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Building new harness for Commscope dipoles

iceman977th

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I was given two DB224-B antennas by a friend that need new harnesses. Instead of only having two 224's, I would like to split them up (since they technically already are) into DB222's to use for some scanner feeds I am putting in to cover the rail bands. Of course, the harnesses are damaged, so they will need replaced. Has anyone done this previously and has measurements, or can point me in the direction, for someone that has never built this style of antenna before? Trying to stick with the KISS method. Thinking about matching the length of the original harnesses and just putting them into some PL259 tee's and either wrapping the crap out of them with coax seal, or have someone build a 3D printed enclosure for the tee.

Mike
 

prcguy

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I would first connect a short 50 ohm test cable to a single dipole and measure its impedance or match at resonance. If its a great match near 50 ohms then you can easily make a phasing harness to feed two or four dipoles out of 75 ohm coax and F connectors and F "T" adapters. RG-6 works fine and RG-11 has lower loss. I have dimensions for Belden 1505A coax and a center frequency around 155MHz. Look at post 5 in this thread, then look at page 4 of the pdf.


I was given two DB224-B antennas by a friend that need new harnesses. Instead of only having two 224's, I would like to split them up (since they technically already are) into DB222's to use for some scanner feeds I am putting in to cover the rail bands. Of course, the harnesses are damaged, so they will need replaced. Has anyone done this previously and has measurements, or can point me in the direction, for someone that has never built this style of antenna before? Trying to stick with the KISS method. Thinking about matching the length of the original harnesses and just putting them into some PL259 tee's and either wrapping the crap out of them with coax seal, or have someone build a 3D printed enclosure for the tee.

Mike
 

rescue161

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I have done this, but it was an old 4-bay dipole made by a different manufacturer. I used a combination of 35, 50 and 75 Ohm coax. I used half on one repeater and the other at another site. There are calculators online that will help you get a perfect match. I did not use adapters. I cut open the old harness and reused the copper sleeves and then wrapped the junctions with mastic sealant tape and covered the junction with marine heat shrink. Both antennas are still working great. You can create your own copper junctions out of copper pipe using a Dremel tool. I did that on one junction as one was missing on the original harness due to it being cut at that point.
 

iceman977th

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Here is the vendor that I have used before.

Thanks for that (and sorry for the late reply) I'll have to order some now. To be honest, I was thinking about doing it with right angle connectors and a tee connector, for simplicity's sake, but I'm not sure if I should adjust anything dimension wise by doing that. I'm not sure how they do the junction in the harness itself.

Mike
 

iceman977th

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Here is the vendor that I have used before.


Dumb question, is RG-83 similar to LMR-400 dimension wise, so I know which connector to order? Also what would be the 75ohm equivalent that matches the RG-83 size if that's the case? I'm drawing a blank tonight for some reason..

Mike
 

rescue161

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It is not the same diameter and is smaller than LMR400. You would not install connectors onto RG83. You would solder it to other pieces of coax in the phasing harness.
 

iceman977th

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It is not the same diameter and is smaller than LMR400. You would not install connectors onto RG83. You would solder it to other pieces of coax in the phasing harness.
From the pdf posted by Talkpair, you use 75ohm to each element then a 35ohm cable to the connector, so I would have to get a connector for it somehow. Remember I’m separating two 224’s into four 222’s.

Mike
 

rescue161

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For mine, I used their method of joining two pieces of coax and added a random length of 50 Ohm coax (RG214) to the RG83. That way, if I ever need to replace a connector in the future, I don't have to worry about the critical length of the RG83.

I would not recommend using any LMR foil type coax on a duplexed antenna harness. Use RG214 instead. The construction of LMR can generate noise on a duplexed system, especially if the coax is exposed to changes in weather conditions (heat/cold).
 
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