[Lowfer] receive antenna transmission line maintenance

[pbunn]

It makes corrosion worse. About a month ago I came in and found the power supply led off on my DC coupler. I figured the power supply had died but when I unplugged the coax it was OK, so then I knew I was looking at a short at the probe or in the coax. Looking at the way the probe circuit works, I didn't see a way a failed transistor could result in a short  that low in resistance.

I emailed Jack Smith and asked hid opinion and he said 90 % likely that I had  a coax problem and the DC bias would corrode a breach in the shield. After a couple hours with the multimeter, I found a pinhole in a buried section of the Belden quad shield. Just as Jack had indicated, the DC current had caused the aluminum shield to turn to powder for s couple of feet. I ended up replacing the entire 300 foot run with new cable.

Pat
N4LTA

"Douglas D. Williams" <kb4oer at gmail.com> wrote:


Interesting thread. I didn't know any of this.

I wonder if the DC current present on outdoor active antennas helps or
hinders corrosion?


While were on the subject of antenna maintenance, how do you guys
weatherproof outdoor BNC connections? I've been using this black silly
putty like substance called "coax seal". It comes in small rolls.
Works well for weatherproofing, but is difficult and messy to remove
later on.

73, Doug KB4OER



On Fri, Jan 25, 2013 at 10:27 PM, Michael Sapp <wa3tts at verizon.net> wrote:
> Stan, W1LE wrote:
>>Do you think a light coating of silicone dielectric grease would more
>>permanently solve that corrosion problem ?
>
>>Two dissimilar metals, plus the electrolyte acid rain = galvanic corrosion.
>>The grease would keep out the acid rain/moisture.
>
>>I would even consider the grease treatment and a waterproof taping
>>on all coaxial joints exposed to the elements.
>
>>Stan, W1LE    Stan, I suppose it can't hurt. Rad Shack & others sell the male cable F connectorspre-silicone-gelled. IMHO it seems in part to stem from the low signal level nature ofa feedline for a passive rx antenna---not enough uVs and pico-amps to overcome the residual resistanceat the F center pin interface that eventually builds up.  Sometimes it seems thermal expansion/contractioninduced with weather temp changes cause the RG6 center conductor to move slightly and change resistanceat the physical connector interface.    I know if I give the rx antenna transmission lines a mild jolt once a week that it solves the problem. If I ran my AL-82 amp on HF more often, the induced milliwatts into the rx antenna would likely be enough power to prevent the issue. John, XIQ, mentioned to me in an e-mail a few minutes ago he turns his rx antenna towards his tx antenna during  tuneup to clean the relay contacts on his rx system as a similar preventative measure....    Likely a goo
 d
>   reason for me to put some relays in the receive antenna transformer boxes for directional switching---the regularDC power cycling of the relays with a DC up the coax arrangement would be an automatic maintenance solution....Perhaps others on the list will share their experiences on the subject.....73  Mike wa3tts
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Lowfer mailing list
Home: http://mailman.qth.net/mailman/listinfo/lowfer
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Lowfer at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html