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|Unichip 80m transceiver|
|Written by Hans Summers|
|Sunday, 05 April 2009 15:36|
This project somehow grabbed my imagination. It's a complete 80m transceiver in one chip designed by Mike King G3MY, the CA3086 transistor array. One transistor for crystal oscillator, one for a PA, and three for the audio amplification after direct conversion in a diode mixer. CLICK HERE for the original SPRAT article (121K). CLICK PICTURES for the larger images.
Martin Rigby G4FUI sent me this very fine hand-drawn diagram from Mike himself... which Martin thinks followed a QSO some time in the 1980's. CLICK HERE for an Adobe PDF of the diagram, which Martin has very kindly cleaned up. Many thanks Martin for sharing this document with us.
I built the unichip + VN66 PA and failed to have any QSO's. The unichip on its own gave only 90mW instead of the 300mW mentioned in the article (something I did wrong?), and the VN66 did not provide any increase in output power, probably due to insufficient drive. I built a new Class-E output stage with an IRF510, which now gives 2W output. After that and using a longwire antenna strung low in some trees, against an "earth" wire just laid out on the ground, I worked G4LAM and G3CWW at distances of 76 and 176 miles respectively (122 and 282 km).
Unichip goes Stateside!
In September 2005 I took the newly constructed Unichip (with only 2 QSO's to its name) with me on a business trip to Greenwich, Conneticut, USA. Also onboard was my homebrew ATU. I operated on three successive evenings, for 2 - 3 hours each evening. The first evening I had no luck, which I eventually traced to an intermittent connection problem in the variable capacitor of the ATU. As long as I kept squeezing the capacitor, everything worked Ok.
As an earth connection I used a PC power cord plugged into the wall, with the PC end socket cut off and a the earth wired to the rig. For an antenna I used 10m of ordinary twin-core speaker cable (split to make 20m), and a 3m length of 4 twisted pairs network cable dismantled and joined (in pairs) end to end. This gave about 32m wire, which I threw over the low branch of a tree outside my upstairs window, and tied the far end to the top of a bush at about 6 foot off the ground. As a power supply, I used eight D-cell batteries laid in line and wrapped in the front page of the New York Times, with wires taped to each end and stood upright against an armchair. The morse key was just the microswitch on the Unichip board. Headphones were just the dirt-cheap in-ear type.
With this incredibly basic setup and signing as W1/G0UPL, I had continuous QSO's, working 9 stations in total during the course of two evenings. They were: W1GUE, K1ARO, W3MNE, W1CFI, N2EY, AF4K, K4JYS, AE5X/2 and W2LJ. The furthest distant of these stations was Brian AF4K in Florida, at a distance of some 1500 miles! Not bad for 2W to a random bit of wire. The radio activity made otherwise boring evenings highly enjoyable.
But there's more to tell! It turned out that John Harper AE5X lived only 5 miles away and worked just over the road. We agreed to meet up for coffee the following morning, and had a very enjoyable chat. I persuaded John to take my rig home with him and have a play. I received the rig back from John a few weeks later in perfect condition and with many more QSO's to its name: he worked 18 states + Bermuda with the rig! Above are some pictures; from left to right:
1: John and I after our coffee meeting
John wrote about the rig and our meeting on his website, too.
Performance measurements from John:
This rig isn't finished. The following further developments are intended, SOMETIME, EVENTUALLY:
1. Fix the semi-QSK circuit so that it does not make nasty noises on changing between RX and TX
|Last Updated on Sunday, 02 January 2011 17:58|