The Tentec 238 tuner does have some values of L and C components in the
circuit when in the Bypass mode. These are L1 which is 0.3uH and C7 &
C8 which are 250 pf in series. The tuner is designed for use between
1.8 and 30 MHz. Thus I would not advise using it as an antenna switch
on 50 MHz and certainly not to resolve a match on 50 MHz.
You may find that adjustment in the ladder line length {just a couple of
ft, more or less, for 6M} will aid in the LDG tuner finding a better
match with existing component values and parasitic capacitance.
73
Bob, K4TAX
On 6/2/2020 10:53 AM, Mark Goldberg wrote:
I failed to mention, my antenna system is a 300 ft long horizontal
loop fed by ladder line with a homebrew two core switchable 1:1 or 4:1
Guanella current mode Balun. The Balun has a measured return loss of
about 32 dB at 50 MHz with a 200 ohm resistive load. That was
surprisingly good, but confirmed with a calibrated VNA. Yes, I spent
some time with Jerry Sevick's book.
The antenna is not deluxe for 50 MHz, but it is all I have. It's just
so happens that only small values are required in the tuner to match
it, and the LDG tuner parasitic capacitance it too high even when in
bypass mode. I expect it is difficult to build a physically large high
power tuner and keep the parasitics down, so the Ten Tec may have
similar issues. As I said, I know nothing about it. From Peter's most
recent email, this may be the case.
73,
Mark
W7MLG
On Tue, Jun 2, 2020 at 8:26 AM Bob McGraw K4TAX <[email protected]
<mailto:[email protected]>> wrote:
As a rule, if one needs a tuner to get a good match on 6M, I'd say
they need to look carefully at their antenna system. My 6M yagi
shows less than 1.5:1 over the lower 2 MHz of the band, 50.0 -
52.0 MHz. The lowest SWR occurs at 50.2 with a Z value of 42 ohms
and an X value of 0.0. Of course higher gain antennas typically
have a bit less bandwidth, but still, the lower 1 MHz should be
totally usable without a tuner.
Besides, tuners only make the transmitter happy and the added feed
line loss due to SWR still remains.
73
Bob, K4TAX
On 6/2/2020 1:09 AM, Mark Goldberg wrote:
I want to mention that my LDG AT-600Pro has a minimum capacitance
that is too high for a good match to my antenna on 6 meters.
Certainly seems like removing the Ten Tec tuner would be a good
thing to try. Can you open the Ten Tec tuner and use an IR
thermometer to monitor the components? I don't know anything
about it's construction. You could see them heating up.
Just running medium power of maybe 500W would slow things down
and let you see the SWR increasing before the amp trips. That
would confirm that something is heating up vs arcing.
73,
Mark
W7MLG
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