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Author Topic: Mosley cl-33 resonance  (Read 1089 times)
NB9N
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Posts: 68




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« on: April 30, 2012, 05:09:25 AM »

Have developed a resoance issue with my mosley cl-33 on 20 meters.   I'm hoping not to have to take it down so would like to explore the other possibilities first. (if there are any)   It is located 40 foot high. Five feet below I have a 80 meter loop and an inverted L for 160 meters.  IN addidtion there is somewhat further down a windom antenna.   There are red pines located right up to the antenna on the North and there is some diffeence (slim) when I turn the antenna.   
On my DMU I record nearly a flat swr on 15 meters, at least 600 kh width on 28 (1.5 and below)  but on 20 meters it is 1.3 on the high side and nearly off the scale on the cw portion.
The point of which it goes way (beyond 3) off seems to begin with the cw portion.  I do have an ugly balun on the tower and without it the swr goes about a half point higher.   So any ideas?   I think that the normal range for this antenna is between flat and 2-1.

Joel/ nb9n
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AA4PB
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Posts: 12685




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« Reply #1 on: April 30, 2012, 05:29:52 AM »

If the antenna is set for the center of the band then the SWR should be about 2:1 at either end, according to the Mosley charts. If the antenna is set for the center of the phone band then the SWR will be greater than 2:1 at the bottom of the CW band. My TA33 manual has length settings for the elements depending on where you want to put the resonant point - the CL33 is probably the same.

If the resonance point was acceptable but has now shifted then you probably need to inspect the traps and make sure all of the fittings are tight and that nothing has moved. Recheck the element length adjustments against the manual. Not much you can do without getting access to the antenna.


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K5LXP
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« Reply #2 on: April 30, 2012, 02:51:07 PM »

Unless the sudden shift was associated with the installation of something nearby, it almost has to be an issue with the feed or traps.  It takes more than something metal in the field to have that dramatic an effect on resonance.

My own CL-33 suffered from cracked insulators in the traps, but that was a pretty dramatic and obvious failure.  It would seem though that something like a trap full of moisture, a bug nest or some other environmental condition may cause what you're seeing.  Clearly, something about the antenna has changed so once you done due diligence in ruling out the feed, it may have to come down for inspection and refurb.

The good news about the CL-33's is you can get any part for any version made, so whatever is wrong you can fix it.  My CL-33 was made in 1967 and still works with nearly all the original parts.


Mark K5LXP
Albuquerque, NM
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NB9N
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Posts: 68




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« Reply #3 on: April 30, 2012, 07:47:01 PM »

thanks for the imput.  I was just wondering if my 15 meter band was relatively flat and ten was good if I could still have cracked insulators or bad caps?  Hopefully it is in the feed but am prepared to take it down this summer if not.

Joel
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NB9N
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Posts: 68




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« Reply #4 on: May 02, 2012, 08:03:20 AM »

Again thanks for the recommendations (ideas).  Actually for the sake of resolution I dropped my 80 meter loop and it went back to normal!   So I can confidently say that an 80 meter loop located beneath (even as much as 17 ft) can have a tremendous effect on a 20 meter yagi.

Joel
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