Antenna Replacement Experiment
 

Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?

Antenna Replacement Experiment
 

"Spin" wrote in message
...
Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?


Hi Spin

I cant offer any information about removing the ferrite antenna and
replacing it with an external loop. But, I can tell you that a few turns
of wire from the loop, wrapped aroung the radio, with the original ferrite
antenna connected as normal, can be made to couple the external loop to the
receiver to greatly improve reception.

Jerry

Antenna Replacement Experiment
 

Jerry;

I know how to couple an external loop to the internal ferrite antenna of the
radio. I believe that i would get better nulls & gain by removing the
internal antenna & directly connecting a box loop in it's place. Please
correct me if i am in error.

"Jerry" wrote in message
...

"Spin" wrote in message
...
Is it feasable to remove the ferrite antenna from an am radio & replace
it with an external multi-turn box loop with the same primary/secondary
inductance?


Hi Spin

I cant offer any information about removing the ferrite antenna and
replacing it with an external loop. But, I can tell you that a few turns
of wire from the loop, wrapped aroung the radio, with the original ferrite
antenna connected as normal, can be made to couple the external loop to
the receiver to greatly improve reception.

Jerry

Antenna Replacement Experiment
 

Spin wrote:
Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?

Most of those internal ferrite antennas that I have
seen are transformers or autotransformers for
impedance matching. It would be hard to couple an
external air core transformer as efficiently as
is possible with ferrite.
--
73, Cecil http://www.w5dxp.com

Antenna Replacement Experiment
 

On Jan 29, 12:41*am, "Spin" wrote:
Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?

I wouldnt say its imposssible but it certainly would be a royal pain
getting the tuning to track right. I have coupled big antennas to
loopstick radios just by wrapping a few turns of wire around the radio
and connecting it to an external antenna. I have also wound a few
turns around the loopstick and brought it out to a jack for this
purpose. At least one commercial SW rx I owned was built this way.

Jimmie

Antenna Replacement Experiment
 

JIMMIE wrote:

On Jan 29, 12:41Â*am, "Spin" wrote:
Is it feasable to remove the ferrite antenna from an am radio & replace
it with an external multi-turn box loop with the same primary/secondary
inductance?

I wouldnt say its imposssible but it certainly would be a royal pain
getting the tuning to track right. I have coupled big antennas to
loopstick radios just by wrapping a few turns of wire around the radio
and connecting it to an external antenna. I have also wound a few
turns around the loopstick and brought it out to a jack for this
purpose. At least one commercial SW rx I owned was built this way.

Jimmie

If you get the same inductances, coupling and can compensate for any
difference in stray capacitance, it should work.

Ferrite antennas are used for their small size. Older tube radios used
larger loop antennas.

Keep in mind there may be some DC voltages present on the ferrite antenna
you may not want to take outside the radio. (In other words, while you
could make the external loop work, there may be other reasons for not doing
so.)

Antenna Replacement Experiment
 

Spin wrote:
Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?


It's hard to beat the SelectAtenna.

http://www.universal-radio.com/catalog/mwant/4316.html

Antenna Replacement Experiment
 

dave wrote:
It's hard to beat the SelectAtenna.
http://www.universal-radio.com/catalog/mwant/4316.html

Wow, "+30 dB signal gain" from a passive tank circuit.
--
73, Cecil http://www.w5dxp.com

Antenna Replacement Experiment
 

Hi Spin

There may be different rules for connecting external antennas depending on
if the objective is to get max gain or to get strongest null response.
An external, capacitor tuned loop is a high Q device and appreciates loose
coupling when used to receive weak signals.
If the objective of the loop is to null out a specific frequency, I
suspect the direct connection of the external loop will result in very
effective nulling.
I hope you try this antenna modification and report the results

Jerry KD6JDJ



"Spin" wrote in message
...
Jerry;

I know how to couple an external loop to the internal ferrite antenna of
the radio. I believe that i would get better nulls & gain by removing the
internal antenna & directly connecting a box loop in it's place. Please
correct me if i am in error.

"Jerry" wrote in message
...

"Spin" wrote in message
...
Is it feasable to remove the ferrite antenna from an am radio & replace
it with an external multi-turn box loop with the same primary/secondary
inductance?


Hi Spin

I cant offer any information about removing the ferrite antenna and
replacing it with an external loop. But, I can tell you that a few
turns of wire from the loop, wrapped aroung the radio, with the original
ferrite antenna connected as normal, can be made to couple the external
loop to the receiver to greatly improve reception.

Jerry

Antenna Replacement Experiment
 

On Thu, 29 Jan 2009 06:41:17 GMT, "Spin"
wrote:

Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?

Those with more than one coil (almost all) are not primary to
secondary relationships. One coil is the RF/Mixer stage, and the
other is the Oscillator stage and the ferrite provides the mixing path
as well as the signal pickup path. If you closely examine the
variable capacitor, you should see that it is also two independent
sections on the same frame (or inside the same enclosure). There
should also be a trimmer for each, one for peaking the RF, the other
for tracking the Oscillator. If there is a TRF stage, it will
probably have another coil/cap combo and probably with that coil as a
separate item.

