[TowerTalk] SWR Problem Balun or,, RESPONSE fr DAVIS RF

[Stephen Davis]

Hi Tony, 

I am a cable design engineer and also a ham for 50+ years.  I  designed Bury-Flex Tm, thank you for using it. It is an extremely popular coax used also by NASA, Lockheed Martin, etc.     What you are experiencing is most likely a good dose of moisture in the coax cable, likely closer to the ant than the xmtr, based on the time delay, but that is not certain (further depends in part on how long the coax is in total.  However, before we jump to that conclusion, what you need to do is to insert a dummy load at every possible point (start at Xmtr) and see when you start getting the same sort of VSWR heat up condition.    You may need to go right up to the connection on the ant, as the last point that could show where the issue is (up to that point, from the last point checked, as I'm sure you follow). 
  It is almost impossible that the Bury-Flex Tm is at fault because the blend of PE that I use for the outer jacket resists even submersion in water or various chemicals.   The most obvious source for water ingress is at the connectors or if an errant 
cut has been made in the jacket.   We have never had any problems with this cable in the over 12 years since inception.
    
 If you have any questions, or if I can help in any way, feel free.   Yes, winter is the worst time for these things !!   HI

73,   Steve,    K1PEK 

DAVIS RF Co.,  Div. of Orion Wire Co., Inc.

Wire, Cable, RF Connectors and wire aerial parts.  

Rope, various blends cut to custom lengths

Cable assemblies, coax, audio, power, etc. 

LMR, Heliax, Eupen
Commercial / Military

Custom Cable Design

tel:  978-369-1738    Please contact Steve Davis    
www.DavisRF.com

 

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> Message: 1
> Date: Tue, 20 Dec 2011 22:11:53 -0800
> From: "Jim W7RY" <jimw7ry at gmail.com>
> Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?
> To: "Tony" <dxdx at optonline.net>,	<towertalk at contesting.com>
> Message-ID: <2AE0C3F9FFFB46869B5FFD525C3EC347 at Laptop>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> 	reply-type=original
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> Are you using the same wattmeter?  Or are you using the meter in each radio?
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> 73
> Jim W7RY
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> From: "Tony" <dxdx at optonline.net>
> Sent: Tuesday, December 20, 2011 9:12 PM
> To: <towertalk at contesting.com>
> Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?
> 
>> All,
>> 
>> I bypassed the lghtning protection and the SWR problem is still there. I 
>> installed a new coax connector on the shack side of the coax as well.
>> 
>> I still have to check the balun, balun leads and the coax-to-balun 
>> connector. There's nothing else inline. The coax (Bury Flex) and balun 
>> (3KW M2) were installed a few years ago.
>> 
>> I just checked the system again with two different 100 watt rigs and 
>> found that:
>> 
>> - I can transmit for 2 or 3 minutes from a cold start before the SWR 
>> starts to rise
>> - the SRW returns to normal 30 seconds after I stop transmitting
>> - it takes a lot less time for the SWR to rise after the 30 second rest 
>> period
>> 
>> I did replace the ground wires with copper strap a few months ago, but I 
>> haven't made any other changes to the tower and antenna system.
>> 
>> Why do these things always happen during the winter ;  )
>> 
>> Tony, K2MO
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>> _______________________________________________
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