Receiving Loop Antenna Question
Spin
is 24" or more per side..... how important would the guage of the wire be &
also solid versus stranded wire? Antenna would be used indoors.
Jerry
"Spin" <noe...@alone.invalid> wrote in message
news:i8Sdl.1341$aI1...@nwrddc01.gnilink.net...
> If i were to construct a square receiving loop antenna for the am bcb that
> is 24" or more per side..... how important would the guage of the wire be
> & also solid versus stranded wire? Antenna would be used indoors.
Hi Spin
Have you seen this site?
http://www.mindspring.com/~loop_antenna/
Jerry KD6JDJ
dave
nm...@wt.net
Doesn't matter much. Maybe a slight difference in Q with thin
vs fat wire, but overall no big deal.
I've got loops made from thin copper motor wire, and also
one from insulated #14 gauge stranded house wire. They all work.
From a mechanical standpoint I think a diamond is easier
to deal with..
Here is one of my favorite designs for a cheap simple PVC
loop. You can slap one together pretty fast. Kind of like PVC
tinker toys.. :/ You do have to drill the holes, but that's easy.
http://home.comcast.net/~nm5k/loop5.jpg
Ian Jackson
<9df9210f-a2aa-4092...@f40g2000pri.googlegroups.com>,
nm...@wt.net writes
(something like 25 wires - the sort used in PCs to connect hard drives
and the like) put away for a rainy-day loop antenna project. While I
could make one large loop using all 25 wires for the really low
frequencies, I'll almost certainly cut it up and make several smaller
loops with fewer wires for the higher frequencies.
--
Ian
PhattyMo
Or put some taps on it,say every 2 turns? each one connected to a pole
of a large 12 position rotary switch.. then you can select a small
loop,or a really large one,for the low stuff. :-) Tuneable!
dave
Stick with a single wire and relatively few loops. More wire won't make
the loop bigger, just harder to tune.
Allodoxaphobia
> Ian Jackson wrote:
>>>
>> What about ribbon cable? I've got a fair length of ribbon cable
>> (something like 25 wires - the sort used in PCs to connect hard drives
>> and the like) put away for a rainy-day loop antenna project. While I
>> could make one large loop using all 25 wires for the really low
>> frequencies, I'll almost certainly cut it up and make several smaller
>> loops with fewer wires for the higher frequencies.
>
> Stick with a single wire and relatively few loops. More wire won't make
> the loop bigger, just harder to tune.
I don't think he meant to connect all those wires in parallel.
But, it would be a little tedious to connect each wire at one end to its
neighbor at the other end (of the loop), and _not_ create an ugly bird's
nest at the 'joint'.
Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm
Cecil Moore
> I don't think he meant to connect all those wires in parallel.
I thought he was talking about a tapped coil with
the unused parts floating. Might result in a new
Tesla coil design. :-)
--
73, Cecil http://www.w5dxp.com
Jerry
"Allodoxaphobia" <bit-b...@config.com> wrote in message
news:slrngnjm0q.19...@shell.config.com...
> On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote:
>> Ian Jackson wrote:
>>>>
>>> What about ribbon cable? I've got a fair length of ribbon cable
>>> (something like 25 wires - the sort used in PCs to connect hard drives
>>> and the like) put away for a rainy-day loop antenna project. While I
>>> could make one large loop using all 25 wires for the really low
>>> frequencies, I'll almost certainly cut it up and make several smaller
>>> loops with fewer wires for the higher frequencies.
>>
>> Stick with a single wire and relatively few loops. More wire won't make
>> the loop bigger, just harder to tune.
>
> I don't think he meant to connect all those wires in parallel.
> But, it would be a little tedious to connect each wire at one end to its
> neighbor at the other end (of the loop), and _not_ create an ugly bird's
> nest at the 'joint'.
>
> Jonesy
Hi Jonesy
For what Its Worth, I tried making a big AM reception loop using some big
ribbon cable, and it didnt work. The cable was/is color coded so it was
easy to connect the ends so the input to output is a series connection of
the wires. The antenna didnt work. I assummed it was due to excessive
'distributed capacity' between windings. I had no interest in researching
the reason for ribbon cable use for AM loop antennas. Besides, it got Very
difficult to assemble the loop onto the mounting frame and have it look
presentable.
" >> Stick with a single wire and relatively few loops. More wire won't
make
>> the loop bigger, just harder to tune."
Jerry KD6JDJ
>
Ian Jackson
<bit-b...@config.com> writes
>On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote:
>> Ian Jackson wrote:
>>>>
>>> What about ribbon cable? I've got a fair length of ribbon cable
>>> (something like 25 wires - the sort used in PCs to connect hard drives
>>> and the like) put away for a rainy-day loop antenna project. While I
>>> could make one large loop using all 25 wires for the really low
>>> frequencies, I'll almost certainly cut it up and make several smaller
>>> loops with fewer wires for the higher frequencies.
>>
>> Stick with a single wire and relatively few loops. More wire won't make
>> the loop bigger, just harder to tune.
>
>I don't think he meant to connect all those wires in parallel.
>But, it would be a little tedious to connect each wire at one end to its
>neighbor at the other end (of the loop), and _not_ create an ugly bird's
>nest at the 'joint'.
>
I'm not sure how many turns would be needed. 4, 5 or 6 at the most
(depending on frequency)? I'd certainly study the available information
before I started. Of course, before I started, any superfluous wires
would be stripped from the ribbon - it's just that the ribbon I've got
has a lot wires.
I really can't see any problem with cutting the ribbon, and then
re-joining it with the end of each wire being connected to its neighbour
This technique MUST have been used before by someone.
--
Ian
Ian Jackson
<jerry...@verizon.net> writes
capacity between the windings. It looks like it's back to the drawing
board!
>
> " >> Stick with a single wire and relatively few loops. More wire won't
>make
>>> the loop bigger, just harder to tune."
>
> Jerry KD6JDJ
Ian
nm...@wt.net
> On Fri, 23 Jan 2009 13:57:40 +0000, dave wrote:
> > Ian Jackson wrote:
>
> >> What about ribbon cable? I've got a fair length of ribbon cable
> >> (something like 25 wires - the sort used in PCs to connect hard drives
> >> and the like) put away for a rainy-day loop antenna project. While I
> >> could make one large loop using all 25 wires for the really low
> >> frequencies, I'll almost certainly cut it up and make several smaller
> >> loops with fewer wires for the higher frequencies.
>
> > Stick with a single wire and relatively few loops. More wire won't make
> > the loop bigger, just harder to tune.
>
> I don't think he meant to connect all those wires in parallel.
> But, it would be a little tedious to connect each wire at one end to its
> neighbor at the other end (of the loop), and _not_ create an ugly bird's
> nest at the 'joint'.
