|My station is located in the attic of my
house. The "shack" is insulated and boarded but
has no windows. So it gets very hot in summer and very
cold in winter. There are about two weeks in spring and
autumn when the temperature is OK :o)
The equipment is mainly homebrew, but I do have a TS-820 to use while I am extending my homebrew rig (see below). If you know how to modify a TS-820 for CW and SSB QRP, please let me know! Carlo, IK3LMA suggests a battery and potentiometer applied to the ALC input. I have not tried this yet, but the manual says the ALC threshold is -6V and ALC can be applied via the Remote or Xverter connectors. Ken WB5UYJ suggests simply turning down the "Carrier" control. I didn't realise this would work on SSB - however, my power meter says it does but I haven't tried it on air to see what the signal sounds like.
So here's some brief descriptions of the bits and pieces "what I built". More pictures one day...
- Update Winter 1999/2000
- Update Summer 2001
- Update Winter 2001/2002
- Update Spring 2002
My HF Rig is built mainly from kits from Sheldon Hands , http://www.rf-kits.demon.co.uk. It started life as a 6m SSB rig, before I passed the Morse code test for my HF licence. Unfortunately, I spent so much time learning CW that although I got it built and apparantly working, I never got a 6m aerial up so never got it on the air before getting my HF licence. Having got hooked on CW, I decided it wouldn't be too difficult to make the rig into an 80m CW/SSB rig, which is what I have done. It works pretty well on CW, and I hope to get SSB sorted out very soon.
The rig is based around the Hands RTXIF 9MHx IF/AF board which uses the GQRP club 2.4kHz SSB filter. I have added the GQRP club 500Hz CW filter, and a Mini-Circuits monolithic amp to overcome the terrible insertion loss! Builders beware: the CW filter is 50 Ohms (yes, FIFTY) and the SSB filter is the more usual 500 Ohms. I added a matching transformer at each end of my additional filter/amp board and used PIN diode switches to select between SSB and CW.
The RTZ50 RF board is a broad-band design, so all I had to do was change the RX and TX band-pass filters. I did this by scaling the values in the 50MHz design to 3.5 MHz. Simple but effective! There are other sources of filter values, eg the GQ2000 design published in SPRAT.
The VFO/MX local oscillator board supplied for the 50MHz rig uses a 38MHz crystal mixed with a VFO that covers a 500kHz range between 3 and 5 MHz. It was a simple matter to retune the VFO to the more standard 5.0 - 5.5MHz and bypass the mixer. This gave me 3.5 - 4.0MHz coverage. Of course, the VFO tunes "backwards" but I soon got used to it.
To this basic setup I added the Hands 3.5MHz low-pass filter and antenna changeover relay, and the RTXCO keyed 9MHz oscillator and TX/RX control. I retuned the USB BFO for use as a CW BFO - the crystal easily pulls far enough - leaving the LSB BFO for SSB. I have all the bits to make a separate CW BFO, but it's way down the list of things to do!
|Finally, I added a passive narrow AF filter from the GQ2000 design which really does help cut out the QRM on 80m, a sidetone oscillator - a single transistor twin-T oscillator which gives a good sinusoid from a simple design, and a permanent supply for the audio amplifier so I could hear the sidetone!|
So that's how the rig stands today, the main boards are fixed in a chassis and the VFO is in a box, but the other boards are only held in place by their connecting wires and sticky tape. I should be ashamed I know, but metalwork never was my strong point, and after all it works! ONE DAY it will all be boxed up and looking pretty, but I fear that time may well be some way off. There's always something else to "just try out before I box it up ..."
On the list of "Things to do" are: get it working for SSB, add an SSB AF filter, add AGC and S-meter, add filters and switching for 20m, build a frequency display, add more bands, and so it goes on, not forgetting to build a proper case at some point!
The rough note of the sidetone hinted at some undesirable RF feedback on transmit, so I decided that a proper case was necessary before any more work on SSB. I fabricated a case from some large sheets of scrap aluminium I obtained from work, avoiding the need to bend it by using aluminium angle from a DIY shop and lots of self-tapping screws. This method was very successful and resulted in a case that is strong enough for me to stand on!
The Hands Electronics AGC board, which also includes a sidetone generator and audio filter has been built.
|I have also built a multi-band filter board to take up to 7 band-pass filters. This board will replace the filters on the Hands RF board. It was to have been used for transmit and receive, but after thinking about it, I decided to build separate RX and TX filters and avoid having too many RX/TX diode switching networks.|
Plans now include a DDS VFO for multi-band operation, but first of all, the existing boards need to be put into the box...
