[R-390] R-390A SSB adapter
Veenstra, Lester
[email protected]
Thu, 24 Jul 2003 08:40:28 -0400
Assuming you want to keep the use of the 2 KHz filter as a basis for the SSB adapter, I do not see a solution around the mechanical dial indication not giving you the SSB carrier freq as you shift from USB to LSB.
There thoughts occur:
(1) Assuming that you do have a true SSB filter(s) in the outboard unit, and that you derive the AGC signal past these filters, and assuming that your outboard product detector has sufficient gain (actually, input sensitivity) that you your AGC feedback to the R-390 will keep its internal IF levels lower than are typical; With is assumption of low IF signal required , you reduce the chance that strong adjacent channel signals passed by a 4, 8 or even 16 kHz position will be a problem, with problem, in this case, meaning intermodulation products generated in the IF chain after the 455 mechanical filter and before the IF output to the external detector.
(2) Heresy? While you are building an external product detector, and want to use the internal 2 kHz filter, why not simply also tap the PTO output and build a pic based counter that can then have it's displayed value shifted for both USB/LSB and for front end offsets, just as you mechanically offset calibrate the PTO readout.
(3) Heresy and Blasphemy? O... Go ahead and simply build an outboard fixed LO frequency I and Q detector, A/D the I and Q channels and hand it to a simple DSP chip to do the heavy lifting.
-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, July 23, 2003 9:26 PM
To: [email protected]
Subject: [R-390] R-390A SSB adapter
I've finished a new solid-state SSB adapter, and thought I'd share my results
with the group. As some may remember, I built a product detector and AVC
circuit which could be added to the R-390A without any mods. My first version
used a variable BFO, so you could tune it to either side of the R-390A filter.
This worked well- it was much smaller tan a CV-591A, and was able to feed
fast AVC to the receiver, making operation of the radio as if it had a built-in
product detector. However it had a couple of drawbacks: First, the
receiver needed to be recalibrated whenever you retuned the BFO to switch sidebands;
second, my BFO circit drifted some.
So I built a new version around a 100 Kc crystal filter I picked up. Uses a
100 KC BFO, and switches sideband by switching the downconversion crystal
oscillator. So its function is similar to the CV-591A. It's much more stable
now, and no recal is needed when switching sidebands (or bypassing the unit
for AM reception). However, it needs to work with the 4 KC bandwidth of the
R-390A, in order to allow a pasband of 2 KC with the 100 KC filter. The
disadvantage is that the receiver AVC is open to all 4 KC of bandwidth, and so the
gain can be affected by signals on the opposite sideband.
Guess there is no perfect solution- I'm going to modify the old SSB adapter
for crystal BFO, then I'll have to decide which one to use. I may hang the
other on my SP-600.
Ed WB2LHI
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