"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.