Re: [amsat-bb] Re: Texas Potato Masher(s)

["Jeff Embry (WI2T)" <wi2t@xxxxxxxxxxxxxxxx>]

Just thought I would drop a note to you that The R. F. Connection (where I
work) carries RG-62 in both PVC and plenum versions.  Give us a call at
800-783-2666 for details.

73

Jeff
WI2T
-----Original Message-----
From: K5OE@aol.com <K5OE@aol.com>
To: jackcolson@x-press.net <jackcolson@x-press.net>
Cc: amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
Date: Sunday, February 14, 1999 10:21 PM
Subject: [amsat-bb] Re: Texas Potato Masher(s)


>Jack,
>I copied the BB in case others had the same questions (Al, XE2YVW, who is
>building a pair of TPMs asked the same question as your no. 2).
>
>>  I had several questions:
>>  1) In Table 1 you
>>  refer to a test procedure using a coax tee and dummy load.   I should
>>  know what this is but I don't!  Would you mind explaining?
>
>This procedure involves using a coax tee (center) on the ANT jack of your
SWR
>meter.  On one side of the tee, place a 50 Ohm dummy load (I use a short
piece
>of coax and two 100 Ohm, 10 Watt resistors).  On the opposite side, place
the
>1/4 wavelength piece of coax, with the end shield shorted to the center
>conductor.  Trim the coax for  minimum SWR.  At resonant frequency, the
>shorted coax looks like a very high Z to the signal and is ignored and all
the
>power is fed into the dummy load.  I find this is a little "broad' at 70
cm,
>so you might try using 1/2 wl of coax and leaving the end open--then cut in
>half after trimming.  Either one works OK.
>
>> 2) Where the two loops cross at the far end of the
>>  antenna, I presume they are not electrically connected.
>
>Correct.  I used insulated #10 wire and applied a drop of glue to the point
>where they crossed.    BTW, modeling shows the shape of the rectangles
affects
>the resonant frequency almost more than the length of wire (when the length
is
>close to resonsant).  If you have trouble getting a low SWR using the
lengths
>in the article, adjust the length-to-width a little and see if that helps.
>
>>  I am glad to see someone using the 1/2 wavelengh cable technique.  I use
>>  it a lot even on HF.
>
>If all SWR meters were really accurate, that step wouldn't be necessary.
But,
>if you are using an impedance bridge (or an MFJ/Autek Ant Analyzer), then
it
>is absolutely necessary to avoid the transformer affect in the testing
line.
>
>>  Thanks for your article, I'm going to build these.  I need to find some
>>  92 ohm coax.  I had hundreds of feet at one time but that was a long
>>  time ago!  Some one in our area has a piece.
>>  73,
>>  W3TMZ
>
>Good luck.  I'm sure somebody near you has some.  I use my TPMs every day
>(although I cheat and use my Arrow sometimes for low AO-27 passes).
>
>73, Jerry
>
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