Re: NOT the feedline

Posted by Bob McGraw - K4TAX on Jun 02, 2020; 4:18pm
URL: http://elecraft.85.s1.nabble.com/Re-NOT-the-feedline-was-KPA-1500-faulting-on-6m-SWR-issues-tp7661502p7661582.html

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 <[hidden email]
> <mailto:[hidden email]>> 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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