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Author Topic: Source Double-Shielded coax? RG400?  (Read 754 times)
K0IPG
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Posts: 252




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« on: September 13, 2003, 07:39:01 PM »

Hello all,
   I'm working on a repeater project, and am looking for about 20' of some double-shielded coax (such as RG400), but I'm having a hard time finding anyplace that sells this. Are there any types of coax comperable to RG400 that I might be able to find more readily? Note that since this is for a repeater project, I really do need double-shielded, and foil-type shielding won't work.

73
Dan K0IPG
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M1ACQ
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« Reply #1 on: September 13, 2003, 07:56:37 PM »

Have you considered the Andrews Heliax range ?? they are exceedingly low loss.  Can be awkward to route as the shield is solid corrugated copper and it costs a fair bit although you can sometimes pick it up second hand.

Frank
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K0IPG
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« Reply #2 on: September 13, 2003, 08:28:15 PM »

Well, I'm really not looking for low-loss. Each run is only going to be about 8' (from the radio to the bulkhead connector on the side of the cabinet). And heliax isn't going to work, because I need something small-diameter. Instead of wasting valuable space in the chassis, and putting up with losses from connectors, I'm just going to solder the coax directly into the radio, and then I'll only have 1 "splice" inside the cabinet.

When I've built repeaters in the past, it's involved drilling 2 holes and installing 2 SO-239 connectors (one for TX, one for RX) in the side of the case. Then, installing hoods on the back of those connectors. Then running jumpers from the radio to bulkhead connectors on the side of the cabinet. This worked fine, but the signal has to pass through 5 separate connectors before it ever leaves the cabinet. And, the hoods on the backs of the SO-239's prohibit me from installing a PL board or anything (there isn't much space in the chassis).
So, I want to run a piece of small-diameter coax directly from the radio to the bulkhead connectors (making 2 "pigtails" on the radio).
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W4TYU
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Posts: 518




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« Reply #3 on: September 13, 2003, 09:08:49 PM »

Talk to Press. The Wireman.

http://www.thewireman.com

Ole man JEAN
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K0HZI
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Posts: 470




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« Reply #4 on: September 13, 2003, 09:17:24 PM »

Dan, Have you tried some of the links listed under "Ham Links", and "Commercial Coax/Wire/Connectors"?   CABLE X-PERTS, INC, Davis RF, Nemal Electronics, The Original Wireman, etc.
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KB0ETC
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Posts: 248




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« Reply #5 on: September 13, 2003, 11:01:57 PM »

You can try Times LMR-400, or even Belden 8268 double sheild silver plated cable.
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K5LXP
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« Reply #6 on: September 13, 2003, 11:25:07 PM »

My preference is Andrews superflex for jumpers in repeater installations.  You can buy it with connectors already attached, and you can't beat a solid copper jacket for shielding.  It's skinny enough to bend wherever you need to fit it in, not like thick hardline.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net
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KB0ETC
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« Reply #7 on: September 14, 2003, 03:27:52 PM »

I think what Mark K5LXP is reffering to is Andrew FSJ4 1/2" superflex.  It is quite flexible!  
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W4QA
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« Reply #8 on: September 14, 2003, 08:52:01 PM »

Belden has a new coax that will fit your application called RF-400.  Try http://www.radio-warehouse.com
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KG4VPV
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« Reply #9 on: September 14, 2003, 09:29:55 PM »

Id go with Beldens RF400.  Not very flexible, but it has great low loss characteristics
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W8JI
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« Reply #10 on: September 15, 2003, 09:17:43 PM »

Back in the 60's I used to use double shielded cable becuase everyone told me I needed to use it.

But as I gained experience, I built dozens of repeaters (some pretty high power) and never needed double shielded cable. I always found the duplexers had much less isolation (100-130dB) than cable "leakage".

I've taped two single shield cables directly together for several feet and measured crosstalk, and it was outside the limit of my test gear.

I'm using foil shielded cable now in a few repeaters, and have no problems at all with cable crosstalk or noise. The system is limited by the six cavity Wacom duplexer notch, not cable crosstalk.

73 Tom
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KF4QVD
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Posts: 17




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« Reply #11 on: September 20, 2003, 02:49:24 PM »

You may want to look for some old Belden thick ethernet cable, very popular 10-15 years ago for large computer networks.  Usually came in yellow or blue and is usually laying around many corporate storerooms.  It has 2 braided shields and 2 foils.  Uses standard N connectors but you may have to drill out the back clamping nut a bit, only slightly larger diameter than RG-213.  Solid copper center conductor.

Be sure to inspect the cable for "vampire holes"... places in the cable where a side tap was made when used on a network.

I've used this stuff even for 900 Mhz projects, great for the price.
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