>
> Jonesy
Yep, it's a continuous single wire. If you used ribbon cable, you
would have to put a cut, and the jumper to jump over to the next
wire on each turn.. Would be a pain.
You just take a single length of wire and thread it around
through the holes until you have the number of turns you need.
You are moving over a row of holes on each turn.
The main thing to consider is you end up building the loop
and deciding the proper number of turns around the
capacitor you have, not the other way around.
A double 365pf cap "730 pf total if jumped together" will let
you be able to tune the whole AM-BC band with most loops.
My 44 inch per side diamond loop for MW has five turns.
My 16 inch diameter circle loop for MW uses 12 turns.
Both are using basically the same cap values.
I also use a single turn coupling loop that is inside and
slightly smaller than the main loop. But it does not effect
tuning, and it's size and spacing from the main loop is fairly
uncritical. The cap is in parallel with the main loop winding.
If you use a portable with a built in loop stick antenna,
you can just couple the radio to the loop and it will
work. But all my radios require a feed line to the antenna.
Cecil Moore
> My 16 inch diameter circle loop for MW uses 12 turns.
I know multiple loop antennas are lossy for transmitting.
Are they adequate for receiving because of the AGC dynamic
range in the receiver?
Art Unwin
I would not be so quick to dismiss the ribbon wire on the basis of
capacitance build up ! If you start from the middle of one end by
joining
the two center wires together and from then on joining the end to end
wires
moving outwards what you have then done is to cancel not only the
capacitance build up but also the inductance build up.
You can then unfasten the first step on the center winding and feed it
from that point
i.e. center fed
Art
christofire
"Art Unwin" <Arthu...@gmail.com> wrote in message
news:888d993a-8305-400f...@o40g2000prn.googlegroups.com...
... but a multi-turn loop in which the self-inductance cancelled wouldn't be
much of a receiving antenna! Production of EMF from the magnetic field
caused by current flowing in the adjacent turns and production of EMF from
the magnetic field component of an incident radio wave rely on the same
principle.
Chris
Richard Clark
<Arthu...@gmail.com> wrote:
>what you have then done is to cancel not only the
>capacitance build up but also the inductance build up
AKA Resistor
Dave
"christofire" <chris...@btinternet.com> wrote in message
news:HP6dnaSm94TWNuHU...@bt.com...
destructive.
Art Unwin
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
As an experimenter I am inclined to give things a try. If everything
can be solved by the brain while sitting on the sofa then it would be
a waste of time! As a recieving antenna all you would need is wire
that has distributed loads and ZERO lumped loads, so why not just get
rid of the lumped loads via cancellation?
The complications that you bring up, I suggest, would be applicable to
transmitting antennas only
thus I feel experimentation is required before looking for a reason to
discard.
Sometimes an innocent experiment provides a long looked for answer to
the most complicated
question
Sal M. Onella
< snip >
>As an experimenter I am inclined to give things a try. If everything
>can be solved by the brain while sitting on the sofa then it would be
>a waste of time! As a recieving antenna all you would need is wire
>that has distributed loads and ZERO lumped loads, so why not just get
>rid of the lumped loads via cancellation?
Resonance? I think we already invented that.
nm...@wt.net
I'm not sure how the AGC comes into play here..
The 16 inch antenna provides plenty enough signal,
even with no preamp used. You could turn the AGC on
or off, wouldn't really matter. No different than any
other antenna you might connect in that regard.
They are lossy for transmitting, but on the MW bands
you have so much excess signal level it's not an
issue as far as receiving. Note the ferrite bar antenna,
which is even more lossy than the open loops I use.
It has no problem providing enough signal for a
cheap portable radio.
You might be surprised just how much level you can
get from a tuned small loop on the low bands.
As an example, that 16 inch loop provides more
signal than the whip on a car. I once tried it with a
delco radio in my truck. I hooked the loop up to it,
and it was as hot as a firecracker vs the standard
whip.
The catch is the system is very high Q, and requires
constant tuning of the cap as you change frequency.
nm...@wt.net
>
> I would not be so quick to dismiss the ribbon wire on the basis of
> capacitance build up !
I would not be so quick to assume I dismissed ribbon wire
on the basis of capacitance buildup. Where do you read
any such thing in what I posted?
Has nothing to do with why I wouldn't use ribbon cable.
Using a ribbon cable would be a pain in the arse.
You would have to cut and jumper each turn to the
next turn. Makes more sense just to use a single
wire and thread it through the holes, row by row
if multiple turns are needed.
JIMMIE
I did this with ribbon cable once and it is actually pretty easy to
do. I couldnt have taken more than 15 minutes to fabticate an 8 turn
coil.
Jimmie
christofire
On Jan 25, 12:11 pm, "christofire" <christof...@btinternet.com> wrote:
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
>
That principle is Faraday's Law which is fully reciprocal, so no, this is
equally applicable to receiving and transmitting antennas.
I hope 'EMF' isn't being misread as anything other than its original meaning
in this context, that is, electro-motive force (the non-ambiguous form of
'voltage').
Chris
Art Unwin
Hi Chris,
I need a bit more with respect to your response in more layman terms
When a multi turn helix is generated it can be used for both
transmitting and receiving.
When generating two helix antennas where one is contra wound and both
are connected at the top
you are saying that it will NOT be suitable for receiving !
We know by common use that the single helix is good for transmitt and
receive . So what exactly
does the addition of the contra winding do to prevent the combination
from receiving?
Looking forward to your take on the question.
Best regards
Art
christofire
On Jan 26, 8:38 am, "christofire" <christof...@btinternet.com> wrote:
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
8><
Hi Chris,
I need a bit more with respect to your response in more layman terms
When a multi turn helix is generated it can be used for both
transmitting and receiving.
When generating two helix antennas where one is contra wound and both
are connected at the top
you are saying that it will NOT be suitable for receiving !
We know by common use that the single helix is good for transmitt and
receive . So what exactly
does the addition of the contra winding do to prevent the combination
from receiving?
Looking forward to your take on the question.
Best regards
Art
OK. The term 'helix' is most often applied to the travelling-wave antenna
invented by John Kraus, often used at VHF and above, which generates or
receives a circularly-polarised wave predominantly in the direction of its
axis. It is also used in 'normal-mode helix' for the type of monopole
element often found on walkie talkies, that generates and receives a
linearly-polarised wave. Both of these are connected to electronics at one
end only.
The discussion was about loop antennas having one or more turns, with both
ends of the winding connected to electronics. This construction can also be
called a solenoid, but it would provoke confusion to call it a 'helix'.
When an alternating current is passed through a solenoid it generates a
magnetic field, H, through its centre and around it - the transmitting case.
