>
>>>
>>> Remember the simplest way to _add_ 2 signals is with 2 resistors, cheap too.
>>>
>>
>>Two resistors to sum voltages, wow, why didn't I think of that! It seems to me
for this to work I'll need to make sure the input
>>impedance of the next stage is much higher.
>
> Actually no,
> you can drive it into a zero ohm inverting opamp input and it will still work.
> Or, if that eludes you, into a 1 Ohm resistor, try it in spice.

What does the "zero ohm" part of "zero ohm inverting opamp" mean?

Getting back to resistor mixers, here's something unintuitive (at least
for me). One of my circuits uses two 10K resistors as a stereo to mono
mixer to drive the 600 ohm input of a Valcom paging/music control unit.
Theoretically one (ie me) expects the exact opposite. That is, for 600
ohms to drive 10K.

--
Don Kuenz

[Jan Panteltje]

On a sunny day (Wed, 17 Jul 2013 10:00:08 -0500) it happened Don Kuenz

<gar...@crcomp.net> wrote in <2013...@crcomp.net>:

>Jan Panteltje <pNaonSt...@yahoo.com> wrote:
>> On a sunny day (Tue, 16 Jul 2013 15:49:53 -0700 (PDT)) it happened "M. Hamed"
>> <mhdp...@gmail.com> wrote in
>> <e03a80a4-66ae-43c0...@googlegroups.com>:
>>
>>>On Tuesday, July 16, 2013 1:06:37 AM UTC-7, Jan Panteltje wrote:
>>>
>>>>
>>>> I admire your step by step approach.
>>>>
>>>>
>>>
>>>Thanks!
>>>
>>>>
>>>> Remember the simplest way to _add_ 2 signals is with 2 resistors, cheap too.
>>>>
>>>
>>>Two resistors to sum voltages, wow, why didn't I think of that! It seems to me
> for this to work I'll need to make sure the input
>>>impedance of the next stage is much higher.
>>
>> Actually no,
>> you can drive it into a zero ohm inverting opamp input and it will still work.
>> Or, if that eludes you, into a 1 Ohm resistor, try it in spice.
>
>What does the "zero ohm" part of "zero ohm inverting opamp" mean?

It means that whatever current you send into it (the input), the output will feedback
so the input stays at the same level, so no voltage will be generated at the input:

----- R1 ----
| |
- in |
opamp out --
|- + in

say you feed 1 mA into the - input in this example, then the output will go negative until
the - input is at ground level again, so Uout / R1 is -1 mA.
This is for an ideal opamp of course with infinite gain and input impedance.

>Getting back to resistor mixers,

Beware, when audio people say 'mixer' they actually mean ADDITION, a linear process,
in fact audio people try normally to stay clear of non-linear processes.

When RF people talk about mixers they are talking about multiplication of signals, basically
a non-linear process.

> here's something unintuitive (at least
>for me). One of my circuits uses two 10K resistors as a stereo to mono
>mixer to drive the 600 ohm input of a Valcom paging/music control unit.
>Theoretically one (ie me) expects the exact opposite. That is, for 600
>ohms to drive 10K.

Audio people often have no clue, do not terminate cables with the correct impedance,
maybe based on the idea that at these low frequencies it is not needed, but that is their idea.
I rather talk to a video man about signals than to an audio one.
And do not get me wrong, I worked in film audio for many years.
And I learned a lot there too from them.

[Glenn]

Hi Don

The inverting opamp is playing I->V converter. The inverting opamp will
via the the negative feedback maintain the inverting input at zero volt
(ideally).

/Glenn

[josephkk]

On Tue, 16 Jul 2013 20:49:44 -0700, M. Hamed wrote:


> Neither. The two fixed oscillators are not for the final receiver. They
> are just for testing purposes and experimenting with mixers and filters.
> The final receiver should be a superhet.

Thank you. I was a bit worried there. Design some Hartleys, some
Colpitts, and a couple other types then. Each one has different valuable
properties.

?-)

[Don Kuenz]

OK. That's just a plain inverting opamp to me.

>>Getting back to resistor mixers,
>
> Beware, when audio people say 'mixer' they actually mean ADDITION, a linear process,
> in fact audio people try normally to stay clear of non-linear processes.
>
> When RF people talk about mixers they are talking about multiplication of signals, basically
> a non-linear process.

Unless one forces it to become a linear process by using Fourier
transforms to move things to the frequency domain. ;)

At any rate, you busted me fair and square. What on earth made me think
of audio mixers in a radio thread?

> Audio people often have no clue, do not terminate cables with the correct impedance,
> maybe based on the idea that at these low frequencies it is not needed, but that is their idea.

"Let he who is without sin cast the first stone." LOL.

--
Don Kuenz

[Jan Panteltje]

On a sunny day (Wed, 17 Jul 2013 22:53:38 -0500) it happened Don Kuenz

It shows the '-' input is zero ohm, behaves as a virtual ground.

>>>Getting back to resistor mixers,
>>
>> Beware, when audio people say 'mixer' they actually mean ADDITION, a linear process,
>> in fact audio people try normally to stay clear of non-linear processes.
>>
>> When RF people talk about mixers they are talking about multiplication of signals, basically
>> a non-linear process.
>
>Unless one forces it to become a linear process by using Fourier
>transforms to move things to the frequency domain. ;)

Yea, trying some escapist moves?

>At any rate, you busted me fair and square. What on earth made me think
>of audio mixers in a radio thread?
>
>> Audio people often have no clue, do not terminate cables with the correct impedance,
>> maybe based on the idea that at these low frequencies it is not needed, but that is their idea.
>
>"Let he who is without sin cast the first stone." LOL.

I should have added (to 'usuallly do not terminate with the correct impedance') that that '600 Ohm'
input of yours is probably not that, but a lot higher (could be diff opamp with 2 10 k resistors).
It is easy to check, scope the signal before and after your 10K resistors,
(600 / (10000 + 600) ) * Vin (I like those ')' ), anyways I am not betting but think it will be more
volts at that imput than that predicts.

[M. Hamed]

#2
---

Toroids arrived. First target is the 550KHz oscillator using the first Hartley oscillator shown in Exp. Methods. Using a JFET, diode, 1MOhm resistor, L, and C.

My toroid calculation were reasonably accurate verified using an LRC meter. About 16 turns of #22 wire. The tap is taken after 4 turns.

Laid out everything on a perf board. Soldered everything to the board. The book recommends taking the tap about 20% from ground. I realized the way I soldered thing was not exactly this. The tap was taken about 12 turns from ground. After a little soldering mishap with a capacitor, I connected power, an oscilloscope, and voila! Output came out at 578 KHz. Not bad at all given that all components are fixed. It also seems the tap location didn't matter.

Off to the second oscillator!

[josephkk]

About 5 percent off in frequency, looks like parts tolerances. How is
the wave shape for being clean? Can you digitize it and do a FFT?

?-)

[M. Hamed]

#3
---
Wired up the second oscillator. The inductor value should come to about 16 uH. Tried 5 turns on FT50-43 with a center tap but this didn't work. My guess here is that for a good Q, the number of turns must be higher.

Switched to FT50-61 with 15 turns, and a tap at turn 4 and the second oscillator started working. I got about 1.5MHz, 0.1 MHz off the target but acceptable.

On this one I had the smaller number of turns closer to ground. At first I thought it wouldn't matter but it seems if it's done this way the output at the top of the tank is larger. Since I didn't want the second oscillator output to be much higher than the first, I reversed the toroid to have the small number of turns closer to the top.

I then connected the two oscillators to the same power and ground points, and connected their outputs to two 10K resistors (per Jan's suggestion) and took the sum from the mid point.

I know I should probably isolate the powers and grounds of both oscillators from each other. Probably similar to when you connect Analog and Digital circuits and have their grounds connected at only one point. I should probably add some capacitor bypassing to power. At this frequency I'm not sure if this is really needed and how much improvement I can get. Further experimentation is needed.

The circuit is here :
https://www.dropbox.com/s/gt4pf8kw4hfqse8/2%20Hartley%20Oscillators%20550K%201600K.asc

Only difference from my actual circuit is that I'm using MPF102 JFET, and I'm too lazy to add the model for it.
------------------------------------------------
Some of the observation with this type of oscillator:

- I do not fully understand the function of the diode and the small 68pF cap connected between the diode and the tank. Exp.Methods book says its purpose is to have the gate at an average negative voltage, but it's not clicking.
- At about 4V the 550KHz starts oscillating. At this point the diode seems fixed at about 0 V and the power supply shows it's drawing milliamps of current. As I increase my supply voltage, the signal at the diode starts increasing and looking more sinusoidal while the sine wave center point starts moving more negative. This is not clicking yet and still mysterious.
- Connecting my VC3165 cheap Chinese frequency counter to the output of any of the two oscillator shifts frequency by a noticeable amount. For example the 1.5 MHz becomes 1.3 MHz. The spec claims a 1MOhm input impedance. Connecting my scope which also has 1MOhm input impedance doesn't do that. This is also mysterious to me. I'm going to try connecting the Scope probe to the frequency counter and see if that works. Maybe the probe gives better isolation from the counter's input circuit.

[M. Hamed]

On Saturday, July 20, 2013 8:30:30 AM UTC-7, josephkk wrote:
> About 5 percent off in frequency, looks like parts tolerances. How is
> the wave shape for being clean? Can you digitize it and do a FFT?
>

The wave looks very clean and nice. It would be nice if I had a spectrum analyzer to look at the spectral purity :)

At the moment I have no way to digitize it and FFT it. I may be able to bring the circuit to work and do that. I have access to a high end scope there.

[M. Hamed]

On Saturday, July 20, 2013 9:00:04 AM UTC-7, M. Hamed wrote:
> - At about 4V the 550KHz starts oscillating. At this point the diode seems fixed at about 0 V and the power supply shows it's drawing milliamps of current. As I increase my supply voltage, the signal at the diode starts increasing and looking more sinusoidal while the sine wave center point starts moving more negative. This is not clicking yet and still mysterious.
>

I forgot to mention that as this happens, the current drawn from the supply goes less and less as I increase the voltage. A bit counter-intuitive.

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 09:00:04 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<d54e66cf-6539-46b4...@googlegroups.com>:

>#3
>---
>Wired up the second oscillator. The inductor value should come to about 16 =
>uH. Tried 5 turns on FT50-43 with a center tap but this didn't work. My gue=

>ss here is that for a good Q, the number of turns must be higher.
>

>Switched to FT50-61 with 15 turns, and a tap at turn 4 and the second oscil=
>lator started working. I got about 1.5MHz, 0.1 MHz off the target but accep=
>table.
>
>On this one I had the smaller number of turns closer to ground. At first I =
>thought it wouldn't matter but it seems if it's done this way the output at=
> the top of the tank is larger. Since I didn't want the second oscillator o=
>utput to be much higher than the first, I reversed the toroid to have the s=

>mall number of turns closer to the top.
>

>I then connected the two oscillators to the same power and ground points, a=
>nd connected their outputs to two 10K resistors (per Jan's suggestion) and =

>took the sum from the mid point.
>

>I know I should probably isolate the powers and grounds of both oscillators=
> from each other. Probably similar to when you connect Analog and Digital c=
>ircuits and have their grounds connected at only one point. I should probab=
>ly add some capacitor bypassing to power. At this frequency I'm not sure if=
> this is really needed and how much improvement I can get. Further experime=

>ntation is needed.
>
>The circuit is here :

>https://www.dropbox.com/s/gt4pf8kw4hfqse8/2%20Hartley%20Oscillators%20550K%=
>201600K.asc
>
>Only difference from my actual circuit is that I'm using MPF102 JFET, and I=

>'m too lazy to add the model for it.

