Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the distance
between the turns will be a little greater than the factory adjusted
coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh

"Ridgh" wrote in
ups.com:

Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the distance
between the turns will be a little greater than the factory adjusted
coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh


You might be able to get it higher with more inductor adjustments, I don't
know the circuit. Maybe have to add some capacitance to the tank.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying is
needed to the receiver in order to hear the narrow band FM better.

It would be easier just to buy a cheap VHF receiver. Talk to the people
in rec.radio.shortwave for ideas on cheap plastic receivers. They're
experts.

SC

Brenda Ann wrote:
"Slow Code" wrote in message
nk.net...
"Ridgh" wrote in
ups.com:

Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the distance
between the turns will be a little greater than the factory adjusted
coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh


You might be able to get it higher with more inductor adjustments, I don't
know the circuit. Maybe have to add some capacitance to the tank.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying is
needed to the receiver in order to hear the narrow band FM better.

It would be easier just to buy a cheap VHF receiver. Talk to the people
in rec.radio.shortwave for ideas on cheap plastic receivers. They're
experts.

Couple problems with your answer. Let's take them one at a time:

You might be able to get it higher with more inductor adjustments, I don't
know the circuit. Maybe have to add some capacitance to the tank.

To raise the frequency of resonance, you would decrease either inductance or
capacitance, or both. I.E. you would remove turns from a coil, or use a
smaller series or parallel capacitor. I have successfully modified a GE
Superadio II to receive as high as 155MHz by removing a turn from each of
the RF, Antenna and Oscillator coils and realigning for proper tracking.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying is
needed to the receiver in order to hear the narrow band FM better.

True, that broadcast FM is wideband (150KHz total, 75KHz deviation), but
most of the frequencies the OP wishes to listen to are in the aircraft comms
band, and are not FM at all, but fairly broad band AM (IIRC, 12KHz). These
can be heard by slope detection on an FM radio, and the discriminator (or
other detector circuit) can be detuned a bit to allow for reception with the
majority of the radio's circuits tuned to the center frequency of the
carrier. The detector circuit could be modified to detect only AM (and
therefor slope detect FM) fairly easily, actually by removing some
components and wiring around them, but overall this is not absolutely
necessary.

I believe you have the slope detection application backwards, i.e. it
allows FM to be demodulated on a radio set up for AM demod.

A slope detection FM demod puts the FM signal through a filter that is
not centered properly, i.e. the signal's frequencies are on the slope
of the filter, not the passband. Then as the frequency changes, the
attenuation of the signal also changes, which effectively has turned FM
into AM. Then you rectify and low pass filter, as you would do with an
AM signal.

Note also that the FM demodulator rejects AM by the use of a limiter.
Thus FM radios reject AM quiet well, but the opposite is not true, i.e.
FM can be demodulated by an AM demodulator that is tuned off center a
bit. High end FM radios will spec their AM rejection:
http://www.fanfare.com/fta100-specifications.html
The AM rejection in this application relates to the ability to reject
atmospheric effects on the FM signal strength, but it would reject
broadcast AM too if somehow the AM was on an FM broadcast frequency.

Thank you very much for your response and good will.
Actually I need it for a surveillance bug working on about 120MHz, not
varicap controlled - so it may be used in AM or wide FM as well (not
narrow FM).
So, almost any receiver is ok - with my scanner I receive it with both
modulation modes equally.
I cannot buy an airband receiver - as in my primitive country it's
not allowed without a special licence. I have a simple one stucked at
the customs for 3 weeks - no way to release it so far.
Thank you again,
Ridgh

Brenda Ann wrote:
"Slow Code" wrote in message
nk.net...
"Ridgh" wrote in
ups.com:

Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the distance
between the turns will be a little greater than the factory adjusted
coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh


You might be able to get it higher with more inductor adjustments, I don't
know the circuit. Maybe have to add some capacitance to the tank.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying is
needed to the receiver in order to hear the narrow band FM better.

It would be easier just to buy a cheap VHF receiver. Talk to the people
in rec.radio.shortwave for ideas on cheap plastic receivers. They're
experts.

Couple problems with your answer. Let's take them one at a time:

You might be able to get it higher with more inductor adjustments, I don't
know the circuit. Maybe have to add some capacitance to the tank.

