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Coax recommendation portable UHF base station

Posted: Tue Sep 05, 2017 9:10 am
by RadioSouth
Hi guys,
Looking for coax recommendation. Setting up a portable VHF/UHF base station with Diamond X-30 on collapsible tripod. Coax run would be 50' and I'm looking for something with a stranded center conductor to minimize breakage. RG58 looks like a 5dB loss, RG8X is a little better. Anything up to the diameter of RG-8/U would be good as long as it's flexible and has a stranded center conductor.

Re: Coax recommendation portable UHF base station

Posted: Tue Sep 05, 2017 11:37 am
by W3AXL
LMR240 ultraflex wouldn't be a bad idea. If you wanted lower loss you could bump up to LMR400 UF. 240 is the size of RG8x and 400 is the size of RG8.

If I wanted portability and low loss I'd put my money with LMR240 UF. At 50' you'd have 3dB of loss on 440. LMR400UF would be ~1.5dB loss at 440.

Re: Coax recommendation portable UHF base station

Posted: Tue Sep 05, 2017 11:56 am
by Astro Spectra
Mechanical ruggedness is much more important than loss for a portable set up. Everything is going to get banged and slammed, so a solid cable is critical. I'd use RG-213.

The X30 is not super rugged but OK. I've used them for transportable systems but they're quite narrow band. I had to use a network analyser to adjust the length of the VHF element to cover the 136-144 MHz range with acceptable return loss. UHF will not work out of the amateur band without major surgery.

Best add a length of woven polyester expanding braid cable protection (hold in place with cable ties) over the coax where it enters the X30 mount tube to avoid wear and tear on the coax outer.

It's a dog assembling the mounting so I use a short length of coax with a PL-259 permanently attached to the antenna (tighten with vice grips) and hanging out with a type N female with a plastic cap. The avoids over using the single bolt that holds the mount tube in place as the thread in the muck metal boss casting is fragile. You may want to Araldite the whole tube in place on the antenna boss or at least Locktite the bolt to stop thing working lose.

With these precautions I've had unmanned crossband relays stay in place using the X30 on a guyed thick walled alloy tube 10' mast in 100mph plus winds on hilltop sites.

Last but not least throw some 1" ratchet strap tie downs in your kit. I pack three to use as mast guys but you can always wrap one around the mast section when fastening to something like a porch upright or sign post.

Re: Coax recommendation portable UHF base station

Posted: Sun Nov 19, 2017 5:19 am
by Jim202
The big issue with any coax cable is the interface between the cable and the coax connector. Using regular type N or PL-259 connectors is that your relying on just the shied to secure the connector to the cable. It is not very strong and won't hold up long to much movement or twisting.

Wedge lock type connectors is a much more secure connection. But they cost and delivery is not that good. Most places don't stock them.

So your next choice is to go with a crimp shell and solder the center pin. These crimp connectors seem to stand up far better than just trying to rely on pinching the shield or soldering the shield to the shell of a PL-259 connector. Draw back is that you need the crimp tool.


Re: Coax recommendation portable UHF base station

Posted: Thu Dec 21, 2017 1:29 pm
by Karl NVW
There's nothng worong with using "the good stuff," either Superflex or Heliax. Those connectors don't rely on the cable braid for mechanical strength. I'd suggest just a short pigtail of 1/4" inside the mounting tube with an N connector at the bottom. Then make up an appropriate length of 3/8" LDF to get over to the transportable base station. Buy one of the outdoor power extension cord weatherproof covers and tie-wrap it to one of the tripod legs. Easy to break down and transport, low enough loss to get the signals in and out, and low cost.

Re: Coax recommendation portable UHF base station

Posted: Thu Dec 21, 2017 10:22 pm
by doi
I use H155 for portable applications. It's light, low loss - compared to similarly thick cables, stranded central conductor.