Those oscillators can be simplified:

+
|----------
| |
|--- d === C3
--------------->| |
| | |-- s ///
L === C1 |
| |------------|
/// === [ ] R1
| C2 |
/// ///

The 'L' provides the grounding of the gate for DC.
The ratio of C2 to C1 is the 'gain', normally I use C2 = 2 * C1
There is no tap needed on the L, and it requires fewer components.

For frequency calculation C1 and C2 are in series.
You do not need R5 (10k to ground) in your circuit either,
the output impedance is about R3 and R4 in parallel.

Decoupling is always required, voltage sources are never ideal, batteries age,
other circuits may be affected by the ripple you create, and vice versa, etc.

>------------------------------------------------
>Some of the observation with this type of oscillator:
>

>- I do not fully understand the function of the diode and the small 68pF ca=
>p connected between the diode and the tank. Exp.Methods book says its purpo=
>se is to have the gate at an average negative voltage, but it's not clickin=

Because it is a strange circuit, in the above example R1 takes care of auto-bias
(source will be positive relative to the gate).

In the above circuit you can, within reason, connect almost any inductor and it will oscillate.
I have used it with 220 pF and 100 pF for C2 and C1 from kHz to many MHz.




.
>- At about 4V the 550KHz starts oscillating. At this point the diode seems =
>fixed at about 0 V and the power supply shows it's drawing milliamps of cur=
>rent. As I increase my supply voltage, the signal at the diode starts incre=
>asing and looking more sinusoidal while the sine wave center point starts m=

>oving more negative. This is not clicking yet and still mysterious.

>- Connecting my VC3165 cheap Chinese frequency counter to the output of any=
> of the two oscillator shifts frequency by a noticeable amount. For example=

> the 1.5 MHz becomes 1.3 MHz. The spec claims a 1MOhm input impedance.

Input capacitance of FET, and also diode capacitance, depends on applied voltage (look up varicap).
So making the anode of the diode negative should decrease capacitance, and increase frequency.
Your Chinese meter (good you have one with a counter) probably has a lot of input capacitance,
this will lower the frequency if in a way parallel to the tuned circuit,
note your hands capacitance to the test leads too, and you to ground, in series.
It is important to notice that if you take signal from the L, then it will also swing _negative_,
that may matter if you connect it to a next stage, that could need a DC blocking capacitor.

[Tauno Voipio]

The diode at the gate (or the gate-channel diode
in a JFET) rectifies your oscillation signal amplitude
and charges the series capacitor so that the gate will
be negative. The larger the amplitude is, the more
negative the gate gets, and the drain current gets smaller.
This is the AGC which keeps the signal reasonably clean.

The trick is from the tube era. A grid-dip meter
functions by measuring the grid/gate voltage by
measuring the current in the grid resistor.

--

Tauno Voipio

[M. Hamed]

On Saturday, July 20, 2013 9:32:25 AM UTC-7, Jan Panteltje wrote:

<Snip>

So you're essentially suggesting to convert to a Colpitts. I have built Colpitts oscillators before and they seem easier to understand. I thought I'd take a shot at this strange Hartley and the use of tapped inductors.

My use of R5 was to test the effect of an external load to ground taken from the summation point. I wanted to see how low my load resistance can go.

> Your Chinese meter (good you have one with a counter) probably has a lot of input capacitance,
> this will lower the frequency if in a way parallel to the tuned circuit,
> note your hands capacitance to the test leads too, and you to ground, in series.

Couldn't find anything in the electrical spec related to input capacitance. It seems they don't specify it.

> It is important to notice that if you take signal from the L, then it will also swing _negative_,
> that may matter if you connect it to a next stage, that could need a DC blocking capacitor.

Could you explain a bit more why? According to the book, L is at DC ground hence the average will always be zero.

[M. Hamed]

Now I'm going crazy. My multimeter connected to the tank shows 100mV in the AC setting when my scope is showing 9V p-p. I thought the Ac setting measures RMS!!

[josephkk]

On Sat, 20 Jul 2013 09:00:04 -0700, M. Hamed wrote:


> - I do not fully understand the function of the diode and the small 68pF
> cap connected between the diode and the tank. Exp.Methods book says its
> purpose is to have the gate at an average negative voltage, but it's not
> clicking. - At about 4V the 550KHz starts oscillating. At this point the
> diode seems fixed at about 0 V and the power supply shows it's drawing
> milliamps of current. As I increase my supply voltage, the signal at the
> diode starts increasing and looking more sinusoidal while the sine wave
> center point starts moving more negative. This is not clicking yet and
> still mysterious. - Connecting my VC3165 cheap Chinese frequency counter
> to the output of any of the two oscillator shifts frequency by a
> noticeable amount. For example the 1.5 MHz becomes 1.3 MHz. The spec
> claims a 1MOhm input impedance. Connecting my scope which also has 1MOhm
> input impedance doesn't do that. This is also mysterious to me. I'm
> going to try connecting the Scope probe to the frequency counter and see
> if that works. Maybe the probe gives better isolation from the counter's
> input circuit.

When the circuit is operating properly it is desirable to keep the gate
from going positive WRT the source as forward biasing the gate source
junction is very bad news for circuit linearity and JFET operation. The
cap charges up against the diode to accomplish this.

[Tauno Voipio]

Jan, that is a Colpitts. Please do not leave the gate capacitor
and resistor out. They provide the amplitude control, see
my previous mail.

--

Tauno Voipio

[Tauno Voipio]

On 20.7.13 8:25 , M. Hamed wrote:
> Now I'm going crazy. My multimeter connected to the tank shows 100mV in the AC setting when my scope is showing 9V p-p. I thought the Ac setting measures RMS!!
>

The multimeter AC measurement is not reliable
on these frequencies, the calibration is for
the line (50 / 60 Hz).

--

-Tauno

[M. Hamed]

On Saturday, July 20, 2013 9:33:20 AM UTC-7, Tauno Voipio wrote:
> The diode at the gate (or the gate-channel diode
> in a JFET) rectifies your oscillation signal amplitude
> and charges the series capacitor so that the gate will
> be negative. The larger the amplitude is, the more
> negative the gate gets, and the drain current gets smaller.
> This is the AGC which keeps the signal reasonably clean.
>

This sounds intuitive but I noticed things are not so linear.

I used two probes on my scope to subtract source from gate voltage (VGS). There are 3 phases of operation:

- Supply is less than about 2.9V. In this case there is no oscillation. Supply is drawing 20 mA
- Supply is from about 2.9-3.9, oscillation starts and as you increase/decrease supply voltage, VGS will go more/less negative. Supply current also goes from 20mA to almost zero very rapidly. You see there is a very small window where this happens. Also there is some kind of hysteresis going so the tripping points will change depending on whether you go up or down.
- As supply goes higher than about 3.9, current almost vanishes, and the change in the negativity of VGS changes very little as you increase your supply.

This reminds me of CMOS inverter action.

The circuit is much more complex than I thought and very ecucational.

[M. Hamed]

On Saturday, July 20, 2013 11:14:29 AM UTC-7, Fred Abse wrote:

> What frequency. What multimeter? You're lucky if you have a meter that
>
> covers more than a few kHz.
>
>
>
> My (expensive) Fluke 87V only goes to 20kHz on *some* ranges. On others
>
> it's 5kHz.
>
>
>
> My even more expensive HP bench multimeters likewise.
>
>
>
> --
>
> "For a successful technology, reality must take precedence
>
> over public relations, for nature cannot be fooled."
>
> (Richard Feynman)

Yes. It was a dumb thing to expect :) What was I thinking?!!

[Phil Hobbs]

Something like an HP3400A, HP3403A, or Boonton 93A can easily do that.
All pretty cheap on eBay if you're patient. (I just got a 93A in
excellent shape for $120 including shipping.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 20:53:24 +0300) it happened Tauno Voipio
<tauno....@notused.fi.invalid> wrote in <kseif4$5vu$1...@dont-email.me>:

>> Those oscillators can be simplified:
>>
>> +
>> |----------
>> | |
>> |--- d === C3
>> --------------->| |
>> | | |-- s ///
>> L === C1 |
>> | |------------|
>> /// === [ ] R1
>> | C2 |
>> /// ///
>>
>> The 'L' provides the grounding of the gate for DC.
>> The ratio of C2 to C1 is the 'gain', normally I use C2 = 2 * C1
>> There is no tap needed on the L, and it requires fewer components.
>>
>> For frequency calculation C1 and C2 are in series.
>> You do not need R5 (10k to ground) in your circuit either,
>> the output impedance is about R3 and R4 in parallel.
>>
>> Decoupling is always required, voltage sources are never ideal, batteries age,
>> other circuits may be affected by the ripple you create, and vice versa, etc.
>
>
>Jan, that is a Colpitts.

Is it really American to give every freaking circuit a name?
I do not even remember those names.

An oscillator is basically an amplifier with feedback so big and a phase so that the thing oscillates.
To give every version of amplifier with feedback > 1 a name is insane.
There are an almost infinite number of ways to make oscillators,
some wanted, some unwanted (parasitic).

>Please do not leave the gate capacitor
>and resistor out.

WTF is it to you?
I provide a better, simpler, cheaper circuit, do you REALLY think the amplitude of this one CHANGES?
For WHAT?

>They provide the amplitude control, see
>my previous mail.

If you want amplitude control add a potmeter in the output, and in my case take the signal from the source.
;-)

[Tim Wescott]

On Sat, 20 Jul 2013 10:25:47 -0700, M. Hamed wrote:

If you want to poke around an RF circuit and take measurements of the
voltages therein, you want an RF voltage probe.

It's really only necessary if your oscilloscope bandwidth is lower than
the voltages in your circuit.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 10:12:25 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<fcc1fc0a-9689-4e88...@googlegroups.com>:

>On Saturday, July 20, 2013 9:32:25 AM UTC-7, Jan Panteltje wrote:
>
><Snip>
>
>So you're essentially suggesting to convert to a Colpitts. I have built Colpitts oscillators before and they seem easier to
>understand. I thought I'd take a shot at this strange Hartley and the use of tapped inductors.

I try to avoid tapped inductors, as well as tapped capacitor, and come to think of it tapped resistors.
See my reply to Voltpro or whatever for names of amplifiers with feedback > 1.

>My use of R5 was to test the effect of an external load to ground taken from the summation point. I wanted to see how low my
>load resistance can go.

Zero, as I explained before.

>> Your Chinese meter (good you have one with a counter) probably has a lot of input capacitance,
>> this will lower the frequency if in a way parallel to the tuned circuit,
>> note your hands capacitance to the test leads too, and you to ground, in series.
>
>Couldn't find anything in the electrical spec related to input capacitance. It seems they don't specify it.

