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

[Roger (K8RI)]

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 at 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 at 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 at contesting.com
>> [mailto:towertalk-bounces at contesting.com]  On Behalf Of RLVZ at aol.com
>> Sent: February 8, 2010 4:44 PM
>> To:  towertalk at 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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