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I worked a number of
stations last Sunday night 2130 - 2340 utc on 137.1
khz
I also had a number of msgs from those who heard the
transmissions, tks for the comments and help.
To: Peter DJ8WL , Hajo DJ1ZB ,
Marzio I5MXX , Mike G3XDV , John
G4GVC
Jaap
PA3GUC , Christer SM6PXJ , Reino
OH1TN , Dave G3YXM .
First I have to say , it was very well worth the effort,
taking all the bits and pieces and setting up the rig and atu to tune the
big antenna. I had wound a new coil on a plastic linen basket , using a
single turn of large heliax co-ax , soldered into
a shorted turn, it worked great as a variometer, but I
did not have time to put tappings in and found it was too large, even with
the variometer function to tune the large 'Tee' to resonance.
Luckily I had brought my two other variometers with me ( they are wound
on plastic paint containers ), I got on the air
just after 2130 utc. The transmitter used is my own circuit (
see LF Sourcebook for details ) using a
pair of IRFP450 mosfet's in parallel. Started off with 3.4
amps into the antenna but after a while that dropped to 3.1 amps. The
power supply transformer was very hot by 2345
UTC when I packed away the bits into the banana box. I use
a Variac , to vary the power supply to the ht
for the Mosfets, that way I can bring up the power in stages and make sure
everything is working fine before full blast. 54 volts on Mosfets at full
bore. I use a very wide spaced coil to ground , which I tap up
to match the transmitter , there is a trade off between,
match, output and current drawn by the P.A.
The receiver used was an Hagenuk rx
1002, a fine receiver, but to be honest after last Sunday I feel
there is a definite need to properly match the receiver to LF. The
way we have things at work is a development from
the old days , when most of our work was on 500 khz. We have
7 receiver's all taking their feed off the one antenna, via a
passive resistive pad of 50 ohms. The band was not that clear
on the receiver last Sunday, there seemed to be an
amount of cross modulation, I even heard the 138.8 khz signal in places I
would never hear it on the band. My next project is to specifically match
the receiver to the band and see what effect that has, or failing that to
run out a seperate wire antenna to a spare support on one of the 50 m masts.
The mast supports are 50m high,
strung between them is the old 500 khz single wire 'Tee', which is
brought to resonance with about 1900 UH. The span is
about 120 metres.
I found all the qso's and reports really
interesting and it makes it worth while setting up the station.
The comments regarding my signal fading way down
and the weak sigs from OH1TN ( I never heard him) shows the effects on the band at long distance, to be
honest , I was quite suprised my signal dropped down so much.
Working into 120 km ENE of Munich , for the first time on LF was
very pleasing, as was working Marzio I5MXX, his signal was very very weak,
but readable, so too was G3XDV, very weak indeed, but again, if I can peak up my receive side I feel I
could pull in a lot more.
I wish I knew how to attach a photo, so that you
could see the set up, plus a picture of the radio station would give you all an idea of what the place is like and where the signal
is coming from
My very best regards to all and thank you for all
your comments.
73's
FINBAR EI0CF
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