[Lowfer] Sealing Current

[Michael Sapp]

Warren & All: My use of the term "Sealing Current" may not be 100 percent accurate. I'm referring to the use of a low to moderate DC current (~20 ma) on my EWE receive transmission lines (and return through transformer primarys) to maintain a low-resistance connection between the mechanically-joined conductors (connectors).

I from my brief key word searches on Google and Google Patent, and Wiki, it was originated in the telecom industry to maintain low line resistance for telecom lines that are not in continuous use....

http://en.wikipedia.org/wiki/Wetting_current

"A related term sealing current (aka wetting current or fritt current) is widely used in the telecommunication industry describing a small constant DC current (typically 1-20mA) in copper wire loops in order to avoid contact oxidation of contacts and splices. It is defined in ITU-T G.992.3 for "all digital mode ADSL" as a current flowing from the ATU-C (ADSLLinecard) via the phone lines to the ATU-R (CPE)."

Some years back I had a Kenwood TS-430 that developed an intermittent rx/tx relay problem. One mod/fix I located (dkmods,etc.) was to add a simple circuit that would trickle several ma of continuous DC on the rx side of the relay to keep the contacts clean. The mod worked well so that fix stayed in the back of my head as a potentially useful tech tip that could be used elsewhere....at the time I did not know it was related to the telecom sealing~wetting current technique...

Since my EWE does not have any remote preamps, it does not see much electrical potential or current on the conductors---as compared to an active e-probe for example). Since I do not get on the air as often these days, I am not inducing much RF power into the EWE and transmission lines as well.  The temporary application of DC is to assist in keeping the F-connector contact resistance low in the RG6 cables I use for receiving....

I was telling John/XIQ a few weeks back I had one old splice on my NE transmission line that was acting up and a short "blast" or DC usually restored the low-ohm condition. Having recently replaced that splice the loop resistance has been very consistent. Last nite it only changed .2 ohms and it has not been "zapped" for a week prior to that.   I was doing the sealing current thing over the winter as it helped the situation without me having to dig and roll around in the snow to find the system fault.  That particular splice was a "gold barrel" and a pair of male F connectors. After removing the coax seal and tape they "looked good" but likely were the cause of the winter time problem as the NE cable no longer tends to be in wandering DC resistance mode.....

Once or twice I've had small animals munch on the cable jackets and once had a transmision line used as a chew-toy, so I check the DC loop resistance once a week or so to verify the cable and connector integuity. Too bad Belden does not impregnate their cable jackets with hot pepper oil (hi)....

73  Mike wa3tts