I answered Dick off line on one e-mail, but as it's a general topic of
interest I think I should redo that one here.
I'm not familiar with the XM-240 which appears to be a Moxon design.
Each diagram I find appears to be a bit different. One had a single
element mounted horizontally on the ends of the antenna elements.
Another had two holes drilled through the element at 90 degrees to each
other and used what looks like the stamped element mounting for TV
antennas. Each element has a double in place at the center with a hold
drilled through both. A screw goes through that, the stamped bracket and
the element to which the 1/4" rod mounts.The rods appear to be mounted
about an inch apart and 90 degrees to each other and maybe about a 1/4
of the distance between the end of the element and the boom.
I had originally though (in quoted post) of a bracket on the end of the
element supporting two tubular sections forming the cross.
Do the doubler and foam I had originally suggested wouldn't be a lot of
help. I really need to see just what the attachment and attach point
look like.
73
Roger (K8RI)
Roger (K8RI) wrote:
> One added note,
>
> In the case of the broken element I'd not use the doubler to repair the
> broken element, but rather make a new element, add the double, epoxy the
> doubler in place and let cure, foam the inside of the tube, let cure,
> and then drill the hole using a centering guide. The foam will actually
> add measurable strength to the element in addition to the doubler.
>
> 73
>
> Roger (K8RI)
>
> Roger (K8RI) wrote:
>
>> RLVZ@aol.com wrote:
>>
>>
>>>
>>> Hi Doung & all,
>>>
>>> In my original post, I stated that some of my "X-Hat rods were falling
>>> off" so I'd like to lengthen the element and eliminate the X-Hat rods.
>>>
>>> A better description would have been I've had some "X-Hat rods breaking
>>> off". I had the new XM-240 in the air for less than a month and one X-Hat
>>> rod broke in two and fell to the ground. I dropped the antenna and
>>> replaced
>>> the broken X-Hat and put the antenna back up. Within another month I had
>>> another broken rod. Each time the rod broke in the middle where the hole
>>> is
>>> drilled thru the center casting.
>>>
>>>
>> I'd at least try what we do with aircraft in areas like that...Use what
>> is called a doubler. find a piece of rigid aluminum that will just fit
>> inside (or outside) of these elements. Redrill the hole so the inside
>> and outside ones match. A centering jig that allows holes to be drilled
>> through the *center* of the doubler and at *right angles* to the element
>> would probably be a good idea. I don't know the length of the pieces
>> that are breaking in two, or the size of said element top hats. The
>> length of the doubler is some what dependent on the size and length of
>> that top hat, but if it's a 1/4" then I'd want at least a 6" doubler. If
>> it's a 1/2" then maybe 8" but I'd need to know how long the element tops
>> hats are to come up with an estimate there.
>>
>> At-any-rate, once the doubler is drilled and fitted so it easily slips
>> over the element or inside (my preference is outside) then put a light
>> coat of epoxy on the mating surfaces and slide the two together making
>> sure the holes line up. Once cured it should never break.
>>
>> Another route would be to fill the top hat tubes full of the good
>> expandable foam that doesn't form large bubbles or expand into rigid
>> foam that will warp door and window frames. It will weight little, but
>> dampen any vibration and is far better than using nylon rope like we
>> used to do.
>>
>>
>>> After losing a single X-Hat rod the
>>> resonant frequency jumped aprx. 200 khz making the antenna unusable on the
>>> CW
>>> portion of the band without a tuner. By the way, I did use the antenna
>>> with
>>> a tuner on the CW portion of the band and now my Cushcraft Balun has a
>>> burn mark on it and it's warped!
>>>
>>>
>>>
>>>
>> That's a sign of a marginal balun.
>>
>>
>>> I do not know what is causing my X-Hat Rods to break off. Perhaps the
>>> rods center casting material was defective.
>>>
>>>
>> Center casting material? Is there some where I could find a photo or
>> drawing of this part?
>>
>>
>>> But more likely it's the large
>>> birds landing on my antennas including Ospreys and Owls... perhaps they
>>> are
>>> flying into the X-Hats?
>>>
>>>
>>>
>> I've never seen them fly into something like that but they certainly
>> will roost on them if they are any where near level. Cormorants busted
>> the boom truss on my 7L C3i 6-meter Yagi.
>>
>>
>>>
>>> So I'd love to eliminate the X-Hat if possible.
>>>
>>>
>>>
>>>
>> You can make the element longer but the bandwidth will probably be
>> narrower than the original design.
>>
>> 73 and good luck,
>>
>> Roger (K8RI)
>>
>>
>>> 73,
>>> Dick- K9OM
>>>
>>>
>>> In a message dated 2/8/2010 9:35:04 PM Eastern Standard Time,
>>> ve5ra@sasktel.net writes:
>>>
>>> X hat rods falling off - that is unusual. I've had my XM240 up for
>>> years and never have the rods fallen off. I installed them as per CC.
>>> So what is causing your rods to fall off or do you mean breaking off?
>>>
>>> Doug
>>>
>>> I'll run the race and I will never be the same again.
>>>
>>> -----Original Message-----
>>> From: towertalk-bounces@contesting.com
>>> [mailto:towertalk-bounces@contesting.com] On Behalf Of RLVZ@aol.com
>>> Sent: February 8, 2010 4:44 PM
>>> To: towertalk@contesting.com
>>> 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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