Posts in several threads by the more knowledgeable and experienced members of this forum have stated a preference for double braided coax (i.e. RG142, RG214) over braid over foil (such as TM's LMR series). After reviewing the published specifications by Belden and Times, it appears, at least when comparing these two manufacturers products, that the braid over foil design surpasses that of double braid in attenuation, capacitance and VOP. This also appears to hold true when comparing Belden's 9913 to RG214.
I would welcome an explanation of the physics involved and/or the applications that lead to the preference for the double braid design. For the purposes of this question, I readily agree a corrugated shield is superior to both for feedline, but I'm referring to jumpers for cavities, duplexers, diplexers, couplers, short antenna feedline etc.
In the interest of disclosure, I should say that we use LMR and 9913 coax in all our applications with no discernable problems. However, if there's a better way . . .
Henry
Coax shields: Double braid vs. braid over foil
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As I understand it, the foil is prone to noise and intermod generation which , of course, do not show up in isolation specs. My personal favorite for duplexer jumpers is RG142 and silver plated connectors. This is what most duplexer manufacturers use. However, I have seen a lot of repeaters using LMR cables with no detectable difference. When I worked for the government, we went through a site and replaced every jumper in the entire site with superflex hardline. Couldn't tell one bit of difference and the hardline was harder to handle when installing or removing a station.
We Say No To Audio Jumpers.
The Audio Jumpers Are A BIG NO-NO
We Would Never Do That.
Yes- I actually saw an installation where they really did use audio cable! It was on a lowband Desktrac. It was installed by one of the "more reputable" shops in town- this being said with MUCH sarcasm! I just hope that they didn't do this and it was already in place being the equipment was purchased used.
This was replaced with UltraLink cable, since it was 33 MHz. and only running a total of about 1-1/2 feet. I'm sure that even Crap Shack cable would have been better.
This was replaced with UltraLink cable, since it was 33 MHz. and only running a total of about 1-1/2 feet. I'm sure that even Crap Shack cable would have been better.
Braid over foil type foam cable is attractive because of its low loss, good shielding properties and low initial cost. These cables often have a stiff solid center conductor.
These properties make it an excellent antenna feed line choice for non repeater type stations, provided that the antenna connector is well sealed. Foam cable has a tendency to suck in moisture when temperature changes occur increasing the losses. Solid dialectic cable on the other hand has less of a problem with moist.
For use with repeaters, this cable will have problems over time because of degradation causing noise. The braid and the foil shield are made out if different materials, causing noise problems over time. Sharp bends, twists and temperature cycling can crack the internal foil cover creating another source of noise in repeater use.
These same problems may also show up when this cable is used for jumpers between repeater and duplexing equipment. Also, because of the stiffness of the cable, additional stress is applied at the equipment coax connectors.
Generally the best cables to use are the silver plated double shielded types with silver plated connectors for jumpers and solid shield Heliax type feedline to the antenna.
But in some cases depending on the application, where loss or noise is not a concern, even lowly plain RG58 will do.
Nand.
These properties make it an excellent antenna feed line choice for non repeater type stations, provided that the antenna connector is well sealed. Foam cable has a tendency to suck in moisture when temperature changes occur increasing the losses. Solid dialectic cable on the other hand has less of a problem with moist.
For use with repeaters, this cable will have problems over time because of degradation causing noise. The braid and the foil shield are made out if different materials, causing noise problems over time. Sharp bends, twists and temperature cycling can crack the internal foil cover creating another source of noise in repeater use.
These same problems may also show up when this cable is used for jumpers between repeater and duplexing equipment. Also, because of the stiffness of the cable, additional stress is applied at the equipment coax connectors.
Generally the best cables to use are the silver plated double shielded types with silver plated connectors for jumpers and solid shield Heliax type feedline to the antenna.
But in some cases depending on the application, where loss or noise is not a concern, even lowly plain RG58 will do.
Nand.
RG58 For Repeater Cables To A Duplexer "NO-NO"
RG58 Cable To A Duplexer Is A Poor
Idea Of Good Workmanship.
The Radio Works But?
We Would Never Do It.
Re: RG58 For Repeater Cables To A Duplexer "NO-NO"
Perhaps you should read the complete text again.Susan157 wrote:
RG58 Cable To A Duplexer Is A Poor
Idea Of Good Workmanship.
The Radio Works But?
We Would Never Do It.
There are situations where single shielded cable works fine. Motorola supplies two RG58 jumpers with their R1225 repeater and also did with their GR300 cabinet. If the split is wide enough, and the cables are not bundled together, there may not a problem.
Also Sinclair for years used cheap single shielded RG8 in some multi-coupler applications.
TX/RX systems in one of their notes suggest that if you run single shielded cable, just to make sure that they are kept apart if the run is to long to prevent coupling between the two cables.
Nand.
Since we don't use RG58 (except for coax that's part of a mag mount), I think I'll stay out of that discussion.
I understand the noise issue braid against foil can create, especially since they are typically dissimiliar metals. This is something I hadn't considered. But, wouldn't there still be noise generated, although less, when two braids rub against each other; begin to age and deteriorate at different rates; have different impedances due to different bend radii, or is there a dialectric material separating them?
Time for some testing: Any recommendations for manufacturers of RG214 and RG142?
Henry
I understand the noise issue braid against foil can create, especially since they are typically dissimiliar metals. This is something I hadn't considered. But, wouldn't there still be noise generated, although less, when two braids rub against each other; begin to age and deteriorate at different rates; have different impedances due to different bend radii, or is there a dialectric material separating them?
Time for some testing: Any recommendations for manufacturers of RG214 and RG142?
Henry
There are all kinds of differences even in just RG214.
The center conductor can be either copper or silver plated copper. The braid can either be copper, tinned copper and silver-plated copper.
The outer jacket can be made with a large variety of materials. Some are flame retardant, some are made with material that leaches into the cable, etc.
With quality silver-plated cable, there is little noise developed between the two layers of braid because of good tight contact between the braids. With the proper covering, the changes of oxidation are kept low.
Other items to look for are the number of strands that the braid is made with. You can get near 100% shield with a single or very few strands wrapped around the cable, but you cannot attach a connector to a few strands very well.
My guess is that any cable with a MIL spec on the jacket is a good cable. But keep in mind that not every situation demands the highest quality cable. Also don’t overlook the quality of the connectors used. Again silver plated connectors are best.
Nand.
The center conductor can be either copper or silver plated copper. The braid can either be copper, tinned copper and silver-plated copper.
The outer jacket can be made with a large variety of materials. Some are flame retardant, some are made with material that leaches into the cable, etc.
With quality silver-plated cable, there is little noise developed between the two layers of braid because of good tight contact between the braids. With the proper covering, the changes of oxidation are kept low.
Other items to look for are the number of strands that the braid is made with. You can get near 100% shield with a single or very few strands wrapped around the cable, but you cannot attach a connector to a few strands very well.
My guess is that any cable with a MIL spec on the jacket is a good cable. But keep in mind that not every situation demands the highest quality cable. Also don’t overlook the quality of the connectors used. Again silver plated connectors are best.
Nand.