Field strength meter -- diode

mkr5000

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Dec 31, 2021, 2:20:03 PM12/31/21

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Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.

Now that I'm old and stupid can someone tell me what that diode is doing please?

Thanks.

Rich S

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Dec 31, 2021, 2:33:46 PM12/31/21

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No worries, "old and stupid" is everyone's fate (if we're lucky).

I assume this is the circuit?:
https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html

the circuit needs a closed DC path in order for current to flow.
A RF coil would do that, but has very low impedance at low
signal frequencies - and so not much output to drive the meter. Using
a diode in its place allows the circuit to work down to a very
low-frequency cutoff (set by that 50n capacitor and the other
components in the circuit).

how practical this circuit really is, I'm not sure...
cheers, RS

mkr5000

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Dec 31, 2021, 3:47:23 PM12/31/21

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Gotcha. I spaced right through it needing a path. Would like to improve on it
to possibly be able to drive an on/off circuit with a 5v pull up/down or something.
Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
to the microvolt output of something like this? -- thanks

Rich S

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Dec 31, 2021, 4:23:42 PM12/31/21

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> Gotcha. I spaced right through it needing a path. Would like to improve on it
> to possibly be able to drive an on/off circuit with a 5v pull up/down or something.
> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> to the microvolt output of something like this? -- thanks

If you just want to see "something is there"
and accuracy is not important, then the simple
circuits, using transistors are fine. But
if you want the reading to mean something
real (electric field strength in V/m, etc.), then
to get better linearity and range, I'd use an opamp.
Any low-power op-amp would be OK, as
long as it works at your battery's voltage.

(If the sensed field strengths are high, then
the amp stage may not be needed - the
output from the diode can drive a sensitive
meter directly.)

I'd pull out my ARRL Handbook at this point.
to give you more details.
(My copy is in my office, far away...)
Maybe we can find something online...

=RS

Rich S

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Dec 31, 2021, 4:46:49 PM12/31/21

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this looks like a good starting design
with a wide signal level range..
http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/Images/Corrected-202107-QST-Schematic.png
(Schematic #2 from ...
http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/ARRL_QST_FDM_Schematic_Corrections.html
)
Though we could do much better, a modern choice,
for the opamp, instead of an LM3900. Like,
MCP6041-I/P
MCP6043-I/P
MCP606-I/P
MCP6141-I/P
MCP6143-I/P
NJU7001D
NJU7021D
NJU7031D
NJU7051D
NJU7061D
OPA705PA
RE46C311E8F
TLV2760IP
TLV2761IP

= RS

Rich S

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Dec 31, 2021, 6:43:32 PM12/31/21

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> this looks like a good starting design
> with a wide signal level range..
> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/Images/Corrected-202107-QST-Schematic.png
> (Schematic #2 from ...
> http://kf3g25cw.altervista.org/Links/ARRL_QST_FDM_Schematic_Corrections/ARRL_QST_FDM_Schematic_Corrections.html
> )
> Though we could do much better, a modern choice,
> for the opamp, instead of an LM3900. Like,

And Let's narrow down that list to just those with Rail to Rail Inputs
MCP6041
MCP6043
MCP6141
MCP6143
OPA705PA
RE46C311

= RS

John Larkin

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Dec 31, 2021, 7:19:59 PM12/31/21

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On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mike...@gmail.com>
wrote:

>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>
>Now that I'm old and stupid can someone tell me what that diode is doing please?
>
>Thanks.

It's basically a 2-diode half-wave voltage doubler.

A low barrier schottky diode might work better than the germanium
antique, especially at high frequencies.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

Phil Hobbs

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Dec 31, 2021, 7:24:25 PM12/31/21

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_Anything_ is better than an LM3900!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

whit3rd

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Dec 31, 2021, 8:19:06 PM12/31/21

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On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:

> > https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
> >
> > the circuit needs a closed DC path in order for current to flow.

> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> to the microvolt output of something like this? -- thanks

<https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>

A moving-needle meter for 30 uA with 100 ohms internal resistance can cover the
3mV range, with 30 uV easily resolved. Add a battery for collector bias, and
use a low-noise transistor B-E instead of one diode, and you're good for lower signals.

So low, in fact, that some frequency tuning is a wise addition.

Jeff Liebermann

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Dec 31, 2021, 8:59:14 PM12/31/21

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On Fri, 31 Dec 2021 16:19:49 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

>On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mike...@gmail.com>
>wrote:
>>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>>Now that I'm old and stupid can someone tell me what that diode is doing please?

>It's basically a 2-diode half-wave voltage doubler.

Yep. More on how it works including an LTSpice model output (without
the actual model):
<http://k6jca.blogspot.com/2020/11/understanding-basic-rf-field-strength.html>

>A low barrier schottky diode might work better than the germanium
>antique, especially at high frequencies.

Yep.
"RF and microwave power detection with Schottky diodes"
<https://www.infineon.com/dgdl/Infineon-AN_1807_PL32_1808_132434_RF%20and%20microwave%20power%20detection%20-AN-v01_00-EN.pdf?fileId=5546d46265f064ff0166440727be1055>
The voltage doubler arrangement is Fig 15 (Pg 10).

--
Jeff Liebermann je...@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

Phil Allison

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Dec 31, 2021, 9:12:44 PM12/31/21

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Thirdwit strike again: whit3rd wrote:

============================

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html

>
> A moving-needle meter for 30 uA with 100 ohms internal resistance

** Such movement have around 3000 ohm R.

> can cover the 3mV range, with 30 uV easily resolved.

** Horse poo.

The meter shown has a 30-0-30 uA range.
Resolution is 1uA.
Equates to 3mV DC
Any DMM will resolve 0.1 mV.

FOAD

.... Phil

jla...@highlandsniptechnology.com

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Dec 31, 2021, 10:09:41 PM12/31/21

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On Fri, 31 Dec 2021 17:59:02 -0800, Jeff Liebermann <je...@cruzio.com>

wrote:

>On Fri, 31 Dec 2021 16:19:49 -0800, John Larkin
><jlarkin@highland_atwork_technology.com> wrote:
>
>>On Fri, 31 Dec 2021 11:19:59 -0800 (PST), mkr5000 <mike...@gmail.com>
>>wrote:
>>>Nothing could be simpler, an antenna, a coil and a 1N4148 diode but I'm seeing some schematics that have 2 diodes with one replacing the coil and the cathode connecting to the antenna.
>>>Now that I'm old and stupid can someone tell me what that diode is doing please?
>
>>It's basically a 2-diode half-wave voltage doubler.
>
>Yep. More on how it works including an LTSpice model output (without
>the actual model):
><http://k6jca.blogspot.com/2020/11/understanding-basic-rf-field-strength.html>
>
>>A low barrier schottky diode might work better than the germanium
>>antique, especially at high frequencies.
>
>Yep.
>"RF and microwave power detection with Schottky diodes"
><https://www.infineon.com/dgdl/Infineon-AN_1807_PL32_1808_132434_RF%20and%20microwave%20power%20detection%20-AN-v01_00-EN.pdf?fileId=5546d46265f064ff0166440727be1055>
>The voltage doubler arrangement is Fig 15 (Pg 10).

BAT15 is a nice part. Almost the same as an SMS7621.

The circuit in fig 15 works better without RL. Go into a cmos opamp or
comparator. The BAT15 has an Is of over 100 nA, so the diodes
discharge the output cap when the signal goes away.

That freaks some people out, which is always a good thing to do.

https://www.dropbox.com/s/oz821ocx7d62lng/K420_Sig_Det.jpg?raw=1

--

I yam what I yam - Popeye

Jan Frank

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Dec 31, 2021, 10:46:59 PM12/31/21

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whit3rd <whi...@gmail.com> wrote:

> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso
> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht
> ml>

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
11 A full scale, and drifts like hell.

The RM109 is $31.46 on Amazon Canada:
https://www.amazon.ca/Alician-RICHMETERS-Multimeter-Backlight-
Voltmeter/dp/B086VH3NNP/

It is probably cheaper on Amazon US.

