Dear Dave, Ken, Dave, Rik, Pete, LF Group,
Thanks for the reports on the beacon signal. If nothing else, it is at least
a viable 500kHz TX antenna - as well as the reports, it is showing up
reasonably well on the G3YXM and G4WGT grabbers. I have now closed down at
2206utc.
The TX power was about 70W maximum, dropping to about 0.3W at the minimum
power level. I haven't done detailed measurements yet, but the loss
resistance is about 70 - 80 ohms, and the antenna current just under an amp
at maximum power. My "guesstimate" of ERP is 100mW at maximum power, down to
0.4mW at the minimum level - I am allowing -6dB for the fact that the
antenna is completely screened by the surrounding trees. The loss resistance
is about 3 x that of my normal antenna, which has much more wire. The high
resistance isn't a great suprise, as the ends of the top load wires are only
a couple of metres from the trees and bushes. From previous experience, in
an actual open /P location the loss resistance should be much lower, and the
ERP significantly higher for a given antenna current.
The TX signal is a .wav file of CW and QRSS recorded from the "digimodes
terminal" in Spectrum Lab, and played back through the linear transverter.
The software generates a smoothly rounded raised-cosine keying envelope
which minimises the bandwidth and results in the "soft" keying. The 5s
dashes have a proportionally slower rise/fall - I left it with the default
settings to see if anyone would notice, I think on balance a faster rising,
sharper keying envelope would be better for a listening test. The variable
power level was obtained by editing the audio level in the .wav file using
some sound editing software.
As Rik observed, I did briefly operate last night as well - power was
slightly lower then.
Cheers, Jim Moritz
73 de M0BMU
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