[Antennas] Multiband elevated radials

Sun Jan 9 20:07:30 EST 2005

Analysis of the Butternut 300 Ohm twinlead counterpoise:
Each radial consists of 27' 2" of twinlead plus 3' of wire on the end, with 
an 8' 4" stub back from the end of the twinlead. The second wire from the 
antenna is 15' 6" long.
Fmc = (246 x VF x End Effect) / length, ft.
Velocity factor, twin lead = .85
End Effect = .97
Fmc = (246 x .85 x .97) / length = 202.8 / length, ft.
Nominal 40M resonance is 202.8 / 30.6 ft = 6.62 Mc.
This may be a bit higher because the last 10% is wire.
Nominal 15M resonance is approx 18 Mc.
Nominal 20M resonance is 202.8 / 15.5 = 13.0 Mc (calculated)
The actual resonance will be lower because of capacitance to the 40M wire, 
perhaps 12.5 mc.
10M stub resonance is 202.8 / 8.3 = 24.4 Mc
Twinlead wire to open end of stub resonance for quarter wave is
202.8 / 19.3 = 10.5 Mc (won't work)
Twinlead wire to open end of stub for 3/4 wave resonance is approx 30 Mc.
Since the stub also tunes the antenna wire leading up to it, (within reason) 
it may work on 10M, but looks like a stretch.
OK. The 40M resonance is probably fine, 20M resonance definitely looks low, 
15M resonance looks low, and the 10M resonance is a dubious proposition. I 
think the saving grace is that a vertical antenna can often be tuned to 
accommodate most any counterpoise. I still don't like it.
Richard Brunner, AA1P 