I can't find it on Banggood, but it is on Aliexpress for about the same
price to Canada. However, beware of counterfeits on Asian sites. I have
been burned badly.

There is another model of the Richmeter that measures temperature. It is on
a shelf I can't reach right now so I can't give you the model number.

Here are the specs for the RM 109 True RMS Multimeter.

DC Current: 60mA/600mA/10A
DC Voltage: 999.9mV/9.999V/99.99V/750V
AC Current: 60mA/600mA/10A
AC Voltage: 999.9mV/9.999V/99.99V/999.9V
Backlight Time: 120 Seconds
Capacitance: 9.99nF/99.99nF/999.9nF/9.99uF/99.99uF/999.9uF/9.999MF
Continuity: Yes
Dimensions: 65x130x32 mm
Diode Test: Yes
Display Type: 4 1/2 digits
Duty Cycle: 1%-99%
Frequency: 99.99Hz/999.9Hz/9.999KHz/99.99KHz/999.9KHz/9.999MHz
Operating Mode: Auto/Manual Ranging
Operating Temperature: 0 - 40
Resistance: 99.99/999.9/9.999k/99.99k/999.9K/999.9M
Special Function: Voltage Function have Low Frequency test function
Square Wave Output: 50Hz/100Hz/200Hz/300Hz/400Hz/500Hz/600Hz/700Hz/800Hz/
900Hz/1000Hz/200

For some bizarre reason they omit the mV range, which you can see on the
Amazon site. It is third up from the OFF position. This is the range that
gives 1uV resolution.

Phil Allison

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Dec 31, 2021, 11:02:36 PM12/31/21

to

Jan Frank wrote:
===============

>
> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.
>
> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.
>
> My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
> 11 A full scale, and drifts like hell.
>
> The RM109 is $31.46 on Amazon Canada:

** See specs INCLUDING the 9.999 mV range.

https://www.alibaba.com/product-detail/RICHMETERS-RM109-Palm-size-True-RMS_60768171490.html

..... Phil

whit3rd

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Jan 1, 2022, 12:02:32 AM1/1/22

to

On Friday, December 31, 2021 at 6:12:44 PM UTC-8, palli...@gmail.com wrote:

> whit3rd wrote:

>> https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html
>
> >
> > A moving-needle meter for 30 uA with 100 ohms internal resistance
> ** Such movement have around 3000 ohm R.

Review the link. Internal resistance is marked as 100 ohms.

> > can cover the 3mV range, with 30 uV easily resolved.
> ** Horse poo.

??
A needle that swings circa 100 mm, you can read to
a millimeter or less.

> The meter shown has a 30-0-30 uA range.
> Resolution is 1uA.

Not if you have normal eyesight. With a vernier scale, you can pick out
a thousandth of an inch. Mirror scales help, too (though neither is on the depicted model).
Anyone who ever used a slide rule knows to interpolate between marks.

> Equates to 3mV DC
> Any DMM will resolve 0.1 mV.

Zero won't be accurate for analog or DMM either, but twitches of the meter
might be more significant than a dancing last-digit of a digital display.

Phil Allison

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Jan 1, 2022, 12:11:25 AM1/1/22

to

Thirdwit Congenital LAIR whit3rd wrote:
================================

> >
> > > A moving-needle meter for 30 uA with 100 ohms internal resistance
>
> > ** Such movement have around 3000 ohm R.
>
> Review the link. Internal resistance is marked as 100 ohms.

** NO it is NOT !!!

> > > can cover the 3mV range, with 30 uV easily resolved.
> > ** Horse poo.
> ??

** Read my post - fuckwit.

> A needle that swings circa 100 mm, you can read to
> a millimeter or less.

** One div is the resolution - at best.

> > The meter shown has a 30-0-30 uA range.
> > Resolution is 1uA.

> Not if you have normal eyesight. With a vernier scale,

** The meter has has no such damn thing, you fucking LIAR !!!,

> you can pick out a thousandth of an inch.

