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tech / rec.radio.amateur.antenna / Re: Testing Cushcraft traps

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o Re: Testing Cushcraft trapsTommy Barber

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Re: Testing Cushcraft traps

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Subject: Re: Testing Cushcraft traps
From: trbarb...@gmail.com (Tommy Barber)
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 by: Tommy Barber - Wed, 21 Jun 2023 18:13 UTC

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.


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tech / rec.radio.amateur.antenna / Re: Testing Cushcraft traps

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