[TowerTalk] Hygain 18AVT trap for 20mtr/40mtr

Wed Apr 14 16:39:27 PDT 2010

I thought about that thanks for the confirmation. 

Yes it is an air cap. Just the coil on a form and the al tubing the form is
attached to does not even go inside the coil form more than 2-3 inches so it
doesn't go all the way thru the form like I thought it would.

My understanding is after reading a bit that the outer al cover makes the
cap based on its proximity to the coil. So I guess I just measure that
carefully and should be reasonably close to the same capacitance.

Then I read about an idea here to use a cutting board for the spacer which I
found on eBay for 5.00. I found the coil form there also in the form of some
delrin rod that is 1/2" by 12". I found the al wire in the form of hobby
wire, but it is not quite 10 awg but pretty close. Problem is the wire is
only in 4 foot lengths. 

So I may go with the al fence top post wire idea brought up earlier.

Then it's just making the coil up for resonance. From what I have read
starting at the feed-point out you put the 10 meter coil then the 15 meter
then the 20 meter coil, then the rest of the antenna is 40 meters and the
'resonator' at the top takes care of 80 along with the top hat.

But to be honest I am not sure I want to try to do the 80 meter band seems
like too much of a compromise for that band.

I remember in the old days when I had my Heathkit Apache TX-1 and
Hallicrafters SX-111, literally loading up a window screen in my second
story apartment for the 40 meter novice band and then I transitioned to an
indoor dipole. I strung the dipole along the joint where the ceiling met the
wall 18 gauge wire. 

Hihi those were the good ol' days.

Bob AD5VJ

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of GEORGE CORTEZ
> Sent: Wednesday, April 14, 2010 5:29 PM
> To: Tower and HF antenna construction topics.
> Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> 
> If its anything like the way they design the traps on their tribanders
> the sleeve is a air capacitor.
> the size is not really critical but id look at the 15m trap and copy
> the
> size for 20 and double it for 40 as a
> starting point. adjust the length as necessary.
> 
> George NE2I
> 
> 
> 
> Bob AD5VJ wrote:
> > Hi Hans
> >
> > Thank you I for some reason never realized it was a linear function
> that
> > will certainly help me to estimate with more confidence.
> >
> > I in fact opened my calculator on windows 7 ultimate not expecting
> much of a
> > calculator but to my surprise, noticed it is much more powerful than
> those
> > versions of windows before it. There is an engineering side to it and
> a
> > converter built in. So you were exactly correct.
> >
> > I also found a gold mine on Google and went here:
> > http://webpages.charter.net/crstrode/calcs/RFcalcs.htm
> >
> > I am playing with some of the coil and "solenoid" apps to see what
> they will
> > do and what they will tell me. So far the one called "trapdip" is
> pretty
> > cool. Just can't figure out how to get it to print other then use the
> print
> > screen function of windows.
> >
> > Best of all they are dos and they are free.
> >
> > Bob AD5VJ
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: towertalk-bounces at contesting.com [mailto:towertalk-
> >> bounces at contesting.com] On Behalf Of hanslg at aol.com
> >> Sent: Wednesday, April 14, 2010 3:55 PM
> >> To: towertalk at contesting.com
> >> Subject: Re: [TowerTalk] Hygain 18AVT trap for 20mtr/40mtr
> >>
> >>
> >>  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 at ad5vj.com>
> >> To: 'Tower and HF antenna construction topics.'
> >> <towertalk at 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 at contesting.com [mailto:towertalk-
> >>> bounces at 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 at contesting.com
> >>> [mailto:towertalk-bounces at 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 at contesting.com [mailto:towertalk-
> >>>> bounces at 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 at contesting.com
> >>>> [mailto:towertalk-bounces at 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 at contesting.com
> >>>>> [mailto:towertalk-bounces at contesting.com] On Behalf Of Bob AD5VJ
> >>>>> Sent: 14 April 2010 03:08
> >>>>> To: towertalk at 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
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>>
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> TowerTalk mailing list
> >>>>> TowerTalk at contesting.com
> >>>>> http://lists.contesting.com/mailman/listinfo/towertalk
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> >>>>> 04/13/10
> >>>>> 21:22:00
> >>>>>
> >>>>> _______________________________________________
> >>>>>
> >>>>>
> >>>>>
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