25.4 mm = 1 inch and it is a linear function e.g. 50.8 mm = 2 inch. Use that
calculator you (probably) have in your computer.
73 de
Hans - N2JFS
-----Original Message-----
From: Bob AD5VJ <ad5vj@ad5vj.com>
To: 'Tower and HF antenna construction topics.' <towertalk@contesting.com>
Sent: Wed, Apr 14, 2010 3:23 pm
Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
John you're a genius great ideas and I appreciate them all. I like the one
about the drinking bottle especially good one there. They are easy to come
by and very adaptive and as you pointed out half of it is already formed for
the task at hand.
Btw I did find some software online for calculating you own coils only thing
is I don't know if it is proven or not. I have also found a mm to inches
calculator online since the application keeps asking me questions in terms
of the metric system.
73
Bob AD5VJ
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of John E. Cleeve
> Sent: Wednesday, April 14, 2010 1:54 PM
> To: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
>
> Hello Bob,
>
> I am not familiar with Folgers Coffee cans, but as long as they
> are
> made from aluminium and not tin plate, which would eventually rust,
> they
> might be fine. If I were in your position, then I would consider
> literally
> "rolling" my own. That is obtaining some very thin, soft aluminium
> sheet,
> such as a used "offset litho printing plate" cut to shape and then
> rolled
> around a wooden former, if you do not have access to a set of "bending
> rolls". You could mechanically seal the two edges together just as a
> tin can
> would be done.
>
> Or, perhaps you might find a spun aluminium bottle shaped water
> container, in your hardware or sports store, which could be purchased
> and
> sacrificed to the cause, the neck could then provide the fixture for
> the top
> of the trap outer, and cutting away the base, would provide the
> aperture for
> a plastic disc to provide mechanical stability.....When you see a
> suitable
> item, you will instantly recognise its potential for adaptive use!
>
> I am sure you will succeed now that you have a clear view of how
> the
> traps were assembled. Sadly, I cannot provide the exact resonant
> frequencies
> that each trap was tuned to, during the factory assembly, but I am sure
> that
> somewhere that information must be written down and available......best
> of
> luck with the restoration, sincerely, John. G3JVC.
>
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Bob AD5VJ
> Sent: 14 April 2010 13:57
> To: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
>
> Hi John
>
> The more I look into this the more I want to try to roll my own so to
> speak.
> I didn't know that the al was used to reduce costs. So I might even end
> up
> with more sensitivity with copper. That a good idea thanks.
>
> I am thinking in terms of the trap covers. Not sure where to go with
> this. I
> think the drink cans might be too flimsy as they are getting thinner
> and
> thinner these days.
>
> Now a small metal Folgers coffee-can might work and Lord knows I drink
> that
> like its going out of style.
>
> Bob AD5VJ
>
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com [mailto:towertalk-
> > bounces@contesting.com] On Behalf Of John E. Cleeve
> > Sent: Wednesday, April 14, 2010 7:41 AM
> > To: 'Tower and HF antenna construction topics.'
> > Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> >
> > Hello Bob,
> >
> > 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.
> >
> >
> >
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com
> > [mailto:towertalk-bounces@contesting.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
> >
> > Hi John
> >
> > Excellent post!!
> > 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.
> >
> > Bob AD5VJ
> >
> >
> > 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
> > > trap
> > > problems, but all off which were repairable.
> > >
> > > To get to the inside of the trap assembly, you undo the self
> > > tapping
> > > 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
> > > you
> > > 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
> > > head
> > > 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
> > > screw
> > > 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
> > > screws,
> > > plus washers. Obtain some aluminium wire of the right diameter, and
> > > simply
> > > rewind the inductors, only a few turns each, in grooved formers,
> > > carefully
> > > 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: towertalk-bounces@contesting.com
> > > [mailto:towertalk-bounces@contesting.com] On Behalf Of Bob AD5VJ
> > > Sent: 14 April 2010 03:08
> > > To: towertalk@contesting.com
> > > Subject: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> > >
> > > I was given an old Hygain 18avt vertical and had plans on mounting
> it
> > > atop
> > > my tower since it is low profile and does well in the wind. But I
> > just
> > > went
> > > 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
> > > I
> > > can find them - Google did not find anything, unless I didn't put
> in
> > > the
> > > right words -- I just Googled "Hygain assy (and then the 870 number
> > in
> > > the
> > > manual).
> > >
> > > 73,
> > > Bob AD5VJ
> > >
> > >
> > > _______________________________________________
> > >
> > >
> > >
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