John
I've been beaconing all evening on 503.5 slow CW. According to your grabber,
you are either transmitting yourself on the same frequency, or you are
receiving me at 90dB over 9!
73
Tom G3OLB
----- Original Message -----
From: "John Pumford-Green GM4SLV" <[email protected]>
To: <[email protected]>
Sent: Thursday, August 09, 2007 3:27 PM
Subject: LF: Antennas & ERP
Hello LF group,
I had another 2-way CW QSO with Finbar last evening at around 11pm Local
Time. His signals were on the whole a bit better than the previous night
and I think mine were better too at the start, although the QRN and QSB
eventually took me down into the noise by the end.
During the day I did some measurements of antenna current vs TX DC input
power (easier to measure) and based on them (and a knowledge of PA
efficiency) I have graphed I^2 against Power to come up with a straight
line, the slope of which should correspond to overall antenna system
resistance.
This has given me a set of figures from where I can quantify
improvements. It has also showed me that tne new antenna installation is
seriously in need of work!
For 50W RF power I get 0.65A RF feed current which implies a resistance
of 118 ohms!!
Other data points for powers between 4W and 50W tend to agree with this
figure. The best fit line is around 115 ohms.
Calculation of likely radiation resistance gives me around 0.14 ohms,
which might be a tad optimistic, so my EMRP will be around 50mW, for 50W
TX power. Obviously I need to improve this, if for no other reason than
that I don't particularly want to run high RF power just to heat up the
worms.
I will attempt to lay some more radials tonight, and add some more earth
rods and then remeasure current vs power.
Hopefully the QRN will be lower this evening for another QSO attempt -
and hopefully make GW this time?
Regards,
John, GM4SLV
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