** You on drugs ? LSD maybe ?? Cocaine ?

> > Equates to 3mV DC
> > Any DMM will resolve 0.1 mV.
>
> Zero won't be accurate for analog or DMM either,

** FFS what a DESPERATE LIAR you are !!!!

FOAD you Dem pig.

whit3rd

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Jan 1, 2022, 12:34:42 AM1/1/22

to

On Friday, December 31, 2021 at 9:11:25 PM UTC-8, palli...@gmail.com wrote:
> whit3rd wrote:

> > > The meter shown has a 30-0-30 uA range.
> > > Resolution is 1uA.
>
> > Not if you have normal eyesight. With a vernier scale,
> ** The meter has has no such damn thing, you fucking LIAR !!!,
> > you can pick out a thousandth of an inch.
> ** You on drugs ? LSD maybe ?? Cocaine ?
> > > Equates to 3mV DC
> > > Any DMM will resolve 0.1 mV.
> >
> > Zero won't be accurate for analog or DMM either,

> ** FFS what a DESPERATE LIAR you are !!!!

Read for content, not for vitriol; the reading on a microvolt-resolution
instrument is only useful for thermocouple circuitry, OR for something
in a stirred constant-temperature bath. Accuracy at that level is impossible
where dissimilar metals and normal thermal gradients abound,
but precision is another story, as is timing (like, looking at a
cellphone sending a burst and causing a periodic brief twitch).

Phil Allison

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Jan 1, 2022, 1:04:42 AM1/1/22

to

Thirdwirt CONGENITAL LIAR : whit3rd vomityed:

===============================

>
> > > > The meter shown has a 30-0-30 uA range.
> > > > Resolution is 1uA.
> >
> > > Not if you have normal eyesight. With a vernier scale,
> > ** The meter has has no such damn thing, you fucking LIAR !!!,
> > > you can pick out a thousandth of an inch.
> > ** You on drugs ? LSD maybe ?? Cocaine ?
> > > > Equates to 3mV DC
> > > > Any DMM will resolve 0.1 mV.
> > >
> > > Zero won't be accurate for analog or DMM either,
>
> > ** FFS what a DESPERATE LIAR you are !!!!
>
> Read for content,

** ROTFLMAO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

BRAIN FUCKED Google monkeys like YOU cannot READ at all.

> the reading on a microvolt-resolution

** MASSIVE RED HERRING !!!!!!!

Your mom was a drug addict and you are brain dead.

Dave Platt

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Jan 1, 2022, 1:32:43 AM1/1/22

to

In article <b623673b-5837-44c7...@googlegroups.com>,

Rich S <richsuli...@gmail.com> wrote:

>Though we could do much better, a modern choice,
>for the opamp, instead of an LM3900. Like,

Just remember that the LM3900 is a Norton amplifier, not a classic op
amp with symmetrical inputs. You may be able to drop a standard
"single supply" op amp into an LM3900 circuit without having to change
things around, but possibly not.

Jan Panteltje

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Jan 1, 2022, 2:37:54 AM1/1/22

to

On a sunny day (Fri, 31 Dec 2021 19:09:23 -0800) it happened
jla...@highlandsniptechnology.com wrote in
<btgvsghggbcuhad95...@4ax.com>:

>The circuit in fig 15 works better without RL. Go into a cmos opamp or
>comparator. The BAT15 has an Is of over 100 nA, so the diodes
>discharge the output cap when the signal goes away.
>
>That freaks some people out, which is always a good thing to do.
>
>https://www.dropbox.com/s/oz821ocx7d62lng/K420_Sig_Det.jpg?raw=1

For a yes / no detector this model works for me:
https://www.ebay.com/itm/313759590627?hash=item490d8768e3:g:31oAAOSwTdlhl2fr

For more info on the source, if between 30 MHz and about 2 GHz:
https://www.ebay.com/itm/272411458376
plenty of free spectrum analyzer software for it around.

