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tomb13

join:2012-07-03
Arlington, VA

[Equipment] Antenna/cable testing

I've recently had a dual band omni antenna and a long run of LMR-400 professionally installed.

The antenna works if I connect directly to it with my modem, but not if I connect to it via the installed cable.

I tested with a separate 100' piece of LMR-400 with pre-terminated connectors plus 10 dB of attenuation to simulate the cable attenuation and the modem worked fine.

I suspect the installed cable is bad, but I want to make sure the installer performs the correct tests when they come back to verify the cable. I think they just did a simple continuity test when it was installed.

Can someone recommend the type of testing I should expect from a professional installer to verify a cable and antenna installation?

Thanks,
Tom


jcremin

join:2009-12-22
Siren, WI
kudos:2

How long is your cable and what frequency are you running over it?


tomb13

join:2012-07-03
Arlington, VA

The cable length is 268 feet of LMR-400. I'm trying to connect to T-mobile in the PCS 1900 MHz band.

The antenna is a Wilson 301101 trucker antenna.


Hahausuck
Premium
join:2003-12-14
kudos:2

268 feet and using lmr-400?!

Your best bet is to call the installer back out. It's their job to make sure the drop works. If it were us, we'd use a tool that measures the SWR or the Return Loss (user selectable) and then if that looked bad, we'd sweep it with the TDR option in the tool to determine where the fault was. Normally we sweep TDR anyways, to determine where all connections, jumpers, or imperfections are (like cable dents/dings or extreme bends or twists).


jcremin

join:2009-12-22
Siren, WI
kudos:2
reply to tomb13

said by tomb13:

The cable length is 268 feet of LMR-400. I'm trying to connect to T-mobile in the PCS 1900 MHz band.

That's going to be about 16db of loss! That's quite a bit of lost signal. Should be pretty close to the same loss as your 100' plus 10db attenuator test, but still a lot of loss. I assume there's no way to shorten the length of the cable?

Like AMD said, the installer should probably be coming back to fix it. If you purchased it from them and paid them to install it, it should be their responsibility to ensure that the cable is working.

tomb13

join:2012-07-03
Arlington, VA

I probably would ask for a quote for LMR-600 if I could start over, maybe next time.

I was considering relocating the equipment and removing most of the slack to reduce the cable length, but when I did my test with the 100' ft of cable and the attenuators, I came to the conclusion that it should be working despite the large amount of attenuation.

I want to know what tests the installer should run before declaring the cable as good when they come back. If they say the cable is not faulty, they are going to charge me a service call fee.

Thanks jcremin and AMD for the advice!


jcremin

join:2009-12-22
Siren, WI
kudos:2

I avoid working with coax wherever possible. Most of my coax is LMR400, but usually only 5 or 10 feet. I think my longest run is 30 feet. So I'm probably not the best one to give any technical advice about what they should test for


Hahausuck
Premium
join:2003-12-14
kudos:2
reply to tomb13

said by tomb13:

I probably would ask for a quote for LMR-600 if I could start over, maybe next time.

I was considering relocating the equipment and removing most of the slack to reduce the cable length, but when I did my test with the 100' ft of cable and the attenuators, I came to the conclusion that it should be working despite the large amount of attenuation.

I want to know what tests the installer should run before declaring the cable as good when they come back. If they say the cable is not faulty, they are going to charge me a service call fee.

In the future, I'd suggest when doing these sorts of things depending on if you are using a BDA device inside the building or not, to spec 1/2-inch coax if your run exceeds 100 feet. I'd feel more comfortable saying 50-feet and longer use 1/2-inch. I really hate LMR400 type cabling to begin with as it is so lossy. For 2-way radio type work, it is good but microwave eh, not so much. Even in the VHF or UHF world, we make it a rule if the run is longer than 100 feet, do not use LMR400, go to LMR600 or larger.

I'd tell them or SHOW them what you did with your mock setup. If they are professionals they should comprehend what you are showing them.

A simple continuity check would entail: center pin to center pin, center pin to shield. You can do this with a digital multimeter on the "ohms" setting. The whole thing should read as close to zero as possible. This is really not a good test to do but it does show you the chances of a short between center and shield are basically zero.

The test they need to do or SHOULD have done if they were 100% serious professionals in the RF world, would be:

VSWR measurement at 1.9GHz

Reading: 1.5:1 or less

--or--

RLOSS: I like 30dB or better. You should expect someting less than 30dB to be possibly problematic.

DTF: I wouldn't worry about a DTF or TDR test with these guys.

Ask them if they have an Anritsu Sitemaster for antenna line testing, or an Agilent Fieldfox, same purpose.

NOTE:
I guess they could use something like a traditional watt meter like a Bird 43 with the correct slugs, but how they would generate the CW 1.9-2GHz signal for testing is, well, good luck doing this outside the lab. That's not the way it is to be done by a field crew.
--
"Above all, I would teach him to tell the truth. Truth-telling, I have found, is the key to responsible citizenship. The thousands of criminals I have seen in 40 years of law enforcement have had one thing in common: Every single one was a liar."
J.E.H.


John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
kudos:5

quote:
Ask them if they have an Anritsu Sitemaster for antenna line testing, or an Agilent Fieldfox, same purpose.
This.