[NLRS] Parts is parts

[Dr. Gerald N. Johnson, electrical engineer]

The PA and the driver module are almost certainly biased only for class
C, not linear. I think that PA transistor is probably operating in
grounded base which makes linear biasing a lot more difficult. I suspect
running the drive up to 902 the combination will put out power, probably
only 10 or 12 watts. That's not a signal to be ignored, its a useful
power level. Possibly trimming some of the PC board matching will get
more power. I'm sure that neither the PA, nor the module cut off rapidly
outside their specified frequency range. I don't see a Motorola RF parts
data book near enough to the top of any of the piles about my computer
to grab quickly.

E.F. Johnson may have the manual for that radio available reasonably.

Here's what I'd try:

I'd run the transmitter up to 903.1 or 902.1 which ever is being used
there. The multipliers may have to be retuned along with the synthesizer
new programming. Then I'd add a keying circuit to the power control
stage, to make it transmit CW with the modulation circuit shorted out.

Oh, you want voice modulation? Then I'd run NARROW FM. If you keep the
FM modulation index way down you get only first order modulation
products and the signal bandwidth is the same as AM and is very copiable
with a SSB receiver by zero beating the carrier. This scheme worked well
on HF in the 30s and 40s and 50s (lack of amplitude modulation kept it
from being copiable on unshielded and unfiltered TV sets and it was very
simple to accomplish, no modulation transformers required), and worked
fine on 2m in the Dallas area in the mid 60s. The theoretical support is
that with first order FM modulation products only, the amplitude
spectrum of the signal is exactly that of AM, the difference is that the
carrier is 90 degrees out of phase from where it would be for AM.
Phasing SSB rigs like the early Central Electronics had an FM provision
where they developed double SSB with a balanced modulator then injected
a phase shifted carrier to make it narrow band FM. They injected a
carrier in phase with the carrier that fed the balanced modulator to
produce AM. I thought the NBFM received in my Collins SSB receiver
sounded better than the signals that were truly SSB.

For receive, tap off to an IF receiver after the first or second mixer.
The FM receiver will he still linear at that point. Do the rough tuning
with the PLL and the fine tuning with the IF receiver.

By working CW or NBFM (and I worked my first 8 or ten states on 432 with
a slightly modified RCA FM transmitter strip running CW) and using the
front end as the receive converter (will need retuning, but I suspect an
E.F. Johnson receiver front end will tune from 800 to 960 MHz at least)
you can have receive converter and workable transmitter all in one
little box. Having an original manual that shows the differences between
the various models for the available frequency ranges could make some of
the frequency shifting easier to accomplish.

73, Jerry, K0CQ
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.