When a solenoid is placed in an alternating magnetic field, if any lines of
magnetic force pass through its winding it will generate an electro-motive
force (EMF) from which current can be drawn to operate a receiver - the
receiving case.
In the transmitting case the physical characteristics (described by the
intrinsic impedance) of 'space' - the air surrounding the solenoid - cause
an electric field, E, to be generated from the alternating magnetic field,
in phase with the H field that caused it (viz. the intrinsic impedance of
space is real not complex) and together these in-phase E and H components
give rise to an electromagnetic wave. A fraction of the input power will be
radiated away from the solenoid in that wave, in directions where their
vector cross-product ExH is not zero. The field strength of either the E or
H component of the radiated wave will decay linearly with increasing
distance.
You can find a good account of this process in books like 'Antennas' by the
late John Kraus but it isn't possible to get very far without use of
mathematics. Chapter 7 of 'Antennas for all applications' by Kraus and
Marhefka, the 2002 edition, covers all this in greater detail and would be
worth obtaining if you're interested.
The 'sense' (i.e. clockwise/anticlockwise with respect to some datum) of the
winding of a solenoid, and the direction of the current applied, affect the
polarity of the magnetic field it produces, and vice versa for the receiving
case. Consequently, the phase with respect to time of the alternating H
field (and the alternating E-field component of the radiated electromagnetic
wave) depend on the 'sense' of the winding, but the polarisation of the
radiated wave depends on the alignment of the axis of the solenoid. By
convention, 'polarisation' is the angular direction of the E field in the
outgoing wave, which is perpendicular to the H-field component, and both are
perpendicular to the direction of propagation, so solenoid with a horizontal
axis radiates a vertically-polarised (VP) radio wave - and receives best
from a VP wave; the ferrite-rod-in-a-broadcast-receiver case.
Back to my original point: if part of the winding of the solenoid is wound
in the opposite sense to the rest of the winding then its contribution to
the generated H field, or the EMF on receiving, will oppose the contribution
from the other part of the winding. If the winding has half in each
'sense', connected in series (like a non-inductive wire-wound resistor),
then it will not generate an H field or develop an EMF from an incident H
field, so it will not work as a transmitting or receiving antenna ... for
the reasons outlined above.
Enough?
Chris
Art Unwin
Chris
First of all thank you very much for the effort that you placed in
your response.
It really what I expected from you after reading your profile ie the
anbsence of derision.
Now I am not fully convinced with your response as the rest of the
newsgroup already suspect
Coming from a different direction with respect to mathematics, when
adding a timevarying field
to a Gaussian field it equates in every way to the laws of Maxwell.
Both of these laws I consider
as an absolute truth. The above therefore states that the presence of
particles is undeniable in the generation of RF communication. Because
of the specificity of a state of equilibrium in a Gaussian field the
following can be stated. A radiator or array can be any size, shape or
varied elevation
..............AS LONG AS IT IS IN A STATE OF EQUILIBRIUM
From the above ground rules which is confirmed by Maxwells laws the
single winding of a wire
is NOT in equilibrium unless the lumped properties are cancelled which
leaves a structure that is in equilibrium ala wire that is conductive
and with no other properties other that he addition of distributed
loads that are common from a conductor.
Your response is based on the generation of fields without which the
radiator cannot receive by incoming waves from a transmitter, Where as
my response is based on the basis of particles impinging on a receive
antenna to create oscillation.
The biggest difference is the interpretation of a tank circuit( a
circuit in equilibrium) where in the perfect case of zero friction
your aproach would define this operation as a zero tx/rc element
My interpretation is that it cannot be zero friction even if the
distributed components were friction free because of the presence of
particles, which must be impelled by force to another radiator to
create oscillation.
So to sum up
Your aproach is from dissipating fields to provide communication and
mine is from non dissipating fields that dislodge particles as it
rotates to and from the distributed loads using both as energy
retainers..
As I have stated before, this is a presently a widely known method in
a macro re enactment of salvage processes that sorts materials by
directional magnetic field thrusts provided by eddy fields
I do need more time to study your response to see the difference
between the field aproach and the particle aproach tho with my present
circumstances I may not be able to determine.
Again, thankyou for your gentlemanly response, a rarity in this
particular newsgroup.
Regards
Art
christofire
On Jan 26, 12:16 pm, "christofire" <christof...@btinternet.com> wrote:
> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
8><
>
You're welcome.
I can't say I understand much of what you've written above but I'm sure
there are often many ways to visualise the same physical process; the
wave/particle duality of EM radiation being one often spoken about. For
this case, I wrote from the viewpoint of the work reported in a large number
of text books: the set of principles that's passed on at universities and
has been used to design the vast majority of antennas that have been used
since the discovery of radio. I'm not aware of any successful antenna
designs, operating lower than EHF, based on a particle theory of
electromagnetic radiation. However I am aware of a few unsuccessful designs
(e.g. the 'crossed-field antenna') for which the creators have purported to
re-write the known (wave) theory of radiation.
I know it's generally bad to generalise (!) but it seems clear to me, and
probably many others, that antennas based on well-documented,
well-understood, theory are always a safer bet! They certainly are in (most
lines of) business where cost matters - but perhaps not in amateur circles
where different motives apply.
Chris
Art Unwin
Understood
I have an applied patent that is on the net somewhere that goes thru
these same motions to obtain an array inequilibrim whbich are then
displayed via the AO pro program whiuch confirms the
equilibrium theoryn that is obtained by the Gaussian field aproach on
Maxwells laws.
On the same patent request I provided an analysis of a verticle dipole
which for maximum gain is tipped with reference to earth. The tipping
force is the weak force or the eddy field I spoke of which is not
included in programs associated with planar forms that are based on
intercoupling coupling.
The same aproach can also be applied using the equilibrium requirement
as I proposed earlier.
The only problem I can see in using MOM programs is the validity of
close spaced conduntors where it is possible to conceive of
interfering eddy currents not impinging upon particles, but it terms
of receiving there is nothing to prevent the impact of particles on
the radiator. At present my tower antenna is made of circularly wound
wires in both the cw and ccw direction, again based on the equilibrium
finding, where the antenna is a travelling wave form that is end fed
which allows for smaller volume antennas to those presently known.
Everything revolves around the extended Gaussion theorem which equates
to Maxwell's laws with the addition of particles within a boundary in
equilibrium. Break that association down then all of mine falls apart.
I will place a dual wound helix on my page in the next couple of days
that is produced via
the AOP Minninec program for antennas by Beasely so that you can see
it for your self. It will not be completely accurate as such an
arrangement requires many more point calculations than I have
available to me. Will be at hospital all day tomorrow so please be
patient on my page issue.
