Matthew M5EVT challenged me to build an N6KR SST-30 for the SOTA 20th Anniversary celebrations earlier this year. I got the rig built but intially it suffered from poor receive performance, it turned out that I’d made a mistake. I corrected my mistake and the receiver seemed more lively, however at high gain settings the rig would motorboat. It turned out that even the proper kit versions were prone to this fault and the design of the AF gain stage is not good. A Zobel network added to the LM386 output as suggested by AA7EE in his blog was the cure that I needed.
I still felt as though the recieve performance was lacking and also the sidetone level was way too loud. Reading through various sources on the internet, it seemed that changing the capacitors in the crystal IF filter to make the response wider would improve things. During the summer, I swapped out the IF filter capacitors. I’m not sure if I tested the rig, I suspect that I didn’t.
I attended the RSGB Convention last weekend and I enjoyed the SOTA presentations. I came away full of enthusiasm for ham radio again, and for SOTA of course! I’ve been spending a bit of time in my shack(read ‘workshop’) this week in order to make the most of my enthusiasm. One of the jobs I had wanted to do was to try a trimmer cap to set the BFO on the SST-30 instead of the fixed value capacitor that I had fitted as prescribed by the original schematic.
Yesterday I took a little time to fit a trimmer cap and using my ancient Tektronix 465 scope, I peaked the audio response of the SST-30. I was aware that the crystals I’d used didn’t necessarily have the same specifications as those in the original SST kits, so the BFO was probably set in the wrong place when using a fixed value capacitor.
Bench testing seemed to indicate that things were working OK, but without a station antenna to use, I’m never quite sure.
I was itching to get out for SOTA and today the forecast promised a dry morning followed by a soggy afternoon. I was eager to try the SST-30 too, so I decided to go up Whernside G/NP-004 as the time from home to summit is probably the shortest available to me, around an hour in total.
As per usual, I like to go with a theme, so I decided on ‘all home brew transceivers’. I packed the SST-30 for 30m, a home brew RockMite 40 for, er, 40m and a home brew RockMite 20.
As I neared the summit of Whernside, it became very windy and rather wet. Thankfully I’d packed my pole guying kit and an old bothy bag. How the antenna stood up for the entire activation I don’t really know! I got inside the bothy bag and did my best to ignore the horrible weather on the outside.
I fired up the SST-30 and called CQ, using a little dot on the front panel to approximate a calling frequency of 10.118 MHz. I was pleased to see that the RBN picked me up on 10.1181 and my rig appeared to stay there without any noticeable drift. (I’ll probably move my dot to recalibrate my dial again! LOL)
I wasn’t quite ready for the pile up! I ended up working 39 stations in around 45 minutes. The signal strengths were mostly very good, including inter G. The little LED which is used in a crude AGC circuit was blinking happily away. I’d noticed the AGC effect whilst aligning the BFO yesterday and I had to reduce my test signal to avoid compression. I’m very impressed with the little SST, it seems to be working like people tell me that they’re supposed to work.
Apologies for the QLF, I was being battered by wind and I’m not 100% in sync with the G4TGJ keyer.
Having spent so long working the 30m pile up down, I felt that I didn’t have time for other bands (and I couldn’t face going outside to swap the links!).