Chet,
I expect you are correct, the sudden change from the week before the contest
where it would take a tune anywhere to about halfway into the contest where it
barely worked at 51MHz was probably due to water in the gamma match. That felt
like way to sudden a change to be due to slow oxidation. I will see what I can
do to prevent water intrusion. Thank you for suggesting this. I knew I needed
to address water in the gamma match it but have been afraid to touch it since
took a full day of work with a spectrum analyzer to get set close to 50ohms and
flat across SSB and FM. I will dive in and seal them up. If I get it wrong I
know my buddy Jacek and his magic blue tooth remote head spectrum analyzer will
get it dialed in next weekend.
Jay,
Thanks, I got very lucky with conditions and a great turn out from Hams on FM.
You asked.......but who does that? Well I do, sort of. I keep Anti-Sieze on
all hardware thats R&R'd, I also keep a die grinder and spare hardware on hand.
I did have my 6m telescoping elements seize up January of 2017 with ice so I
now coat all my antenna's with silicon spray (including inside the telescoping
tubes) before the January contest. The silicon spray is used to keep ice from
forming inside the tubes locking the telescoping tubes together (I pull outers
for transport). It also lets all antenna's shuck ice as it forms during the
contests. 0300 UTC, 25 degrees and dropping, soaking wet, numb fingers, all
alone on a mountain top trying to pack up with seized telescoping elements, ah
the joyous memories we make contesting.
Thanks guys. I appreciate the advice. Always learning.
73JohnKM4KMU
-----Original Message-----
From: Chet S <chetsubaccount@snet.net>
To: vhfcontesting <vhfcontesting@contesting.com>
Sent: Tue, Dec 25, 2018 9:01 pm
Subject: Re: [VHFcontesting] Polishing the Yagi
Hi John,
If this antenna has a gamma match, my guess is that water got into the gamma
rod, thus changing the effective series capacitance, and de-tuning the match.
73 and Merry Christmas,
Chet, N8RA
-----Original Message-----
From: VHFcontesting <vhfcontesting-bounces@contesting.com> On Behalf Of John
Young via VHFcontesting
Sent: Tuesday, December 25, 2018 7:08 PM
To: vhfcontesting@contesting.com
Subject: [VHFcontesting] Polishing the Yagi
In sept of 2017 a buddy came over with a spectrum analyzer and we dialed in the
vswr for my four low band Yagis to under 1.5:1 for FM and under 2:1 for SSB.
Everything was great through the weekend before september 18, though I did need
use the radios built in tuner for 6m going into sept 18.
Midway into the sept 18 contest I got rained on quite a bit and 6m vswr started
rising to the point where the tuner couldnt get the 6m vswr under 3:1 on 52.525
(which cut power way back) but I could just barely get a tune around 51MHz so I
QSY'd FM to there. No problems working SSB in the 50's using the tuner.
The antenna is a cushcraft 5el beam with telescoping elements. The smaller
tubes have wraps of tape on them for stops so I can disassemble for transport
and quickly assemble it.
Last week I disassemble the elements and found light oxidation on all the
mating surfaces. Using 220grit paper in a dowel rod as a flapper I polished
inside the tubes and then polished th outside of the small tube by hand with
220 grit.
Today I got around to testing. Without the tuner I got 1.5:1 @ 52.525 and was
able to 1.2:1 with the tuner from 50 to 53MHz. Hope to get to 1.1:1 on 52.525
after it gets hooked up to the analyzer.
Heard that polishing is an XYL's tale but I am a believer. Anyone had a
similar experience?
73
John
KM4KMU
Sent from AOL Mobile Mail
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