I've always had an interest in 160 metres since I picked up a couple of local Amateurs when I was fiddling with the family radio one Sunday morning back in the 60's. When I got my Class B licence in 1984 I fully intended to go for the Morse, but I had so much fun messing around on VHF, UHF and microwaves that it never happened. Then the powers-that-be announced that we were all Class A's and we could enjoy HF to our hearts' content. Strewth!

At first I used a shop-bought rig - an IC706 - for topband, but it seemed such a waste (I wasn't much interested in the other HF bands) that I sold it and set about home-brewing my own single-band rig.

Here it is when it was nearing completion. It's quite simple - no synthesizers or DDS, just AM and SSB generation at 455KHz and a stable VFO running on the high side. The only 'digital' electronics is a counter/display from Cumbria Designs which shows the frequency on a nice LCD. SSB is generated in the usual way, with an NE602 balanced mixer (fed with 453.4 KHz) followed by a 2.7KHz filter. AM uses the same arrangement, but the NE602 is slightly unbalanced to produce a carrier and the carrier osc is centred on 455KHz. An 8KHz filter allows both sidebands through as God intended. After careful filtering and level control, the signal arrives at the driver/PA board and whacked up to 20w PEP by a pair of very manly BUZ901 powerfets. To keep the talk-power up, the mic amp incorporates a wee bit of compression and clipping.

On the right is the rig pictured just after I'd fitted the lid. The hole in the top lets the sound out. On the front, the controls are: Tuning (left) - this is a proper tuning cap with a slow-motion drive. Below it is a fine-tune control. The display is the green thing; it shows frequency, mode and RX/TX status. The two little green buttons are for AM/SSB selection and AM 'netting'. The S-meter drove me nuts! Eventually I got enough AGC range to properly indicate up to S9+30 with 6dB per S-point all the way, but it took ages. The two knobs at the bottom right are for audio gain (volume) and TX power, 0 to 20 watts PEP. I've had excellent reports with this rig.

I have recently made an interesting modification to this rig - see the DYNA-MOD page for details.

On Friday and Sunday evenings at 8:30 local time, 1963 KHz is where you'll find several of us chatting. The net was started in the early 90's and many people have come and gone, but there's always a core of dependables who turn up regularly. Subjects range from trams and Real Ale to synthesizers and microwaves - it depends who is on.  It's all very relaxed and you'll be made welcome. And it's AM only!

Dec 2007: On the right is my current antenna for 160 metres. It is a near-the-top loaded vertical which was very hastily knocked up after the 'spiral top' antenna was wrecked in the high winds of 19 Nov 2006. The loading coil was left over from the top-capacity loaded version of September 2005, and so did not have enough inductance with the short upper section of this one. So about ten-billion turns (that's what it felt like!) were added on the mast itself to get it within the band.  This was only a temporary arrangement, and I quickly set about making a new coil.

In preparation for winding the new loading coil, I shinned up the ladder and measured the total inductance of the existing windings with my Peak Electronics LCR meter. What a Godsend this little instrument is!  It told me that a coil of 332uH would be required, so the next step was to wind one....

Done that, and the picture is now of the vertcal with  the new coil fitted. Or it was... I've just updated this photo to show a recent height extension. He can't leave it alone, you know.

If you'd like to take the guesswork and industrial-strength cursing out of coil-winding, I can recommend the LCR meter:  http://www.peakelec.co.uk/acatalog/jz_lcr40.html

This is the setup, much the same as used with the spiral-top. The aerial is resonated just at the HF end of 160m, and the tuning box contains a small adjustable inductor to bring the resonance to the required frequency. I keep promising myself I'll fix up some kind of remote tuning, but somehow I never get around to it.

My first toband antenna went up in March 2003. It was a rather half-hearted 20ft roach pole, loaded at the base. It didn't work very well, so I quickly moved on to better things.

July 2003: After acouple of failed attemps, I ended up with this much more effective 27ft, centre-loaded vertical which kept me happy until I became convinced that I could do better...

..and up went this capacity-hat loaded vertical in September 2005. It was mounted on the wall and the 'vertical' was actually a sloping wire to keep it away from the house. According to reports, this was slightly better than the previous one.

The dreaded spiral top-loaded vertical went up in April 2006, after I re-read an old Tech Topics article all about them. The consensus was that this was slightly better still. A bit wobbly in the wind though! Too wobbly as it turned out, and the gusty winds of 19 Nov 2006 cracked the mast and down it came.

This is where we came in.....

I have a collection of transistor radios, ranging from a modern Sony 7600GR to some relics from the 1960's. At a loose end one day, I decided to convert one of the old ones into a Topband portable, and to make it as good a performer as possible. It would have to have SSB as well as AM, as there isn't much AM to listen to these days. On went the iron...

The first job was to whip out all the germanium PNP transistors and replace them with modern NPN BC547's and reverse the electrolytics, thus converting the radio to 'negative earth'. Don't worry, this was done with the utmost respect and due consideration for the venerable OC45's and associated circuitry. The transistors went in 'the drawer' for future repairs. The audio amplifier board containing an OC81D, two OC81's and a couple of sturdy transformers was removed and replaced with a dead-bug board featuring an LM386 chip amp. Much nicer. This board also had room for the proposed product detector and its carrier insertion oscillator. On test, the IF board had so much gain that it stuck itself to the shack ceiling and refused to come down until a bit of emitter degeneration was installed. I used the original mixer/osc circuitry purely as an oscillator, feeding its signal to an NE612 mixer on an add-on board which also contained a fet RF amplifier. I also fitted a longer ferrite rod aerial to cop as much signal from the ether as possible. On the final leg now - a crystal osc(!) on 455KHz and a dual-gate fet product detector were constructed on the remaining space on the audio board, and mode-switching was handled by the original wavechange switch. After a lot of fiddling with the RF/Osc tracking, it worked, and it worked well!

Here's a view of the innards. Partially hidden under the tuning gang and the add-on front end board is the original IF board. You can see the oscillator coil on the left. The bunch of grapes above it is a collection of caps to make it track. Over on the right is the CIO/product detector/audio board.

How does it perform? On moderate signals, there is little to choose between my posh Sony 7600 and the Topband Special, but on weak sigs the Special shines. Soon after finishing it, I heard a station on the other side of Manchester doing some AM tests. On his normal 10w output, he was a decent signal on both radios, but then he turned down the wick and became inaudible on the Sony. However, on the Special he was weak but perfectly readable! Result! I suspect the Sony is noisy, as its ferrite rod is untuned and is followed by an RF amp to make up the gain. Probably.