RE: Hi QRP SWR on R7 vertical vs. QRO

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From: JEVERHART@cayman.vf.mmc.com
Date: Tue Aug 29 1995 - 22:29:03 EDT


Stuart, K5KVH, wrote the following in response to Bill's query about varying
SWR on an R7:

<SNIP>

>As you reassemble the antenna, check that the traps are working with an Autek
>RF-1 or MFJ Antenna Analyzer. Some R7 trap failures have been reported on
>this list in the past. I have seen a wind Damaged R5 still give low QRO SWR
>with some of the upper section missing! Apparently, the bandwidth will suffer
>first; before the SWR goes all to pot.

I've observed a similar effect on my Butternut HF-6VX and concur with Stuart's
remedial measures. I wrote up the phenomenon in QRP Quarterly a while ago in
conjuction with using a low power antenna analyzer (MFJ-249) to test the
antenna. Seems that the resonances were all wrong using the analyzer with its
milliwatt output. But when my bonecrushing Argo 509 was pressed into service,
resonances and SWR were ok. A recheck with the -249 also showed good readings.
BUT, when the antenna had not had rf power applied for a period of (as I
remember) several weeks, the -249 again showed bad readings. Cleanup of the
joints and some "Butter-snot" fixed it for several months.

SO.... you can get a handle on things by using a low power antenna tester, but
once you have applied power, things may change. Gotta understand the
phenomenon as Stuart described it to cure it!

72/73,

Joe E., N2CX


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