[Lowfer] W1VD modified Amrad whip tested (matching jfetsnotneeded?)

[Dick Goodman]

Guys ... This has been a very interesting thread. I have been using the
Amrad E-Field probe from the month it was published in QST. It's a great
antenna and I'm using it in the original configuration. I have however,
wanted to build something to take out to RF quiet sites that wouldn't
require the 24 volts and the heatsink for the transistor. Sounds like the
J310's will work almost as good as the the original $13.00 transistor.

Thanks!

Dick, WA3USG


-----Original Message-----
From: lowfer-bounces at mailman.qth.net
[mailto:lowfer-bounces at mailman.qth.net]On Behalf Of Dave Brown
Sent: Wednesday, December 08, 2010 2:30 PM
To: Discussion of the Lowfer (US, European, & UK) and MedFer bands
Subject: Re: [Lowfer] W1VD modified Amrad whip tested (matching
jfetsnotneeded?)


Steve/Jay- thanks for the replies on this- your test results Steve are
just the sort of detail I was interested in.
Think I have about 20 in  a bag here so will go through them and see
what the spread is like.
73
 Dave
ZL3FJ

----- 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: Thursday, December 09, 2010 8:17 AM
Subject: Re: [Lowfer] W1VD modified Amrad whip tested (matching jfets
notneeded?)


> Just to see what happens when the two jfets aren't matched at all, I
> went
> through my bag of J310's and tried to find two with very different
> Idss. I
> picked one with 51.8 mA and one with 30.6 mA and put them in the
> same
> circuit I tested yesterday. Here are the IMD results, same setup as
> yesterday. (My results from yesterday, with two matched 36 mA jfets
> are
> shown too.)
>
> 24.0 volts/59 mA
> 1 MHz +80.5 OIP2
> 2 MHz +34.3 OIP3
> 5 MHz +34.1 OIP3
> 7 MHz +79.8 OIP3
>
> 13.5 volts/41 mA
> 1 MHz +80.7 OIP2
> 2 MHz +33.6 OIP3
> 5 MHz +32.7 OIP3
> 7 MHz +73.1 OIP2
>
> It doesn't appear that matching jfets does much if anything, but
> being able
> to adjust the bias with an IMD test setup is the main thing. Since
> few folks
> have that capability, perhaps just setting the bias for similar
> currents to
> what I obtained would be good enough.
> 73,
> Steve AA7U
> NE Oregon
>
> ----- Original Message -----
> From: <jrusgrove at comcast.net>
> To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer
> bands"
> <lowfer at mailman.qth.net>
> Sent: Wednesday, December 08, 2010 3:09 AM
> Subject: Re: [Lowfer] W1VD modified Amrad whip tested
>
>
>> 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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