This uses an OLED:
http://panteltje.com/pub/SWR_bridge_IMG_5051.JPG
http://panteltje.com/pub/SWR_bridge_circuit_diagram_IMG_5053.JPG

Not sure I published the code, the bridge idea is not mine:
http://panteltje.com/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG

I have a more SWR stuff.

Jeff Layman

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Jan 1, 2022, 2:56:07 AM1/1/22

to

Excuse my ignorance, but why in the "Description" does it say that it's
a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
Range: -300-0-300μA"?

And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
connected in series in the circuit, the higher end of the "G" terminal
is used." That would give it an FSD of 72mV, wouldn't it? Is there a
reason why it's 2.4kohm rather than another value?

--

Jeff

whit3rd

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Jan 1, 2022, 3:28:20 AM1/1/22

to

On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
> On 01/01/2022 01:19, whit3rd wrote:
> > On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
> >> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
> >
> >>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
> >>>
> >>> the circuit needs a closed DC path in order for current to flow.
> >
> >
> >
> >> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
> >> to the microvolt output of something like this? -- thanks
> >
> > <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>

> Excuse my ignorance, but why in the "Description" does it say that it's
> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
> Range: -300-0-300μA"?

Yeah, that's a mystery.

> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
> connected in series in the circuit, the higher end of the "G" terminal
> is used." That would give it an FSD of 72mV, wouldn't it? Is there a
> reason why it's 2.4kohm rather than another value?

It's usual in these things to provide some damping (a shunt resistor or R-C
snubber) across the bare galvanometer, and there's a particular value
that (with the coil inductance) is most effective. That's the only
resistor value I'd expect to see built-in. The merchant might not
know what it's for, but damping makes the needle return to zero
between measurements instead of oscillating for a few seconds.

Jeff Layman

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Jan 1, 2022, 4:06:56 AM1/1/22

to

On 01/01/2022 08:28, whit3rd wrote:
> On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
>> On 01/01/2022 01:19, whit3rd wrote:
>>> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
>>>> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:
>>>
>>>>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html
>>>>>
>>>>> the circuit needs a closed DC path in order for current to flow.
>>>
>>>
>>>
>>>> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
>>>> to the microvolt output of something like this? -- thanks
>>>
>>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>
>
>> Excuse my ignorance, but why in the "Description" does it say that it's
>> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive
>> Range: -300-0-300μA"?
>
> Yeah, that's a mystery.

Probably just a misprint or mistranslation.

>> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is
>> connected in series in the circuit, the higher end of the "G" terminal
>> is used." That would give it an FSD of 72mV, wouldn't it? Is there a
>> reason why it's 2.4kohm rather than another value?
>
> It's usual in these things to provide some damping (a shunt resistor or R-C
> snubber) across the bare galvanometer, and there's a particular value
> that (with the coil inductance) is most effective. That's the only
> resistor value I'd expect to see built-in. The merchant might not
> know what it's for, but damping makes the needle return to zero
> between measurements instead of oscillating for a few seconds.

OK. Makes sense. Just don't try try to push it to -300-0-300μA! :-)

--

Jeff

mkr5000

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Jan 1, 2022, 11:18:57 AM1/1/22

to

Thanks for the suggestion on the BA15T -- just ordered the one with 2 diodes enclosed. I have just a single 5v supply to utilize so hoping I can get a circuit going using an LM358 ? I have a ton of those. Unless another single supply op amp would be better. (I'm a play around with it till it works guy -- you guys are the legit designers). The goal is to get a digital on/off when an rf field is detected on one side of a comparator. Should be easy enough.

It's for an amateur radio situation. Hopefully just a piece of wire near the xcvr will be fine. (Rather than maybe having to rely on the antenna). We'll see..... things are pretty well shielded these days.

It's not the old Knight kit I had.

Now quit pickin' on each other you guys. !

Phil Hobbs

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Jan 1, 2022, 9:12:56 PM1/1/22

to

Jan Frank wrote:
> whit3rd <whi...@gmail.com> wrote:
>
>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso
>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht
>> ml>
>
> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift.
>
> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.
>
> My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
> 11 A full scale, and drifts like hell.

