Roger,
I simulated the antenna based on your description (with MMANA) and the
current through the vertical wire seems to be quite constant. So the
tophat works well and the effective height will be more or less the
physical height.
The simulation gives a radiation resistance of 0.074 Ohm, so with 0.12
A a radiated power just over 1mW EMRP (1.75mW ERP).
In the real world it will be some dB's less (as Jim stated recently),
probably something like 0,5 to 1mW ERP.
Very impressive that it covers over 1200km.
73, Rik ON7YD - OR7T
Quoting Roger Lapthorn <[email protected]>:
All,
Yesterday I did a recalculation of the G3XBM ERP based on the
classic formula and re-measurements of my antenna current. My
antenna is a 5m long vertical with a spiral top hat of about 7 turns
about 1.5m x 1.5m. Not being clear how to model the top hat I
assumed effective heights of 5, 4 or 3m. The measured antenna
current is 0.12A.
My results are as follows:
Assumed effective height 5m ERP = 1.53mW
Assumed effective height 4m ERP = 0.98mW
Assumed effective height 3m ERP = 0.55mW
So, I believe my 1mW ERP previously calculated is not a bad
estimate, and it may indeed be lower than this figure.
73s
Roger G3XBM
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM
G3XBM GQRP 1678 ISWL G11088
|