Measure it?

>> It is important to notice that if you take signal from the L, then it will also swing _negative_,
>> that may matter if you connect it to a next stage, that could need a DC blocking capacitor.
>
>Could you explain a bit more why? According to the book, L is at DC ground hence the average will always be zero.

say the amplitude is 10Vpp, that would be 5 V below zero, and awfully cold.
And it is not always a good idea to grab from L, ads that loads it (Q that was so precious to you),
in my example take signal from source,

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 10:25:47 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<921bb92a-860a-46b6...@googlegroups.com>:

>Now I'm going crazy. My multimeter connected to the tank shows 100mV in the AC setting when my scope is showing 9V p-p. I
>thought the Ac setting measures RMS!!

Does you multimeter go to 1 MHz? most hardly to 100kHz.

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 12:42:37 -0700) it happened Fred Abse
<excret...@invalid.invalid> wrote in
<pan.2013.07.20....@invalid.invalid>:

>On Sat, 20 Jul 2013 19:31:13 +0000, Jan Panteltje wrote:
>
>> Is it really American to give every freaking circuit a name? I do not even
>> remember those names.
>

>Americans, Brits, and (I believe) Australians, Germans, and Frenchmen
>honor designers by naming their designs after them. Even your idols, the
>Soviets did.
>
>I'm sure I could name some Nederlanders, too, given time.

A lot of time,
I would not call any amplifier with feedback > 1 an 'invention'.
I once called a circuit he designed after my boss,
but after a while he told me not do do that.

With these things and inventions: Edison invented the light bulb,
but IIRC an Englishman was there first (Edison lost the patent),
and a while back I was surprised to read a German invented the computer,
etc etc...
National pride, egos, money, it is all in the game.
I agree like with naming stars XYZ1232132 from some catalog,
naming circuits with some alpha numeric would make it more difficult
perhaps, but why bother, we can always show the diagram.

Here are 2 other oscillators that may make your head spin:
http://panteltje.com/pub/5_dollar_LNB_PCB_IMG_3582.GIF

Do you see those 2 round white ceramic disks?
That is what I happen to be playing with these days.

[M. Hamed]

> >On Saturday, July 20, 2013 9:32:25 AM UTC-7, Jan Panteltje wrote:
>
> >My use of R5 was to test the effect of an external load to ground taken from the summation point. I wanted to see how low my
>
> >load resistance can go.
>
> Zero, as I explained before.
>

Ok, now it's starting to sink in! Thanks.

[John S]

On 7/20/2013 2:42 PM, Fred Abse wrote:
> On Sat, 20 Jul 2013 19:31:13 +0000, Jan Panteltje wrote:
>

>> Is it really American to give every freaking circuit a name? I do not even
>> remember those names.
>

> Americans, Brits, and (I believe) Australians, Germans, and Frenchmen
> honor designers by naming their designs after them. Even your idols, the
> Soviets did.
>
> I'm sure I could name some Nederlanders, too, given time.
>

It is frequently convenient to refer to standard circuits by name to
assist communication between discussers ;-)

[John S]

On 7/20/2013 12:12 PM, M. Hamed wrote:
> On Saturday, July 20, 2013 9:32:25 AM UTC-7, Jan Panteltje wrote:
>
> <Snip>
>
> So you're essentially suggesting to convert to a Colpitts. I have
> built Colpitts oscillators before and they seem easier to understand.
> I thought I'd take a shot at this strange Hartley and the use of
> tapped inductors.

The Hartley can be constructed using two inductors rather than one that
is tapped. In my opinion, that makes it sort of a Colpitts anyway. I
don't like tapped inductors because it is harder to change for
experiments. YMMV.

While I'm thinking about it, I had some problems getting a Colpitts to
start and run properly. I learned that my ceramic caps had high (for
ceramic) dissipation factors (low Q). Replacing them with NP0 cured the
problem. You may not run in to this problem, but it might be worthwhile
to remember.

You're doing great. Keep up the good work.

Cheers,
JohnS

[John S]

On 7/20/2013 9:02 PM, John S wrote:
> On 7/20/2013 12:12 PM, M. Hamed wrote:
>> On Saturday, July 20, 2013 9:32:25 AM UTC-7, Jan Panteltje wrote:
>>
>> <Snip>
>>
>> So you're essentially suggesting to convert to a Colpitts. I have
>> built Colpitts oscillators before and they seem easier to understand.
>> I thought I'd take a shot at this strange Hartley and the use of
>> tapped inductors.
>
> The Hartley can be constructed using two inductors rather than one that
> is tapped. In my opinion, that makes it sort of a Colpitts anyway. I
> don't like tapped inductors because it is harder to change for
> experiments. YMMV.

Yow! I just looked at your LTSpice thing. Your simulation is actually
using 4 inductors, not 2. The reason is that you do not provide coupling
between the tapped parts.

Just FYI.

JohnS

[Glenn]

On 20/07/13 21.31, Jan Panteltje wrote:
> On a sunny day (Sat, 20 Jul 2013 20:53:24 +0300) it happened Tauno Voipio
> <tauno....@notused.fi.invalid> wrote in<kseif4$5vu$1...@dont-email.me>:

...

>> Jan, that is a Colpitts.
>
> Is it really American to give every freaking circuit a name?
> I do not even remember those names.

...

Jan - then you do not know the Vacker oscillator either ;-)

E.g. Why do engines have names V8, Stirling Engine, Jet Engine and so on.

-

My presumption is that all variable LC oscillators ought to be using
Vacker design to correctly maintain oscillation combined with low
feedback and amplitude - over a small - or especially wide frequency
variation.

With all the electronic made in the last 30 years, why has no one found
this design (again)? Why has no one been educated about this oscillator?


The Vackar VFO oscillator:
http://www.qsl.net/va3diw/vackar.html
Quote: "...
Jiri Vackar [Jiří Vackář] invented his VFO oscillator during late 40s.
It is probably the most stable VFO oscillator known. Thanks George!
...
The frequency tuning range is above 2.5, not observable in any other
type of oscillator. The Coupling ratio is fixed; typical range is 1:4 up
to 1:9.
[]
The tuning is provided independently of coupling. Transistor's
parametric variables are isolated from the resonator. The transistor
input is not overloaded as Clapp or other circuits.
...
The stability is close to XO.
...
Ordinary oscillator has poor tuning range, the output voltage swing is
unstable, and the frequency stability is poor as well. The industry
tries hard to make its sale pitch, to replace single oscillator with 50
ICs, digital dividers, approximation registers, thermostats, and other
junk. Now what?
...
The best regulator of all times is maybe the LM723. [really :-)]
...
The VFO is better solution than the AD9850,AD9891 DDS - direct digital
synthesizer chip.
...
Do you want to spend time calling around and dealing with ten weeks lead
time? An old cap from an old TV tuner can help to solve your problem.
The treasures are around you.
..."

Scanning of original paper:
http://web.archive.org/web/20120219062848/n1ekv.org/Oscillators/Vackar_wholepaper.pdf
http://n1ekv.org/Oscillators/Vackar_wholepaper.pdf

http://n1ekv.org/Oscillators/2003%20MUD%20resources.htm

-

A regenerative receiver ought to be easier to tune with Vacker design.
Why has anyone not thought of that - assuming no one did - please
correct me if I am wrong.

Glenn

[Glenn]

On 20/07/13 22.10, Jan Panteltje wrote:
...

> Here are 2 other oscillators that may make your head spin:
> http://panteltje.com/pub/5_dollar_LNB_PCB_IMG_3582.GIF
>
> Do you see those 2 round white ceramic disks?
> That is what I happen to be playing with these days.

White Hockey puck oscillators...

[erichp...@hotmail.com]

On Sunday, 21 July 2013 08:05:02 UTC+1, Glenn wrote:
> > Do you see those 2 round white ceramic disks?

> White Hockey puck oscillators...

Named after their inventor Dr White-Hockey? ;)

[Glenn]

On 21/07/13 09.00, Glenn wrote:
> On 20/07/13 21.31, Jan Panteltje wrote:
>> On a sunny day (Sat, 20 Jul 2013 20:53:24 +0300) it happened Tauno Voipio
>> <tauno....@notused.fi.invalid> wrote in<kseif4$5vu$1...@dont-email.me>:

> ....

>>> Jan, that is a Colpitts.
>>
>> Is it really American to give every freaking circuit a name?
>> I do not even remember those names.

> ....

>
> Jan - then you do not know the Vacker oscillator either ;-)
>
> E.g. Why do engines have names V8, Stirling Engine, Jet Engine and so on.
>
> -
>
> My presumption is that all variable LC oscillators ought to be using
> Vacker design to correctly maintain oscillation combined with low
> feedback and amplitude - over a small - or especially wide frequency
> variation.
>
> With all the electronic made in the last 30 years, why has no one found
> this design (again)? Why has no one been educated about this oscillator?
>
>
> The Vackar VFO oscillator:
> http://www.qsl.net/va3diw/vackar.html
> Quote: "...
> Jiri Vackar [Jiří Vackář] invented his VFO oscillator during late 40s.
> It is probably the most stable VFO oscillator known. Thanks George!

> ....

> The frequency tuning range is above 2.5, not observable in any other
> type of oscillator. The Coupling ratio is fixed; typical range is 1:4 up
> to 1:9.
> []
> The tuning is provided independently of coupling. Transistor's
> parametric variables are isolated from the resonator. The transistor
> input is not overloaded as Clapp or other circuits.

> ....

> The stability is close to XO.

> ....

> Ordinary oscillator has poor tuning range, the output voltage swing is
> unstable, and the frequency stability is poor as well. The industry
> tries hard to make its sale pitch, to replace single oscillator with 50
> ICs, digital dividers, approximation registers, thermostats, and other
> junk. Now what?

> ....

> The best regulator of all times is maybe the LM723. [really :-)]

> ....

> The VFO is better solution than the AD9850,AD9891 DDS - direct digital
> synthesizer chip.

> ....

> Do you want to spend time calling around and dealing with ten weeks lead
> time? An old cap from an old TV tuner can help to solve your problem.
> The treasures are around you.

> ...."

>
> Scanning of original paper:
> http://web.archive.org/web/20120219062848/n1ekv.org/Oscillators/Vackar_wholepaper.pdf
>
> http://n1ekv.org/Oscillators/Vackar_wholepaper.pdf
>
> http://n1ekv.org/Oscillators/2003%20MUD%20resources.htm
>
> -
>
> A regenerative receiver ought to be easier to tune with Vacker design.
> Why has anyone not thought of that - assuming no one did - please
> correct me if I am wrong.
>
> Glenn

http://en.wikipedia.org/wiki/Vack%C3%A1%C5%99_oscillator
Quote: "...
Specifically, Vackář found that forward transconductance varied as ω3
for the Clapp oscillator, as 1/ω for the Seiler oscillator, and as ω/Q
for his design, where the Q factor of the coil (L1) increases with ω.
..."

