[GreenKeys] 170 shift to 850 shift converter??

[John Vendely]

It's frequency division multiplexed, and the radio portion was normally 
full duplex, as you suspected. The microphone connects to the MD-522, 
the baseband voice signal is bandlimited, and the 85 shift FSK signal is 
placed just above the voice band.  In full-duplex mode, a second GRC-106 
R/T unit was used as an auxiliary receiver, and two separate antennas 
were used.  It could be used OWR, though.  This might be done if the 
transmitting operator had a long tape to send, and wanted to use the 
voice channel like a one-way order-wire to the receiving operator.

The FSK/Voice multiplex mode was an improvement over the older AN/GRC-26 
and -46, which could multiplexed by FSK of the AM voice carrier.

The MD-522 is indeed a sophisticated modem.  Its audio-frequency 
discriminator system was a significant improvement over the older IF/FM 
systems (e.g., CV-116 and CV-278), but is less effective than the best 
of the later two-tone limiterless AM types.  When conditions are good, 
there's little difference in 850 shift BER between the the MD-522 and 
e.g., a Dovetron MPC-1000, though the error characteristics are a bit 
different.  The MD-522 is a bit more susceptible to interference, and 
the MPC-1000 distinctly outperforms it in disturbed condx.  Overall, 
though the MD-522 is an excellent modem.

Not much hope for 170 shift operation with the MD-522 without 
significant modification, though.  The MD-522 can copy 170 shift in a 
half-assed manner if signals are strong and if the tuning is carefully 
adjusted, but it doesn't work at all well, as the tones just don't fit 
the discriminator curve properly.  I've thought about modifying a second 
MD-522 for 170, but never could bring myself to actually go through with 
it.  I just use an ST-8000A or MPC-1000 for 170.

The AFSK modulator switches between one of two independent crystal 
oscillators, and therefore has excellent frequency accuracy and 
stability.  HOwever, it's therefore not phase-continuous FSK but is more 
properly considered FEK (Frequency-Exchange-Keying).

The frequency diversity mode is very effective and requires only one 
antenna, a big improvement over the GRC-26, which required two widely 
spaced antennas for space diversity, which was logistically difficult.  
With an MD-522, you can enjoy the benefits of diversity even with the 
vehicle on the move.  And, you can used the diversity tone pair in mark 
state as a handy 2-tone generator for checking out the GRC-106...

If anyone is interested in some 850 or 85 shift QSOs, I have a 
full-duplex AN/GRC-122E RATT van and am always looking for an excuse to 
put it on the air...

73,

John K9WT

On 3/15/2019 10:29 AM, John, W9DDD wrote:
> Yes, how about that voice and RTTY simulcast.  This must presume 
> duplex operation, otherwise how would one coordinate PTT between voice 
> and RTTY?  Perhaps someone knows how this worked?  My 05C40 training 
> didn't cover this.
>
> Can you picture the committee that wrote the specification for this?
>
> John, W9DDD
>
> On 3/14/2019 11:41 PM, Harold Hallikainen wrote:
>> Wow! Complicated device! On the transmit side, it looks like they use
>> crystal controlled mark and space oscillators, then frequency divide 
>> them,
>> then heterodyne them to the output frequency. On the receive side, they
>> use a temperature controlled UJT oscillator to heterodyne the received
>> audio to a frequency appropriate for the discriminator. It also does
>> diversity transmission and reception with a wide shift and narrow shift
>> signal sent simultaneously and received simultaneously. It would be
>> interesting to know if this does any better than using an XR2206 to
>> generate the FSK and XR2211 to demodulate it (and it even supplies mark
>> hold with no additional parts!).
>>
>> Harold
>>
>>
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