After 18 months of neglect (I was busy doing other things) the rig is finally beginning to take shape. I am now making a concerted effort to get it boxed up and working, although I am sure it will never really be "finished" :o)
A multi-band low-pass filter board has been designed and built, which will handle all bands from 3.5 to 50MHz. The IF filter board has been rebuilt with a new PCB and relay switching for CW/SSB and TX/RX. Diode switching just seemed to end up with too many bias resistors and blocking capacitors so I wasn't convinced it was the best way to go...
Much drilling of metal is taking place now and I have all of the board fixings in place for the top side of the enclosure, plus the low-pass filter board which sits on the back wall. A prototype front panel is being put together to check that everything really does fit before making the final panel!
Plans for the DDS VFO have been revived. It will consist of a 200MHz AD9857 which has a 14-bit DAC which should help overcome some of the performance problems associated with earlier DDS VFOs. The DDS will be controlled by a PIC 16F876 which has much more to offer than the fantastic but somewhat limited 16F84. However, I need to write some software, build a programmer ... more jobs to add to the list ...
The AD9857 comes in a 0.65mm pitch 80-pin quad flat pack package, so watch this space to see how I get on with mounting it on a home-made PCB!
The PIC and DDS hardware has been designed and the (long) task of writing the software has begun. The boards will not be made until the software is written, just in case the design changes... I expect the software development to progress slowly, since there is more to life than writing software!
When everything is working, I will publish the design here. If you can't wait and wish to collaborate on the software, please drop me a line and we can sort something out.
With the software outline designed, I was happy that the hardware design was OK, so I built the PIC PCB. I have started writing the software now and so far I can display a message on the LCD. Progress indeed! :o)
The DDS PCB is still to be built, and there's a good bit more software to write yet!
This is another kit, this time from C.M.Howes. Very straightforward and seems to work well. I did notice that it seemed to swallow some of my power on 2m when it was left in-line as a power meter.
My QRP ATU is a homebrew CLC circuit. I was lucky to get two variable capacitors of roughly the right value at a reasonable price. The coil was wound on a piece of 38mm plastic pipe, the sort used for waste water. To keep the turns tight I drilled a double row of holes along the pipe and wound short lengths of wire between each pair of holes. The wire finished by going down one hole and up the opposite one to lock it in place. The next piece of wire was then joined to the first , forming a tap, and wound round to the next pair of holes. The coil dimensions were arrived at by referring to a variety of texts and making something about the right size and number of turns using the materials available. There are about 4 turns between each tap, 12 taps in all. One day a 12-way switch will select which tap is used, but for now a croc' clip on a flying lead suffices!
Now this proves that almost anything can, and frequently does, work!
I wanted to work 80m because I got my licence at the bottom of the sunspot cycle and I only get to operate at night. Work and children keep me occupied during the day. Unfortunately I have a VERY small garden, so I just strung up as much wire as I could. I eventually managed to get 70' (about 20m) out in a very strangely bent shape, with the highest point about 35' (12m) above the ground. The aerial starts at the ATU (at least there are no feeder losses!) and the first 8' is in the house (far from ideal). The next 15' is vertical, then a 35' almost-horizontal run to the end of the garden, with the final 12' sloping down at about 45 degrees. However, it does work! My homebrew rig has managed QSOs over Europe from Norway to Spain. I borrowed a rig when I was first licenced - an elderly TS520 - and with that I worked USA, Canada and the Canary Islands on 20m, and Asiatic Russia on 40m. All this with 5W CW to a grotty bit of wire too close to the ground, and at the bottom of the solar cycle!
I did have the ubiquitous G5RV (the most popular 80m antenna in Britain?), but since it is 102 feet long, and my garden is somewhat less than that, some ingenuity was called for. The centre section of each half was folded into triangles, 0.75m on each side. 4 triangles compressed 12m of antenna into a 4m space. The idea came from an old copy of "Practical Wireless" and the theory is that the triangular folding is non-inductive. It looks a bit strange, but it seemed to work.
I'm not sure the G5RV was really working that well. It was been replaced by a 20m dipole which does fit on my property in a straight line! It only works on 20m, but it does work. QSOs (100W SSB) with Thailand, Azerbaijan, USA, and Venezuala prove it!
In the quest for multiband operation, half a W3DZZ was constructed and used as an inverted L against earth. It works fairly well, but I suspect the earth connection could be better. More work required!
The ground connection is to two pieces of copper (water pipe) earth rods hidden in the flower bed, connected by some very heavy braid. During the CQ WW WPX contest, I worked Argentina, Brazil, USA and Canada on 21MHz (100W SSB), so it must be working fairly well!
This is an RS Components digital clock module that I was given when it became surplus to requirements at work. Since it always reads UTC it has no adjustments on the outside, all the time-setting switches are hidden inside.
Last updated: 16 March 2002
Email me at email@example.com
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