[UK-CONTEST] Noisy Antenna

[Clive Whelan]

Hi Neil

There are about a million variables! However, a 110ft doublet and an A3S are
apples and pears on 10Mhz and the comparison is not really valid.

 If you are happy that your 80m dipole was quieter , AND was coax fed, my
best guess is digital hash from your computer and other stuff. How far is
the ladder line from the shack? I really didn't have a problem on LF, but
tuned feeders here with so much digital stuff around have-unfortunately-
become very difficult above 14Mhz. If the raw SWR on the coax from the balun
is not too high, and your main concern is LF I'd recommend moving the balun
as far as reasonably practicable from the shack, and use coax to take up the
slack.

Of course, it has to be said that any balun operating with a finite SWR
across it, will also generate common mode currents on the coax , which could
also port the digital noise back along the coax. If you suspect the above
maybe true, it's just a question of experimenting. btw when dissing
computers et al for test,  make sure you pull the plug, 'cos most all are
connected to the AC supply even when the front panel switch is off. Lousy
engineering practice, but we just have to live with it I fear.

Of course if you see any alien space craft around, it's more likely them ;-)


73


Clive
GW3NJW

-----Original Message-----
From: uk-contest-bounces at contesting.com
[mailto:uk-contest-bounces at contesting.com]On Behalf Of G3RIR
Sent: 20 October 2005 09:01
To: UK-Contest at contesting.com
Subject: [UK-CONTEST] Noisy Antenna


st1\:*{behavior:url(#default#ieooui) }
I am afraid I might beslightly off topic here so if you think this should
have been posted elsewhereplease let me know.



I am in need of some ideasplease regarding a new antenna which is very
noisy.



I have recently replaced myrather bent 80m dipole with a 110 ft top doublet
fed with about 50 feet of300ohm "ladder" line coupled to my FT1000mp via a
balun and a tuner.The centre of the doublet is on my tower a few feet below
the A3s beam.



The objective of changingthe antenna was to give me 3.5 MHz 7 MHz, 10 MHz ,

18 MHz and 24 MHz and maybeeven 1.8 MHz (strapping the feeders) to
complement my A3s 3 ele tribander on14, 21, 28 MHz.



I can get a good match (2:1on 7MHz and 1.5:1 or better on the other
bands)into the doublet on all of therequired bands ( I know a dummy load
provides a good match).



So far I have only tried touse the antenna on 10 MHz but the noise pick-up
is horrendous. I was listeningto an EX5 last evening who had a small pile
up. On the doublet he was S9 but sowas the noise so he was copyable but not
comfortably. I then switched to mybeam but still listening on 10 MHz and the
EX5 signal was now down to about S2on the meter but the noise was S0 so the
readability was dramatically improved.



I am not likely to be ableto hear any real DX with so much noise pickup on
the doublet. Does any one haveany ideas?



Neil, G3RIR









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