[TenTec] Orion, NRD-545, DSP, filters etc

[Adam Farson]

Hi George,

<<< It primarily is a result of the time it takes for the phase lock loop to
lock. >>>

<< That is included in the overall 10-msec delay. I wasn't aware that you
are so intimately familiar with the operation of the PRO2 . . .>>

Just for grins, to address concerns that the Pro2 synthesiser may slew when
switching from RX to TX, I checked the block diagram. It does not. The LO
frequency is unchanged when keying (unless 2-frequency split is activated).
The reason for this is that the receive and transmit intermediate
frequencies are identical.

I then ran a little test with the spectrum analyser. I loosely coupled the
instrument 's RF input to the VFO A output, and tuned the radio to 10.100
MHz,.  I then tuned the analyser to fo = (64.455 + 10.1) = 65.555 (actually
65.5), with 5kHz/div dispersion and 1kHz RBW, and centred the LO spike. I
then keyed the transmitter, and there was absolutely no perturbation of the
LO signal. Even with the HP853 mainframe's digital storage, the spike image
did not exhibit any of the horizontal smearing characteristic of a phase
perturbation caused by PLL lockup latency. (The Pro/Pro2 1st IF is 64.455
MHz).

Typically, only transceiver architectures which are superheterodyne on
receive, but straight-through on transmit (synthesiser output freq. =
transmit freq.) have a slew lockup issue during T/R switching. A typical
example is a VHF-FM mobile radio.

Cheers for now, 73,
Adam VA7OJ/AB4OJ