Sunday, 24 March 2013

SW-20+ Keyer speed control

After all this time I finally got around to fitting a CW speed control to the front panel of my SW-20+
This rig has been a 'work in progress' for a long time. I intended to use the rig for SOTA as my main 20m rig but then I managed to secure one of the limited run of KD1JV's Mountain Toppers (aka 'MTR'). I did manage to work a few contacts with the SW-20+ during testing, including a QSO with Bill, NG2D, in Pleasant Valley, New York.

I tried the rig out on one SOTA activation from Rombalds Moor G/NP-028, and the rig seemed to do OK, but I found that it was a bit tedious to change the speed of the keyer chip that I had fitted to the rig. I had used the PicoKeyer chip from Dale, N0XAS, and built a little Manhattan style keyer circuit fixed the the rear of the SW-20+ case. I had omitted the speed control potentiometer for simplicity, the speed can be set through the menu accessed by pressing the front panel button. I found that I wished that I had fitted the speed control.

During building and testing of the rig, I decided to tweak the tuning range to cover a larger portion of 20m rather than the standard 30 to 40kHz. There is a capacitor that sets the tuning range, I had changed the value to give me band coverage from 13.999 MHz to around 14.070 MHz, I found that the tuning was a little on the difficult side, a slight touch of the tuning knob and you would QSY a number of kHz. Whilst I was inside the rig to fit the speed control, I swapped out the capacitor that sets the tuning range, I now get around 37kHz of swing from about 14.026 to 14.063MHz, this should make the tuning a little easier. I noticed that a lot of the SOTA ops in NA tend to operate above 14.060 MHz, usually 14.061 or 14.062MHz, I thought it was important to have these frequencies covered, whilst still allowing as much tuning below 14.060 as possible.

I ordered the 50k potentiometer from Ebay one afternoon and the very next morning it arrived in the mail, it almost seemed as though the vendor had posted it before I had ordered it! Fitting the potentiometer took quite a bit of work, I had to remove the FreqMite (PIC based frequency counter) from it's front panel bracket first. I left the FreqMite hanging from it's wires and as to be expected I suppose, some of the wires broke off. I then had to remove the fixing screws for the main PCB and move the entire PCB sideways out of the enclosure because I had broken one of the cover fixing brackets, doh! Luckily there is just enough gap between the cover fixing brackets to squeeze the PCB through - good design or pure luck? :-) I repaired the cover fixing bracket and then I removed the sticker on the front panel that said 'SW-20+', of course the sticker had to bring some of the silver front panel paint didn't it?!

Drilling the hole for the potentiometer actually went very well, I managed it without damaging any more of the silver paint. The potentiometer was finally wiggled in to its hole after a bit of persuasion; one of the IC's on the main PCB was just in the wrong place and was fouling. The next task was to rebuild the rig; the main PCB was pushed back into it's correct position and screwed into place. Then all the broken wires had to be fixed to and from the FreqMite. The FreqMite would no longer fit in the same place as before; I had to move the board away from the front panel a little bit and make a bracket extension to support it.

I wired up the new speed control pot to the PicoKeyer board and then it was time for a test - the usual law states that all potentiometers will be wired up 'backwards' i.e. the speed will go from fast to slow, rather than the expected slow to fast. Upon powering up the rig, I was greeted by the usual '73' from the PicoKeyer and the usual babble from the FreqMite asking it's questions, I tried the speed control and I had actually wired it up correctly! How I managed that, I will never know!

Whilst the cover was off the rig, I gave it a re-alignment just to make sure it was properly set up. I found that I could squeeze 2 watts on transmit from a 12v supply, so I think that's pretty good. I backed the power down to 1.5w and left it set at that.

So now the rig is just about finished I reckon, there is not much more room left in the case for further additions. I gave the top cover a quick polish up with some car polish, it's now super shiny! I could do with touching up the silver paint sometime and putting some lettering over the speed control knob, just to finish the rig off.

I am determined that I will do a proper SOTA activation with this rig, it's too nice to just have stored away in some cupboard.

Well, that's it for now folks, my next blog entry will probably be about building an MTR from the second batch of 149 kits - yes, I managed to secure another one! :-)

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