[TowerTalk] XM-240 Shorty-Forty: X-Hat Modification

Tue Feb 9 15:15:52 PST 2010

Darl Deeds wrote:
> That's exactly what happened to mine.
>
> Darl  NA8W
>
> --------------------------------------------------
> From: "Joe Subich, W4TV" <lists at subich.com>
> Sent: Tuesday, February 09, 2010 3:22 PM
> To: "'Tower and HF antenna construction topics.'" <towertalk at contesting.com>
> Subject: Re: [TowerTalk] XM-240 Shorty-Forty: X-Hat Modification
>
>   
>>> I wonder why they fall off?
>>>       
>> The original X-hat elements were solid rod 3/16" in diameter
>> with a 1.25" long by 3/8" OD sleeve crimped over the center
>> of he rod before drilling for the #8-32 x 1.75" mounting bolt.
>>
>> Newer antennas - or at least some production runs - appear to
>> lack the crimped sleeve as they fracture through the mounting
>>     
I thought I was seeing the beginnings of a pattern between "mine broke 
within a month or two  and mine has been up for years" in the reports. I 
think Dicks idea of going to a bit larger rod with a doubler at the 
center is a good idea.  How the extra diameter will affect the 
performance of the "top hat"? I'd expect to see if have a bit more of an 
effect so the resonant frequency may be a bit lower, but that's pure 
guess work.

Unfortunately the "good grades" of aluminum tubing are expensive 
compared to the lesser grades due to compounding the alloy and tempering 
it. This likely means the doubler is of soft aluminum instead of 
something like T-6 which is used in aircraft.

It's preferable to get a rod and sleeve that fit snug, but movable 
before resorting to using epoxy. I'd also probably lengthen the doubler 
to 4" rather than 2".

BTW IF you have what is called a "slip roller" or know some one who 
does, they can carefully reduce the size of the sleeve so it is a snug 
fit on the rod. Another approach is to just hunt for a rod and sleeve 
combination that will provide a tight but movable fit.  Calling a 
supplier  and just asking might get what you want.  It'll likely cost 
more than the present system, but is much preferable.  Although there 
are many sources, just off the top of my head the only one I can think 
of that is not local would be Texas Towers.  They also follow this 
reflector, or have in the past so some on may be able to come up with 
the specific sizes needed.

The smaller rod might hold up if the doubler were epoxied in place 
instead of crimped. Much depends on the fit of the doubler. As it's 
presence on the smaller rod is critical, or at least I'd call it 
critical, I'd make it about twice as long as present length and make 
sure it was a snug fit using epoxy if necessary.IF the doubler doesn't 
fit tight it takes a bit of doing to get the epoxy to fill the void.  As 
aluminum has a very large coefficient of expansions the epoxy has to be 
able to be capable of handling the movement without breaking, or coming 
loose from the rod of sleeve.  There are several ways to approach this 
with both requiring an epoxy with a viscosity low enough to get it to 
flow between the rod and sleeve.  Make sure the rod and sleeve are clean 
with no oil residue on them. Use a good quality, strong epoxy. Ace 
Hardware sells an assortment. I use the strongest one they carry. I 
assume that Lowe's and Home Depot also carry this type of epoxy. 
(Particularly one rated for aluminum). Don't get this stuff on your 
wife's carpet as you are unlikely to ever get it out. Some of it is 
supposed to even seal or repair high density polyethylene. Read the 
directions carefully as some of this, and particularly the stronger 
mixes, have some very nasty compounds in them requiring they be used in 
an open area.

1.  You can use one side of the drilled hole while blocking the opening 
on the other. Use one of the cheap plastic syringes That will hold 
between 3 and 10 CC without a needle to inject the mixed epoxy in the 
hole  until it comes out at both ends of the sleeve. Hopefully the fit 
is good enough you won't need near that volume. Then remove the tape and 
inject a little more until it comes out the other side.

2.  The second approach is to  drill a small hole in the undrilled 
sleeve/doubler very close to one end. Put the doubler in place at the 
center the new, un-drilled rod. Wrap tape over the end of the sleeve 
)that has the small hole drilled in it )to seal it to the rod You'll 
likely have to clean the tape away from the drilled hole.  Inject the 
freshly mixed epoxy into the small hole  until the space between the 
sleeve and rod is filled and epoxy comes out other end. The following 
may not be necessary, particularly if the sleeve is a fairly close fit 
on the rod.  Being careful not to move the sleeve on the rod, remove the 
tape and give it another shot of epoxy to fill the void that will likely 
form opposite the drilled hole.  Let cure for the proscribed time before 
drilling the center hole and installing.

As I said earlier, I'd resort to the epoxy only if I could not get a 
sleeve and rod combination that were not a snug, but movable fit.

73 and good luck,

Roger (K8RI)
>> hole due to vibration.  My guess is that the sleeve was
>> eliminated as a cost cutting measure <G>.
>>
>> 73,
>>
>>   ... Joe, W4TV
>>
>>
>>
>>
>>
>>
>>     
>>> -----Original Message-----
>>> From: towertalk-bounces at contesting.com
>>> [mailto:towertalk-bounces at contesting.com] On Behalf Of Gregg Seidl
>>> Sent: Tuesday, February 09, 2010 1:57 PM
>>> To: Tower and HF antenna construction topics.
>>> Subject: Re: [TowerTalk] XM-240 Shorty-Forty: X-Hat Modification
>>>
>>>
>>> I wonder why they fall off?  I've never heard of that. Mine
>>> have been up for
>>> 6 years now.  Gregg  K9KL
>>> ----- Original Message ----- 
>>> From: <RLVZ at aol.com>
>>> To: <towertalk at contesting.com>
>>> Sent: Monday, February 08, 2010 4:43 PM
>>> Subject: [TowerTalk] XM-240 Shorty-Forty: X-Hat Modification
>>>
>>>
>>>       
>>>> Hi Guys,
>>>>
>>>> I've had problems with the X-Hat Rods falling off of my XM-240.
>>>> Therefore, I would like to eliminate the X-Hat by lengthening the
>>>> elements.  I'm wondering if anyone has done this
>>>>         
>>> successfully and how
>>>       
>>>> much length must be
>>>> added to the elements?
>>>>
>>>> Or if anyone has modeled the removal the XM-240 X-Hat by
>>>>         
>>> lengthening
>>>       
>>>> the elements... please share what element lengths you came up with.
>>>>
>>>> Thanks!
>>>>
>>>> Dick- K9OM
>>>> _______________________________________________
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>>>>         
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