I have carried out a number of tests on the MiniWhip cct. and like you, I
found that at +12V DC supply there were signs of inter-mod products - such
as weak phantom broadcast stations just below 400kHz which should not be
At +15 and above, they pretty well dissappear. I also then tweaked the
values of the 2.2K/10K potential divider feeding the base of the 2N5109 to
drop the base voltage a bit because with the original values, the
collector-base voltage was only about +2V which is not really enough I
think. I was also using about 150ft of 50 ohm RG58U coax to the shack from
the garden but with hind sight, I think it woiuld be better to have used
70ohm feeder to reduce the capacitive load on the emitter of the 2N5109 and
probably insert a 70 ohm series resistor at the emitter to provide a better
source impedance for the cable and help absorb reflections back down the
line although wouild incur a 6dB signal loss.
I have had to take my MiniWhip down temporarily due to building work on a
conservatory at the back of the house, but I intend to return to the subject
when all the mess is cleared away!! I still think it is very neat design and
mechanically simpler than the AMRAD design.
73 de Derek Atter G3GRO
PS - I seem to remember that the Royal Navy used to employ an RX antenna
multi-coupler using several 807 tetrodes years ago!
----- Original Message -----
From: "Scott Tilley" <[email protected]>
To: <[email protected]>
Sent: Sunday, February 11, 2007 5:56 PM
Subject: LF: TIL Grabber back online...
After an epic struggle with my miniwhip I discovered that it likes a much
higher input voltage then documented in the construction article...
Running it at around 17V seems to clear up the intermod problem.
So the grabber is back up.
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