When I put up my TA-33 they recommended grounding one side of the driven
element to the boom with the supplied strap. I found that the antenna had
two points of minimum swr. One was in the ham bands and the other was below
the bands. I forget how much lower. I finally removed the element ground
strap so that the driven element operated as a balanced driven element
(driven thru a coax balun) and the swr curve then looked like a normal
antenna should. It was also now narrower than original with one side of the
driven element grounded.
Mosley advertises the antenna as having a very wide bandwidth and it indeed
was very wide and just about what the instructions said it should be. It
seems that they get that bandwidth by unbalancing the driven element.
Calls to mosley only got replies of "we never heard of that".
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Butch Butler
> Sent: Tuesday, February 27, 2007 9:53 PM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Mosley TA-33 problems.........a bit long
>
> Hi All.....
>
> I was recently given a Mosley TA-33 on the occasion of my tower purchase.
> I
> immediately set forth to disassemble every piece in turn for inspection
> and
> cleaning.
>
> I lovingly put brillo to every piece of aluminum, replaced all the
> hardware
> with stainless steel, double-checked the parts list against what I had on
> the floor, disassembled the traps - checking for damage, bug nests, etc.,
> bagged everything and set it aside until the 40-Meter Add-On kit arrived
> from Mosley.
>
> When the 40M kit arrived a few days later, I assembled everything for the
> PHONE section of the band according to the two assembly manuals and
> double/triple-checked the measurements.
>
> I nested and tilted the 52ft. Crank-over tower and mounted the antenna on
> the mast. I knew that with the tower laid over, any VSWR information I
> found
> would be different once the tower was vertical and cranked to full height
> -
> so, I raised the tower to vertical and broke out the MFJ-259B.
>
> The initial readings (using the frequency settings recommended by Mosley
> and
> with the tower nested) were as follows:
>
> 10M...................28.8..............2.2:1
> 15M...................21.3..............2.1:1
> 20M...................14.25............2.8:1
> 40M...................7.175............2.0:1
>
> Lowest VSWR read on each band was as follows:
>
> 10M................28.21..............1.6:1
> 15M................20.815............1.4:1
> 20M................14.0.................1.5:1
> 40M................7.22.................1.6:1
>
> The readings seemed to me to indicate a longer antenna than it should be,
> so, hoping I could bring the resonant frequencies up the band a little, I
> shortened the distance between the two inboard traps (those closest to the
> boom) by 1-1/2" on each side and took another reading. Strangely enough,
> the
> resonance went DOWN the band - not UP....confusing!!
>
> I relocated the sections of the radiator to their original position and
> step-by-step made each of the possible variations in length for the
> radiator
> - ie., between the two traps on each side of the boom and the length of
> the
> ouboard element sections as measured from the outboard (40M)
> traps.........No appreciable change.
>
> I then removed the 40M kit and replaced the original TA-33 element pieces
> since I had not checked the antenna prior to installing the
> kit............things got worse!!
>
> Lowest VSWR on each band:
>
> 10M...........28.136 @ 1.7:1
> 15M...........20.643 @ 1.4:1
> 20M...........13.927 @ 1.6:1
>
> As you all probably know, Mosley leaves very little room for
> mistakes.........they color-code the traps and all element parts are
> drilled
> to a specific location instead of using hose clamps, so it's really
> difficult to put one of these antennas together incorrectly.
>
> The only caveat is this (and I'm not sure if it is a factor): My tower
> base
> is by necessity 12 feet from a 40 x 60 metal quanset building. But the
> bldg.
> Is only 15 ft. high and the antenna is at 53 feet. Can this be an issue?
>
> Thanks for reading my ramblings and I'd appreciate any and all help.
>
> 73,
> Butch
> k4nau
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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