Best regards
Art
Dave
>
> I can't say I understand much of what you've written above but I'm sure
> there are often many ways to visualise the same physical process;
and be glad that you don't understand it! its pure bafflegab, unless you
really like magical levitating diamagnetic neutrinos that hop off the
antenna to make em waves.
Art Unwin
> "christofire" <christof...@btinternet.com> wrote in message
David
Your accusations doesn't bother me. After all, you got a degree by
memorising the books
without checking from first principles for yourself. Choosing from
a,b,c or d is a similar short cut for education without the
application of personal intelligence
It would be suicidal for any student to not parrot phrases and
teachings ennunciated by their professor. He is the one who reads your
work and determines whether you have earned a degree or not, thus
conformity is a requirement. When you stated that statics has no
place with respect to radiation or words to that effect it was
understandable for me as the aproach that I ventured is not covered in
any of the books presently being published. The point that all should
know is that you cannot build a castle on sand, or in other words, all
theories must rest on a sound foundation or findings and since your
degree was obtained by being a follower your reaction to that which is
not in compliance with the books of the day is perfectly
understandable
Take care
Art Unwin KB9MZ.......xg (uk)
Art Unwin
ok Chris
I have to get ready for an operation early tomorrow so I collected
some stuff from the past and just put it into a package for my son to
post for me. It will at least give you some stuff to look at until I
get back. The important thing to remember is all other polarizations
are always 3db down from 'max gain' and with only one circular
direction with horiz and vert. The object is to choose the
polarization required which you are aiming for to get the purest of
radiation which helps in the reflected signal when searching for
weather abnormalities at airports such as wind shear with minimum
distortion. Sorry I could not plan the offering so I have not vetted
what is posted
See....,. http://users.sdsc.edu/~unwin/
Best regards
Art unwin KB9MZ.......xg (uk)
maxpo...@yahoo.com.au
> (something like 25 wires - the sort used in PCs to connect hard drives
> and the like) put away for a rainy-day loop antenna project. While I
> could make one large loop using all 25 wires for the really low
> frequencies, I'll almost certainly cut it up and make several smaller
> loops with fewer wires for the higher frequencies.
> Ian- Hide quoted text -
>
Hello Ian,
I have used 16 core ribbon cable, with each core connected in series
for an AM broadcast band loop antenna. It was about 1 metre long in
circumference which gave me a total length of 16 metres. I used a
cheap tuning variable capacitor with a switch which connected another
capacitor to increase the total capacitance so I could tune down to
the bottom of the AM band. It is coupled through the internal ferrite
antenna in the radio. On my main tuner in the house, it has
connections for an antenna on the back, so I made another ribbon cable
loop antenna and put a single wire with it as a pick up wire. Each end
of the pick up wire is connected to the antenna inputs on the tuner. I
have made four of them. They are easily made, not too fiddly and they
work well. Cheers
Max
Ian Jackson
<fd7be51c-f1d9-4798...@y1g2000pra.googlegroups.com>,
maxpo...@yahoo.com.au writes
advice. I was thinking about a somewhat larger loop - maybe using 2 or
3m of ribbon, but with fewer turns - but I can't see why 'working well'
should no longer apply.
I have no preference for using ribbon - it's just that is seems like a
simple way of getting several turns 'in one go' (if you know what I
mean). Obviously, you will reduce the self capacity (and have a greater
potential tuning range) by using a loop with the turns well spaced -
although the inductance will probably be a bit less, and you'll need to
add a turn or two to compensate.
My next question is about using varicap diodes to tune the loop. Most
designs use a conventional capacitor, but a varicap would enable the
loop to be located (say) in the loft, and the tuning varied from the
shack downstairs. Is this technology worth perusing (ie Googling)? Or
has it been found to be a waste of time?
Thanks again.
--
ian
christofire
"Ian Jackson" <ianREMOVET...@g3ohx.demon.co.uk> wrote in message
news:kDDg+6Oy...@g3ohx.demon.co.uk...
Varicaps are fine and you will find devices containing pairs like the BB212,
specifically intended for tuning domestic receivers. They're used in all
the modern radios that are digitally controlled. The trick is to use them
in balanced pairs so strong signals don't push a single diode into
conduction.
Chris
Richard Clark
<chris...@btinternet.com> wrote:
>> My next question is about using varicap diodes to tune the loop. Most
>> designs use a conventional capacitor, but a varicap would enable the loop
>> to be located (say) in the loft, and the tuning varied from the shack
>> downstairs. Is this technology worth perusing (ie Googling)? Or has it
>> been found to be a waste of time?
>Varicaps are fine and you will find devices containing pairs like the BB212,
>specifically intended for tuning domestic receivers. They're used in all
>the modern radios that are digitally controlled. The trick is to use them
>in balanced pairs so strong signals don't push a single diode into
>conduction.
Hi All,
The strong signal issue goes well beyond the possibility of
conduction. When you think about a voltage controlled capacitor, you
have to account for the effects of the voltage of the signal you are
tuning (and those you are not tuning). The BB212 application is found
characterized for signal levels less than 100mV (typically far less).
Why? A half volt signal level at the terminals of the device (taking
the BB212 for example) biased at 1V will swing the capacitance 100pF
above and below where it would be thought to be tuned. Of course,
correspondingly smaller signals have correspondingly smaller swings -
it all depends on how much you can tolerate.
This swing is also a problem for PIN diodes used as voltage variable
attenuators.
73's
Richard Clark, KB7QHC
Ian Jackson
<kb7...@comcast.net> writes
>On Wed, 28 Jan 2009 13:03:45 -0000, "christofire"
><chris...@btinternet.com> wrote:
>
>>> My next question is about using varicap diodes to tune the loop. Most
>>> designs use a conventional capacitor, but a varicap would enable the loop
>>> to be located (say) in the loft, and the tuning varied from the shack
>>> downstairs. Is this technology worth perusing (ie Googling)? Or has it
>>> been found to be a waste of time?
>
>>Varicaps are fine and you will find devices containing pairs like the BB212,
>>specifically intended for tuning domestic receivers. They're used in all
>>the modern radios that are digitally controlled. The trick is to use them
>>in balanced pairs so strong signals don't push a single diode into
>>conduction.
Thanks for the advice, however......
>
>Hi All,
>
>The strong signal issue goes well beyond the possibility of
>conduction. When you think about a voltage controlled capacitor, you
>have to account for the effects of the voltage of the signal you are
>tuning (and those you are not tuning). The BB212 application is found
>characterized for signal levels less than 100mV (typically far less).
>
>Why? A half volt signal level
(that's surely one hell of an RF signal?)
>at the terminals of the device (taking
>the BB212 for example) biased at 1V will swing the capacitance 100pF
>above and below where it would be thought to be tuned. Of course,
>correspondingly smaller signals have correspondingly smaller swings -
>it all depends on how much you can tolerate.
>
Varicap diodes will always suffer from having their capacitance
modulated by an RF signal impressed upon them. However, they do seem to
work well enough - even when the RF level is pretty high (which must be
the case especially with varicap-tuned oscillators - ie most VCOs and
PLL systems).
Presumably, the effect of this modulation will be to generate
intermodulation products. In VCOs, this will simply appear as harmonics
of the oscillator signal (which you would get anyway - even with a
conventional tuning capacitor). Where multiple-frequency signals are
present (like you have with the receiving loop), the most apparent
effect of the modulation of the diode capacity will appear as
crossmodulation and other nasties on the other signals in the passband.
However, as varicaps ARE used for the tuning of the input of receiver RF
stages, how do they 'get away with it'?
>This swing is also a problem for PIN diodes used as voltage variable
>attenuators.
>
My understanding of things is that the effectiveness of PIN diodes
relies on them having a very poor performance at RF (especially at VHF
and UHF). In attenuator circuits, they are forward biassed, and the DC
current passing through them varies their RF resistance. However, the
charges flowing through the junction are so 'sluggish' that they don't
react to the rapidly-changing RF voltages. There is therefore negligible
modulation of the RF resistance by the RF signals passing though them.
--
Ian
Jerry
"Richard Clark" <kb7...@comcast.net> wrote in message
news:ep31o4h5t3js4iefd...@4ax.com...
Hi Richard
I made a capacitator rotator for my 6 foot AM loop using a hobby shop
servo to rotate the air variable cap. It works quite well and the
components are affordable.
The 3 section air capacitor allowed the use of each section by switching
to the appropriate section with a TO-5 relay.
That is Brute Force to tune an AM loop, but sure makes sense and uses
affordable parts.
Jerry KD6JDJ
Richard Clark
<ianREMOVET...@g3ohx.demon.co.uk> wrote:
>Thanks for the advice, however......
>>Why? A half volt signal level
>
>(that's surely one hell of an RF signal?)
I can see you don't know what environment you are living in. That, or
you live out in a pastoral setting and the house has no significant RF
contribution. Most of the world is urbanized and folks live within
short distances of large transmitters.
>Varicap diodes will always suffer from having their capacitance
>modulated by an RF signal impressed upon them. However, they do seem to
>work well enough - even when the RF level is pretty high (which must be
>the case especially with varicap-tuned oscillators - ie most VCOs and
>PLL systems).
You don't put the Varicap into the high level part of the circuit.
This is obvious from the outset.
>Presumably, the effect of this modulation will be to generate
>intermodulation products. In VCOs, this will simply appear as harmonics
>of the oscillator signal (which you would get anyway - even with a
>conventional tuning capacitor).
A conventional cap (and a conventional inductor, much less) will not
contribute harmonics because it is linear. Harmonics comes from
nonlinear components added by the circuit (partial conduction of an
active component that aids in the oscillation).
>Where multiple-frequency signals are
>present (like you have with the receiving loop), the most apparent
>effect of the modulation of the diode capacity will appear as
>crossmodulation and other nasties on the other signals in the passband.
>However, as varicaps ARE used for the tuning of the input of receiver RF
>stages, how do they 'get away with it'?
They don't if you are in such an environment. Again, if you don't
know your environment, then it's all a crap shoot. There is no
"getting away with it." The alternative is that the designer of a
product fully anticipated these issues and purposely chose a design
that minimized the effect of accidental contributions. Not all
designers are up to speed on the topic. The web is full of reported
failed projects that do not take bias Z and filtering into
consideration.
>>This swing is also a problem for PIN diodes used as voltage variable
>>attenuators.
>>
>My understanding of things is that the effectiveness of PIN diodes
>relies on them having a very poor performance at RF (especially at VHF
>and UHF). In attenuator circuits, they are forward biassed, and the DC
>current passing through them varies their RF resistance. However, the
>charges flowing through the junction are so 'sluggish' that they don't
>react to the rapidly-changing RF voltages. There is therefore negligible
>modulation of the RF resistance by the RF signals passing though them.
Poor performance when a PIN diode is first and foremost a diode for RF
and microwave applications? Only if you are using it for the wrong
reason (like using a 1N23 for 120V 60HZ power rectification).
PIN diodes are used as resistors and switches, not rectifiers.
Further, don't confuse the switch application as meaning fast turn-off
in the pico-to-subnanoseconds. Speed is relative to the application
of signal path steering where 100s of nanoseconds is more than
adequate.
Consult:
http://www.ieee.li/pdf/pin_diode_handbook.pdf
Richard Clark
wrote:
> Hi Richard
>
> I made a capacitator rotator for my 6 foot AM loop using a hobby shop
>servo to rotate the air variable cap. It works quite well and the
>components are affordable.
> The 3 section air capacitor allowed the use of each section by switching
>to the appropriate section with a TO-5 relay.
>
> That is Brute Force to tune an AM loop, but sure makes sense and uses
>affordable parts.
>
> Jerry KD6JDJ
>
Hi Jerry,
You have certain advantages over most of the correspondents here. You
are something of a gear head, you know where to find things, you know
how to put them together, and you actually do it.
When I was a kid, I had the same bent, but my resources were from
government surplus when you needed 400Hz 26V supplies (or other such
oddities). It was back in the 60s when I started experimenting with
Varicaps except they were 1N23 style diodes sold for their Varicap
properties (which comes free with almost any diode); the real Varicaps
sold for far too much for my allowance. Wasn't much tuning ratio back
then either - about 3:1 to 5:1 - today's have more range than most air
caps.
Ian Jackson
<kb7...@comcast.net> writes
>On Wed, 28 Jan 2009 20:12:15 +0000, Ian Jackson
><ianREMOVET...@g3ohx.demon.co.uk> wrote:
>
>>Thanks for the advice, however......
>
>>>Why? A half volt signal level
>>
>>(that's surely one hell of an RF signal?)
>
>I can see you don't know what environment you are living in. That, or
>you live out in a pastoral setting and the house has no significant RF
>contribution. Most of the world is urbanized and folks live within
>short distances of large transmitters.
>
high power - are located well out of town. I'm 20 miles west of London,
and the nearest MW TX is about 25 miles away (20 miles north of London,
the area which it is intended to serve).
>>Varicap diodes will always suffer from having their capacitance
>>modulated by an RF signal impressed upon them. However, they do seem to
>>work well enough - even when the RF level is pretty high (which must be
>>the case especially with varicap-tuned oscillators - ie most VCOs and
>>PLL systems).
>
>You don't put the Varicap into the high level part of the circuit.