/Glenn

[Jan Panteltje]

On a sunny day (Sun, 21 Jul 2013 09:05:02 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51eb881e$0$300$1472...@news.sunsite.dk>:

Right, the fun is the 'pucks'(been a while since I played hockey)
are not really mechanicaly or electrically ? connected to anything.
They are EM coupled however to 2 nearby mircro strips,
and one oscillates at 9.75 GHz (the big one), and the other at 10.6 GHz.
http://en.wikipedia.org/wiki/Dielectric_resonator

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 14:18:42 -0700) it happened Fred Abse
<excret...@invalid.invalid> wrote in
<pan.2013.07.20....@invalid.invalid>:

>On Sat, 20 Jul 2013 20:10:53 +0000, Jan Panteltje wrote:
>
>> Do you see those 2 round white ceramic disks? That is what I happen to be
>> playing with these days.
>

>Yes, I see them. Tell me more.

See my reply to Glenn.
or
http://en.wikipedia.org/wiki/Dielectric_resonator

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 20:42:56 -0500) it happened John S
<Sop...@invalid.org> wrote in <ksfdvm$4kc$1...@dont-email.me>:

Yes good point.
I guess I am no discus (sers).
https://en.wikipedia.org/wiki/Discus_throw

Actually, apart from all the fun,
lately the following (deep) thought pooped (eeeh Freudian? [1]), should be popped LOL),
up in my mind:
There are those who read a book and get the story.
There are those who spell it word by word and argue about the words, those are the pundits of today.
And there are those who write the stories,
and there are those who live the stories.

[1]
Maybe not 'o' is next to 'p'.

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 21:02:16 -0500) it happened John S
<Sop...@invalid.org> wrote in <ksff3v$c5b$1...@dont-email.me>:

Right, I had that problem several times,
perhaps ceramic caps dissipate away energy by mechanical vibration.

I often write 'poly' next to tuning caps,
in one of those voltage converters the ceramic caps actually got hot.
Was way below their specified operating voltage.

[Jan Panteltje]

On a sunny day (Sun, 21 Jul 2013 09:00:23 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51eb8707$0$300$1472...@news.sunsite.dk>:

>On 20/07/13 21.31, Jan Panteltje wrote:
>> On a sunny day (Sat, 20 Jul 2013 20:53:24 +0300) it happened Tauno Voipio
>> <tauno....@notused.fi.invalid> wrote in<kseif4$5vu$1...@dont-email.me>:
>...
>>> Jan, that is a Colpitts.
>>
>> Is it really American to give every freaking circuit a name?
>> I do not even remember those names.
>...
>
>Jan - then you do not know the Vacker oscillator either ;-)

Right, did not see that one before.
I have used that circuit I drew for VCO at 1.5 MHz, and it is really really stable (wit hteh right caps).
I guess stable enough for SSB.

Of course the 1.5M was added to some multiplied xtal to listen to the 21 MHz band.
It was sure more stable than my Trio tube short wave receiver tha tI needed to
keep the hands on the VFO to keep picth with SSB...

>
>E.g. Why do engines have names V8, Stirling Engine, Jet Engine and so on.

Yes, to a point, we call this thing 'oscillator' remember,
do you know how many types of jet engines there are?
Maybe not as many as oscillators, but really close ;-)

>-
>
>My presumption is that all variable LC oscillators ought to be using
>Vacker design to correctly maintain oscillation combined with low
>feedback and amplitude - over a small - or especially wide frequency
>variation.
>
>With all the electronic made in the last 30 years, why has no one found
>this design (again)? Why has no one been educated about this oscillator?

Well these days it is all about integration, silicon is very cheap.
It allows also very small structures that work in the THz range.
Dividing down is digital and takes little silicon space,
so there is a solution, make any frequency step you like.
The need for VCO's has gradually decreased I think.

Regenerative receivers radiate a lot usually,
interfering with other receivers listening for the same frequency.
If you look at stuff like the RTL DVB-T sticks
(rtl_sdr as used for software radio), I can only be amazed that
thet what once was a big cabinet full of capacitors, inductors,
tubes, and 'do not breathe while using this' signs,
is now the size of a postage stamp with way better specs,
and a zilions times the power requirement.
Elonix 4000 tuner chip...

1940 tech was huge.

[Jan Panteltje]

On a sunny day (Sat, 20 Jul 2013 14:08:42 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<baf56d8b-a8cd-4ee1...@googlegroups.com>:

OK, now things are sinking, you missed an opportunity
to CALCULATE the capaciatnce of your meter.

You had L, C, and frequency f.
You added the meter, and found now a lower frequency f2.
L has not changed, so now you can calculate C meter (plus hands etc).
No need to even measure it.

You talked about where to put the tap on the coil,
and noticed it made little difference.
Do you realize that sets the gain?


tuned cicuit -> amplifier -> feedback network -
| |
| |
---------------------<-- A-------------------

Cut circuit open at 'A', and it all becomes much simpler.

For oscillation to start, that gain (and notic phase,
it is all complex math), must be > 1.
If it is >> 1 it will oscillate anyways,
maybe not so nice as yo uwoudl like for very high gains.

And that is how simple it is.


I remember I had to calcualte those freaking things,
there is
http://en.wikipedia.org/wiki/Th�venin's_theorem
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws

and a few more.

[Glenn]

These YIG-stones is also smart - great oscillator and filter balls - but
not named after any human? They are also EM coupled:
http://en.wikipedia.org/wiki/Yttrium_iron_garnet
http://en.wikipedia.org/wiki/YIG_sphere

Used in elder quality spectrum analyzers.

[josephkk]

On Sun, 21 Jul 2013 08:39:12 +0000, Jan Panteltje wrote:


> Right, I had that problem several times, perhaps ceramic caps dissipate
> away energy by mechanical vibration.
>
> I often write 'poly' next to tuning caps, in one of those voltage
> converters the ceramic caps actually got hot. Was way below their
> specified operating voltage.

Wouldn't surprise me. Most of the High K ceramic dielectrics are
piezoelectric in nature. They also make physically resonant filters with
the same materials.

?-)

[Glenn]

On 21/07/13 10.39, Jan Panteltje wrote:
...

> in one of those voltage converters the ceramic caps actually got hot.
> Was way below their specified operating voltage.
>

The reason is high ESR. Even ce-capacitors are divided in "normal"-ESR
and low-ESR.

http://en.wikipedia.org/wiki/Equivalent_series_resistance

In window "Applications" you can choose SMPS filtering:
http://www.digikey.com/product-search/en/capacitors/ceramic-capacitors/131083

Capacitor Values:
Don�t Believe the Label:
http://powerelectronics.com/site-files/powerelectronics.com/files/archive/powerelectronics.com/passive_components_packaging_interconnects/packaging/705PET21.pdf

Therefore some ceramic types can be used for measuring voltage or
temperature, because the capacitance vary.

[Jan Panteltje]

On a sunny day (Sun, 21 Jul 2013 14:08:54 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51ebcf57$0$292$1472...@news.sunsite.dk>:

>On 21/07/13 10.39, Jan Panteltje wrote:
>...
>> in one of those voltage converters the ceramic caps actually got hot.
>> Was way below their specified operating voltage.
>>
>
>The reason is high ESR. Even ce-capacitors are divided in "normal"-ESR
>and low-ESR.
>
>http://en.wikipedia.org/wiki/Equivalent_series_resistance
>
>In window "Applications" you can choose SMPS filtering:
>http://www.digikey.com/product-search/en/capacitors/ceramic-capacitors/131083
>
>Capacitor Values:

>Don�t Believe the Label:
>http://powerelectronics.com/site-files/powerelectronics.com/files/archive/powerelectronics.com/passive_components_packaging_inter
>connects/packaging/705PET21.pdf

Good data!

>Therefore some ceramic types can be used for measuring voltage or
>temperature, because the capacitance vary.

I had, just a few weeks ago, used ceramic SMD 100 nF caps to decouple some tuning
voltage, well I _tried_, until I noticed that any movement of the board
threw my 1.5 GHz VCO way of frequency, in the end just blowing against the board,
the sound of air hitting it, was enough to send the VCO all over the place.
Replaced those caps with 1 uF electrolytics... problem gone.

-- 220k --- VCO
|
|
===
|
///

I am sure if I had fed the output into a FM demodulator it would have made good audio.
Hey, an idea: cheap ceramic microphones, re-branded caps...
(China will pick up now ;-) ).

SMDs are specifically sensitive as any board bending puts huge forces on those.

[M. Hamed]

On Saturday, July 20, 2013 7:02:16 PM UTC-7, John S wrote:
> The Hartley can be constructed using two inductors rather than one that
> is tapped. In my opinion, that makes it sort of a Colpitts anyway.

Yes. That was done on purpose. I remembered reading somewhere that coupling is not needed (I think it was in Hayward's Introduction to RF Design).

> I don't like tapped inductors because it is harder to change for
> experiments. YMMV.
>

It was something I wanted to try and it saves me an extra toroid. Wounding both inductors on the same toroid would have been essentially the same.

>
>
> You're doing great. Keep up the good work.
>

Thanks John. I appreciate the encouragement.

[M. Hamed]

On Saturday, July 20, 2013 7:02:16 PM UTC-7, John S wrote:

> While I'm thinking about it, I had some problems getting a Colpitts to
> start and run properly. I learned that my ceramic caps had high (for
> ceramic) dissipation factors (low Q). Replacing them with NP0 cured the
> problem. You may not run in to this problem, but it might be worthwhile
> to remember.
>

From my readings, capacitor low Q is usually not an issue up to high frequencies. Before that the inductor Q is more important. I am compelled to ask at which frequencies was this a problem to you?

[M. Hamed]

The discussion about capacitors reminded me of a good article I read a few weeks back on EDN:

http://bit.ly/12cukvF

It has mention of piezoelectric effects and also variations with voltage which are often not specified.

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 10:52:41 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<ace86833-f421-42ca...@googlegroups.com>:

>The discussion about capacitors reminded me of a good article I read a few weeks back on EDN:
>
>http://bit.ly/12cukvF
>
>It has mention of piezoelectric effects and also variations with voltage which are often not specified.

Thanks, nice table.

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 10:52:41 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<ace86833-f421-42ca...@googlegroups.com>:

>The discussion about capacitors reminded me of a good article I read a few weeks back on EDN:
>
>http://bit.ly/12cukvF
>
>It has mention of piezoelectric effects and also variations with voltage which are often not specified.

Thanks, nice table.

PS, as mentioned on that site, there is also an other issue with at least some ceramic caps:
they are not perfect insulators, and cause noise by themselves.
In this project:
http://panteltje.com/panteltje/pic/mag_pic/
at one point I thought I was seeing the magnetic variations in the earth core...
(Those exists at very low level), but in this case it turned out
to be fluctuating DC current changes (say varying leakage) in those
brown 470nF caps...
Bummer...

OK those were cheap caps...

