LF/MF Wspr From a Small Garden - Part 1: MF

The problem for me in recording my experiences on 630m and 2200m is that I no longer have the antenna I used. In point of fact, it is a case of I no longer have all of the tree I had to support the antenna wire. So those days are now behind me. However I have decided to try and recall how I came to be interested in these two bands and what happened. It was hard work and expensive back then (just over 4 years ago, how fast the radio world changes). So please allow for some inaccuracies however the general 'shape' of what happened is correct. I'll add pictures etc. later...

First up I shall go back to 2009. I had by then grown bored of HF Wspr, it was just too easy. One day I was spotted in VK and ZL with just 5w on 20m. Nothing unusual in that, Wspr can achieve such things and it is good. What surprised me was my antenna, unbeknown to me, had fallen down. Now I live up a slight hill so it is probable the antenna height (electrically speaking) was not at floor level. The water table is somewhat lower than the ground surface, at least in summer. Also it has to be said HF conditions were superb at the time. I managed spots on all continents and (although I did not carefully record it) many countries across the world. This was true of most HF bands. Wspr is just that good at getting through. So I started to wonder about other bands: 6m/4m/2m - particularly 4m but that is another story.

Fast forward three more years and I began to wonder, if it was so much fun trying to put out a Wspr signal on VHF then, what about bands below 160m? I'd always considered MF/LF beyond a small garden, even if ours did have a 20m high tree at the bottom of it. However I had noticed the 630m signals appearing on Wspr-Net...

I did not have a radio capable of transmitting on 630m at that time. Of course this is easy to achieve now with, for instance, an 'opened' IC-7300. So I did the usual 'research', i.e. messing around on Google, and came up with four options. Option one an old Icom 735 with mod. However people seemed to have heard of this already and prices were very high on eBay. Option two was a possible SoftRock 630m version, I did email about this, but I do not know if it ever materialised. Option 3 was build a transverter and use one of my HF rigs, I was just about to go down this route when I discovered a fourth option. This was a Genesis G11 one version of which could be built for 630m only. The G11 was/is an SDR transceiver. I had a spare PC so I decided to have a go at building one of these. I did record my efforts on video here.

G11 Board - click pic to see video

Building the G11 was quite scary. I did not have much in the way of test equipment and I did not and do not fully understand the workings of the software/hardware/pc connections/soundcards required. But I had owned a Flex 1500 and with the support of Jim, GM4FVM, I had used it on air for a while and got to know the basics - thanks Jim! It is hard to go back to ordinary radio once you have got used to an SDR display. It was also my birthday (a big one) so I had the kids and XYL buy me the kit with case (not cheap) and with the help of my children's eyesight (some small components although all the SMD was already done) I got the thing working. I'll always keep it - even if it is 'obsolete' now - it is the only time my kids have been involved with radio. Anyhow this page deals with MF/LF rather than SDR so what next?

Well the next thing to do was build an antenna. For me this is the best part. I had some ideas of how I might be able to put out some kind of a signal but thinking ain't doing so I got stuck in there. One thing I soon discovered was it was much easier if you have the correct tools. To this end I purchased a Rig Expert AA-30.

Nice dip at 477khz

It might be possible to use trial and error on MF and get a resonant antenna, perhaps even on LF given enough years. However, being in the dark as to what was required I found this device invaluable. The first coil I wound was on a white PVC bucket. First of all I wound the coil to match the long wire which I had fired over the tree with a catapult. This wire was about 40m of stranded PVC covered flexweave, and after a few attempts I found it was possible to get the antenna resonant on 474.200 (the Wspr tx frequency) quite easily.

Plasterers Bucket Coil - Note tap for impedance transformation. Top of bucket goes to antenna wire, Bottom to earth

Of course this kind of antenna needs a ground. I purchased 4x 2.4m earth rods. I dug down into the lawn to ensure there were no sewer pipes then drove them into the soil. I connected all four with earth cable and buried the lot. Hard work on a hot day.

So I now had a resonant antenna element and a ground system (of a sort). Of course I now needed a way to match this lot to the 50 ohm output of the Genesis G11. Graham, G0NBD, he of Opera fame, was kind enough to email me some photographs of his antenna system. I followed his advice and used a tapped impedance transformer style feed - in this case about six more turns below the feedpoint - (as well as later a variometer which is a nice addition though not strictly necessary at least at 630m in my experience if you stick to one frequency). In some ways it is possible to just tune the whole thing to the point you get maximum output - as 10w from the G11 showed on the meter. As it happened I soon had an indicated 10w from the G11. Difficult to be sure of the accuracy because few modern meters are designed for this job, my Welz SWR meters certainly were not. It is much more problematic on 2200m as shall be seen later. At least it matched what I saw into a dummy load.

So I had an antenna. A radio. And no need of an NOV as 470khz had just (I believe, I might be mis-remembering) been released to UK amateurs. I liked the idea of being on or about 500khz as Liverpool is a maritime city. I have lived most of my life by the sea. I cannot remember if I actually did have an NOV for a while, come to think of it perhaps I did... anyway I tested everything, adjusted the soundcard settings with help believe it or not from a VK station (I will add his callsign when I can find it), these are pretty critical on a G11 and waited. I tried transmitting by day, no joy. In fact there appeared to be no one to hear if the Wspr-net map was telling the truth (there can be RX stations who do not show up until you TX and they spot you these days - I am now one of them- see forthcoming Red Pitaya page). So I waited for night. It was really rewarding when the first spots came in. Those who think Wspr is not a proper RF mode have not built a monster antenna, their own SDR, installed an earth system and wound huge coils just to get that first spot! It was brilliant. After that it was the usual case of trying to perfect the antenna, to see just how far it would go...

Bird Pond Coil - replaced bucket coil

In time I added a small amplifier (50w input into antenna - tiny amout of ERP nonetheless) with high power homebrew LPF, a small Russian variometer (more input power actually seems to change the antenna so it is nice to be able to adjust it) and managed to be spotted as far as Eastern Europe. Not quite VK/ZL on a fallen wire, but much more rewarding somehow. I knew my garden was too small for 2200m - well wasn't it? - and so I was content with this. For now....

Russian Variometer

Of course it wasn't long before I got to wondering about this: what if?

Part 2: 2200m