To raise the frequency of resonance, you would decrease either inductance or
capacitance, or both. I.E. you would remove turns from a coil, or use a
smaller series or parallel capacitor. I have successfully modified a GE
Superadio II to receive as high as 155MHz by removing a turn from each of
the RF, Antenna and Oscillator coils and realigning for proper tracking.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying is
needed to the receiver in order to hear the narrow band FM better.

True, that broadcast FM is wideband (150KHz total, 75KHz deviation), but
most of the frequencies the OP wishes to listen to are in the aircraft comms
band, and are not FM at all, but fairly broad band AM (IIRC, 12KHz). These
can be heard by slope detection on an FM radio, and the discriminator (or
other detector circuit) can be detuned a bit to allow for reception with the
majority of the radio's circuits tuned to the center frequency of the
carrier. The detector circuit could be modified to detect only AM (and
therefor slope detect FM) fairly easily, actually by removing some
components and wiring around them, but overall this is not absolutely
necessary.

Brenda Ann wrote:
wrote in message
ups.com...
Brenda Ann wrote:
"Slow Code" wrote in message
nk.net...
"Ridgh" wrote in
ups.com:

Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the
distance
between the turns will be a little greater than the factory adjusted
coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh

You might be able to get it higher with more inductor adjustments, I
don't
know the circuit. Maybe have to add some capacitance to the tank.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying
is
needed to the receiver in order to hear the narrow band FM better.

It would be easier just to buy a cheap VHF receiver. Talk to the
people
in rec.radio.shortwave for ideas on cheap plastic receivers. They're
experts.
Couple problems with your answer. Let's take them one at a time:

You might be able to get it higher with more inductor adjustments, I
don't
know the circuit. Maybe have to add some capacitance to the tank.
To raise the frequency of resonance, you would decrease either inductance
or
capacitance, or both. I.E. you would remove turns from a coil, or use a
smaller series or parallel capacitor. I have successfully modified a GE
Superadio II to receive as high as 155MHz by removing a turn from each of
the RF, Antenna and Oscillator coils and realigning for proper tracking.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying
is
needed to the receiver in order to hear the narrow band FM better.
True, that broadcast FM is wideband (150KHz total, 75KHz deviation), but
most of the frequencies the OP wishes to listen to are in the aircraft
comms
band, and are not FM at all, but fairly broad band AM (IIRC, 12KHz).
These
can be heard by slope detection on an FM radio, and the discriminator (or
other detector circuit) can be detuned a bit to allow for reception with
the
majority of the radio's circuits tuned to the center frequency of the
carrier. The detector circuit could be modified to detect only AM (and
therefor slope detect FM) fairly easily, actually by removing some
components and wiring around them, but overall this is not absolutely
necessary.
I believe you have the slope detection application backwards, i.e. it
allows FM to be demodulated on a radio set up for AM demod.

A slope detection FM demod puts the FM signal through a filter that is
not centered properly, i.e. the signal's frequencies are on the slope
of the filter, not the passband. Then as the frequency changes, the
attenuation of the signal also changes, which effectively has turned FM
into AM. Then you rectify and low pass filter, as you would do with an
AM signal.

Note also that the FM demodulator rejects AM by the use of a limiter.
Thus FM radios reject AM quiet well, but the opposite is not true, i.e.
FM can be demodulated by an AM demodulator that is tuned off center a
bit. High end FM radios will spec their AM rejection:
http://www.fanfare.com/fta100-specifications.html
The AM rejection in this application relates to the ability to reject
atmospheric effects on the FM signal strength, but it would reject
broadcast AM too if somehow the AM was on an FM broadcast frequency.

You are correct, but 'slope' detection also works to detect an AM signal on
a discriminator or ratio detector. By tuning slightly off frequency (or, by
tuning the detector circuit slightly off frequency from the center carrier..
i.e. detection on the slope of the modulated signal) you can receive AM
modulated signals. As stated, I have successfully converted an SRII to
receive up to 155 MHz, including the 108-132~ AM aircraft band. Perhaps if
the signal from these AM aircraft stations (and the aircraft themselves)
were of a higher amplitude, then the limiter would affect them.. i.e. if you
were close to your local airport's control tower. Even a stock standard
AM/FM radio (not one with an RF amp, those have too much image rejection)
will receive aircraft comms between 108 and 129.4 MHz due to various mixing
products if the signal is closeby, and this with no modification at all.


