Pity about the missing traps, but I am glad you were able to
diagnose the problem with the 15m trap. Now you can see how they were made,
it should not be difficult to obtain plastic tube or rod to use as the
former, with the added aluminium tube to fit at each end.
The outer trap cover forms the fixed capacitance, coupled to the
coil and the lower antenna element, and the plastic spacer adds some
mechanical stability; however, it may be possible to re-use aluminium drinks
cans, after you have drunk the contents, to form the basis of your
replacement HB traps. You will need to work out the inductance and
capacitance to work on the missing bands, but with some ingenuity, and a
GDO, I am sure you will succeed. You could use copper wire of course; the
aluminium stuff was used by Hygain because it was cheaper!
The last resort might be to seek another 18AVT from Ebay or your
friends....I have two in my garage, both destined to be used as phased
verticals at my remote GM site, but both those came from friends who had
upgraded to verticals with WARC capability. The user manual for the 18AVT is
available as a .pdf on the internet.....best of luck with the rebuild,
sincerely, John G3JVC.
[mailto:email@example.com] On Behalf Of Bob AD5VJ
Sent: 14 April 2010 13:20
To: 'Tower and HF antenna construction topics.'
Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
Thanks very much for sharing this.
I had looked at one of the traps late last night and thought it can't be
that hard to take it apart and examine it.
So I actually did exactly what you described. I took the 15 meter trap apart
and it actually came apart very easily once the screws were taken out of the
one end and you turned the spacer a little.
Just as you said one of the screws holding the inductor wire to the tubing
had rusted and released its hold on the inductor wire.
Looks like about 12 awg wire. Now I am seriously considering making my own
for 20 es 40 meters since they are missing. I could get some 1/2" delrin rod
to wrap onto for the coil and the al wire. A couple of pieces of 1 inch al
tubing and would be 90 percent home free. Now the trap cover might be a
different story, not sure how to get that.
The only problem is I cant find any al wire more than around 14 awg and it
only comes in 4 foot lengths. Need to find longer spool of wire.
hn E. Cleeve
> Sent: Wednesday, April 14, 2010 4:37 AM
> To: 'Tower and HF antenna construction topics.'
> Cc: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> Hello Bob,
> I have used, and still have and 18AVT/WB which has served me well
> for many years, both in the UK and abroad. However, there have been
> problems, but all off which were repairable.
> To get to the inside of the trap assembly, you undo the self
> screw which fixes the outer cover of the trap to the antenna element
> assembly, then you rotate the inner plastic spacer at the bottom of the
> trap, until you can slide the entire cover etc. down and away from its
> original position.
> This will expose the inductor, and at each end of the inductor
> will find a self tapping screw which connects the inductor wire, at
> each end
> to the antenna element. In my example this self tapping screw
> originally was
> not made of stainless steel, and it did not have a washer beneath the
> of the screw, and so, on assembly the screw head "bit" into the
> aluminium of
> the inductor wire, and eventually the rust from the screw and the
> stress on
> the inductor wire, which caused the inductor wire to fracture at the
> head/wire contact, that caused the problems I experienced. There is a
> similar situation at each end of the 80m top loading inductor too.
> So, I suggest you obtain some new stainless steel self tap
> plus washers. Obtain some aluminium wire of the right diameter, and
> rewind the inductors, only a few turns each, in grooved formers,
> tighten the new self tap screws and then coat the junction of the
> screw/washer/inductor wire with a non hardening insulation, and then
> reassemble the outer covering, and you should be back in business.
> Sincerely, John. G3JVC.
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com] On Behalf Of Bob AD5VJ
> Sent: 14 April 2010 03:08
> To: firstname.lastname@example.org
> Subject: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> I was given an old Hygain 18avt vertical and had plans on mounting it
> my tower since it is low profile and does well in the wind. But I just
> to Hygain's website and it appears they don't stock parts for it.
> I am needing the 20 meter and 40 meter traps anyone have any idea where
> can find them - Google did not find anything, unless I didn't put in
> right words -- I just Googled "Hygain assy (and then the 870 number in
> Bob AD5VJ
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