[Lowfer] W1VD modified Amrad whip tested

[Dave Brown]

Jay/Steve
Did either of you use any special selection/matching of the J310s?

----- Original Message ----- 
From: "Steve Ratzlaff" <steveratz at wildblue.net>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer 
bands" <lowfer at mailman.qth.net>
Sent: Wednesday, December 08, 2010 11:54 AM
Subject: [Lowfer] W1VD modified Amrad whip tested


>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
>
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