>This is obvious from the outset.
>
Surely it is at the high voltage part of the circuit where the tuning
capacitor will be most effective in tuning (ie most kHz per pF)?
>>Presumably, the effect of this modulation will be to generate
>>intermodulation products. In VCOs, this will simply appear as harmonics
>>of the oscillator signal (which you would get anyway - even with a
>>conventional tuning capacitor).
>
>A conventional cap (and a conventional inductor, much less) will not
>contribute harmonics because it is linear.
Well, of course it won't. And neither will be an inductor (especially if
it's air-cored, as in a loop antenna).
>Harmonics comes from
>nonlinear components added by the circuit (partial conduction of an
>active component that aids in the oscillation).
>
>>Where multiple-frequency signals are
>>present (like you have with the receiving loop), the most apparent
>>effect of the modulation of the diode capacity will appear as
>>crossmodulation and other nasties on the other signals in the passband.
>>However, as varicaps ARE used for the tuning of the input of receiver RF
>>stages, how do they 'get away with it'?
>
>They don't if you are in such an environment. Again, if you don't
>know your environment, then it's all a crap shoot. There is no
>"getting away with it." The alternative is that the designer of a
>product fully anticipated these issues and purposely chose a design
>that minimized the effect of accidental contributions.
That's what I am interested in finding out. Just how DO they make
varicap diodes work adequately in (say) receiver front ends?
>Not all
>designers are up to speed on the topic. The web is full of reported
>failed projects that do not take bias Z and filtering into
>consideration.
>
>>>This swing is also a problem for PIN diodes used as voltage variable
>>>attenuators.
>>>
>>My understanding of things is that the effectiveness of PIN diodes
>>relies on them having a very poor performance at RF (especially at VHF
>>and UHF). In attenuator circuits, they are forward biassed, and the DC
>>current passing through them varies their RF resistance. However, the
>>charges flowing through the junction are so 'sluggish' that they don't
>>react to the rapidly-changing RF voltages. There is therefore negligible
>>modulation of the RF resistance by the RF signals passing though them.
>
>Poor performance when a PIN diode is first and foremost a diode for RF
>and microwave applications? Only if you are using it for the wrong
>reason (like using a 1N23 for 120V 60HZ power rectification).
>
My main personal experience with PIN diodes has been limited to their
use as 'variable resistors' in matched-impedance variable attenuators in
cable TV equipment. The essential characteristic is that there is a
chunk of ordinary (intrinsic) silicon between the P and the N layers. If
the RF signal alternates quickly enough, the electrons don't have time
to travel across the intrinsic layer before the polarity changes. As a
result, the diodes don't rectify. The higher the frequency, the better
they get at 'not rectifying'.
>PIN diodes are used as resistors and switches, not rectifiers.
See above.
>Further, don't confuse the switch application as meaning fast turn-off
>in the pico-to-subnanoseconds. Speed is relative to the application
>of signal path steering where 100s of nanoseconds is more than
>adequate.
While I've used ordinary diodes as RF switches, I can't remember if I
have used PIN diodes. I think that, at the RF levels involved in CATV,
an 1N4148 junction diode worked just as well or better.
>
>Consult:
>http://www.ieee.li/pdf/pin_diode_handbook.pdf
>
Thanks. Yes, I'll have a look, but it's how to use varicaps that I
really want to know about.
--
Roy Lewallen
> . . .
> That's what I am interested in finding out. Just how DO they make
> varicap diodes work adequately in (say) receiver front ends?
Very carefully. One of the main tricks is to severely limit the tuning
range by using fixed capacitors, switched as necessary, to make up the
bulk of the circuit capacitance. This reduces two serious problems,
nonlinearity which causes distortion, and temperature sensitivity.
Harmonic distortion can be mitigated by following the tuned circuit with
filters (provided that the total tuning range is narrow enough), but
this doesn't correct intermod problems caused by the nonlinearity. A
third potential problem if you use varicap for wide tuning range is that
the control voltage has to be heroically filtered to prevent any noise
or ripple from modulating the capacitance. The problem of nonlinear
tuning is often solved by using a control loop, for example an AFC to
detect whether the desired signal is properly tuned and to automatically
adjust if it isn't.
I remember one of my first encounters with a varicap, where I naively
used it as the bulk of the circuit capacitance in a homebrew VHF-to-BCB
converter. I was leaning over the prototype, trying to find a signal,
but hearing only hearing blip. blip-blip-blip. blip, sounding like
signals going by as if a tuning dial was being spun. Then I realized it
was synchronized with my breathing. Every time I exhaled,
blip-blip-blip-blip. Then when I inhaled, they'd go by a little more
slowly, the other way. That temperature sensitivity, incidentally, is
extremely difficult to compensate, since it's different at every reverse
bias setting. The only way to have a chance is to swamp the varicap C as
much as possible with fixed C, then approximately compensate the
remaining temperature drift.
Roy Lewallen, W7EL
Clifford Heath
> Ian Jackson wrote:
>> . . .
>> That's what I am interested in finding out. Just how DO they make
>> varicap diodes work adequately in (say) receiver front ends?
>> . . .
>
> Very carefully.
Might it help to use strings of varicaps? Sure I've seen that
done somewhere.
Jerry
Hi Richard
I worked for Hoffman Labs in 1960 and had responsibility for designing and
developing a sweep frequency receiver for the US Navy. I used a varicap
to sweep the L.O.. I am not inclined to use a varicap where a lumped
capacitor will do the job.
Jerry KD6JDJ
Roy Lewallen
The only advantage I can see is that it would increase the amount of
distortion for a given level of signal, since the amount of capacitance
change with signal voltage would decrease. The tradeoff would be a
reduction in the capacitance and an increase in the required tuning voltage.
Roy Lewallen, W7EL
Clifford Heath
> Clifford Heath wrote:
>> Might it help to use strings of varicaps? Sure I've seen that
>> done somewhere.
> The only advantage I can see is that it would increase the amount of
> distortion for a given level of signal
Decrease, I think you mean. And yes, that's what I was thinking of.
Richard Clark
wrote:
> Hi Richard
>
> I worked for Hoffman Labs in 1960 and had responsibility for designing and
>developing a sweep frequency receiver for the US Navy. I used a varicap
>to sweep the L.O.. I am not inclined to use a varicap where a lumped
>capacitor will do the job.
>
Hmmm, a swept frequency receiver for the Navy. Sounds like something
the spooks would listen to. Crypto or surveillance gear?
Jerry
Hi Richard
You figured that out rather well and quickly too.
Jerry KD6JDJ
Richard Clark
wrote:
Hi Jerry,
I trained with CTs (Communication Techs, otherwise those who
maintained and used Crypto or surveillance gear). When they couldn't
figure out a technical problem they always called the Cal Lab (we had
total responsibility for anything electronic).