Nah, there's the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Jan Frank

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Jan 2, 2022, 12:50:01 AM1/2/22

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>
>> I was thinking of replacing the input transistors with an LMC660 or modern
>> equivalent and may do so if I ever need to monitor weak currents over a
>> period of time.
>
>You can do a good job with that. I've been meaning to build a nice
>100-pF charge-dispensing loop electrometer, but so far the 610C or even
>the old tube-based 405 have been better than good enough.
>
>>
>> But a better option would be to get a used 616 which offers autoranging
>> and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on;
>> eBay - around $295 or so.
>
>I haven't got a lot of use for a digital electrometer. Down in the
>picoamps and lower, seeing trends is much more important than high
>precision, not least because leakages are very unlikely to be stable to
>3 sig figures.
>
>(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for
>the 610C on my bench.
>
>Cheers
>
>Phil Hobbs

--

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Jan 3, 2022, 9:59:20 AM1/3/22

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Ah, yes. Thanks Phil, for naming those.
We have a drawer full of those
back in the lab. Their purpose is obvious
but I didn't know their origin.
(We have a lot of old Tek repair parts
tucked away, unless they were victims
of another "5s+2 event".)

John, thanks for sharing. Your
"integrator" is pretty leaky (Rf=510 R) :-)
Is that Cf a 'virtual capacitor'? It seems
to be hidden in the wiring photo.

The output caps, Are they special film
that you chose to minimize Dielectric Absorption*?
Or given that the node impedances are so low
(220 R) any plastic is OK?
(*Ref: https://www.sciencedirect.com/topics/engineering/dielectric-absorption)

= RS

Rich S

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Jan 3, 2022, 10:38:33 AM1/3/22

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> I haven't got a lot of use for a digital electrometer. Down in the
> picoamps and lower, seeing trends is much more important than high
> precision, not least because leakages are very unlikely to be stable to
> 3 sig figures.
>

Phil, this is an excellent point, that I want to
amplify. Even if accuracy is lacking, the
precision and stability of a piece of equipment
(no matter how old it is) is still valuable.
Thanks! = RS

jla...@highlandsniptechnology.com

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Jan 3, 2022, 11:38:18 AM1/3/22

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The opamp is a unity-gain follower. The 510r could be zero ohms, but I
thought I might add an offset pot some day, which I didn't.

>
>The output caps, Are they special film
>that you chose to minimize Dielectric Absorption*?

No, ordinary ceramics. We have a lot of RF in our place from Sutro
Tower, and I wanted to keep that out. Opamps like to rectify RF.

>Or given that the node impedances are so low
>(220 R) any plastic is OK?
>(*Ref: https://www.sciencedirect.com/topics/engineering/dielectric-absorption)
>
>= RS

The measurements are DC, slow, so DA is not a concern.

It worked terribly until I figured out that the RatShack nylon binding
posts were super leaky, and added the lexan plate. That was messy.

I have a set of Pomona banana plugs with various resistors from 1K to
1T ohms. One of those plugs in as Z1 or Z2, and the DUT becomes the
other. Then measure the two voltage drops.

Another aluminum chassis is used as a shield, upside down, and can be
bolted down. That avoids errors from local e-fields, like people
walking and breathing in the room, or 60 Hz fields.

jla...@highlandsniptechnology.com

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Jan 3, 2022, 11:42:30 AM1/3/22

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Keithley recommended that some of the resistors inside the 610 be
replaced regularly. Mine might be 40 years old, and I doubt anyone did
that.

You can buy a few high-ohm resistors and check the meter now and then.
Mine seems fine.

There's probably a way to check it with capacitors too.

