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Old September 3rd 11, 02:56 PM posted to rec.radio.amateur.antenna
dave dave is offline
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First recorded activity by RadioBanter: Jan 2009
Posts: 5,185
Default MFJ-868 SWR/Wattmeter

Jeff Liebermann wrote:


Back to MFJ bashing... On my desk is yet another MFJ-259B for
repair, probably with the two blown shottky diodes that I previously
mentioned. One of the local hams heard me talking about the problem
over the local repeater, and decided that maybe I could fix it for
him. Usually, they wait until the week before Field Day for such
repairs but he's installing a tower next week and wants it fixed
yesterday. Sigh.


Have you discussed this with Martin Jue? I think it's rude to bad-mouth
a fellow ham behind his back. I don't see how the diodes are a problem,
if you follow directions. If you live somewhere dusty or snowy and dry
enough to make static, use a gamma match or an UnUn or some other means
to keep your antenna at DC ground. I have been using germanium diodes
for 50 years and can't remember frying one in a small signal RF
application. What does Martin say about bleeder resistors?

I have a 4" pigtail around the ground lug and a male banana plug on the
end that lives in the middle of the SO-239, unless I am making
measurements. I use the banana plug as a shorting stick to neutralize
any residual capacitive charge in the device/coaxial cable under test.
Center conductor to cable ground. If I am especially concerned I'll
groung the 259B to my extensive safety ground system. When dealing with
little diodes you always want to make sure none of the sparks go through
them. Ground, ground and ground.