After the capture of the USS Pueblo, it was said by my buddies that
Marine sentries were posted at the entrances to the comm room - "just
in case."
Of course, this was a lead they offered so I would ask "To protect
them from the boarders?" to which they would say "No, the Marines
would go in and shoot the CTs." This was similar to my own days
aboard the USS Holland, which, when it went out to sea was accompanied
by a submarine whose reputed orders were to sink us if we were in
jeopardy of being taken over. We had a technical library full of
systems plans for the Boomers.
I also served with pig-boat submariners who spoke in hushed tones
about the USS Thrasher and Scorpion. Then there was my time with the
CBs who had spent more time in Nam than any Marines.
There was a lot of Black Humor in those days.
Roy Lewallen
Yep, sorry, I did mean decrease. Thanks for catching it.
Roy Lewallen, W7EL
Clifford Heath
> Sounds like something the spooks would listen to.
Whereas now they're listening to this:
<http://www.winradio.com/home/g526e-ep.htm>
Sal M. Onella
<snip >
> After the capture of the USS Pueblo, it was said by my buddies that
> Marine sentries were posted at the entrances to the comm room - "just
> in case."
>
> Of course, this was a lead they offered so I would ask "To protect
> them from the boarders?" to which they would say "No, the Marines
> would go in and shoot the CTs." This was similar to my own days
> aboard the USS Holland, which, when it went out to sea was accompanied
> by a submarine whose reputed orders were to sink us if we were in
> jeopardy of being taken over. We had a technical library full of
> systems plans for the Boomers.
I was a CT from 1962 to 1972, when I foolishly volunteered for conversion to
EW (but that's another story). A few CT's were ordered to sensitive
assignments aboard submarines and the rumors ran hot and heavy for that
program, too. They included, "You need uniforms with other rating insignia.
Nobody can see a CT coming off a submarine." and "On liberty overseas, you
have an armed guard with you to shoot you if there's any chance you'll be
captured."
There is no greater rumor mill than the US military. (If asked, I'm ready
with a "square needle in the left nut" story.)
JosephKK
>On Jan 25, 9:52 am, Cecil Moore <nos...@w5dxp.com> wrote:
>> n...@wt.net wrote:
>> > My 16 inch diameter circle loop for MW uses 12 turns.
>>
>> I know multiple loop antennas are lossy for transmitting.
>> Are they adequate for receiving because of the AGC dynamic
>> range in the receiver?
>> --
>> 73, Cecil http://www.w5dxp.com
>
>I'm not sure how the AGC comes into play here..
>The 16 inch antenna provides plenty enough signal,
>even with no preamp used. You could turn the AGC on
>or off, wouldn't really matter. No different than any
>other antenna you might connect in that regard.
>They are lossy for transmitting, but on the MW bands
>you have so much excess signal level it's not an
>issue as far as receiving. Note the ferrite bar antenna,
>which is even more lossy than the open loops I use.
>It has no problem providing enough signal for a
>cheap portable radio.
>You might be surprised just how much level you can
>get from a tuned small loop on the low bands.
>As an example, that 16 inch loop provides more
>signal than the whip on a car. I once tried it with a
>delco radio in my truck. I hooked the loop up to it,
>and it was as hot as a firecracker vs the standard
>whip.
>The catch is the system is very high Q, and requires
>constant tuning of the cap as you change frequency.
That bites you when you use resonant loops. Of course non-resonant
loops don't have nearly the effective performance. Initial
selectivity to reduce the noise bandwidth before amplification or
mixing is why it is so common.
JosephKK
<chris...@btinternet.com> wrote:
>
>"Art Unwin" <Arthu...@gmail.com> wrote in message
>news:4529fac2-7612-4314...@o4g2000pra.googlegroups.com...
>On Jan 26, 8:38 am, "christofire" <christof...@btinternet.com> wrote:
>> "Art Unwin" <ArthurUn...@gmail.com> wrote in message
>
>8><
>
>Hi Chris,
>I need a bit more with respect to your response in more layman terms
>
>When a multi turn helix is generated it can be used for both
>transmitting and receiving.
>When generating two helix antennas where one is contra wound and both
>are connected at the top
>you are saying that it will NOT be suitable for receiving !
>We know by common use that the single helix is good for transmitt and
>receive . So what exactly
>does the addition of the contra winding do to prevent the combination
>from receiving?
>Looking forward to your take on the question.
>Best regards
>Art
>
>
>OK. The term 'helix' is most often applied to the travelling-wave antenna
>invented by John Kraus, often used at VHF and above, which generates or
>receives a circularly-polarised wave predominantly in the direction of its
>axis. It is also used in 'normal-mode helix' for the type of monopole
>element often found on walkie talkies, that generates and receives a
>linearly-polarised wave. Both of these are connected to electronics at one
>end only.
>
>The discussion was about loop antennas having one or more turns, with both
>ends of the winding connected to electronics. This construction can also be
>called a solenoid, but it would provoke confusion to call it a 'helix'.
>
>When an alternating current is passed through a solenoid it generates a
>magnetic field, H, through its centre and around it - the transmitting case.
>When a solenoid is placed in an alternating magnetic field, if any lines of
>magnetic force pass through its winding it will generate an electro-motive
>force (EMF) from which current can be drawn to operate a receiver - the
>receiving case.
>
>In the transmitting case the physical characteristics (described by the
>intrinsic impedance) of 'space' - the air surrounding the solenoid - cause
>an electric field, E, to be generated from the alternating magnetic field,
>in phase with the H field that caused it (viz. the intrinsic impedance of
>space is real not complex) and together these in-phase E and H components
>give rise to an electromagnetic wave. A fraction of the input power will be
>radiated away from the solenoid in that wave, in directions where their
>vector cross-product ExH is not zero. The field strength of either the E or
>H component of the radiated wave will decay linearly with increasing
>distance.
>
>You can find a good account of this process in books like 'Antennas' by the
>late John Kraus but it isn't possible to get very far without use of
>mathematics. Chapter 7 of 'Antennas for all applications' by Kraus and
>Marhefka, the 2002 edition, covers all this in greater detail and would be
>worth obtaining if you're interested.
>
>The 'sense' (i.e. clockwise/anticlockwise with respect to some datum) of the
>winding of a solenoid, and the direction of the current applied, affect the
>polarity of the magnetic field it produces, and vice versa for the receiving
>case. Consequently, the phase with respect to time of the alternating H
>field (and the alternating E-field component of the radiated electromagnetic
>wave) depend on the 'sense' of the winding, but the polarisation of the
>radiated wave depends on the alignment of the axis of the solenoid. By
>convention, 'polarisation' is the angular direction of the E field in the
>outgoing wave, which is perpendicular to the H-field component, and both are
>perpendicular to the direction of propagation, so solenoid with a horizontal
>axis radiates a vertically-polarised (VP) radio wave - and receives best
>from a VP wave; the ferrite-rod-in-a-broadcast-receiver case.
