[Lowfer] W1VD modified Amrad whip tested

[Steve Ratzlaff]

I built a version of Jay's modified Amrad active whip and tested it on the 
bench today, checking IMD at supply voltages of 24 and 13.5 volts, adjusting 
the bias for optimum 2IMD for each voltage. I used 10 pF as the series input 
cap to simulate a 36-39 inch whip, and my standard 3 and 4 MHz IMD test 
tones. This circuit won't output my normally-used 0 dBm to the spectrum 
analyzer so I used -10 dBm output. (I used 17 bifilar turns on FT50-75 
toroid for the transformer.)
supply voltage 24.0 volts (60 mA optimum bias)
1 MHz +76 OIP2
2 MHz +36.5 OIP3
5 MHz +35.8 OIP3
7 MHz +76 OIP2

supply voltage 13.5 volts (36 mA optimum bias)
1 MHz +79.8 OIP2
2 MHz +34.2 OIP3
5 MHz +33.7 OIP3
7 MHz +72 OIP2

Not much IMD improvement is gained running at 24 vs. 13.5 volts. As Jay has 
found, this modified circuit should work OK for many uses and is inexpensive 
to build compared to the expensive transistor needed for the original Amrad 
circuit.

73,
Steve AA7U
NE Oregon