Testing Coax 1

[zenlikeme]

Hey there. I work for a small company that employs WLANs and Point to Point Bridges. We often pull our own cable. Mostly LMR-400. Can anyone tell me a good tester. I'm looking for something that will verify terminations are good and that the cable hasn't been compromised. Something that will confirm the perfomance.
thanks

 

[wires]

Two ways to do it.

1. Time Domain Reflectometer. A TDR will show variations in impedence which (depending on instrument sensitivity and operator skill) can show a multitude of problems. Here is a decent overview:

http://www.tscm.com/riprcop.html

. TDRs are best at finding fairly massive problems.

2. Performance testing using a Spectrum Analyzer and a test signal. The test signal can either be broadband noise or a swept signal. This sort of testing is more likley what you had in mind when you said "Something that will confirm the perfomance."

Here is a article on using noise:

http://mrtmag.com/mag/radio_broadband_noise_generator/

These people make some affordable spectrum analyzers:

http://avcomofva.com/products/default.asp?page=psa1727b

Also affordable is the LPT-2750 has a optional tracking generator:

http://www.lptech.com/

 

[zenlikeme]

Thankyou! That was very helpful. Can you recommend a user friendly handheld TDR? It'd be nice to have something that any of my techs could easily use.

thanks

 

[wires]

Most current field type TDRs are designed to test at CATV frequencies. Here are some links to both Riser Bond and Tempo:

http://www.riserbond.com/Industries/CATV/catv.html

http://65.36.183.19/prod_subcat.cfm?cat=950

Since you are working at almost twice CATV frequency you won't find much except lab grade stuff to confirm performance at 2.4 gHz in a TDR. If you really want check the performance of a installed cable at 2.4 gHz a RF test with a spectrum analyzer is much more reliable.

Personally I use a Tektronix (now Tempo) TS90 TDR for general wire troubleshooting. I got it off eBay for under $200 and it works well on almost any type of cable (even romex). For more difficult problems I use a LP Tech LPT-1250 spectrum analyzer and a old Avcom sweep generator. None of these instruments will give much useful information to a untrained user.

Since the RF industries are not as well defined as LAN testing there is no easy to use device that does exactly what you want it to do. The Riser Bond 1205CXA and the Tempo TV200 are about as close as you are going to get for ease of use. I have my doubts as to their usefulness for finding anything but gross faults at 2.4 gHz.

eBay is a good place to look for test equipment. Be sure that any equipment you buy is still supported by the manufacturer.

 

[zenlikeme]

Thanks again. Very Helpful.

 

[daronwilson]

Very sound advice.

One thing that i see a bit frustrating (though comforting to us old guys with experience) is the desire to have a 'go/no-go' test for things. In fiber, most of my guys just want to push a button and see if it passes. I personally prefer to look at the OTDR shot as well and see if there are any other issues, see how the connector loss looks, etc.

Very similar for the RF portion of things. I carry a spectrum analyzer with tracking generator for the RF stuff i need to do, but as wires stated the equipment is a bit more complex and requires some experience to understand the results.

If you are serious about the RF side of things, an Anritsu sitemaster or similar piece of test equipment may be what you need. When we do 450Mhz or 800/900Mhz SCADA work i depend on AEA antenna analyzers and the trusty Bird wattmeter with the appropriate slug to determine system performance. Generally the engineers want to see proof of performance of the entire system, which requires a bit more testing than just the coax.

So many tools, so little time and money....

good luck!

Daron J. Wilson, RCDD
Solving 'Real World' problems

 

[cwc3]

hey you could put 75 ohm or 52 ohm terminator
on the end of each run and throw a meter across each
run that ia a go no go!

 

[daronwilson]

Well yes, but only for DC continuity. A very nice piece of cable at DC could be pretty much useless at 5 Ghz. I personallly do a DC continutiy check on every patch cable i make if i have both ends available, just to make sure I have continuity and no short. For HF and VHF stuff it's not such a big deal, but at UHF and above it is prudent to sweep it in some manner and make sure the installation is sound.

We do use the termination test with a Paladin tester on controlnet cabling. Several variable speed drive controllers and PLC hardware use RG6 as a medium and their proprietary protocol for communications. As such, we can't really do much testing except to put a terminating resistor on the end and make sure we see it with the tester.

Good Luck

Daron J. Wilson, RCDD
Solving 'Real World' problems