Victor,
Somewhere in the collection of radio stuff I own, there is a Johnson
Matchbox which I haven't used in 20+ years, but I do remember a few
things about it. From what you say, I infer that you are using the KW
version, mine is the 275 Watt unit. I believe they used similar designs.
One of the things I sort of recall is that it was really a balanced feed
antenna tuner that could be used for unbalanced load tuning. And yes, it
was high Q meaning it was useful, sort of, for some filtering. However,
the final amplifier output circuit in the Johnson gear of the time was a
pi network which is useful as a low pass filter. And in those days low
pass filtering was important and the antenna tuner was important for its
intended design, matching only. Tuner efficiency was important as there
could be a lot of heat as AM, full carrier, was the mode of the day,
unless you ran CW. I did own a Johnson Viking II in my early days.
73,
Barry
K3NDM
------ Original Message ------
From: "Victor Rosenthal 4X6GP" <[email protected]>
To: "Elecraft Reflector" <[email protected]>
Sent: 12/22/2018 12:03:05 AM
Subject: [Elecraft] Tuners and spurious responses
I just replaced my single-ended T-network tuner plus balun with a massive old
Johnson Matchbox. It is very selective, unlike the T network. It is as if there
is a sharp bandpass filter between the antenna and the rig.
This may be totally imaginary, and there's no easy way to A/B test it, but it seems as
though the K3 sounds "cleaner" in some sense.
Could it be that since the mixer sees a much narrower spectrum, there are fewer
spurious responses?
Do those of you who use bandpass filters for SO2R or multi-transmitter
contesting notice such an effect?
It also seems that the better balance (my antenna system is a dipole fed with
balanced line) has reduced RF in the shack and possibly local noise pickup.
-- 73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
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