Saturday, August 8, 2015

New Radios on the Bench at N6QW

New Radios in the Queue!

 While I await some of the beam parts to arrive I have taken up building (or should I say rebuilding) some new radios. The two new builds are SSB transceivers with one being on 40 Meters and the second on 20 Meters.
Beginnings of a new 40M SSB Transceiver.

The 30M CW Transceiver is Sacrificed!

In 2013 I was convinced to write an Article for QRP Quarterly that would center around a 30M CW transceiver complete with narrow filter and even an RIT. I built that project wrote the article and even had two QSO's with the radio. After having taken some nice photos for the article the radio was put into the back of the closet. That seemed a good place for the project seeing as I had no emails of inquiry and despite having some nice features no one was interested in building it. Previously I had another CW article only this one was for a 40M CW transceiver. Again not much interest.
The most interest has come from my SSB radio projects and the recent LBS series of articles is testament that most new to homebrewing want to yak and not key. We have received over 100 emails about the LBS and we know for a fact that many are under now construction. Need I say more. The hobby has room for all sorts of interests and in fact I find the SSB radios to be more of challenge to design and build than the CW ones. But to each is own.
One of my bents is to reuse circuit module blocks -- if something works then why reinvent the wheel. In the course of building the LBS, the ZIA and LBS-II it suddenly came to me that many of the blocks I would have to build where sitting in the 30M CW transceiver and since that had been all but abandoned -- a ready source of modules. The LBS has the pre-driver, driver and final stage. The ZIA ended up with the bidirectional amplifier module and the LBS-II has some of the knobs, pots and relays. Thus the sacrifice of the 30M CW transceiver was taken in earnest.
One module still intact was the mainboard which had the 30M BPF, RxTx Mixer stage (TUF-1) two bilateral amplifiers which used BF991 Dual Gate MOSFETs, the 5.0 MHz CW Filter, the Product Detector was an NE602 and the audio amp was a 2N3904 with an LM386 --and it even had a FET silencer on transmit. This main board with some modification looked like a perfect start of another 40 Meter SSB transceiver.
The 30 Meter BPF consisted of two 42IF123 Back to Back IF transformers that are nominally set to 10.7 MHz --a slight tweak to the cores put those on 30M. If you add a 68 PF Cap to each tuned winding and change he coupling cap between the IF cans to 4.7 PF --this will tune to 40M (Just like in the LBS). A quick installation of the three caps now moved the filter to 40M. The four pole 5.0 MHz filter was fairly narrow and useless for SSB. I pulled out those parts. Several years ago I experimented with building a 6 pole 5.0 MHz SSB Filter using the AADE design software. When I built it, there was a question in my mind that it worked. Throwing caution to the winds I temporarily "haywired" it in the circuit. Surprise, Surprise -- it works very well and so made a permanent part of the board. The NE602 will have to be replaced and I plan on using a homebrew DBM with a surface mount BFO/CIO.

The original 30 Meter CW transceiver used a varactor tuned heterodyne VFO and that enabled easily adding the RIT. None of that old school crap in this new radio. Having a few AD9850 DDS modules in the bin, I suited up an Arduino Pro-Mini as the controller and now had a chance to use a 8X2 cool blue display. What a great addition to even older radios. Now we have a nice stable LO signal for SSB.

I should add that the Dual Gate MOSFET bilateral amps are based on the work of Ron Taylor (G4GXO) and while have the gain fixed by applying 8 VDC to Gate 2, you could just as easily add AGC and/or ALC to these devices -- so lots of possibilities. I have actually done this is several other radios using this same bilateral circuit.
I have taken some videos of the receiver in action and when finalize the edit will upload those to youtube
Pete N6QW