2200m Wspr From A Small
Garden - Danger, Fire Hazzard. Do Not Copy!
Of course after a while even 630m became a little too 'easy'.
Perhaps radio amateurs - those who really stick at it - are
actually masochists. I looked at the final 630m coil I'd made with
a former of a small pond and decided, you know what that coil is
titchy small (to quote Roald dahl). What I really needed was a
coil with hundreds more turns and which stood two metres from the
ground. This was constructed from several formers (the
aformentioned pond, and several huge garden pots fixed together
with cable ties and 10mm bolts. It took about 200m of PVC covered
flex weave to make the coil. Given that the wire costs about £1 a
metre I have only now realised how expensive it all was. But...
Prototype 2200m coil
Usig the Rigexpert AA-30 which (thankfully) will go down as low as
100khz I managed to fit a coil to the end of the same wire I used
for 630m and have it resonant at 0.137500mhz give or take a hz
here or there. This is the Wspr TX frequency for 2200m.
Part of a later coil
2200m Variometer
But what to use for a radio?
Well this was more difficult, but also much simpler. More
difficult as I did not have anything I could use to transceive on
this band. I also did not want to build another G11, too
expensive, or a transverter until I was sure there was any chance
of success. Fortunately I did have one of the most useful devices
ever put on the earth for radio hams. I am talking about Hans Summers' U3s.
I had in fact built several of these over the years and consider
Hans a friend such has been our communications over the years. Who
said data modes are not sociable? I knew Hans could provide
an LPF kit for the U3s so I ordered one, made it and fitted it to
the U3s. Unfortunately the output from the U3s was just too small
at these frequencies. The losses in the huge coil must be very
high. I needed some more power to enable me to tune the coil for
efficiency. Again I plumped for the impedance transformer
approach. My SWR meters were useless down here. What to do?
An Ultimate 3S
I found a circuit online for a simple single FET amplifier and
soon had it built. I also built a larger LPF as I suspected more
power would be required in time. Driven by the U3s I suspected I
was seeing about 20w into a dummy load. I used the power meter on
my Welz SWR and tuned for maximum forward power. Transferring this
to the tapped coil of the antenna it was possible to adjust the
tapping point to see something similar. I had a 'tuned' antenna, a
Wspr transmitter, an amp with LPF all I now needed was darkness
and all would be revealed...
Well not quite. It was Autumn. I transmitted for days/nights and
nobody spotted me. I knew there was a signal as I could spot
myself, I just did not know how much of a signal. Eventually
autumn headed for winter, the clocks fell back, and, with the aid
of a LF converter I was able to use the antenna to receive my
first LF Wspr spots. G8HUH being among the very first as I recall.
Then one day, it was a Sunday, and it was morning about 11am I was
spotted for the very first time by a station about 50 miles away
in Wales. This made the MF spots seem like a piece of cake, now I
was hooked.
The next thing I found was a WW2 NOS RF Ammeter in USA. I remember
the theory from my RAE but had never used one. I ordered it. It is
a lovely thing and arrived a couple of weeks later. I was
disappointed to see such a low amount of current (under 0.7 amps)
from my homebrew amp (using IR squared from the RAE it is less
than 25w). Given the antenna was probably <1000th efficient it
is surprising my signal was spotted at all. It was obvious more
power was required if I was ever getting beyond the UK.
Lovely RF Ammeter by General Electric
Doing some more 'research' I came across an old thread which
talked of using FET audio amplifiers for LF RF. It seemed there
was a UK amplifier with specifications beyond 136khz. I managed to
track one down on eBay. When it arrived I was disappointed to find
it was dead. It turned out the connections from the
autotransformer inside had been cut and the fuse was blown.
First Audio amp - BK CA110 (mono)
I
repaired the connections and replaced the fuse then stood well
back. Fortunately all was well. I now had a possible 100w at
136khz if i could figure out how to match it to the antenna.
Bigger Audio Amp = more current
The answer was large ferrite rings and transformation of
impedance. It was easy to match the input to the amplifier the U3s
did not seem to mind. The output of the amplifier was something
else. Many hours of trial and error and eventually I got to see
about 1.25 amps into a (big) dummy load on the RF Ammeter. With a
few adjustments to the homebrew variometer I was able to replicate
this current into the loading coil of the antenna. And VOILA! my
first spot into Holland, my U3s had reached as far as Europe.
There were far fewer receive stations back then (18 months ago!)
and so it took a while, but gradually I was spotted as far as
France.
[I learned a lot during these (expensive) experiments.
Impedance transformation is all about efficiency. Mismatched
impedance simply would not allow the amplifiers to transfer
power. Of course I did not just start making these devices I
used the information supplied by others for free on the
internet. As I find the links (if they are still active) I will
add them to this page at the bottom.]
Then I saw a larger amplifier on eBay at a very reasonable price.
It was cheap because one channel was down. However it was a 600w
unit so I reasoned, even if I could not fix the 2nd channel that
still left 3x the power. So of course i bought it. And yes it did
deliver 3x the power. In fact as I managed to fix the other
channel I was able to get both channels via a centre tapped
transformer to feed the antenna. I was now seeing >3amps (3
squared x 50 = 450w?) into the coil. I managed my first (and last)
1000km spots into the heart of Europe. Brilliant!
One channel of the (stereo) BK Electronics MXF 600
Not quite.
This was the cause of my first and last antenna fire. I know I am
not the first and in my case I was lucky, it was only the tree
which went on fire. And it soon extinguished itself as it rained.
But I have a wife and kids, a night time fire was not a risk worth
taking. I had seen what other people had reported and decided
enough was enough. Also we were due building work which entailed
the cutting back of the tree (it survived) and so now I cannot put
enough wire out even for a decent 630m signal. So all was packed
away. Which leaves me only with my memory of those fun adventures
on 630/2200m bands. Now the building work is complete. The
amplifiers, coils, variometers are stored away... so who knows,
one day perhaps? Actually I do know. Been there, done that. As it
says at the top, do not copy. You can put out a 2200m Wspr signal
from a small garden. BUT as the wire radiating element has to be
shoe horned in fire is an ever present risk at this frequency and
at the input power required.
