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Hi James et all ...
James=> In the LF range, and
loop inductances of the order of 10s of uH, 0.1 ohm will be significant.
The copper octagon inductance
I'm using to test (4.8m perimeter) is 3.48 uhy, so not so low. The HF
resistance (skin effects) are something like 0,018 ohm at 260KHz.
This values, generated by
Rejloop1 and Antenna Optimizer - both softwares gave basically the same results
- was used on a third calculation tool (RF1.1 from Academic Tech -
Au).
The C values that Rej1 states,
when applied to Antenna Optimizer, made loop shows 0,0XX ohm +/-j
0,00XX.
Using this values on RF 1.1 I tried to model this
loop this simplified way (software accepts xformer inductances/DC
resistance):
Then trimming turn ratio,
the calculated Z aproaches 50 ohm. I know it's a simple aproximation,
there's more losses but ... The good part: I
built a 50 ohm resistive swr bridge and using the signal generator I could
confirm the predicted SWRs on 120, 260, 400 and 600 KHz (27 ... 68 ohm j +/-
0).
James => Bearing in mind multiple switches will
probably be needed, this can be a real problem. We found relays were really the
only option for remote switching, and even then you have to be careful - reed
relays had losses around 0.1 - 0.5 ohms, much higher than their DC resistance.
The best bet are relays intended for UHF antenna changeover duty.
It's a receive only design for now. But I'll re-run
calculations adding common relays/capacitor losses to see what
expect.
My other objective is cross measured FS versus
predicted software values.
Thanks on the sugestions James.
73
Marcus
PY3CRX/PY2PLL
S. B. do Campo -
GG66rf
http://py.qsl.br
Active from "DC" to
24GHz
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