Vic K2VCO wrote:
>
>One possibility is that a large amount of RF on the 'grounded' side of
>the tuner is upsetting the SWR measurement. You say it worked before --
>have there been changes in the path from the tuner to ground, or to
>whatever is serving as the counterpoise for this antenna?
>
A very strong possibility is that a coax shield connection has opened up
somewhere, so you suddenly have RF currents crawling all over your
system.
Quite likely the tuner is only showing the symptoms, but is not the root
cause. (My money's on a PL-259.)
The only reliable way that I know to find out is to check over the
system with a clamp-on RF current meter. Take 10 minutes to throw one
together, and you'll be a convert! [1-3]
If you find RF currents on the outsides of coax where no currents should
be, it could be getting out from almost anywhere. The largest current
readings are not always closest to the fault, so the only way to locate
the fault is methodically, step by step.
Start from the bare transceiver and check that with a dummy load - the
power cord and the outside of the coax patch lead should obviously be
completely 'dead' to RF. One by one, re-connect the other 999 patch
leads in your station until the RF current pops up, and you've found the
fault.
Try it - it really does work.
[1] Homebrew:
http://www.ifwtech.co.uk/g3sek/clip-on/clip-on.htm
[2] http://www.w8ji.com/building_a_current_meter.htm
[3] In commercial products that I reviewed, the MFJ-854 is good:
http://www.mfjenterprises.com/products.php?prodid=MFJ-854
Warning: the MFJ-853 is a "Don't Buy" - you can't even trust the meter
needle to move in the right direction!
--
73 from Ian GM3SEK
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