Jan Panteltje

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Jan 9, 2022, 5:57:59 AM1/9/22

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On a sunny day (Sun, 09 Jan 2022 10:25:32 +0100) it happened Jeroen Belleman
<jer...@nospam.please> wrote in <sre9mc$prb$1...@gioia.aioe.org>:

>On 2022-01-09 00:51, Clifford Heath wrote:
>> On 8/1/22 9:43 pm, Jeroen Belleman wrote:
>>> On 2022-01-08 10:53, Jan Panteltje wrote:
>>>> PS see https://github.com/jdesbonnet/RCWL-0516
>>>>
>>>>> Now I just received some about 3 GHz? (still have to measure
>>>>> it) doppler motion detectors that work through glass etc. from
>>>>> a local shop, also for about 2 Euro a piece, on ebay those are
>>>>> even cheaper: https://www.ebay.com/itm/311911747154 Is using
>>>>> that frequency even legal here? Plenty of stuff play with!
>>>>
>>>
>>>
>>> Interesting gadget. I suppose Q1 does double duty as oscillator and
>>> mixer. The schematics are of no help to figure out how it really
>>> works. Anyone care to comment? The secret is all in the PCB layout
>>> around Q1, clearly.
>>
>> I believe it's the same approach that used to be used by the 10GHz
>> automatic door detectors that used to trigger automotive radar
>> detectors. Oscillator and mixer in one device, pick out the audio
>> Doppler signal.
>>
>> CH
>
>I gathered that much, yes. I was more interested in a discussion
>of the PCB traces and how they work together to make an oscillator
>and antenna.
>
>I'm trying to guess the signs of the reactances between the
>terminals of Q1 at 3GHz. The trouble is that everything is
>coupled to everything else and I'm at a loss to tell what
>is dominant. Every damn bit of trace around Q1 looks like
>a resonator that could be either capacitive or inductive at
>3GHz!
>
>At least I'm convinced that none of the actual /components/
>on the schematic are involved in determining this oscillator.
>(Except for Q1, of course.) It's all in the PCB traces.
>
>Jeroen Belleman

Yes
it is all not so different from the twisted wire oscillator, but mine is simpler:
http://panteltje.com/pub/2.4GHz_twisted_oscillator_IMG_3629.GIF
circuit:
http://www.panteltje.com/pub/twisted_wire_oscillator_IMG_6629.JPG
probably can make my own GHz Doppler RF with that...

Jeroen Belleman

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Jan 9, 2022, 6:58:59 AM1/9/22

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When analyzing an oscillator, I always start by identifying
the reactances between BE, EC and CB. (Or whatever the equivalent
nodes are on the actual gain element.)The first pair should
have the opposite sign from the last, i.e., if the BE and EC
reactances are capacitive, the CB reactance should be inductive
and we have a Colpitts. In the reverse case, we have a Hartley.

Any of the reactances could be a resonator of some sort, so
what counts are the reactances at the intended oscillation
frequency. I often see oscillators that use parasitic elements
for one or more of these reactances. That seems to be the case
in your example too. I usually try to avoid dependence on such
elements when designing an oscillator.

The next step is to get the magnitudes of those reactances and
calculate the loop gain. Of course, they aren't pure reactances,
but I usually neglect that at first. Nine times out of ten, that
turns out well enough.

Jeroen Belleman

Jan Panteltje

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Jan 9, 2022, 9:17:09 AM1/9/22

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On a sunny day (Sun, 09 Jan 2022 12:58:49 +0100) it happened Jeroen Belleman
<jer...@nospam.please> wrote in <sreilq$mnp$1...@gioia.aioe.org>:

Sure, I am but a neural net and just blob these things down without much maaz.
In the twisted wire oscillator case I started with a longer twisted pair
resulting in a much lower frequency and then cut pieces of until I had the 2.4 GHz.
Basically a wavelength related thing, twisted just to hold it together.
On the PCB of that other thing you also see a feedback path.
But I just think in [ parts of ] a wavelength.
S parameters last time I used those was in school for the exams...
One experiment is worth a thousand hours of theory, no spice in use here for this either.
In the 'twisted' LOL case maybe a low-pass from the collector will also show Doppler difference frequency
if that twisted pair picks up any reflections.
On their PCB it looks like they somehow couple it to some bigger circular area on the other side of the PCB
to get more radiation.