It would help if you identify the "am radio."

73's
Richard Clark, KB7QHC

Antenna Replacement Experiment
 

"Richard Clark" wrote in message
...
On Thu, 29 Jan 2009 06:41:17 GMT, "Spin"
wrote:

Is it feasable to remove the ferrite antenna from an am radio & replace
it
with an external multi-turn box loop with the same primary/secondary
inductance?

Those with more than one coil (almost all) are not primary to
secondary relationships. One coil is the RF/Mixer stage, and the
other is the Oscillator stage and the ferrite provides the mixing path
as well as the signal pickup path. If you closely examine the
variable capacitor, you should see that it is also two independent
sections on the same frame (or inside the same enclosure). There
should also be a trimmer for each, one for peaking the RF, the other
for tracking the Oscillator. If there is a TRF stage, it will
probably have another coil/cap combo and probably with that coil as a
separate item.

It would help if you identify the "am radio."

73's
Richard Clark, KB7QHC

This is why you would do just as well to add some turns to the ferrite
loopstick for an external antenna and simply shield the radio. That method
of coupling is very efficient.

Antenna Replacement Experiment
 

"JB" wrote in message
...
"Richard Clark" wrote in message

snip

... you would do just as well to add some turns to the ferrite
loopstick for an external antenna and simply shield the radio. That
method
of coupling is very efficient.

In a weak signal area (metal building, basement, etc), any wire that runs
outside can simply be wrapped a few times around the radio and grounded.
The wrapping direction is dictated by the orientation of the internal
loopstick. With a left-to-right loopstick, you wrap over the top and bottom

When I was in the Navy, I liked having a bedside radio, so that was my
method. On one ship, I was near a door to an open deck, so I snaked a wire
outside and strung about 30 feet of it behind a pipe. On another ship, I
connected my wire through a cap to the telephone wire. I got a lot of
click/pop noise on that one but I had a half-dozen AM stations I could hear
OK.

Best reception job was on a carrier. The "weather-guessers" were high up,
on the 07 level and I ran a cable to my office on the 02 level. They had
their own WEFAX whip antenna feeding an antenna filter panel (AN/SRA-12, if
you know what that is.) They didn't use the BCB output of the filter panel
(but I did). It's good to be the Department Leading Chief.

Antenna Replacement Experiment
 

On Thu, 29 Jan 2009 08:31:28 -0800, Richard Clark
wrote:

On Thu, 29 Jan 2009 06:41:17 GMT, "Spin"
wrote:

Is it feasable to remove the ferrite antenna from an am radio & replace it
with an external multi-turn box loop with the same primary/secondary
inductance?

Those with more than one coil (almost all) are not primary to
secondary relationships. One coil is the RF/Mixer stage, and the
other is the Oscillator stage and the ferrite provides the mixing path
as well as the signal pickup path. If you closely examine the
variable capacitor, you should see that it is also two independent
sections on the same frame (or inside the same enclosure). There
should also be a trimmer for each, one for peaking the RF, the other
for tracking the Oscillator. If there is a TRF stage, it will
probably have another coil/cap combo and probably with that coil as a
separate item.

It would help if you identify the "am radio."

73's
Richard Clark, KB7QHC

Sorry no, they are not going to inject the LO via the loopstick. That
would lead to illegal and unacceptable emissions.

Antenna Replacement Experiment
 

"JosephKK" wrote in message
...
On Thu, 29 Jan 2009 08:31:28 -0800, Richard Clark
wrote:

On Thu, 29 Jan 2009 06:41:17 GMT, "Spin"
wrote:

Is it feasable to remove the ferrite antenna from an am radio & replace
it
with an external multi-turn box loop with the same primary/secondary
inductance?

Those with more than one coil (almost all) are not primary to
secondary relationships. One coil is the RF/Mixer stage, and the
other is the Oscillator stage and the ferrite provides the mixing path
as well as the signal pickup path. If you closely examine the
variable capacitor, you should see that it is also two independent
sections on the same frame (or inside the same enclosure). There
should also be a trimmer for each, one for peaking the RF, the other
for tracking the Oscillator. If there is a TRF stage, it will
probably have another coil/cap combo and probably with that coil as a
separate item.

It would help if you identify the "am radio."

73's
Richard Clark, KB7QHC

Sorry no, they are not going to inject the LO via the loopstick. That
would lead to illegal and unacceptable emissions.


I thought this sounded wrong, and I've certainly never encountered a
domestic receiver designed to radiate its LO! Such a design could wreak
havoc in the medium wave band (where a low-side LO would be in-band for part
of its range).

Chris

Antenna Replacement Experiment
 

On Sun, 01 Feb 2009 10:46:26 -0800, JosephKK
wrote:

Sorry no, they are not going to inject the LO via the loopstick. That
would lead to illegal and unacceptable emissions.

Maybe so.

73's
Richard Clark, KB7QHC