Is there any modern-day equivalent to the old Johnson Matchbox? I use
several different MFJ tuners with good results. My favorite is the
"Differential-T" 986 which tunes everything with very little effort. I
don't actually know how efficient it is but it tunes my 132' doublet fed
with 450 ohm ladder line very well. I use the antenna mostly on
160-80-60-40-30 where it seems to perform well. The ladder-line comes to
a 1:1 high power balun just outside the shack and 10' of rg213 comes
inside to the tuner. The only interesting observation is that it seems
noisier than my multi-band trapped dipole - as much as 1-2 s units
sometimes. Otherwise, if I only had one antenna it would be the doublet.
Very versatile. The tuner gives the rig a good under 1.5:1 match 160
through 6.
73, Doug -- KJØF
On 10/10/2019 11:59 PM, Vic Rosenthal wrote:
You bet. The Johnson Matchbox is as good as any expensive band pass filter.
Victor 4X6GP
On 11 Oct 2019, at 2:57, Joe Subich, W4TV <[email protected]> wrote:
The one "multiband" antenna one can use in a multi-transmitter
configuration is the flat-top with open wire feeders and a
*Link coupled* tuner. The link coupled tuner is a bandpass filter
that significantly reduces harmonic/broadband noise just like the
"Q" of a single band antenna.
73,
... Joe, W4TV
On 2019-10-10 7:44 PM, Don Wilhelm wrote:
Bob,
Bandpass filters at each station will help a lot, but they do not have infinite
out of band rejection.
There is still a huge benefit with single band antennas. My club uses both.
Last Field Day (3F operation) one station got on the air with a multiband
vertical, and all other operators jumped on that operator to shut him down
quickly! The multi-band antenna radiated harmonics of the radio. Even though
the transmitter met the -43 dB harmonic required by the FCC, the proximity of
the multiband antenna to other antennas caused problems (that station was not
using a bandpass filter).
So for Field Day multi-station operation, single band antennas, bandpass
filters and transmitters with low phase noise are important. We were not able
to orient the antennas end to end due to space considerations at the EOC site,
so we had to compromise on that, which makes the other factors very important.
I need to point out that as an experiment, a 2nd station used an antenna on 20
meters separated from the main 20 meters, and we were able to operate one on CW
(K3) at the same time as the other station (Icom) used digital and SSB modes.
We had some mutual interference, but it was minimal. The K3 did not interfere
much with the Icom due to the K3's low phase noise, but the Icom did raise the
background noise level on the K3.
73,
Don W3FPR
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--
73 de Doug -- KJ0F
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