GB> 75th Anniversary of FM Radio Special Event

kd4e doc at KD4E.COM
Wed Dec 3 10:50:45 EST 2008

Perhaps an experimental NET could be started where HF-NBFM 
stations could communicate with one-another to test out some 

In general the challenge has been both technical and 
practical, trying to get a decent signal from commonly 
available gear, and the absence of others using the mode on HF.

Might make for a fun new avenue of experimentation and a 
creative article series for QST!

> I keep wanting to try some very narrowband FM (i.e. less
> than +/- 0.5 kHz deviation) on HF just to see how well it
> works.  I have the Collins NBFM adapter in my 75A-3 and
> by using the crystal phasing the bandwidth of the
> receiver can be reduced in proportion to the transmitted
> bandwidth.  Now I am not certain as to if there is enough
> audio gain in the receiver, at least enough gain to
> produce a comfortable audio level in a speaker.  As for
> headphone operation I am pretty certain that there will
> definitely be enough audio gain.
> It wouldn't be that much trouble to start with an old
> tube type lowband FM transmitter using the crystal
> oscillator and modulator and then use something like a
> Heath DX-20, DX-35, DX-40, or DX-60 to provide the Class
> "C" amplification.  Depending on the actual lowband
> frequency many of those transmitters used crystals within
> the 75 meter phone band.
> Frankly, I just have to find the time to experiment.
> Remember, NBFM, which used deviation of +/- 3 kHz was
> being "pushed" by the ARRL and others in the late 1940s
> and well into the 1950s.
> Glen, K9STH


Thanks! & 73, doc, KD4E
Free OS :
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