[Lowfer] W1VD modified Amrad whip tested

[jrusgrove at comcast.net]

Dave, LF

Matched them for Idss. Only had to go a half dozen deep into a bag of 50 to get a match. The spread 
didn't appear to be too great - at least in the batch I had. Quick and easy to do the test ...

Jay


----- Original Message ----- 
From: "Dave Brown" <tractorb at ihug.co.nz>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Wednesday, December 08, 2010 1:58 AM
Subject: Re: [Lowfer] W1VD modified Amrad whip tested


> 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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