[TowerTalk] Check that tape !

[Grant Saviers]

Re constant on voltages in remote boxes:

I found the innards of my DX Eng 4 sq receive boxes a bit of a mess 
around the soldered on F connectors.  One 4 sq had problems in the 
switch box but the antenna boxes were ok and the another 4sq bought used 
just the reverse.  The problem was a collection of white/tan crud around 
and shorting the soldered on F connectors.  It isn't possible to measure 
the resistance of the crud since the RG6 cables are transformer driven.  
However, they didn't look good and others on the reflector commented 
that the strong intermittent noise (S9+20) problem I was having can be 
caused by 10k ohm shorts.  The crud source I am pretty sure was 
inadequate cleaning of the PCB residual solder flux and the essentially 
constant application of 12v DC on the RG6 cables in the presence of 
moisture.  The antenna is in a very wet part of my lot and it does rain 
a bit here in the Pacific NW.  I aggressively brushed and flux remover 
cleaned off this crud and defluxed the entire board.  Then I applied two 
coats of acrylic conformal coating on each connector etch pattern (4 
mounting studs and center pin) on the solder side.  I couldn't brush 
under the connector bodies so used the wand sprayer to clean the 
component side and could not apply acrylic there either.

This antenna is a bear to diagnose problems, particularly intermittent 
noise.  Plus no schematics from DXE, but I did find the W8JI patent and 
think it is approximates the actual circuits.   As predicted by DXE 
support, the most significant noise cause was a connector damaged by the 
lawn guys and cosmetically repaired by them, but I think it does perform 
better after the crud removal.

My advice is to thoroughly clean all residual flux off PCB's and 
connectors going into remote anythings and to conformal coat them after 
the cleaning.  Also, turn off the power when not in use.

Remember that small galvanic voltages and thus currents cause propellers 
to fail and bolted keels to fall off sailboats.  Hence sacrificial zincs 
are placed and replaced regularly.  IMO, the only desirable voltage is 
one that protects the critical components from galvanic corrosion, but I 
don't know how that might be appropriate in amateur radio antenna systems.

Grant KZ1W

On 2/23/2017 16:48 PM, RCM wrote:
>>
>>
>> I also read rumours last year from a Belgian or German guy who was wondering
>> about DC always being on a coax line and his corrosion that ensued.  This
>> intrigues me as up until today I have had that RCS-4 coax switch on pretty
>> much 24/7-365 for years and years, only turning it off if I am on vacation.
>> A little voice inside my electronics head has to wonder if a small DC
>> current on that coax for many years has contributed to my 'current' mess.
>> (no pun intended)
>>
>>
>
> I was led to believe a little current flow kept corrosion away.
>
> Messing in the two way radio game for lots of years and dancing with telephone companies over leased control lines to
> remote base stations, we specified “sealing current”. Since there was no “talk battery” voltage or “ring voltage” to keep the
> connections clean.
>
> The base stations were low level tone control and just audio up and back. No volts.
>
> If the phone guys swapped pairs to fix something and didn’t look at the original order to put the current on the line, it wasn’t
> long before it quit working.
>
> I’ve fixed a few, just having them put the juice back on the pair.
>
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