On Thursday, May 2, 2013 at 5:26:36 PM UTC-4, J. C. Mc Laughlin wrote:

This eleven year old message sure contains some useful information.
73, Mac N8TT

wrote in message
news:9ea7f6aa-1b6b-464c...@googlegroups.com...
On Wednesday, January 23, 2002 3:37:52 PM UTC-5, Neil wrote:

(The following is provided as an opinion only, and without warranty of
ANY kind. You take all the risk. If you are NOT comfortable doing
this job, STOP, you may ruin your antenna. That being said, my own
results have been very good...)

Hi Alf;

I was in the same situation as you when I embarked on a project of A4S testing and recovery. It's been a long slow path, but the end result
is very satisfying. The unit I have includes the 40 meter add-on kit.

As you, I found that the "support" at Cushcraft amounted to little
more than a junior employee telling me he didn't know of any trap problems...YEAH RIGHT!

You need to decide what makes the most sense for you. You can
properly restore the antenna, or try to band-aid it hoping for the
best. If you do the latter, depending on your weather and climate,
you will likely see regular trap failures, partucularly in wet or icy conditions. Sometimes they will clear up when things dry out again,
but sometimes you can get internal arcing or opens, in which case the
only remedy is to bring the whole antenna down and work on it. If you don't mind doing this every six months or so, then you're more
energetic than I.

The resonant points of the traps are neither intutive nor easy to
measure with any certainty. In my experience the best approach to
dealing with this antenna is to open up EVERY trap and give it a
thorough going-over (described below). If you do this, then the
chances are very good that you've got at least several years of
worry-free operation, hurricanes notwithstanding.

So here goes:

1. During disassembly, mark each trap according to its type, TA, TK,
etc. with a black magic marker on the outside of the metal can. Also
draw an arrow -> pointing toward the boom (this is not really
necessary, but can help avoid a backwards mounted trap).

2. Pick a trap to begin with and remove the end caps. Note whether
they are cracked or dried. (You'll want to order a bunch of
replacements from Cushcraft, be sure to order a few extras.)

3. Notice that the trap has on one end a region of the can that has
been stamp-formed inwardly, and has a screw attaching it to the
element tubing (remove this screw and save it). The other end of the
can has a few dimples that have been impressed into it. These dimples
rest in a groove in a spacer doughnut inside the end of the trap, and
will make disassembly very hard.

Now for the tough part...

4. Using only as large a drill bit as necessary, drill out all of the pesky dimples. Don't drill any deeper than you have to, you just
have to penetrate the aluminum can. Yes, this drilling will very
slightly change the capacitance, but experimentally it hasn't seemed
to matter. It's best to use a drill press for this step so you can
better control how deep you go. Now, the discovery...telescope the
trap "guts" and the spacer doughnut out that end of the trap, and see what's inside (for better or worse)!

5. Inspect for insects, dirt, arcing or burn marks, etc. Clean up the
trap contents, but do NOT use any solvents nor abrasives on the body
of the coil. In most cases a soft bristle brush and a vacuum cleaner
will do fine. Compressed air is also a help.

6. Notice that each end the coil is fastened to the tubing with a thread-cutting screw. This interface is where most of the contact
problems occur, due to the copper-to-aluminum interface.

Here's the messy part...

6. Remove each coil-end screw (2) and observe if the screw itself has rusted/corroded warranting replacement. If so, get a stainless screw
of the same design and size. Now lift the end of the copper coil
slightly and abrade the two contacting surfaces (one copper, one
aluminum) using a fine grit double sided emery file (or a diamond-dust double-sided nail file). You can also clean up the top of the copper
wire (just at that point) so the screw will have a clean contact area
to clamp onto. Using Penetrox-A, grease up all of the contact areas thoroughly, and tightly reinstall the two hold-down screws (don't
strip them!). Work clean, keep a clean rag handy, and be careful not
to get Penetrox on the coil windings, nor anywhere else for that
matter (not easy).

7. Reassemble the trap. Using a similar approach, abrade and grease
up the contacting surfaces where the screw removed in step 3 goes.
Replace this screw with a new one if it's badly corroded, tighten well
but don't strip.

8. Replace the plastic end caps, either with your originals (if
intact) or with new ones. Now, ohm out the trap, you should see a
small fraction of 1 ohm, in other words a DC short. If you see any appreciable resistance, something's wrong, don't continue till you
resolve it.

9. Repeat with all traps.

10. Reassemble the antenna, putting a layer of Penetrox-A in each of
the tubing joints prior to insertion.

Once you do this, and get the antenna tuned up to the band centers you like, it should be very stable for a very long time.

Note: If in this process you find one or more trap coils that appear
to be heavily coated with carbon powder or residue, you've got an arced-over trap that needs replacement. This can be the result of too
much power, an insulation failure, or using it on a non-supported band (such as 17m).

Hope this helps.

Neil, K1VY

email to K1...@arrl.net

P.S. On my A4s I still occasionally see some motion of the resonance center point in icy conditions, what I understand is that the ice
makes the antenna look electrically longer, thus the resonant
frequency decreases until the ice melts off at some point.

On Wed, 23 Jan 2002 18:15:48 GMT, "Alf Green"
<alf....@honeywell.com> wrote:

Greetings,

Sometime in the next few months, before it gets too hot to climb the >tower,
I want to put my A4S (20/15/10 4-ele beam) back in the air. It worked >fine
when I took it down, but has been in pieces laying on my roof for several >years, and some of the traps are showing signs of cracking on the end >seals.

Although they have not been exposed to standing water, it's possible that >moisture could have crept in. I'd rather not dissemble them >unnecessarily,
so am looking for a way to test them as is.

I have the original datasheet for the A4S but it does not include any >details. Neither is Cushcraft forthcoming with anything useful (not that >I
would really expect them to under the circumstances). I expect each inner >trap to be a parallel-resonant circuit at 28MHz, and the outer ones to be >resonant at 21MHz, but that may be too simplistic. I'd also like to get >some
assurance that the power handling hasn't been degraded, even though I >probably wont be running much over 100w.

I have a good selection of test equipment, I just need some ideas as to >what
exactly I need to look for.

All suggestions welcome.

73 Alf NU8I
Scottsdale AZ DM43an

Neil, which "end" of the traps are to point "inwards" in reference to the dimpled tube end and formed inward screw end? Meaning if you held the trap with say the "dimpled" end on the left side, which if the ends are to point inwards towards the boom/mast? ----------------------------------------------------------------------------

J. C. Mc Laughlin
Michigan U.S.A.

The end with the plastic "donut" is on the boom end. Look at the 15M trap that has the reduced diameter end and you will see which end goes where.

Tom - NT4OM

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