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Author Topic: attaching coax to Mosley Tribander  (Read 3977 times)
VK2CRI
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Posts: 3




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« on: December 08, 2010, 11:24:07 PM »

Hi I have a Mosley Tribander.for  20 15 10   I have it erected ,The feedline is no longer connected ,cant remember if it was origionally used with or with out a  a balun , would like to know If I can connect a 1.1 balun between the 50ohm RGU Coax and directly to t he antenna or do I connect with out a balun, I have  a balun which I can use and would prefer to use as a connection to the coax.
Been off the bands for many years ,cannot remember the setup or theory , The origional connection was destroyed by big birds on top of the antenna which now I have realized I must this time shield with some type of plastic box.
Also is there a chat room online , where I could contact and speak to other Hams , Couldnt get the correct IRC download for Hams , appreciate any help VK2CRI ex VK2GQQ ZL2AGE
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WB2EOD
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Posts: 219




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« Reply #1 on: December 09, 2010, 05:47:54 AM »

The Mosley tribander (at least the TA-33 series) is direct 50 ohm feed. 
You may want to coil a few feet of coax (maybe 10 turns 8" diameter) at the feed point but this is not absolutely necessary. 
Both sides of the driven element are insulated from the boom by plastic blocks. One side is (or should be) groundstrapped to the rest of the antenna.  Be sure you connect the shield to that side. 
   
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K7UNZ
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« Reply #2 on: December 09, 2010, 06:18:19 AM »

The quick answer is yes, you can use a balun.  In fact Mosley suggested their BN-86 balun, but I would think any 1:1 would do.
73, Jim/k7unz
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AD4U
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Posts: 2179




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« Reply #3 on: December 09, 2010, 06:48:07 AM »

I have a Mosley Classic 33 tri-bander, which is the "big brother" to the TA-33.  These two Mosley antennas have driven elements that are insulated from the boom, hence they are a "balanced feed", which means a balun probably "should" be used to preserve the radiation pattern.  Whether or not using a balun will have any noticeable effect in the real world is another matter for discussion. 

As I remember and it has been a LONG time, I don't remember Mosley making or offering a balun.  The BN-86 balun is (was) a HyGain product.  However it should work perfectly well with the Mosley beam.

Dick  AD4U
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AA4PB
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« Reply #4 on: December 09, 2010, 07:17:31 AM »

Mosley used to say NOT to use a balun. Directly connect the coax making sure the shield is attached to the side with the ground strap. Mosley also told me that removing the supplied ground strap DOES NOT improve the performance.

There should be nothing wrong with using 10 turns of coax coil in order to help keep any common mode currents off the coax shield if you want - but I don't think it is a Mosley recommendation.

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VK2CRI
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« Reply #5 on: December 10, 2010, 02:41:17 AM »

Thanks so much , really appreciate all replies VK2CRI
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N1LO
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« Reply #6 on: December 10, 2010, 08:19:18 AM »

For my 10-20m tribander, I used a simple coax choke balun, 6 turns @8" dia. I think I used a gallon paint can as a form, slipped the coil off, and unitized the coil with Scotch super-33, which will withstand UV exposure for years.

I also soldered 14 ga insulated wire pigtails with ring terminals to the end of the coax. You must seal up the open end of the coax thoroughly to prevent moisture from eventually degrading it and your performance.

If you just twist the shield and apply sealant, water will still wick its way inside through the fine conductors. Tinning the shield completely, but only at the sealing point, will stop the wicking.

Coax has 3 rf conductors. You want to stop the rf on the outside of the shield.

- - · · ·  M A R K · N 1 L O · · · - -
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N5RMS
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Posts: 37




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« Reply #7 on: December 29, 2011, 04:52:06 PM »

I have the MP-33.  I was getting TVI until I added a ferrite balun to my antenna! Also lowered the swr by adding an "inductomatch".

73,
N5RMS
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W8ATA
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Posts: 326




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« Reply #8 on: December 30, 2011, 02:50:01 PM »

When Carl Mosley designed the TA-33 back in the 1950's his intent was to make a rugged, effective and easy to put up tri-bander. That was a selling point and it worked well. I had one of the original batch of 50 that were made in as I recall the summer of 1957. It was all of the above, rugged, effective and easy to put up with no balun needed . Although the coax feed line connected directly to the driven element with one side of the element grounded seemed counter-intuitive to our thinking, Moseley said it was designed to work the way he designed it. Gary the present owner of Mosley maintains the same original thinking. I know that because he and I have had phone conversations related to the design. We know a lot more about common mode current than we did in the 1950's and today I think it is prudent to use a choke "balun" at the feed point. For a long time I ran it without one and then added several turns of coax as mentioned above (the ugly balun) and more recently Bob Rumsey's, Balun Designs 1:1 choke.

Of course all this is just my opinion. Your mileage may vary.

73,
Russ
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NJ3U
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Posts: 125




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« Reply #9 on: January 01, 2012, 09:44:08 AM »

John,  I have a TA33jr and the connections are made directly to the antenna driven elements with the shield grounded via the Mosely strap.  I added Five ferrite cores to prevent common mode in my coax and all is well.

If you want to check out the pigtail and other aspects of the install go to my photobucket page for extensive project photolog.

http://s47.photobucket.com/albums/f190/dad250/Mosley%20Beam%20Antenna%20Project/?albumview=slideshow



Good Luck and 73 KC2UML Rory
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