[Glenn]

Some pesky ceramics are superconductors:
https://en.wikipedia.org/wiki/YBCO

[M. Hamed]

On Monday, July 22, 2013 11:12:11 AM UTC-7, Jan Panteltje wrote:
> PS, as mentioned on that site, there is also an other issue with at least some ceramic caps:
>
> they are not perfect insulators, and cause noise by themselves.
>
> In this project:
>
> http://panteltje.com/panteltje/pic/mag_pic/
>
> at one point I thought I was seeing the magnetic variations in the earth core...
>
> (Those exists at very low level), but in this case it turned out
>
> to be fluctuating DC current changes (say varying leakage) in those
>
> brown 470nF caps...
>
> Bummer...
>
>

Gives me an idea of a new FM modulator element, the capacitor modulator. Changes in audio voltage produces equivalent changes in capacitance and frequency changes accordingly :)

[M. Hamed]

On Sunday, July 21, 2013 2:21:24 AM UTC-7, Jan Panteltje wrote:
> OK, now things are sinking, you missed an opportunity
> to CALCULATE the capaciatnce of your meter.
> You had L, C, and frequency f.
> You added the meter, and found now a lower frequency f2.
> L has not changed, so now you can calculate C meter (plus hands etc).
> No need to even measure it.
>

Actually I did both. But measurement showed about 100 nF capacitance which is strange because that would have changed the frequency by much much more than the observed change. I also tried the calculation method which produced a capacitance of a few pico Farads.

> You talked about where to put the tap on the coil,
> and noticed it made little difference.
> Do you realize that sets the gain?
>

Yes, I did hence I reversed the coil so the gain isn't so much.
>
>
<Snip>

>
> I remember I had to calcualte those freaking things,
> there is

> http://en.wikipedia.org/wiki/Thévenin's_theorem

> http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws
>
>
> and a few more.

I was trying to calculate the output impedance of the circuit but failed.

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 20:34:58 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51ed7b53$0$293$1472...@news.sunsite.dk>:

Yes I have some, from here:
http://www.can-superconductors.com/levitation-bulk.html

This is my sterling cooler:
http://panteltje.com/pub/cryo/index.html

This is how I measure temperature:
http://panteltje.com/panteltje/pic/th_pic/

More info on this type of cooler:
http://fpsc.twinbird.jp/legacy/en/faq_e.html#fpsc01

Mine is from a superconducting filter from cellphone towers.
When the material starts super-conductiong the Q goes way up (no R),
and that makes it possible to make increadble steep filters.

So I also have a super filter somehere...
;-)

Beware some types of high temperature superconductors contain Thallium,
and can kill.

And those Sterling coolers are very very expensive normally ( >10,000 $ ), got it cheap on ebay.
Seller seems to have figured out the real value by now, last time I looked his
price was way up.

Now how to make your own rocket fuel...

[Glenn]

Is this mixer better than the Gilbert cell?

The Tayloe Sampling Mixer - also called:
Tayloe Detector
IQ based tranceiver
Dirodyne
linear detector
Quadrature Sampling Detector QSD
http://9y4ar.tripod.com/tayloe_mixer.htm

Actually it is a "bang-bang"/digital mixing that ought to produce a lot
of aliasing products.

It seems to have something in common with the diode ring mixer:
https://en.wikipedia.org/wiki/Ring_modulation

What you really need is an analog multiplier, but this is emulated by a
Gilbert cell - and maybe a diode ring mixer?:
https://en.wikipedia.org/wiki/Analog_multiplier

But then how do you theoretically optimize the diode ring mixer for low
IP3 and other "false" mixing products? "Of cause" you can not suppress
the signal mirror unless IQ-mixing is used.

Actually another techniques is used with e.g. a harmonic diode mixer -
or you are just "tuning" for the "false" product :-) :
http://en.wikipedia.org/wiki/Harmonic_mixer

I happened to find the harmonic diode mixer techniques in the HP 141T's
8555A input mixer - and it can be a "bad" techniques because of
aliasing, that is why an external preselector is needed in front of the
harmonic mixer.

-

Gilbert cell:
https://en.wikipedia.org/wiki/Gilbert_cell


Historical:

James Long, Ph.D., P.E. Analog and RF Consulting Engineer
History of Mixer Technology
(And Other Stories of Misplaced Credit)
Things are seldom as they seem. Skimmed milk masquerades as cream.
http://www.analog-rf.com/mixer.shtml
Quote: "...
All of mixer technology in use today was mathematically known several
hundred years ago and reduced to practice by 1935 when the DPDT vibrator
modulator was used in low frequency amplifiers. By 1949 this function
was performed by the 7360 vacuum tube in radio circuits and six vacuum
tubes in rocket telemetry circuits.
..."

Glenn

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 21:21:43 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51ed8648$0$296$1472...@news.sunsite.dk>:

>Is this mixer better than the Gilbert cell?
>
>The Tayloe Sampling Mixer - also called:
>Tayloe Detector
>IQ based tranceiver
>Dirodyne
>linear detector
>Quadrature Sampling Detector QSD
>http://9y4ar.tripod.com/tayloe_mixer.htm
>
>Actually it is a "bang-bang"/digital mixing that ought to produce a lot
>of aliasing products.

These days you can get cheap SAW filers with a precise bandpass curve,
other frequencies will be surpressed by a lot of deebees,
So I dunno how much it matters, you need to see the whole setup to make a choice.

Dual conversion, greater offset of the mirrors, it is a design choice.

[Glenn]

On 22/07/13 21.10, Jan Panteltje wrote:
> On a sunny day (Mon, 22 Jul 2013 20:34:58 +0200) it happened Glenn
> <glen...@gmail.com> wrote in<51ed7b53$0$293$1472...@news.sunsite.dk>:

...
>> Some pesky ceramics are superconductors:
>> https://en.wikipedia.org/wiki/YBCO
>
> Yes I have some, from here:
> http://www.can-superconductors.com/levitation-bulk.html
>
> This is my sterling cooler:
> http://panteltje.com/pub/cryo/index.html

That is cool!

-

Somebody has used a superconductor cavity to trap and detect a single
microwave photon - they say:

Centre National De La Recherche Scientifique (2007, April 2). Life And
Death Of A Photon 'Filmed' For The First Time. ScienceDaily. Retrieved
March 22, 2008:
http://www.sciencedaily.com/releases/2007/04/070402122514.htm
Quote: "...
A photon is an elementary particle of light. In general it can only be
observed when it disappears
...
The end result is that the atom changes to state 1 if the cavity
contains a photon and remains at state 0 if it is empty, as in the
standard method. However, this time the energy absorbed by the atom is
taken from the auxiliary field and not from that of the cavity. As a
result, the photon is still there after having been seen, and is ready
to be measured again
...
Suddenly the atoms appear in state 1, showing that a photon has been
trapped between the mirrors. The photon comes from the residual thermal
radiation which surrounds the cavity
...
The moments at which the photons appear and disappear reveal the quantum
jumps of light, which occur at random
..."

-

Maybe you can detect its OAM modulation? ;-) :
https://en.wikipedia.org/wiki/Orbital_angular_momentum_of_light

Nov 1, 2012, physicsworld.com: Spooky action with twisted beams:
http://physicsworld.com/cws/article/news/2012/nov/01/spooky-action-with-twisted-beams
Quote: "...
Using this technique, Zeilinger and co-workers found they could obtain
differences in quantum number as high as 600 (in other words l = +300 on
one photon and l = �300 on the other). Lapkiewicz points out that there
is, in theory, no upper limit to a photon's l value, which suggests that
a photon � a quantum object � could acquire as much OAM as a macroscopic
object, leading to what he calls a "tension between the quantum and
classical worlds"
..."

Glenn

[Tauno Voipio]

On 22.7.13 10:21 , Glenn wrote:
> Is this mixer better than the Gilbert cell?

The Gilbert cell is a four-quadrant analog multiplier,
which should be the best mixer, but due to the imperfections
in the multiplication gives often worse results than a raw
bang-bang switching mixer (diode bridges, rings, 7360 beam-
deflection tube, CMOS analog switches).

> The Tayloe Sampling Mixer - also called:
> Tayloe Detector
> IQ based tranceiver
> Dirodyne
> linear detector
> Quadrature Sampling Detector QSD
> http://9y4ar.tripod.com/tayloe_mixer.htm
>
> Actually it is a "bang-bang"/digital mixing that ought to produce a lot
> of aliasing products.

It does, but it it very linear for the signal channel.

There are two things in the mixing which should be
considered separately:

1. How to get an effective analog multiplication and
linearity, at least for the signal input;

2. How to suppress unwanted mixing responses.

In practice, point 1 is difficult to achieve, especially
for a large input amplitude range. For many practical
purposes it is sufficient to multiply with sign of the
oscillator signal, which is much easier to implement
linearly for the signal channel.

The quadrature methods (phasing, IQ) attack question 2,
by implementing a full complex number multiplication
(called analytic signal in DSP theory).

--

-Tauno Voipio

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 21:41:35 +0200) it happened Glenn
<glen...@gmail.com> wrote in <51ed8af0$0$299$1472...@news.sunsite.dk>:

>one photon and l = �300 on the other). Lapkiewicz points out that there

>is, in theory, no upper limit to a photon's l value, which suggests that

>a photon � a quantum object � could acquire as much OAM as a macroscopic

>object, leading to what he calls a "tension between the quantum and
>classical worlds"
>..."
>
>Glenn

Yes I read physics world newsletter.
As to 'kwantum' and 'photon', I think the quantization of light is
just the exchange with our every day matter (kick an electron in an higher orbit,
or wave disturbance in aether when electron changes orbit),
The whole 'kwaantuum computah' is in my view complete nonsense and will never bring anything
as they are trying to make an analog computer, as light is NOT a stream of particles,
at least not at that gross a level as our matter,
You see indeed the whole kwaantumm fund raising jive is limited by the error rate,
the same as we had with analog computahs, and the same as we have with multilevel FLASH memories.
Not a paper is published these days that does not end with: 'And we think this will bring the quantum computer so much closer,
given X years more funding blah blah, WOW we dunnit!' and then just like fusion power at ITER
ever and ever more into the future.,

The practical thing I may want to use my cooler for is perhaps one day cool some amplifier to get noise down (SETI).
Unfortunately the Sterling cooler has a lot of vibration, but long time ago somebody
already cooled webcams, and got better night pictures. Condensation is a problem with cameras...
Some RF preamp cooled should give better noise figure...

[David Platt]

In article <51ed8648$0$296$1472...@news.sunsite.dk>,

Glenn <glen...@gmail.com> wrote:

>Is this mixer better than the Gilbert cell?

Depends how you define "better".

Some of the more recent high-performance amateur-radio transceivers
are using the Tayloe-type H-mode mixers. The biggest benefit I've
seen mentioned is that these mixers can have a very high dynamic range
and very high IP3 / overload level. Their ability to reject/ignore
strong, close-in interfering signals can be very good indeed.

I believe the radios using this design are becoming very much favored
for use in Field Day and DXpedition operation, where there can be
multiple transceivers operating in very close physical proximity.

The Gilbert Cell mixers usually have significant conversion gain,
while the Tayloe mixers are more like diode-ring mixers in that they
have conversion loss... you need to put your desired gain elsewhere in
the signal chjain.

>Actually it is a "bang-bang"/digital mixing that ought to produce a lot
>of aliasing products.

Like most diode-ring mixer setups it will also "detect" signals on the
odd harmonics. It's usual to include a low-pass filter prior to the
mixer so that only the fundamental is fed in.