I've pulled the tuner out of cheap ghetto blasters and performed this
mod simply by pulling apart the turns of the various coils in the
front-end and retweaking for maximum signal. It is much easier if you
have a sig generator which lets you generate the proper frequencies, or
an airport nearby with a continuous ATIS broadcast.

jak

"Brenda Ann" wrote in
:


"Slow Code" wrote in message
nk.net...
"Ridgh" wrote in
ups.com:

Hello,
I need to convert a domestic analog FM receiver to the 108-140 MHz
band.
I've bought a Sony ICF-S10MK2 receiver and found that the oscillator
tank has a 4 turns of 22 gauge. I've turned them apart, so the
distance between the turns will be a little greater than the factory
adjusted coil, and could receive up to about 115MHz, no more.
Is this the way to do it? Maybe to cut one turn will be better?
I'm not stucked to this receiver, I'd like to know if other cheap
receivers may be converted, and if this is the way, or if I have to
adjust anything else. I have all the gear needed, oscilloscopes,
counters etc. - but no much knowledge on this particular field.
I'll be very thankful for your help.
Ridgh


You might be able to get it higher with more inductor adjustments, I
don't know the circuit. Maybe have to add some capacitance to the
tank.

Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying
is needed to the receiver in order to hear the narrow band FM better.

It would be easier just to buy a cheap VHF receiver. Talk to the
people in rec.radio.shortwave for ideas on cheap plastic receivers.
They're experts.

Couple problems with your answer. Let's take them one at a time:

You might be able to get it higher with more inductor adjustments, I
don't know the circuit. Maybe have to add some capacitance to the
tank.

To raise the frequency of resonance, you would decrease either
inductance or capacitance, or both. I.E. you would remove turns from a
coil, or use a smaller series or parallel capacitor. I have successfully
modified a GE Superadio II to receive as high as 155MHz by removing a
turn from each of the RF, Antenna and Oscillator coils and realigning
for proper tracking.

Like you say, it depends on whether you as add capacitance in series or
parallel.



Here's your real problem though. Broadcast FM is wideband. FM
communications 135-175 MHz are narrow band. That means more modifying
is needed to the receiver in order to hear the narrow band FM better.

True, that broadcast FM is wideband (150KHz total, 75KHz deviation), but
most of the frequencies the OP wishes to listen to are in the aircraft
comms band, and are not FM at all, but fairly broad band AM (IIRC,
12KHz). These can be heard by slope detection on an FM radio, and the
discriminator (or other detector circuit) can be detuned a bit to allow
for reception with the majority of the radio's circuits tuned to the
center frequency of the carrier. The detector circuit could be modified
to detect only AM (and therefor slope detect FM) fairly easily, actually
by removing some components and wiring around them, but overall this is
not absolutely necessary.

Missed the 108 - 140 part.

Ridgh wrote:

I cannot buy an airband receiver - as in my primitive country it's
not allowed without a special licence.

What countries don't allow VHF airband radios for civilians? Weird.

--
stephanie weil
new york

Stephanie Weil wrote:
Ridgh wrote:

I cannot buy an airband receiver - as in my primitive country it's
not allowed without a special licence.

What countries don't allow VHF airband radios for civilians? Weird.

Germany, for one....

jak

--
stephanie weil
new york

Switzerland, France, Belgium, Israel, Egypt.... and many more
jakdedert wrote:
Stephanie Weil wrote:
Ridgh wrote:

I cannot buy an airband receiver - as in my primitive country it's
not allowed without a special licence.

What countries don't allow VHF airband radios for civilians? Weird.

Germany, for one....

jak

--
stephanie weil
new york

In any case, if anyone can and wish to help me, here is the image of
the receiver:
http://www.petrutech.com/images/496848_DS_Page_1.jpg

Brenda Ann wrote:
"jakdedert" wrote in message
...
Stephanie Weil wrote:
Ridgh wrote:

I cannot buy an airband receiver - as in my primitive country it's
not allowed without a special licence.

What countries don't allow VHF airband radios for civilians? Weird.

Germany, for one....

South Korea for another.. actually, I think you will find that MOST
countries don't allow any VHF reception other than broadcast unless you are
a ham operator or military affiliated (or a user of the individual
services).