Thanks Jim for the explanation.
Was wondering how you could produce such a "massive" signal.
FYI it was about the same as Nitonrdo/GNI Navtex. I believe they run
1000 or 400W and QRB 450km. (Yr abt 350km)
Many PA stations enjoyed your presence in the last days of their license.
Thanks!
Jan/pa3abk
Op 29-3-2011 1:47, James Moritz schreef:
Dear Dennis, Roger, LF Group,
Thanks for the additional reports for M0BMU/P. Here are some details
of the station - see the attachment for pictures:
The TX antenna was a 15.3m fibreglass mast with 4 x 10m long top
loading wires sloping down to just over 9m. The ground system was 4 x
1m ground rods spaced on a 2m circle round the base of the mast. The
antenna was tuned with approx 300uH fixed inductance near the base of
the mast, and connected to the 18 - 70 uH fine tuning variometer in
the shack about 15m away by a transmission line wire about 1.5m above
the ground. The antenna ground was also connected to the tuner via a
return wire about 300mm off the ground. The tuner contained the
variometer, ferrite cored matching transformer, and a common mode
choke to isolate the antenna ground return from the shack ground. This
arrangement puts the tuning and matching controls in the shack, and I
found it was easy to adjust, with no problems due to unwanted
resonances or ground loops. The total antenna resistance was only
about 11ohms, including 2 or 3 ohms due to the loading coil and
variometer, so antenna current was approx. 3A with 100W PA output. I
estimate the antenna effective height was 11m, giving Rrad of 0.53ohm,
and ERP of 8.6W.
The receive antenna was a single K9AY terminated loop, oriented to
reject wideband noise coming from the Brookmans Park BC site to the
west, and give good reception of Eu stations from the east. I found a
terminating resistor of about 200ohms gave a good null - this is
rather lower than the values quoted for the HF bands. The RX antenna
was positioned about 50m from the TX antenna, to minimise interaction,
and give the RX preamplifier an easier life!
I used my 200W EER transverter rig, although just for CW on this
occasion, driven by an IC-718 as the IF. The minimalist shack ("hutch"
might be a better name for it :-)) was supplied with 130m of mains
cable going to an outbuilding and into a slightly dodgy mains socket,
but much less hassle than a generator or batteries. It was also quite
handy to be able to follow the cable and find the gate in the dark!
Cheers, Jim Moritz
73 de M0BMU
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pa3abk<-> dordrecht jo21it
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