On 26 Jun 2002 at 5:47, Donald Chester wrote:
> I have been noticing lately a dropoff in performance of my beverage.
>
> The degradation in performance suggested that the lightning had also
> zapped the terminating resistor. It consists of several 1 to 5 watt
> carbon composition resistors in series-parallel configuration to give
> approximately 500 ohms. Sure enough, checking with an ohmmeter, I got
> an oper circuit reading. The resistors were mounted in a little
> plastic Radio Shack box. I opened the box, and the resistors checked
> ok, but moisture had got into the box and corroded all the connections
> until there was no longer continuity. I had used top quality nickel
> plated brass hardware but nothing would take solder, not even the
> tinned copper hookup wire. When I constructed the unit, I sealed up
> everything - box lid and wire feed-through terminals - using silicon
> glue and roofing tar. The only way the water could have got inside is
> by condensation after the unit would cool off at night and create a
> partial vacuum and suck in moist air. With such a small box, I hadn't
> anticipated that happening.
>
how you solved the problem of
> protecting the terminating resistor from the weather and moisture
> condensation.
>
> Don K4KYV
>
This sounds like a situation where good use could be made of
an epoxy encapsulant- just a suggestion. Condensation alone
led to the open circuit?
You must have used some non-soldered connections that
rely on the pressure from a tightened screw head or nut to
assure contact, it sounds like. For outdoor use, I have always
preferred soldered connections. I solder wires in parallel with
any mechanical (hardware) connection.
This has been done for years with commercial baluns,
where they provide flying leads directly soldered to
the windings on a ferrite rod core, and have you bring them out
past the screw eyes and then twist and solder directly to the
antenna wire connected to those eyes. This has always been
quite reliable for me, no matter how bad the solder joints
or the wires looked after a few years of weathering. There
are some exceptions, such as the W2AU baluns, which seem
to perform well with outside solder lugs held in place by the
compression of a nut.
BTW many commercial baluns are intentionally vented to the
outside, with one or more 'weep holes' on the bottom, as a
cheaper alternative to encapsulation. This bolsters my
contention that all-soldered construction is adequately
reliable for outdoor use- for a few seasons, at least. I have
not seen a properly soldered joint exposed to the weather
fail either open circuit or by becoming non-ohmic (rectifying).
They just get a bit ratty looking after a few years.
I have never bothered with applying any weather sealant to
these joints, as I see them as being 'temporary' in any case.
As long as the solder workmanship is good, I would not
expect problems with reliability. BTW some hams don't seem
to be all that great at soldering, but they think they are. :o)
I have seen a number of bad solder joints over the years.
The most common mistake seems to be *way* too little
heat used on joints with large conductors- the solder
never gets a chance to properly 'wet' and flow. Liquid rosin
applied to these larger joints also seems to help a lot in
that regard. I virtually always use it for bigger stuff, like
joining two #12AWG wires, etc. And finally, I have seen much
evidence that many folks do not adequately clean the surfaces
of the wires to be soldered. I often take the trouble to
completely pre-tin all conductors before I crimp and solder
the joint. 73, David K3KY
|