[Antennaware] symptoms of balun saturation?
atrampler at att.net
Mon Jul 13 13:34:15 PDT 2009
I agree regarding the months/years/never for coax to dry.
Now the coax never sat outside on the ground, etc, or was out there without its connector and unattached to the antenna; likewise, it has been sealed.
That doesn't mean water could not have gotten int it, especially as it is a vertical run from the box housing the balun, etc.
No offense to Hy-Gain/MFJ, but I tend to trust their baluns less than some others that are out there. I will most likely replace the 4:1 voltage balun that is original with a 4:1 UNUN and separate current choke, and see what this does.
I know this is the more costly "fix" as opposed to cutting and replacing the last 10' of coax, but this is an excuse to make that change. If I still have the problem, I'll cut off the last 10 or 15 feet of coax and replace it with new coax.
There are two exposed ends (one at the ground rod and surge protector) and the other at the antenna. Both have been wrapped with coax sealing tape (the tape that hardens instead of gooey coax seal) since being put up.
I think a larger unun will allow me to use it, with some limited success, on 80 meters as well as many others have done. I don't have good room for an 80 meter antenna at this time.
So in a few weeks I'll report back. I was not aware of the effect of core heat on saturation (I have to google "curie temperature") and will give this a try first.
Thanks--will report back,
--- On Mon, 7/13/09, Stephen Kangas <stephen at kangas.com> wrote:
From: Stephen Kangas <stephen at kangas.com>
Subject: RE: [Antennaware] symptoms of balun saturation?
To: "'DAVID CUTHBERT'" <telegrapher9 at gmail.com>, atrampler at att.net
Cc: antennaware at contesting.com
Date: Monday, July 13, 2009, 3:23 PM
I respectfully disagree with dismissal of moisture as a cause. It normally
takes months for coax to dry out (assuming low humidity) when moisture has
seeped into it (and when it does, it often goes several feet into it). Art
didn't say where he lives, so I'm assuming a "normal" weather pattern of
rain at least once per month.
From: antennaware-bounces at contesting.com
[mailto:antennaware-bounces at contesting.com] On Behalf Of DAVID CUTHBERT
Sent: Monday, July 13, 2009 3:57 AM
To: atrampler at att.net
Cc: antennaware at contesting.com
Subject: Re: [Antennaware] symptoms of balun saturation?
since it happens when it is not raining or damp we can discard the moisture
'evidence.' It certainly sounds like the core is simply heating. When it
reaches its curie temperature the relative permeability drops sharply. As
the flux swings in the core there is loss which heats the core.
The solution? Reducing power is the simple fix. I don't know about modifying
the "matching unit." Is it sealed? Another fix is to replace the AV640 with
a different antenna.
On Sun, Jul 12, 2009 at 2:48 PM, Art Trampler <atrampler at att.net> wrote:
> Hi All,
> I have an AV640 vertical from Hy-Gain, which is about 18' off the
> ground at the feed point. Overall I have been satisfied with its
> performance, which has generally met or exceeded (apparently realistic)
> My chief complaint comes with respect to QRO. When running a KW or
> more into it (fed with LMR400, about 125'), my SWR will initially stay
> flat. I am a CW operator and after two or three ragchew exchanges the
> SWR will begin to increase a bit, and then suddenly go high (8:1 or
> better). It seems that this happens more frequently if it is damp/has
> been raining.
> Can you help me understand what is likely going on? Is this likely a
> symptom of balun core saturation which is somehow related to heat,
> rather than simply the power/magnetic flux?
> Or is it more likely this has something to do with the RF choke from
> the vertical element used to give a discharge path for static electricity?
> choke is 470uh, .3 amp. Is there any reason not to replace it with
> something of greater current handling capability, and is the
> inductance critical (would 500uh work just as well?).
> Thanks for your replies.
> Art, K0RO
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> Antennaware at contesting.com
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