I believe that the Tayloe mixer has an advantage over the diode-ring,
in that the switching signal (LO) and the incoming signal (RF) are
coming through different types of paths... the RF signal isn't getting
into the "switch control" pathway at all. For this reason, different
signal components in the RF aren't going to mix with one another (as
can happen in a diode-ring mixer) and there will be fewer spurious
mixing products than with a diode-ring arrangement.

>But then how do you theoretically optimize the diode ring mixer for low
>IP3 and other "false" mixing products? "Of cause" you can not suppress
>the signal mirror unless IQ-mixing is used.

As I understand it, the strong-signal robustness of a diode-ring mixer
requires that the LO signal (which is in effect "switching" the
direction of the ring) be sufficiently stronger than the strongest RF
signal being received.

Commercial diode-ring mixers are available with several different
design points for the LO signal. 50-ohm mixers seem to start out at
about +7 dBm and go up from there in 3- or 6-dBm increments. I
believe that the ones requiring the "hotter" LO signals are build with
several diodes in series in each leg of the ring.

You could think of a Tayloe mixer's behavior as being sort of an
ultimate-limiting case of a diode ring mixer, perhaps... the LO
signal is "so incredibly strong" that it's in effectively complete
control of the mixer's switching behavior, and the incoming RF signal
can't perturb the switch timing at all. As a result, the only
sidebands created by mixing between different RF components, will be
due to the residual nonlinearity in the switched-signal pathway.

At least, that's how I understand it. Corrections welcomed!

[Robert Baer]

>> one photon and l = �300 on the other). Lapkiewicz points out that there

>> is, in theory, no upper limit to a photon's l value, which suggests that

>> a photon � a quantum object � could acquire as much OAM as a macroscopic

>> object, leading to what he calls a "tension between the quantum and
>> classical worlds"
>> ..."
>>
>> Glenn
>
> Yes I read physics world newsletter.
> As to 'kwantum' and 'photon', I think the quantization of light is
> just the exchange with our every day matter (kick an electron in an higher orbit,
> or wave disturbance in aether when electron changes orbit),
> The whole 'kwaantuum computah' is in my view complete nonsense and will never bring anything
> as they are trying to make an analog computer, as light is NOT a stream of particles,
> at least not at that gross a level as our matter,
> You see indeed the whole kwaantumm fund raising jive is limited by the error rate,
> the same as we had with analog computahs, and the same as we have with multilevel FLASH memories.
> Not a paper is published these days that does not end with: 'And we think this will bring the quantum computer so much closer,
> given X years more funding blah blah, WOW we dunnit!' and then just like fusion power at ITER
> ever and ever more into the future.,
>
> The practical thing I may want to use my cooler for is perhaps one day cool some amplifier to get noise down (SETI).
> Unfortunately the Sterling cooler has a lot of vibration, but long time ago somebody

* --------------------^ Stirling en.wikipedia.org/wiki/Stirling_engine

[Jan Panteltje]

On a sunny day (Mon, 22 Jul 2013 18:01:08 -0800) it happened Robert Baer
<rober...@localnet.com> wrote in <pBkHt.138345$T55.1...@fx16.iad>:

>> The practical thing I may want to use my cooler for is perhaps one day cool some amplifier to get noise down (SETI).
>> Unfortunately the Sterling cooler has a lot of vibration, but long time ago somebody
>* --------------------^ Stirling en.wikipedia.org/wiki/Stirling_engine

Yea, was probably still thinking about the price and thought:
https://en.wikipedia.org/wiki/Pound_sterling


:-)

Does it get colder now?

[John S]

1.8 MHz. I changed to C0G (NP0) and it cured the problem.

[M. Hamed]

#4
---

I realized how much fun oscillators are and how Sine waves are so beautiful so I decided I'm going to up it a notch and take a shot at a 100 MHz oscillator.

I tried a Colpitts variation of the Hartley oscillator I posted earlier with the same MPF102 JFET, a diode, 1 MOhm Res, the tank, and its surrounding capacitors. Inductors and Caps had to get much smaller. So L is in the nH range and C is in the low pF.

Couldn't get the thing to oscillate at all no matter how hard I tried. I tried too many things to keep track of. I was suspecting the inductance is so low and the inductor Q is inadequate. I tried different types of air-core wire turns. Eventually I moved to the Toroid version but no luck.

Next, I decided a JFET isn't the thing for this and decided to move to BJT. I used a 2N3904. I played a lot with the number of turns and capacitor values until I reached a circuit similar to this:

https://www.dropbox.com/s/fp3dv13ahmu6pzh/Collpits.asc

My L is 3-5 turns on a 68-6 toroid. The value on the circuit is just a guess based on the frequency I'm getting. I had the following observations:

- I had a big 300p cap for C2 this killed the ability to oscillate (later I realized it had to do with the amount of feedback. If you reverse C1 and C2 however, simulation shows the voltage swing is low. I am guessing it has to do with transistor gain. Increasing C1 should probably also mean decreasing R3. I am taking shots in the dark here, I will try to do some analysis later).
- Even with C2=300p, increasing C3 to 66p restored oscillation.
- After reducing C3 back to 33p, I was able to reduce C3 back to 33p and get oscillation.
- I kept on trying to reduce inductance to increase frequency but that came with a price of reducing the voltage swing at the tank.
- I still do not have a unified theory of how the values of L and Cs affect frequency and voltage swing but it seems I should strive for having higher L for better stability and voltage swing. This means I need to reduce the C's to as low as I can get.
- In the end I was able to reach 67 MHz as the max I could squeeze out of my circuit but it's not very stable.
- Even with everything laid out on a perf-board and with no power supply bypass you still can see 67 MHz of oscillation that is clean looking on a scope. Stability is another matter.
- Soldering and de-soldering is a pain when you have try different things.
- a plain vanilla 2N3904 can go long ways!
- I don't like JFETs. I love BJTs.

-------------------------------------------------
Next steps:

- Add more turns to my toroid
- Try a better a toroid core, may be a 2 or 6 Mix
- Reduce caps to the minimum possible.
- Hope for 100 MHz.

[Jan Panteltje]

On a sunny day (Sat, 27 Jul 2013 13:36:50 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<32a280bd-642b-4d82...@googlegroups.com>:

>#4
>---
>
>I realized how much fun oscillators are and how Sine waves are so beautiful=
> so I decided I'm going to up it a notch and take a shot at a 100 MHz oscil=
>lator.
>
>I tried a Colpitts variation of the Hartley oscillator I posted earlier wit=
>h the same MPF102 JFET, a diode, 1 MOhm Res, the tank, and its surrounding =
>capacitors. Inductors and Caps had to get much smaller. So L is in the nH r=

>ange and C is in the low pF.
>

>Couldn't get the thing to oscillate at all no matter how hard I tried. I tr=
>ied too many things to keep track of. I was suspecting the inductance is so=
> low and the inductor Q is inadequate. I tried different types of air-core =

>wire turns. Eventually I moved to the Toroid version but no luck.

1 MOHm ?????? WHERE?
+ 12
|-------
|--- d |
----------------------->| BF245 ===
| | |--- | 100n
5 turns === 47p | ///
8mm diam. |------------|
1 cm length === [ ] 470 Ohm to about 1k
| | 100p |
/// /// ///

You need the right kind of JFET, BF254 are around for a few cent on ebay and
go up to 700 MHz.



>Next, I decided a JFET isn't the thing for this and decided to move to BJT.=
> I used a 2N3904. I played a lot with the number of turns and capacitor val=

>ues until I reached a circuit similar to this:
>
>https://www.dropbox.com/s/fp3dv13ahmu6pzh/Collpits.asc

Would it not be simpler to DC bias from the cold side of the coil?
+
|
|--------
|/ |
--------------------| ===
| | |>\ | 100n
( === 47p | ///
( L |------------|
+ ( === [ ] 1k
| | | 100p |
33k [ ] | /// ///
|------|
| |
15k [ ] === 10n
| |
/// ///
Now L is no longer damped by 33k paralel with 15 k, only by the transistor Zi, and that is about beta x 1k (Re).






>My L is 3-5 turns on a 68-6 toroid. The value on the circuit is just a gues=

>s based on the frequency I'm getting. I had the following observations:

At many MHz it is unusual to use toroids, those have a high Al, you want low.
Toroids can have huge losses too at higher frequencies, depends on the material,

>- I had a big 300p cap for C2 this killed the ability to oscillate (later I=
> realized it had to do with the amount of feedback. If you reverse C1 and C=
>2 however, simulation shows the voltage swing is low. I am guessing it has =
>to do with transistor gain. Increasing C1 should probably also mean decreas=
>ing R3. I am taking shots in the dark here, I will try to do some analysis =

>later).
>- Even with C2=300p, increasing C3 to 66p restored oscillation.

>- After reducing C3 back to 33p, I was able to reduce C3 back to 33p and ge=
>t oscillation.

Confusing circuit, C3, IF you must have it, should be on the other side, connected to R1, R2,
and a much higher value (10nF), as it purpose is ONLY decoupling,
It should not be part of the tuning parameters.
C2 C3 should then be connected to the coil.


>- I kept on trying to reduce inductance to increase frequency but that came=

> with a price of reducing the voltage swing at the tank.

>- I still do not have a unified theory of how the values of L and Cs affect=
> frequency and voltage swing but it seems I should strive for having higher=
> L for better stability and voltage swing. This means I need to reduce the =

>C's to as low as I can get.

>- In the end I was able to reach 67 MHz as the max I could squeeze out of m=

>y circuit but it's not very stable.

Use an air coil, as drawn in the above diagram, for 100MHz and up, like in this picture:
http://tvforfree.files.wordpress.com/2012/09/georgesmartfcd.jpg


>- Even with everything laid out on a perf-board and with no power supply by=
>pass you still can see 67 MHz of oscillation that is clean looking on a sco=

>pe. Stability is another matter.
>- Soldering and de-soldering is a pain when you have try different things.
>- a plain vanilla 2N3904 can go long ways!
>- I don't like JFETs. I love BJTs.

JFETS are cool, they make good low noise amps too.
I once did a cascode JFET input amp that beat the better BJTs at that time.
It also depends on what make MPF120 you have,
one datasheet here shows a graph that its gain is flat to 700 MHz.
Remember that when using a source follower as gain element the VOLTAGE gain of the JFET stage
itself is always a bit less than 1.
So to get > 1 feedback you need to step up with either a transformer (tap on coil or extra turn),
or as in this case with the right ratio of capacitors, AT LEAST 2 to 1, or even higher.
try again.

>-------------------------------------------------
>Next steps:
>
>- Add more turns to my toroid

No toroids!!!!

>- Try a better a toroid core, may be a 2 or 6 Mix

Air core!!!
Use a trimmer capacitor, or a small coil former with a core you can screw in and out for adjustment.,

>- Reduce caps to the minimum possible.

No, no, that will only create instability,
Around 100 pF should be fine.

>- Hope for 100 MHz.

100 MHz is nothing,
how do you measure frequency? Not loading that LC with a counter I hope?
Use an FM radio tuned to 100 MHz, and a 50 to 250 pF (or there about) antique
air spaced variable capacitor, of if not in possesion of such a wonderful piece on engineering,
bend the air coil, and turn or bend until you hear 'flop flop' sounds from that radio.
And make sure that is not just an harmonic...

