[TowerTalk] Heliax acting strangely: Help?

[StellarCAT]

I had a somewhat similar scenario happen on my (somewhat) recently installed 
tower. The rotary 80 dipole at the top would have a low SWR until it rained 
when it would go up quite high. Within generally a couple days it was back 
to normal. I checked everything associated with the antenna to no avail. I 
did that because the installer had reassured me all coax connectors had been 
properly sealed when he installed everything.

Months later we're installing a 6 meter yagi on the tower and the tower guy, 
a different guy, goes to plug its coax in to the relay box ... he says 
"they're all wrapped with the exception of one of them which is only 1/2 
wrapped and partly exposed" .... yes - it was the 80. He wrapped it with 
seal and although it took a couple weeks it eventually got to the point 
where the SWR is constant - and low once again. So water was getting in to 
the connector - over time it has dried out. If this were anything other than 
80, possibly 40 I'd change out the coax - being 80 I don't think there was 
any long term damage as it appears to have dried out through use. Of course 
when it happened my first thought was connections - but I dismissed that 
because of the installer ... turns out I shouldn't have. That is not to pass 
blame as we can all make mistakes no matter how experienced we are - it is 
however a lesson learned. One that I have 'learned' and relearned many times 
in my 50 years as a ham ... never assume.

Gary
K9RX



-----Original Message----- 
From: John Lemay
Sent: Sunday, August 27, 2017 8:55 AM
To: 'chuck.gooden' ; kr2q at optimum.net ; towertalk at contesting.com
Subject: Re: [TowerTalk] Heliax acting strangely: Help?

Yes, water ingress.

If you are lucky, it is at one end or other.

Remove both connectors, examine for dampness / corrosion. If necessary allow 
to air dry or use gentle heat. Re-check for infinite resistance between 
inner and outer.

John G4ZTR

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of 
chuck.gooden
Sent: Sunday, August 27, 2017 12:53
To: kr2q at optimum.net; towertalk at contesting.com
Subject: Re: [TowerTalk] Heliax acting strangely: Help?



Improperly installed connetor that allowed water to ingree the cable?

Chuck Gooden - K9LC

-------- Original message --------
From: kr2q at optimum.net
Date: 08/27/2017  6:25 AM  (GMT-06:00)
To: towertalk at contesting.com
Subject: [TowerTalk] Heliax acting strangely: Help?

I put out a 160 foot run of 7 eights heliax last year.  Worked great.  Last 
time I was QRV was end of January, 2017.

I recently put some RF out (100 watts...HP for me) and was surprised to see 
an SWR in the shack of about 3:1.

Setup:
Outdoor antenna switch box just outside the shack. From there, very short 
run of RG8 (under 4 feet) to "start" of Heliax.
160 foot run of Heliax to "back" tower.
Then another "short run" of RG8 to about 80 feet of RG217, which goes "up" 
my crankup tower.

What I have done:
Put a dummy load at the rig: shows 1:1 SWR.

Put the dummy load at the "far end" of the heliax by "breaking" the 
connection from the Heliax to the short run of RG8.  SWR in the shack still 
3:1 (all HF bands).

Put the dummy load at the end of the short run of RG8 coming from the 
antenna switch box.
SWR in the shack shows 1:1 (dummy working, coax to that point working).

OK, so seems like something is wrong with the Heliax.

I disconnected the Heliax at both ends.  If I short inner to outer, it shows 
dead short at the "other" end.  I know, DC is not RF.

I measure the resistance between center conductor and outer shield of the 
Heliax.  I expected "infinite," but using my crappy RS ohmeter, it shows 
about 500k ohms.  I measured other runs I have RG217 (nothing connected at 
either end, about same length), and the crappy RS meter shows infinite, as 
expected.

So what could go "wrong" with my 7 eights inch Heliax?  It is above (on) 
ground for the entire length.

I walked it yesterday, picking it up about every 10 feet.  Looked "normal" 
to me.

Any help/suggestions?

Thanks,
de Doug KR2Q


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk