[TowerTalk] 2 el 40m beams

Fri May 25 09:34:50 PDT 2012

Go to K3LR's site and check the mods to make that antenna a Moxon.  the 
performance is quite a bit better.

The original 40-2 you could easily crush the ends of the boom when 
tightening down the elements.  I would add an insert to the ends to that 
does not happen.  They also had metal overheads.  I replaced them with 
Philystran.  In addition to the worm clamps I would pin the elements 
with a #10 or so SS bolt and nylock nut.  I would change all the nuts 
for nylock.

There are number of good articles about beefing up this antenna.

Mike W0MU

W0MU-1 CC Cluster w0mu.net:23 or w0mu-1.dnsdynamic.com
Http://www.w0mu.com

On 5/25/2012 10:24 AM, Roger Cooke wrote:
> I have the Cushcraft 40-2CD which I am about to put up this summer. It has never been assembled, much
> less put on a tower.  Has anybody modified one of these beams?
>
>   
>
>
> Regards from Roger, G3LDI
> Swardeston, Norfolk.
>
>
>
>
>> ________________________________
>> From: Paul Staupe<staupe at gmail.com>
>> To: towertalk at contesting.com
>> Sent: Friday, 25 May 2012, 16:20
>> Subject: Re: [TowerTalk] 2 el 40m beams
>>
>> Last summer I joined a group of YCCC club members in a project to rebuild
>> my XM-240 into a Moxon (Grant's V2).  Several of us built this version, and
>> Tony, K1KP decided to build the V3. We've all been very pleased with the
>> results.
>>
>> It took a lot of time, a lot of SS nuts and bolts and a good drill press to
>> get the job done, but I finally was able to get the antenna up in the air
>> in January, thanks to a mild winter here in Minnesota.  Since I had too
>> many trees near the base of the tower, I had to assemble the Moxon piece by
>> piece on the tower so it went up without testing.  I was shocked that it
>> worked perfectly, had the published SWR and real gain.
>>
>> The Moxon sits 18' above a 4L SteppIR which is at 77' so it's totally
>> exposed. We've had some severe winter gales and recent straight line winds
>> combined with thunderstorms here that I no longer worry about.... the Moxon
>> is rock solid, and sheds the wind "gracefully."  I can't say enough good
>> things about this antenna.
>>
>> Best regards,
>>
>> Paul W0AD
>>
>>
>>
>> Date: Thu, 24 May 2012 21:28:35 -0700
>> From: Grant Saviers<grants2 at pacbell.net>
>> Subject: Re: [TowerTalk] 2 el 40m beams
>> To: lkeller73 at roadrunner.com
>> Cc: towertalk at contesting.com
>> Message-ID:<4FBF0A73.3050904 at pacbell.net>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> The W6NL 40M  Moxon has several design iterations.  As far as I know
>> there are 4 versions, in time sequence I think they are
>>
>> V1 - 2006 original Cushcraft modified XM-240
>> V2 - 2007 center of element strengthening of V1, also known as the
>> "K3LR" version
>> V3 - 2010? the "120 MPH" design, a scratch build from raw stock, no
>> antenna is modified
>> V4 - 2012 "100 MPH" design for W2SC, modified from the XM-240
>>
>> K6KR and I opted to parallel build two V3's in my garage.  I cannot
>> attest to any relative comparisons since I haven't owned the other
>> Moxons or commercial 2L alternatives.  However, I've done some basic
>> mechanical analysis of the V3 and can confirm it is in the strength
>> ballpark as specified.  One reason we decided on the scratch build is we
>> could buy known alloys whereas starting with the now MFJ built Cushcraft
>> has some unknowns, and neither of us had one.  Also, as the build
>> progressed, we became convinced that Dave's element segment connections
>> are superior.  In rebuilding and strengthening a used F12  EF120C to use
>> a Tornado variable center coil I found many loose or missing rivets and
>> changed to the V3 bolting technique.  YagiMech predicted structural
>> failures at about 70MPH and it had damage where predicted.
>>
>> Performance wise, the V3 Moxon was exactly as expected, testing at 92'
>> with an AIM4170.  Observed pattern seems about right.  Measuring gain
>> and elevation pattern is not feasible for me (who can? :-( ).  I've had
>> some 1/2" icing and all was ok, but it has been on the tower for only 7
>> months.
>>
>> There is nothing particularly difficult about building this antenna, but
>> there are many parts and it does take considerable time and
>> concentration to build it (we made a little scrap).  Getting all the
>> tubing sizes is a bit of a challenge.  The ballpark material costs for
>> us, going first class with all DXE element saddle clamps and SS hardware
>> was around $1700 per antenna.  W3TX emailed me that he may be interested
>> in commercially building it.
>>
>> I doubt there is anything commercial that is stronger.  Dave in a recent
>> QSO (Moxon to Moxon) said "it is the largest antenna I can keep together
>> at my QTH"  I think he has recorded 160MPH gusts.  At my Redmond, WA QTH
>> the wind so far has been negligible, I'm back from the ridge edge and
>> 100'+ trees all around make a huge difference.
>>
>> Grant KZ1W
>> _______________________________________________
>>
>>
>>
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