uBITX Ver. 5 Completion Report

Ora Smith

I recently finished (? - is it ever done?) a uBITX version 5.1 kit with the nice blue case that I received as a gift.  I must admit that when I opened the box and realized it was mostly a bag of parts with no instructions I nearly quit before I started - really glad I kept going. Though occasionally frustrating (it's not a Heathkit!), I now have a very capable 80-10 meter SSB/CW transceiver. It brings back the magic of old time radio.  I find myself using it to the exclusion of a bunch of other fancy radios. I discovered a few things along the way I thought I would share. Perhaps none of this is new, but here goes anyway.

Calibration: The calibration instructions mystified me, so I ended up tuning the carrier frequency to 10 MHz on my Flex, which is pretty accurate.  BFO adjustment was far off initially. I found that it also affected carrier suppression. Tuning the BFO by the "sounds good" technique resulting initially in only 25 db of suppression. QST reported 49 db suppression, so I suppose I could tweak some more, but at 35 db it's OK, about what I see with my S-line. Opposite sideband suppression looks very good on the Flex scope - I can't see anything.  Spectral purity (carrier spectrum) is not as good as expensive commercial rigs, but I have had no complaints on the air. 

I have made a number of barefoot contacts (first contact was with Curacao on 20 meters) but the rig also will drive my Ten Tec Titan (pair of 3CX-800's) to 1000 watts on 80, about 500 on 40 and 20, and 300 on 17 meters. Have not tried other bands.  The trick is how to key the amp. I installed a keying relay inside the case - $1 for a relay, 6 cents for diodes, and a couple of bucks for a piece of solderable breadboard.  However, the keying relay I installed is activated by PTT instead of by the radio T/R switch.  In order to key the amp on CW, I Rube Goldberged a hand PTT switch in parallel with the amp keying line. That way I can key the amp in CW mode to tune it. Operating CW this way would be cumbersome, but mostly I am on SSB. I do see a noticeable power output spike on first key down, but have not investigated, and have not looked at the keying characteristics.

I get great audio reports using the included mic element.  It doesn't seem to have polarity marked, so if it doesn't work, reverse the wires. That happened to me. I put the little element in a D-104 mic head with a grip-to-talk stand. Now the mic is almost as big as the radio.

The radio came with a few defective parts that gave me some grief: the shaft encoder was bad, but I found an exact replacement at Digikey for about $1.60. Also, the fuse holder was defective (may have been my fault), and the fuse that came with the radio was high resistance and intermittent. I ended up bypassing the case's fuse holder and putting an automotive type in-line fuse cartridge in the power lead. The on/off switch that came with the case was defective, but I ended using the switch in one of the included volume controls.

I found the internal speaker to be tinny sounding, so I just plugged an amplified speaker I already had into the ear phone jack.

The lack of AGC on the receiver is bothersome. I have to ride the volume control constantly when there is QSB or a roundtable with greatly varying signal strengths.

By the time I got to installing the T/R LED it was too much trouble to pull the main board out of the case, so I just skipped it.  

Overall it's an amazingly good radio. Wish I had this in 1961 instead of an S-38 and DX-35.  The radio is a great QSO conversation topic.  I've only been harassed by one group (75 meters, of course), HI!



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