>
>Back to my original point: if part of the winding of the solenoid is wound
>in the opposite sense to the rest of the winding then its contribution to
>the generated H field, or the EMF on receiving, will oppose the contribution
>from the other part of the winding. If the winding has half in each
>'sense', connected in series (like a non-inductive wire-wound resistor),
>then it will not generate an H field or develop an EMF from an incident H
>field, so it will not work as a transmitting or receiving antenna ... for
>the reasons outlined above.
>
>Enough?
>
>Chris
>
Say Chris, how about you set your Outhouse Express news/mail client to
use a quote character. It is good manners in news groups.
christofire
"JosephKK" <quiett...@yahoo.com> wrote in message
news:lhlbo4trrog632tsh...@4ax.com...almighty snip -----
> Say Chris, how about you set your Outhouse Express news/mail client to
> use a quote character. It is good manners in news groups.
>
Joseph, please explain (and excuse my bad manners!) - use a quote character
for what?
Are you referring to my use of the pairs of single quotation marks 'xxx' in
what I'd written? I usually reserve double quotation marks "qqq" for actual
quotations; things that people have said ... but I suspect you're referring
to something else.
Chris
Richard Clark
****************************
An example follows:
>On Mon, 26 Jan 2009 18:16:22 -0000, "christofire" <chris...@btinternet.com> wrote:
>
>>Hi Chris,
>>I need a bit more with respect to your response in more layman terms
>>
>>When a multi turn helix is generated it can be used for both
>>transmitting and receiving.
>>When generating two helix antennas where one is contra wound and both
>>are connected at the top
>>you are saying that it will NOT be suitable for receiving !
>>We know by common use that the single helix is good for transmitt and
>>receive . So what exactly
>>does the addition of the contra winding do to prevent the combination
>>from receiving?
>>Looking forward to your take on the question.
>>Best regards
>>Art
>>
>>
>>OK. The term 'helix' is most often applied to the travelling-wave antenna
>>invented by John Kraus, often used at VHF and above, which generates or
>>receives a circularly-polarised wave predominantly in the direction of its
>>axis. It is also used in 'normal-mode helix' for the type of monopole
>>element often found on walkie talkies, that generates and receives a
>>linearly-polarised wave. Both of these are connected to electronics at one
>>end only.
>>
This sample, directly above, shows no distinction between your writing
and the post you responded to. I pointed this out last week in
another thread. However, at the top of this post above the starred
line, you clearly follow quoting conventions.
christofire
I have the 'Plain Text Settings' option 'Indent the original text with >
when replying or forwarding' ticked in OE and I can't account for why it
isn't working. I guess an incomplete sequence of cascaded >>>s could make
the historical record difficult to follow. I wonder if this has happened
when I have snipped the accumulated message trail.
Chris
Dave
"christofire" <chris...@btinternet.com> wrote in message
news:TfCdndM02PwooBvU...@bt.com...
its not your fault. some news senders, like art, send in a format that oe
can't figure out how to indent and >. i have tried lots of combinations and
the only one that works is to send in html format with the vertical bar
quoting.
christofire
"Dave" <no...@nowhere.com> wrote in message
news:xaKhl.819$eK2...@nwrddc01.gnilink.net...
Thank you for that ... and I gather some get equally irritated about people
sending HTML.
Chris
Dave
it that way.
Richard Clark
>> Thank you for that ... and I gather some get equally irritated about
>> people sending HTML.
>>
>of course. i prefer the nice safe plain text, but i guess not everyone sees
>it that way.
Hi All,
Not everyone sees in HTML either, and getting drenched by all of those
superfluous mark up script tags doesn't add to the conversation.
Outlook has a horrible reputation for launching insecure processes and
for spreading virus through marked up pages - no one knows the risk
offered by the content of any post until they open it. I use Agent
which has a safe HTML renderer, but I still don't need someone's
infected posting sitting in the thread.
The addition of charts, graphs and pictures could be put to good use
here. It "might" even bring sense to contrary current flow of
gaussian vector particels. In that sense, HTML would be a virtue;
however that isn't the convention of an already established text-based
group. (And the counter graphics of contrary current flow "might"
bring a blush to the easily offended.)
But if we went fully marked-up - what new vistas for rhetorical
exploration would be found there! ....and it still wouldn't solve
anything.
Sal M. Onella
> On Sun, 25 Jan 2009 14:27:33 -0800 (PST), nm...@wt.net wrote:
< snip >
> >You might be surprised just how much level you can
> >get from a tuned small loop on the low bands.
> >As an example, that 16 inch loop provides more
> >signal than the whip on a car. I once tried it with a
> >delco radio in my truck. I hooked the loop up to it,
> >and it was as hot as a firecracker vs the standard
> >whip.
> >The catch is the system is very high Q, and requires
> >constant tuning of the cap as you change frequency.
>
> That bites you when you use resonant loops. Of course non-resonant
> loops don't have nearly the effective performance. Initial
> selectivity to reduce the noise bandwidth before amplification or
> mixing is why it is so common.
>
I recall medium-size table radios having a loop antenna in/on the back
cover. I don't know whether there was also a ferrite rod inside.
Sal M. Onella
< snip >
> But if we went fully marked-up - what new vistas for rhetorical
> exploration would be found there!
We'd have smiley-faces and frowney faces. That would be good ... wouldn't
it? (Just kidding. No brickbats, please.)
Richard Clark
<salmo...@food.poisoning.org> wrote:
>> But if we went fully marked-up - what new vistas for rhetorical
>> exploration would be found there!
>
>We'd have smiley-faces and frowney faces. That would be good ... wouldn't
>it? (Just kidding. No brickbats, please.)
:-(
JosephKK
There was not one in the clock radio that i grew up with. I know, i
had it apart by the time i was ten.
JosephKK
I am not so sure that is only OE having a bad reaction to some other
non-conforming news reader. Just the same i can easily see OE getting
confused by a non-conforming news post more easily than any other news
client.
dave
> On Wed, 4 Feb 2009 00:12:54 -0800, "Sal M. Onella"
>>>
>> I recall medium-size table radios having a loop antenna in/on the back
>> cover. I don't know whether there was also a ferrite rod inside.
>>
> There was not one in the clock radio that i grew up with. I know, i
> had it apart by the time i was ten.
>
Most 5 tube All-Americans had a loop glued inside the Masonite back
cover. Fewer had a loopstick.