Hi Gang,
Mark, N2VPK, asked if anyone had built the SWR/PWR meter from Dan's
Small
parts. I have and it works great. It is based on a circuit from
Hambrew magazine last year. I built mine into my Super Tee antenna
tuner and I like the combination. The board didn't come with my kit so
just did it "ugly bug" style.
You can build it one of two ways. With two meters, one to read
reflected power and one to read forward power. OR...you can add a
couple of more resistors and capacitors and use a differential circuit
to read "net" power out. Resistors are cheaper than meters. As the
instructions suggest, the more smoke out the antenna, the higher reading
you get. I've hooked an MFJ 816 (?) in-line between the tranceiver and
my little $10 job/antenna tuner to see if my "best" power out reading is
the same as
the lowest reflected/highest forward on the MFJ....Yep, it is. Now, I
just adjust my tuner to maximize the power going out through the $10
meter into the antenna and I've been making contacts just fine...except
for the FOX hunt last week when I had a weak and very chirpy signal.
Sorry guys, but I had a screw loose...and one in the antenna tuner as
well. A bad antenna connection leads to high SWR leads to a very chirpy
signal on my MXM-40. Guess that mighty PA transistor just goes into
orbit with too much RF coming back at it. Since then, I tightened up
the antenna connection and my signal sounds OK again. Moral of the
story is that the differential circuit showed some power going out, but
didn't show the high SWR coming back at me. I thought it was funny that
the meter reading wasn't kicking as high as usual. If I were to do it
again, I'd
spend another $3.50 for a second meter from Dan and use a two meter
version to show both forward and reflected power simultaneously.
I've got to finish my next roll of film and get some new pictures on the
web. Since my last web page update...last summer...I've completed the
NW20, the Green Mountain 15, the SuperTee antenna tuner, the White
Mountain 20 meter SSB and the Embedded Research Atomic Keyer. Now,
maybe this weekend I can tear into the NC38S, it's been on my bench for
several weeks, just a grinnin' at me.
Opps, forgot I'll be working on my tan during the FYBO contest here in
Texas this coming weekend. Not sure I'll get the portable air
conditioner rigged for the tent in time so it could be a long, tough
weekend. I did test out the "dry ice thermometer holding device" and it
works pretty good down to about -150 degrees. Wow, what a multiplier!
[Just kiddin', of course]
See y'all on the air.
Gary, KJ5VW
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