[Milsurplus] Whazzit - MD-209/UC HF transmitter phase modulator

[Kenneth G. Gordon]

Nick:

Narrowband FM and PM BOTH can be received on a normal AM receiver  by "slope 
detection". NBFM and PM were both popular voice modes about the same time amongst 
U.S. hams, so perhaps someone in the military thought it might fly with mil rigs.

NBFM and NBPM both sound identical to the receiving station.

This may have been an attempt to allow any normal CW transmitter to also transmit voice 
signals.

An advantage to both NBFM and NBPM is that no heavy and power using modulator is 
needed.

In an FM receiver, FM and PM sound identical.

ARRL handbooks of the 1950s period contain a section detailing methods of NBFM and 
NBPM. If you have one, look in a 1956 ARRL handbook. It will be in there.

Ken W7EKB


On 20 Nov 2016 at 16:31, Nick England wrote:

> 
> Info at
> http://www.navy-radio.com/xmtrs.htm#md209
> 
> What was this used for? - adds audio freq phase modulation to an HF (4-20mc) transmitter. 1955 
> manual. OK, I give up - what was this used for and who was receiving such signals? Fax?
> 
> =================
> The MD-20 9/UC is a device for electronically
> shifting the phase of a radio frequency
> signal at an audio frequency rate. Its use
> permits audio frequency transmission by an
> A-1 emission type transmitter. Audio frequency
> modulation signals used for this purpose
> must be in the frequency range 250 to
> 6000 cps.
> The modulator is designed to phase modulate
>  n RF signal in the range 2 to 5 mc. It is
> intended to be used with transmitters whose
> output frequency is in the range 4 to 20 mc.
> A "MODULATION RANGE" control is provided to
> reduce phase shift in proportion to the frequency
> multiplication used. The RF input is
> terminated in a 51-ohm resistive load. An RF
> input level between 1 to 20 volts is required.
> The nominal maximum modulation capability
> is ±1/2 radian of RF phase shift at
> all modulating frequencies within the above
> limits. Audio modulating signals should be
> between -20 dbm and a +10 dbm to satisfactorily
> modulate the RF signal. The audio output
> circuit matches a line of 600 ohms impedance.
> ===========================
> 
> Cheers,
> Nick England K4NYW
> www.navy-radio.com



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