atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Asked to move a radio with external antenna - Requesting advice

I have been asked to produce a bid to move some equipment from an old office to a new office. PCs, IP phones, stuff like that...

One of the pieces of the puzzle is a Vertex Standard VXR7000 Repeater/Base Station. There is on antenna connected to the unit.

Looking at the jacket of the Coax cable, LMR 400 is the brand. I could not safely access the antenna side.

My saving grace is the radio is going nearer to the antenna and I have a good chance of being able to pull back all cable with the connector on the end and just rerunning it to where the head unit will be.

My middle case scenario is that I can pull the cable back some and would then have to cut it and install a new connector (an N-plug I believe). I was able to pull back the cable some so I am confident I will have enough slack to get to where I need to go. There is quite a service loop on the cable (excess I suspect) and I might actually have enough to cut where this goes into to wall and still have slack.

My worst case scenario is that my guesstimate of slack is incorrect and that I will need to fashion some kind of an extender.

Accessing the antenna side would require a lift rental and some coordination with authorities since I would have to work on the street/sidewalk.

I have worked with Coax for cameras and I know the trick is getting the right fittings and tools for this.

Any advice? I am confident I can do this, just don't want to bite off more than I can chew or get trapped in the "I should have known..." scenario.

Any recommendations for a good tool and fittings would also be appreciated. Been a while since I have done Coax work.

Thank you in advance for your help. ~ Mike

If the length of the antenna cable is changed then the SWR may need to be recalibrated.

I would call an FCC-licensed radio installation company, who have the tools, expertise, insurance, experience in dealing with permits, test equipment, and proper parts in stock.

If you don't have all of those things in that list, I think it would be prudent to sub the job, make a few bucks on the sub, and sleep easy.

If the roles were reversed, would you like Radio Man to move the phone system and install your "RJ45's" ?

By law I don't think you can touch it unless you are a FCC licensed technician since it contains a transmitter. If your customer is using this unit they should have a company that maintains it. I would suggest that you call them.

-Hal

Gentlemen - Thank you for the explanations. I can see now that it is not quite as simple as just moving/cutting the cable. I can see this is out of my league and will likely decline. There are businesses in my community that specialize in business radio systems and I can sleep fine at night referring to them.

Again, thank you for saving me from myself...

@ Arthur - You tipped the scale since if that happened and I saw the aftermath I would respond with "What the hell was this guy thinking...?" I don't want to be on the receiving end of that thought train.

NOW that I am sitting down and THINKING, the Contractor's license we have for Low Voltage does not cover this kind of work so I shouldn't even touch this..

Mike

Technically, you would need a FCC 2nd class radio telephone license to modify the transmitter antenna, including changing the length of the cable since the whole thing is a calibrated resonant circuit. Merritt and Arthur are correct and getting involved would put you in the cross hairs of the local authorities and, most especially, the FCC field office nearest you.

You made a wise decision to back away. Losing this rabbit may be a way to get the moose.

Rcaman

Rcaman -
"You made a wise decision to back away. Losing this rabbit may be a way to get the moose."

Couldn't have put that half as well with twice as many words. ~ Mike

I agree with the conclusion, but to clear up some misconceptions:

- LMR 400 is a type (think, Category), not a brand. Many people make it.
- There hasn't been a second class phone ticket since there was a Bell System.
- Its successor, the GROL, is only valid for maritime, aeronautical, and fixed stations, and not a land mobile (Part 90), GMRS (Part 95), Amateur (97), etc. installation.
- So, who can do what depends on how this repeater is being used. (You don't even need a license to touch a broadcast transmitter these days.) More information is required.
- Typically the length of the feedline shouldn't have a ton of impact on SWR unless it's badly mismatched, in which case they've got other problems.

That said, unless you have the proper crimpers for LMR-400, and a service monitor, don't mess with it. A nice modern system like that will fold back power and not be damaged if there's a problem with the antenna system, but you never know who is going to come looking when it doesn't work right.

One of the other things that has fallen by the wayside is the requirement to post the license next to any installation, but it's good practice and I make sure copies are posted next to anything I'm responsible for, as well as my contact information.

You might suggest they get in contact with whomever is responsible for this system. It got installed somehow (they may have done it themselves.)

I did a lot of (contracted) point to point microwave radio in the late '90s. We were not licensed (we did get "certified" by the manufacturer), but the people we were doing the work for (ATT, Winstar, Art) were, of course licensed.

I'm not sure what the equipment does, but any antenna I've ever worked with has to be pointed at a particular site (terrestrial or satellite) and then tuned in exactly (the actual beam is quite narrow).

If you have to cut the cable and reconnectorize it, you will need the proper tool and connector. But......

If you can't tune the antenna in, don't touch the job.

Sam

Gentlemen - Thank you for all of your input. From what I can determine it is some type of 2 way radio for comms with their tour guides. The antenna appears to be an Omni-directional on a post attached to the roof.

Realizing that I can't really fix this if something goes wrong related or unrelated to my touching this, I declined the job. The water can't get muddy if I don't jump in and I can never be called back on the "it worked just fine until you..." call.

I also, over time, got a vibe from the owner that just made me want to shy away from this even more. He was telling me that all I had to do was drill a hole through the roof (this is on a building he leases from someone) and drop the cable. This town in Hawaii gets 100+ inches, yes, 100+ inches of rain a year and anyone with a lick of common sense knows you don't drill the roof. Just seems like more trouble than profit/goodwill.

He mentioned he had someone else looking at doing this work and I purposefully bid the stuff I could do high to encourage him to use the other guy. Just not a good feeling from this at the end of the day.

I don't hold the classification for 2 way radio as a Contractor in this state. Low Voltage does not cover this so it ended up being a moot point and a means for me to politely decline the radio work allowing us to both save face. ~ Mike