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Saturday, January 21, 2012

JBOT Installed in Azores 17 Meter SSB Rig

Even though one of their Coronal Mass Ejections is due to hit us soon, the radio gods have been quite kind to me this morning. I installed the JBOT amplifier board in the 17 meter SSB transmitter that I had built out in the Azores during the last solar cycle. The board went in without any trouble. And I was a very surprised when it DIDN'T break into oscillation and instability! Holy Cow! This one was stable from the start! Even when connected to my antenna! Eureka!

The rig still needs some peaking and tweaking. I'm only getting about 2-3 watts out and I should be getting 4-5. I did a quick and dirty "by ear" alignment --- I just listened to my own signal with my trusty Drake 2-B and moved the carrier oscillator freq around a bit until the SSB audio sounded good (you never have to do that with DSB!).

For those of you not familiar with this rig, here is some background:
-- Built on the chassis of an old Heath DX-40
-- Crystal filter at 5.174 MHz. Filter rocks and carrier oscillator rocks from an old Swan 240 I picked up in the Dominican Republic from Pericles Perdomo HI8P (SK).
-- Based on a design published in SPRAT by Frank Lee, G3YCC (SK).
--Heterodyne oscillator is a G3RJV Universal VXO circuit running at around 23.3 MHz.
-- That orange cord to the big meter that you are no doubt wondering about is just a little circuit that monitors total current drawn by the rig. It bounces up and down as I talk. I put it in there mostly because I wanted to make use of a beautiful old Simpson meter that I picked up in 1973 at the Crystal Radio Club (W2DMC) in Valley Cottage, New York.

Going around, clockwise from below the meter: G3RJV VXO, carrier oscillator and two diode balanced modulator board, crystal filter (with NE602 mixer and post-filter bandpass filter to the left), JBOT PA. Audio amp (using op amp) below the chassis. T/R relay in the center (antenna changeover relay below the chassis).

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