In an office trailer beside a truck weighing scale the use of the two way radio (CB I guess, but I'll double check next trip)that the dispatcher uses at one end of the 34 foot trailer knocks out the phone the guy on the other end is using every time it's used. The antenna is on the roof over the dispatcher's end, and these are cord sets I believe, although I better double check that, too. (I was hurrying off when they dropped this gem on me)'

All wired in unshielded Cat 5 under the trailer. It doesn't just bleed over the phone while mike is keyed, but actually cuts off the connection. Any thoughts?

Hrm...sounds like an interference problem. First thing to check would be if any wires are nicked or damaged at any point. Also a long shot, but, any sort of battery chargers in the area?

What's the history here. Did this problem just start or has it been happening all along? What kind of radios are these (can't believe they are CB's) and what are they used for? EXACTLY what kind of phones are being used?

Without this information it would be just a guessing game.

-Hal

Several things can cause this problem.

Radio caused problems:
Has this always been a problem since the beginning? Has anything changed? Especially up on the roof. If this is a magnetic mount antenna, is there a uniform piece of steel underneath the antenna? Something roughly about the size of 3 feet by 3 feet. That wold be the ground plane for the antenna.

Check VSWR between the radio and the antenna. If there is a gross mismatch between the antenna and the radio, the RF energy is going to go everywhere else than out the antenna. Check for loose connections, damaged cable, jury rigged connections, wrong antenna i.e. cell phone external antenna for CB etc.

Phone side problem:
"Land line" I assume you mean a newer phone system that can have multiple phone lines, intercom, hold function, speaker phone, all in a little plastic housing with 4, 6, or 8 conductors feeding it. If so, these local systems are very susceptable to strong Electro-Magnetic Interference (EMI). Do all of the lines light up when this happens? Even the ones not connected. Your best option is try to eliminate the source of interference. Next route would be to stop the interference from entering the phone system. This includes running the phone cable in a grounded steel conduit to as close to the phone as physically possible.
Adding a ferrite choke to the phone cable as close to the phone as possible. Putting the phone in a steel enclosure to shield it.

Larry

poorguy,
I'd go along with LarryC's comments.
Check the coaxial cabling to the antenna, first off.
Signal leakage and SWR problems are rife with dodgy connections.
For some odd reason, CB installations seem to have a lot of suspect wiring.
Other side of the coin, if this is a 27MHz set, I'd advise a Low-Pass filter be fitted between the transciever and the antenna.
This can cure a lot of EMI problems, it sounds like there could be a Harmonics issue with the transciever.

I'm going to make a wild guess here.

The 2-way radio is not CB, it's a 900 MHz trunked system, and the cordless phones are also 900 MHz FM. The phones aren't designed well enough to reject higher-power adjacent channels, and they choke.

Solution: None.

Am I close?

i will be back at this facility in a few days and will get the specifics. Sorry to post this with so few details but glad for the feedback so I will know what to look for. BTW, this is a brand new install and has done this from the moment it began operating.

I believe he said that the phones were corded. Also, now we know that this has been a problem from day one.

I wouldn't knock myself out over this, I doubt there is anything that will help other than moving the antenna or changing the phones. The RF is getting into the phones themselves and causing severe problems, some phones are better with RF than others. Not much you are going to do other than putting more distance between them.

-Hal

*** bump ***

Was there any resolution to this? Any further info?

Thought I would have gone back to this place by now, have to finish a small project there. We are so busy now, however, that I haven't been able to get there. It is not an earth shattering problem to them, but I would like to figure it out for my own education and curiosity and also so I can convince them that I am "some ol' smart". They don't have to know you guys helped me figure it out!

They will be screaming at me to finish their little project soon, and I'll be sure to get you some more facts.

Was back to this job today, it is a CB, using CH 26, and the dispatcher said he had someone check the radio all out for "RF leakage", said it was OK. Also, he said that sometimes when someone is on line 1 and a call comes in on line 2 it cuts off line 1. Guess there's a little more going on than they first thought. These ARE corded sets for multi-lines and I would need Sherlock Holmes to get the right info out of these guys, esp. when they are busy. They aren't too concerned about the problem and I am real busy, so I am not going to see it resolved I guess.

Sorry this little "brain teaser" from real life wasn't more fun, thanks for the input.

The best bet is to try separation of the phone wires if they are near the antenna/feedline. Next would be curative measures at the phone end. The ham radio magazine "QST" has ads for telephone filters and phones that are bullet proofed. The magazine can probably be obtained at your local library or just do an internet search. I don't know if the filters are designed for commercial type phones or just residential. In either case, most of the folks selling these devices used to work in the telco/communications industry and might be able to give you some detailed information specific to your problem.

It's a sad thing that there are no mandatory RF immunity standards in this country; we are the only industrialized country in the world without any. I used to hear this type of complaint just about everyday and the complainants don't want to hear they have to cure the problem. I worked for the FCC for 30+ years in the Saint Paul MN field office, so I am quite familiar with the issues.

poorboy,
Is there some sort of a phone-patch on this between the phone and the CB transciever?

There shouldn't be.. phone patches are not permitted in the CB service.

Check to make sure that they have a good ground for the antenna/tranceiver. Also make sure that they are not using any amplifiers with the radio, as the ones that are available for CB are generally of poor construction, and are highly illegal to possess or use.
http://www.kyes.com/antenna/interference/tvibook.html http://www.sncmfg.com/telecom/noise_protection/rid.html

techie,
I've got a heap of CB manuals here that state how to (in the US) hook up a CB transciever to a phone patch.
What's your take InspectorE?.

Right from the horses mouth...

Title 47: Telecommunication
PART 95—PERSONAL RADIO SERVICES
Subpart D—Citizens Band (CB) Radio Service
How To Operate a CB Station


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§ 95.420 (CB Rule 20) May I connect my CB station transmitter to a telephone?
(a) You may connect your CB station transmitter to a telephone if you comply with all of the following:

(1) You or someone else must be present at your CB station and must—

(i) Manually make the connection (the connection must not be made by remote control);

(ii) Supervise the operation of the transmitter during the connection;

(iii) Listen to each communication during the connection; and

(iv) Stop all communications if there are operations in violation of these rules.

(2) Each communication during the telephone connection must comply with all of these rules.

(3) You must obey any restriction that the telephone company places on the connection of a CB transmitter to a telephone.

(b) The CB transmitter you connect to a telephone must not be shared with any other CB station.

(c) If you connect your CB transmitter to a telephone, you must use a phone patch device with has been registered with the FCC.
====================================

This is the "plain english" cb rules that were adopted quite some time ago. The upshot of telephone interconnect in cb is that one of your own transmitters has to be at the connection point. If a cb station is going to connect five different users, each of the five would have to provide a transceiver. The lawyers essentially wrote the rules this way to prevent someone from becoming a telephone system. It would have cut into the $$$ that the regular telephone companies were making with the old style mobile telephones. You've got to remember, this was long before cellular telephones. Some folks carried pagers, but not that many. And, ships at sea still used manual morse code to communicate.

You're right.. I was thinking of automatic patches.. I may also have been thinking of FRS and MURS, for which connections to the PSTN are not allowed.. [ 95.193(e), 95.1313 ]