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
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