types of coax

[brin831]

hey guys i wanted to start a little discussion, really because i had questions more than anything ...

i think with a little time reading most of us know the difference between rg6, rg58, rg8/lmr400, then there are larger gauge and hard line cables as well

my question is more about some of the install cables ... i always see brown/tan color coax on various duplexer cavities as the jumpers what is that stuff called and what are the advantages of it vs regular rg8/58 etc.

thanks

 

[KT4HX]

hey guys i wanted to start a little discussion, really because i had questions more than anything ...

i think with a little time reading most of us know the difference between rg6, rg58, rg8/lmr400, then there are larger gauge and hard line cables as well

my question is more about some of the install cables ... i always see brown/tan color coax on various duplexer cavities as the jumpers what is that stuff called and what are the advantages of it vs regular rg8/58 etc.

thanks

I've worked with these before. If memory serves correctly (and that is almost always debatable! :wink, the ones I handled were RG-174 cable. They are often used for such applications because of their small size and flexibility. As far as I know there is nothing particularly special about them. Since they tend to be very short, the losses are negligible.

 

[prcguy]

Your probably referring to RG-142 double shielded with silver plated braid and center conductor. This is primarily used on duplexers for the double shielding which provides more isolation than single shield cable for this application.

RG-142 is about the same diameter as RG-58 and the brown color is from the particular flavor of Teflon used on the outer cover. This cable is stable for use up to about 12GHz.
prcguy

hey guys i wanted to start a little discussion, really because i had questions more than anything ...

i think with a little time reading most of us know the difference between rg6, rg58, rg8/lmr400, then there are larger gauge and hard line cables as well

my question is more about some of the install cables ... i always see brown/tan color coax on various duplexer cavities as the jumpers what is that stuff called and what are the advantages of it vs regular rg8/58 etc.

thanks

 

[brin831]

yes i think looks like it after a quick search ...

i would imagine there are larger sizes as well like an rg8 equivalent ??

 

[KT4HX]

Your probably referring to RG-142 double shielded with silver plated braid and center conductor. This is primarily used on duplexers for the double shielding which provides more isolation than single shield cable for this application.

RG-142 is about the same diameter as RG-58 and the brown color is from the particular flavor of Teflon used on the outer cover. This cable is stable for use up to about 12GHz.
prcguy

Yeah, that's it! Told ya my memory fails me way too often! :lol:

 

[davidgcet]

LMR400 is pretty close to the specs of 1/2" hard line so either it or 1/2" super flex would be the equivalent to RG-142 in a larger size. depending on frequency, in a RX only situation you can use pretty much any 50 ohm cable for a short run, but larger cables are better for long runs. higher freqs and longer runs it is always advisable to go up in cable size. if you need flexibility at the radio end of the line, but have a long run to the antenna, then you use a smaller cable for a short jumper. each connection point will lose about 1 db give or take a little, but this is less than what you lose trying to run 100' of RG58!

 

[kb0nly]

RG-400 is also used on many duplexers... I see it on almost every Motorola i have worked on, its kind of a sem-transparent tan/brown insulation.

 

[jim202]

The reason that coax is being used is because of both the frequency being used and the TX RF power
that can be present at the combiners. The cable is in fact teflon insulation on the center conductor
and the outer jacket may be of different material. Never bothered to look at the spec sheet.

What I found over time is that the normal coax will heat up and the center conductor will then migrate
to the outer double shield on the RG8 and RG214 type cables. When this happens you end up with
a high SWR that just adds to the problem. Given enough time, the center conductor will short to
the shield and then you have even more problems.

The heating of the coax cables became apparent with the installation of 900 MHz paging transmitters
when they first came out in the mid 90's or so. Unless you were using the teflon cables, your
transmitting coax cables tended to melt away inside the equipment racks and combiners. Once
you made it to the larger coax cable, everything was fine. Wish I had a $1 for every cable I had to
replace along those days of the learning curve.

Hope this provides you with the reason for those funny looking semi clear jacketed cable.

Jim

 

[prcguy]

RG-400 is a stranded center conductor version of RG-142. Its also used on aircraft where flexibility and vibration are a problem..
prcguy

RG-400 is also used on many duplexers... I see it on almost every Motorola i have worked on, its kind of a sem-transparent tan/brown insulation.

 

[zz0468]

...each connection point will lose about 1 db give or take a little, but this is less than what you lose trying to run 100' of RG58!

You missed a decimal point. Quality connectors will cause less than 0.1 db loss per connector, if installed correctly, at frequencies most people are likely to be operating at.

 

[davidgcet]

yeah good connectors rated for the desired band and installed properly are .1db or less, but how many folks spend the money for a quality connector on a non-commercial system? Anritsu says figure it on 0.28db per connector when sweeping a line if the actual connector loss is unknown, and this is for connectors installed by folks who know what they are doing. so 1db is not far off at all for a 2 connector point, especially since so few untrained folks actually put a wrench on the connector and tighten them to each other! i can't count the number of spraying problems and poor range issues were solved by turning a connector 1/2 turn tighter. sadly, not all of these are done by untrained folks, i know a few "techs" who don't do it either.

i love using my unidapt kit because of ease of switching between various connectors for testing. but when we sweep lines for cellular/pcs companies we are strictly forbidden from using them just due to the fact that if the jumper turns it can back the tension off the joint and create a false reading on the sitemaster.

EDIT: when i say untrained, i mean folks who neither install RF cables for a living nor have had proper instruction on connector installation. i honestly never thought about it before i got into doing PCS sites in 2001, then once i was trained in using a sitemaster i started to see how easy it was to screw up a connector that passes the open/short ohmeter test! prior to that i always assumed it was good if the connector was tight, not shorted center to shield, and had near zero ohm continuity center to center and shield to shield.

 

[zz0468]

yeah good connectors rated for the desired band and installed properly are .1db or less, but how many folks spend the money for a quality connector on a non-commercial system...

Well, I'm trying to bust the myth that rf connectors are automatically 1 db loss each, because it's simply NOT true. Making blanket assessments that include poorly installed connectors is needlessly misleading.

As to the sitemaster, yes, it's a marvelous instrument. I won't use unidapters for critical measurements either, but after seeing many many statements here at RR claiming that coaxial connectors have around 1 db loss, I decided to measure them, BNC, UHF, mini-UHF, N, and SMA. Below 1 GHz, figure the loss at closer to 0.1 db each. Even low quality Radio Shack UHF connectors have minimal loss from VHF down.

If you're going to include poorly installed connectors in a blanket statement, than maybe 1 db isn't enough. It could be 10 db. Or 20 db. Or...?

 

[davidgcet]

keep in mind i did NOT say 1db per connectOR, i said around 1db per connectION give or take a little. it was not a blanket statement saying all connectors are 1db of loss.