[M. Hamed]

On Saturday, July 27, 2013 2:01:37 PM UTC-7, Fred Abse wrote:
> You've stumbled upon "resonant impedance". There was some discussion about
> that, here, a while ago.
>
> To a first approximation, the impedance seen across an LC circuit, with
> loss only in the inductor, at resonance is:
>
> L/CR, where R is the inductor's series loss resistance (higher than at DC
> because of skin effect).
>
> Simply put, the higher the L/C ratio, the higher the voltage across the
> oscillator tank.
>

I went back to the thread. So in essence it's the equivalent parallel resistance of the inductor and we want to keep that high I presume by increasing the unloaded Q of the inductor which can be achieved by increasing inductance.

[M. Hamed]

On Sunday, July 28, 2013 1:10:31 AM UTC-7, Jan Panteltje wrote:
> 1 MOHm ?????? WHERE?

At the gate of the JFET in parallel with a diode. Similar to the Hartley circuit I got from EMRFD and linked to earlier in the thread (dropbox).

> You need the right kind of JFET, BF254 are around for a few cent on ebay and
> go up to 700 MHz.
>

At the moment I have a few MPF102 JFETs. The datasheet labels it "VHF amplifier" so I assumed it's adequate.

> Would it not be simpler to DC bias from the cold side of the coil?
>
> +
>
> |
>
> |--------
>
> |/ |
>
> --------------------| ===
>
> | | |>\ | 100n
>
> ( === 47p | ///
>
> ( L |------------|
>
> + ( === [ ] 1k
>
> | | | 100p |
>
> 33k [ ] | /// ///
>
> |------|
>
> | |
>
> 15k [ ] === 10n
>
> | |
>
> /// ///
>
> Now L is no longer damped by 33k paralel with 15 k, only by the transistor Zi, and that is about beta x 1k (Re).
>

Interesting idea. I'll try running some simulations.

> At many MHz it is unusual to use toroids, those have a high Al, you want low.
> Toroids can have huge losses too at higher frequencies, depends on the material,
>

I was suspecting that is the case. The T68-6 is recommended up to 40 MHz. I have a few toroids on order that are recommended for higher frequency and have lower AL (mix 10). I started with an air form but when it didn't oscillate I thought my inductance must be too low to be usable. After all the iterations I went through I am going to go back and reexamine this. Thanks for the hint.

> JFETS are cool, they make good low noise amps too.

<snip>
> try again.
>

Will do!

> >- Reduce caps to the minimum possible.
>
> No, no, that will only create instability,
> Around 100 pF should be fine.
>

Here is the dilemma. For 100 pF @100 MHz, L is around 25 nH. This is very small. How is that more stable when it's susceptible to parasitic lead inductances and also am I not supposed to keep L/C ratio high?

> how do you measure frequency? Not loading that LC with a counter I hope?
> Use an FM radio tuned to 100 MHz, and a 50 to 250 pF (or there about) antique
> air spaced variable capacitor, of if not in possesion of such a wonderful piece on engineering,
> bend the air coil, and turn or bend until you hear 'flop flop' sounds from that radio.
> And make sure that is not just an harmonic...

Oops. Yes I was. Not the counter but I was using a scope. I figured out a few hours ago. More details in my next post. PS: I do have this wonderful pieces of engineering!
http://www.tubesandmore.com/products/C-V365


Thanks for the time you took responding!!

[M. Hamed]

#5
---

Went ahead with my plans of increasing L and reducing Cs. Started with a relatively larger inductance, and reduced the tank cap to 6pF and the other caps are 6, 10, 10 pF. I got around 40MHz then I progressively reduced the number of turns on the inductor. At some point slightly above 66 MHz, oscillations seized.

Then it occurred to me what I should have known better. All this time I've been probing the tank with my oscope probe. Effectively I'm adding a cap in parallel that would shift frequency and hurt the L/C ratio, especially when my tank caps are 6 pF.

After this simple realization, I added a JFET source follower and connected the scope to the JFET source, and voila! My scope showed around 80 MHz. It was a matter of shaving off one extra turn from the inductor and there I got 108 MHz! Goal achieved.

The JFET datasheet lists input capacitance as 7pF @ 1 MHz and 15VDC. So my guess is that the tank resonant frequency is probably around 200 MHz without the JFET load!

At some point I got concerned that I could be generating interference and my little oscillator could be acting as a transmitter. Sometimes I cranked up my power supply voltage to 18V and with the supply showing less than 1 mA drawn, that's 18mW which I thought should be nothing.

To test the theory I tuned my FM radio to 108 and I got some ugly sounding noise. That got me scared a bit that I could be jamming something somewhere so I immediately turned off my supply. With such low power and at 100 MHz I don't expect my interference would travel very far. But at least now I understand the importance of shielding.

[M. Hamed]

On Sunday, July 28, 2013 3:23:05 AM UTC-7, M. Hamed wrote:
> To test the theory I tuned my FM radio to 108 and I got some ugly sounding >noise. That got me scared a bit that I could be jamming something somewhere so I >immediately turned off my supply. With such low power and at 100 MHz I don't >expect my interference would travel very far. But at least now I understand the >importance of shielding.

I will probably invest in one of these little fellows:

http://micro.arocholl.com/index.php?option=com_content&view=article&id=48:introducing-rf-explorer&catid=40:article&Itemid=64

[Jan Panteltje]

On a sunny day (Sun, 28 Jul 2013 03:04:45 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<87cfcaf0-c6e9-4551...@googlegroups.com>:

>> try again.
>>
>
>Will do!
>
>> >- Reduce caps to the minimum possible.
>>
>> No, no, that will only create instability,
>> Around 100 pF should be fine.
>>
>

>Here is the dilemma. For 100 pF @100 MHz, L is around 25 nH. This is very s=
>mall. How is that more stable when it's susceptible to parasitic lead indu=

>ctances and also am I not supposed to keep L/C ratio high?

I do not want to critisise other posters, but really,
the 100 MHz was 5 to 7 turns 8 mm diameter coil spaced over 1 cm with one of those air dielectricum caps as tuning cap.
Open up any old FM radio, and look, or better yet, this is an ebay FM transmitter board tuned to 107.2 I use
http://panteltje.com/pub/ebay_fm_transmitter_board_coil_IMG_3967.JPG
Look at that coil!
It is a close up from this project:
http://panteltje.com/panteltje/pic/fm_pic/


The "Q' story as quoted is a bit different:

Bandwidth:
B = f0 / Q

From:
http://en.wikipedia.org/wiki/Selectivity_(electronic)
<quote>
LC circuits are often used as filters; the Q ("Quality" factor) determines the bandwidth of each LC tuned circuit in the radio.
The L/C ratio, in turn, determines their Q and so their selectivity, because the rest of the circuit
- the aerial or amplifier feeding the tuned circuit for example - will contain present resistance.
**For a series resonant circuit, the higher the inductance and the lower the capacitance, the narrower the filter
bandwidth (meaning the reactance of the inductance, L, and the capacitance, C, at resonant frequency will be relatively high
compared with the series source/load resistances).
**For a parallel resonant circuit the opposite applies; small inductances reduce the damping of external circuitry.
<end quote>


For exmaple, this is LTspice my run for the 25 MHz DVB-S transmitter exciter filter at 25 MHz with a 220 pF capacitor and 184 nH coil:
http://panteltje.com/pub/220p.gif

And this with a 22 pF capacitor and 1.84 uH coil (factor 10 change, same frequency)
http://panteltje.com/pub/22p.gif

Now look at the bandwidth of the first one, compared to the second,
At 50 MHz (2 x f0) attenuation is better than 33 dB.

And then the second one:
at 50 MHz (2 x f0) attenuation is about -14 dB, not very usable as filter.

That is why I wrote in a previous post that bigger C is better, for a given circuit load (1 k Ohm here), in a parallel setup.

Bigger C is also better as there is less influence from parasictic capacitances, like input C of transistors, PCB wiring, test leads, what not.
And less turns, made with nice silvered wire, on a good coil former is more stable than some ferrite with unkown properties,
on top of that sensitive to magnetic infuences.

Look at the silver wire:
http://panteltje.com/pub/25MHz_184nH_tunable_IMG_3966.JPG

Remove the core, and it should give you 100MHz with that big variable capacitance.
Big bigger diameter helps.


>> Use an FM radio tuned to 100 MHz, and a 50 to 250 pF (or there about) ant=
>ique
>> air spaced variable capacitor, of if not in possesion of such a wonderful=
> piece on engineering,
>> bend the air coil, and turn or bend until you hear 'flop flop' sounds fro=

>m that radio.
>> And make sure that is not just an harmonic...
>

>Oops. Yes I was. Not the counter but I was using a scope. I figured out a f=
>ew hours ago. More details in my next post. PS: I do have this wonderful pi=
>eces of engineering!
>http://www.tubesandmore.com/products/C-V365

That is very nice, really.

[Jan Panteltje]

On a sunny day (Sun, 28 Jul 2013 03:27:32 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<379a64e4-b804-4342...@googlegroups.com>:

>On Sunday, July 28, 2013 3:23:05 AM UTC-7, M. Hamed wrote:

>> To test the theory I tuned my FM radio to 108 and I got some ugly soundin=
>g >noise.

If you are on-frequency and have a clean power suply, then your radio should become very quiet,
as it sees an 'unmodulated' (= stable in frequency) carrier.

[Jan Panteltje]

For example, this is LTspice my run for the 25 MHz DVB-S transmitter exciter filter at 25 MHz with a 220 pF capacitor and 184 nH coil:

http://panteltje.com/pub/220p.gif

And this with a 22 pF capacitor and 1.84 uH coil (factor 10 change, same frequency)
http://panteltje.com/pub/22p.gif

Now look at the bandwidth of the first one, compared to the second,
At 50 MHz (2 x f0) attenuation is better than 33 dB.

And then the second one:
at 50 MHz (2 x f0) attenuation is about -14 dB, not very usable as filter.

That is why I wrote in a previous post that bigger C is better, for a given circuit load (1 k Ohm here), in a parallel setup.

P.S.
Actually this is really simple to understand if you look at his configuration as a combined high and low pass
(as that is what it is, 'resonance' is just a phase zero frequency where the complex part cancels).

in --- R ----- out
| gives better attenuation at higher frequencies for bigger values of C.
===
|
///

and:

in --- R ----- out
| gives better attenuation at lower frequencies for smaller values of L.
L usually smaller values of L have lower resistance due to less turns,
| causing a dead short versus a slight output at DC.
///

:-)

[Jan Panteltje]

On a sunny day (Sun, 28 Jul 2013 09:13:58 -0700) it happened Fred Abse
<excret...@invalid.invalid> wrote in
<pan.2013.07.28....@invalid.invalid>:

>On Sun, 28 Jul 2013 14:30:12 +0000, Jan Panteltje wrote:
>
>> For example, this is LTspice my run for the 25 MHz DVB-S transmitter
>> exciter filter at 25 MHz with a 220 pF capacitor and 184 nH coil:
>> http://panteltje.com/pub/220p.gif
>>
>> And this with a 22 pF capacitor and 1.84 uH coil (factor 10 change, same
>> frequency)
>> http://panteltje.com/pub/22p.gif
>>
>> Now look at the bandwidth of the first one, compared to the second, At 50
>> MHz (2 x f0) attenuation is better than 33 dB.
>>
>> And then the second one:
>> at 50 MHz (2 x f0) attenuation is about -14 dB, not very usable as filter.
>>

>> That is why I wrote in a previous post that bigger C is better.
>
>
>That's misleading. The Q of each circuit, as drawn, is not the same; the
>difference in bandwidth is due to Q, not L/C ratio.
>
>The effective Q of the 220pF circuit is 38.
>The effective Q of the 22pF circuit is 3.8.

