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Commercial Radio Antennas Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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  #21 (permalink)  
Old 07-10-2012, 7:16 PM
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Here is about an inch section of the cable i cut off the end...
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  #22 (permalink)  
Old 07-10-2012, 9:52 PM
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Quote:
Originally Posted by centuryvrproductions View Post
Here is about an inch section of the cable i cut off the end...
Calibrated eyeballs say this stuff is 75 ohm.
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Old 07-12-2012, 1:45 PM
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looks like commscope cable.
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Old 07-13-2012, 7:26 PM
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as soon as i find time, i will make connectors and try it out
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Old 11-06-2012, 6:46 AM
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Here's a quick question :

I'm in the process of installing a GMRS repeater in my home due to the rather high location of the building. (on top of a mountain). To start the "project", I ran approximately 125' of LMR-400 (actual Times Microwave brand, not an off-shore knockoff) and terminated the " antenna end" (currently coiled up in the attic) with an "N" connector soldered on.... I wanted to run larger "Heliax" hard-line (min. 7/8", but decided to cut costs a bit -- hopefully not a long-term mistake)

I was forced to install the repeater in the basement due to cooling concerns and also wanted it install it in a rack fairly close to my generator, etc... , so I simply ran the feedline in a spare "attic to basement" Carlon "Innerduct" run that I had installed when I did my electrical rough-in (prior to drywall installationk, I ran alot of emt & pvc & innerduct for "future use" <G> along with a few hundred thousand feet of wire between cat6, RG6QS, fiber & coax for cctv cameras in addtion to ton of NM for lighting & branch ckts.etc. ) . Alongside the LMR, I ran a piece of #4 THWN stranded copper for grounding/bonding and left a coil at each end.

Here's my dilemna: I want to add an additional UHF repeater and a VHF (both bus. band) repeater at the house. I have plenty of spare conduit and/or innerduct running from attic to basement, but don't know whether or not to use LMR400 again, spend the extra $$ for Andrews Heliax -- or -- I happen to have 1000' of Belden RG-11 PVC jacketed 75 ohm coax and tooling to install compression fittings on it ("F" connectors though... so I'd have to adapt over to "N" or other connector to attach to the radio gear).

Any suggestions? The VHF repeater will not be going in for a year or so. Until then, I'll probably be installing a simplex base with a more economical antenna as a temporary solution. (Eventually, I'll probably be installing Quantar repeaters w/ Super Station Master antennas for all 3 systems.)


And.. Assuming I rule out hardline completely: How would 100-150' of RG-11 compare to LMR-400 in terms of impedence matching/swr/attenuation - loss / etc??

Thanks in advance !
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Old 11-07-2012, 7:25 PM
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You are using 75 Ohm Cable on a GMRS Repeater?
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Old 11-07-2012, 9:52 PM
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LMR-400 is a bad coax choice for duplex repeater use. There are serious issues with passive intermod when using LMR-400 for duplex operation due to the foil over braid shield design. Use the Andrew Heliax and you shouldn't have these issues. The heliax will also give you much lower loss over the same size run.

You can often find "end of reel" lots on the heliax for nearly what you pay for LMR-400 on a per foot basis at hamfests or on eBay. "End of reel" doesn't always equal short runs, often they are over 100'+ lengths. While these lengths are not enough for a commercial install on tall towers, they're plenty long enough for many installations.
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Old 11-10-2012, 11:05 AM
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Quote:
Originally Posted by rpurchases10 View Post
And.. Assuming I rule out hardline completely: How would 100-150' of RG-11 compare to LMR-400 in terms of impedence matching/swr/attenuation - loss / etc??
You can calculate loss here: Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator

If you use 75 ohm coax without making any attempt to match it, you'll end up with moderate vswr issues. Performance wise, it may show up on a repeater as desense because a duplexer performs best when it's properly matched.

The loss calculator above does not take into account additional loss caused by vswr problems, which could be substantial.
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