I think you misunderstand something.
You can actually only talk about Q ( > 1 ) if you get some voltage increase,
that would be the case, as you mentioned, if you were driving with a current source.

That current source could be a collector of a BJT (pretty flat Ic versus Vce).

In this case, you may notice from the simulation that the output voltage is always LOWER than the input voltage,
so from your POV Q is < 1 perhaps.

In the most ideal case, in 'resonance' the impedance of the LC is infinite
(if it has a huge Q by itself) and the circuit is just a resistor,
and, given the infinite impedance of the LTspice voltmeter, Uin = Uout.

That reduces the circuit to a low pass and high pass outside f0,
and in the case of low - and high passes, L and C, DO make all the difference,

Look here at the situation without L:
http://panteltje.com/pub/no_l.gif
At 50 MHz it is practically the same attenuation as the LC version, the C no longer does much.



>That's a 10:1 bandwidth ratio, right there. Nothing to do with L/C ratio.
>
>Assuming the same wire gage, a 1.84uH inductor will have sqrt(1000) times
>the resistance of a 184nH coil. That's about thirty times. You used the
>same resistance in both cases.


That was a joke right ;-) although it is true, at DC the R will give
a residual voltage... more for a multi turn L.

It think you pay way to much attention to R of L in this,
logically as you still think infinite current drive.

If you really want to see Q put up voltage swing, do this

C L
zero output impedance amp --|>--- R ---||-----L ----| gnd
|
out

>Your simulation doesn't prove your case, regarding "bigger C", which is
>wrong, anyway.

Are you arguing with LT spice?


>Now go figure how to simulate L/C ratios properly...

Well, I gave a practical example,
but you seem still fixed on your current source.
The above circuit shows how to drive from a low impedance voltage source.

In the oscillator example this is all about low impedance drive however,
the LC is loaded with a fixed resistor, and there is no 'infinite source' driving it.
So maybe you should do some self inspection...

But if that is your religion...
;-)

[josephkk]

On Sun, 28 Jul 2013 03:23:05 -0700, M. Hamed wrote:


> To test the theory I tuned my FM radio to 108 and I got some ugly
> sounding noise. That got me scared a bit that I could be jamming
> something somewhere so I immediately turned off my supply. With such low
> power and at 100 MHz I don't expect my interference would travel very
> far. But at least now I understand the importance of shielding.

Hooray. You are actually doing very well. Good enough to make jealous
of all the fun you are having. Keep going.

?-)

[YD]

Late at night, by candle light, "M. Hamed" <mhdp...@gmail.com>
penned this immortal opus:

>#5
>---
>
>Went ahead with my plans of increasing L and reducing Cs. Started with a relatively larger inductance, and reduced the tank cap to 6pF and the other caps are 6, 10, 10 pF. I got around 40MHz then I progressively reduced the number of turns on the inductor. At some point slightly above 66 MHz, oscillations seized.
>
>Then it occurred to me what I should have known better. All this time I've been probing the tank with my oscope probe. Effectively I'm adding a cap in parallel that would shift frequency and hurt the L/C ratio, especially when my tank caps are 6 pF.
>
>After this simple realization, I added a JFET source follower and connected the scope to the JFET source, and voila! My scope showed around 80 MHz. It was a matter of shaving off one extra turn from the inductor and there I got 108 MHz! Goal achieved.
>

Congratulations, you've just discovered the buffer amplifier, to
isolate the oscillator from the load. From there you can take the
signal and do something with it without disturbing the frequency.

>The JFET datasheet lists input capacitance as 7pF @ 1 MHz and 15VDC. So my guess is that the tank resonant frequency is probably around 200 MHz without the JFET load!

And now you know to take parasitics into account. Good work!

>
>At some point I got concerned that I could be generating interference and my little oscillator could be acting as a transmitter. Sometimes I cranked up my power supply voltage to 18V and with the supply showing less than 1 mA drawn, that's 18mW which I thought should be nothing.
>
>To test the theory I tuned my FM radio to 108 and I got some ugly sounding noise. That got me scared a bit that I could be jamming something somewhere so I immediately turned off my supply. With such low power and at 100 MHz I don't expect my interference would travel very far. But at least now I understand the importance of shielding.

At that power it's probably detectable at some tens of metres at most.

- YD.

--
Remove HAT if replying by mail.

[YD]

Late at night, by candle light, "M. Hamed" <mhdp...@gmail.com>
penned this immortal opus:

<snipperoodah>

>
>Here is the dilemma. For 100 pF @100 MHz, L is around 25 nH. This is very small. How is that more stable when it's susceptible to parasitic lead inductances and also am I not supposed to keep L/C ratio high?

So recalculate for some more reasonable L, like 60 nH. You probably
already know, but when you have two of f, L or C you can calculate the
third by

f = 1/(SQRT(2 * pi * L * C))
L = 1/(4 * pi^2 * f^2 * C)
C = 1/(4 * pi^2 * f^2 * L)

For winding the coil, do a search on "inductor calculator", there's a
lot of them on-line.

[M. Hamed]

On Sunday, July 28, 2013 3:52:21 AM UTC-7, Jan Panteltje wrote:
> http://panteltje.com/pub/ebay_fm_transmitter_board_coil_IMG_3967.JPG
> Look at that coil!
>

Very nice pictures. May I ask you what material you are using that is surrounding the coil?

[M. Hamed]

On Sunday, July 28, 2013 4:10:02 AM UTC-7, Jan Panteltje wrote:
> If you are on-frequency and have a clean power suply, then your radio should become very quiet,
>
> as it sees an 'unmodulated' (= stable in frequency) carrier.

It turned out connecting my cheap frequency counter is the source of this noise. It probably totally messes up the biasing. When I don't have that connected, I get exactly the effect that you mentioned. It's pretty cool when the frequency on my radio matches the frequency readout on my scope!

[M. Hamed]

I have to admit I am getting confused by the L/C ratio. I read it in another book that for parallel resonance the L/C ratio should be small. A bit counter-intuitive to me.

[M. Hamed]

On Sunday, July 28, 2013 1:03:16 PM UTC-7, josephkk wrote:
> Hooray. You are actually doing very well. Good enough to make jealous
> of all the fun you are having. Keep going.
>

Thanks! It's been a lot of fun and a lot of learning

On Sunday, July 28, 2013 3:53:06 PM UTC-7, YD wrote:
> Congratulations, you've just discovered the buffer amplifier, to
> isolate the oscillator from the load. From there you can take the
> signal and do something with it without disturbing the frequency.

I am seeing a strange effect though. When I am not probing at the FET the frequency is slightly higher (someone at work happened to have a wireless sniffer). So the load on the FET affects the tank frequency. My only guess here would be Miller effect?

[M. Hamed]

#6
---
The fact that every cap in my oscillator circuit seems to be able to affect the frequency bothered me. The fact that I couldn't analyze the circuit bothered me more. I ended up taking a shot at trying to figure out how f is related to all the C's.

After a few agonizing hours with the math and seven pages of symbols, I actually figured it out and came up with a formula.

2pi.f = sqrt ( (c3*c4 + c2*c3 + c2c4) / ( L * (c1*c3*c4 + c2*c3*c4 + c1*c2*c3 + c1*c2*c4)) )

I put down the formula in an Excel spreadsheet that would computer the frequency and it almost always matched simulation especially if the cap ratios are reasonable. C1, C2 are the tank caps and C3,C4 are the tap caps.

Further simplification can be made if C3,C4 >> C1,C2 then the frequency could be simply:

2pi.f = sqrt ( 1 / (L * (C1+C2)) )

This is the first time I analyze such a circuit and probably the most math I have ever done outside of college. It's also the first oscillator that I could mathematically figure out. proud of myself!

[Jan Panteltje]

On a sunny day (Wed, 31 Jul 2013 09:50:32 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<bfde7445-ba33-47b0...@googlegroups.com>:

?
air?
ferrite core
< >
0 || < >|| plastic former
|| < >||0
0 || < >||
|| < >||0 silvered wire
0 || ||
|| ||0
0 || ||
=============|=
-------------------
---------------------
PCB

[Tauno Voipio]

If you do not have it yet, get the ARRL Handbook (a slightly old
printing will do). It will save you countless hours of guesswork.

Link: <http://www.arrl.org/>

--

Tauno Voipio, OH2UG

[Jan Panteltje]

On a sunny day (Wed, 31 Jul 2013 09:52:32 -0700 (PDT)) it happened "M. Hamed"
<mhdp...@gmail.com> wrote in
<75a3fa6e-af31-49c3...@googlegroups.com>:

>On Sunday, July 28, 2013 4:10:02 AM UTC-7, Jan Panteltje wrote:

>> If you are on-frequency and have a clean power suply, then your radio sho=

>uld become very quiet,
>>
>> as it sees an 'unmodulated' (= stable in frequency) carrier.
>

>It turned out connecting my cheap frequency counter is the source of this n=
>oise. It probably totally messes up the biasing. When I don't have that con=
>nected, I get exactly the effect that you mentioned. It's pretty cool when =

>the frequency on my radio matches the frequency readout on my scope!

Yep!

Now if you put some music from a sound card via a capacitor of say 100 nF,
and a series resistor of say 100 k, to the base or collector of that oscillator,
you get an FM transmitter, especially if you have some collector resistance.
Because if Ic varies then Vce varies, and the capacitance of the collector base junction varies,
and that slightly changes the frequency.
Then you have your first radio transmitter,

You can change frequency too by connecting a reversed biased diode across the coil,
and modulate the bias with the sound card (or mp3 player or whatever) audio:
+
|
[ ] 100 k ~10 pF
|--------------||---> to coil hot side
---- |
/ \ [ ] 100k
--- |
| === 100n
/// |
| 1Vpp audio from soundcard or player

The diode should be a small signal diode,
or simply use a transistor with base and emitter connected to ground and the collector at the 100 k
(NPN if + supply), so the collector acts as a revere biased diode.
Variations are endless, almost _anything_ will FM modulate your circuit.
Not all very linear, but that can be fixed too...

[Robert Baer]

Q: is there a #7 etc in the works?

[M. Hamed]

I guess this deserves an update. It's been almost a year and a half. Since then I gave up radio and RF because it was too difficult and too time consuming and a lot of material had to be digested.

However since then I got my amateur radio license, learned Morse code, and added a few more tools to my toolbox. Then I stopped all radio related activities and got busy with other things. But after a year and a half I couldn't resist coming back to radio and electronics. The idle soldering iron, the dusty scope, and untouched part boxes didn't give me a good feeling. I realized I was approaching this the wrong way and I was making it too difficult for myself.

So, I will have less ambitious goals, and I will be starting a new Log :)