localized interference problem near Sheridan, OR

This is my first post on this forum.

Some of my customers have reported an interference problem at/near the mobile home factory at Sheridan, OR.

Some background:
The radio systems I'm talking about are low-power (FCC licensed pt-15) systems used by mobile home transporters to run their taillights/turn signals/strobes on the back of the house they are pulling without the bother of running a multi-conductor cable up the side of the house to the semi that hauls it. All of the systems operate on 418MHz, but with an individual 4-byte address code to eliminate cross-talk between systems..

When they are at the mobile home builder near Sheridan, the systems refuse to work until they get a mile or 2 down the road. Something is generating a rather large continuous signal on 418MHz in the area. Some people speculate that something at the nearby prison is the source, but I have no hard info, and haven't spent the tme to attempt to locate it.

Does anybody here know of a signal source in that area?

Theatronix said:

This is my first post on this forum.

Some of my customers have reported an interference problem at/near the mobile home factory at Sheridan, OR.

Some background:
The radio systems I'm talking about are low-power (FCC licensed pt-15) systems used by mobile home transporters to run their taillights/turn signals/strobes on the back of the house they are pulling without the bother of running a multi-conductor cable up the side of the house to the semi that hauls it. All of the systems operate on 418MHz, but with an individual 4-byte address code to eliminate cross-talk between systems..

When they are at the mobile home builder near Sheridan, the systems refuse to work until they get a mile or 2 down the road. Something is generating a rather large continuous signal on 418MHz in the area. Some people speculate that something at the nearby prison is the source, but I have no hard info, and haven't spent the tme to attempt to locate it.

Does anybody here know of a signal source in that area?

Click to expand...

The FCC does not list a license in Oregon on 418.000. Is that the exact freq.?
Try entering the info. you know at this site. to find it.
License Search - Advanced License Search

418.0000 is a Federal Frequency and won't generally be found in an FCC Search
(do you have the FCC ID #)

Without looking at a map, my notes have various 41x users in Oregon, including Links from VHF to UHF for the USFS

You also have a Federal Prison in that same band

Theatronix said:

This is my first post on this forum.

Some of my customers have reported an interference problem at/near the mobile home factory at Sheridan, OR.

Some background:
The radio systems I'm talking about are low-power (FCC licensed pt-15) systems used by mobile home transporters to run their taillights/turn signals/strobes on the back of the house they are pulling without the bother of running a multi-conductor cable up the side of the house to the semi that hauls it. All of the systems operate on 418MHz, but with an individual 4-byte address code to eliminate cross-talk between systems..

When they are at the mobile home builder near Sheridan, the systems refuse to work until they get a mile or 2 down the road. Something is generating a rather large continuous signal on 418MHz in the area. Some people speculate that something at the nearby prison is the source, but I have no hard info, and haven't spent the tme to attempt to locate it.

Does anybody here know of a signal source in that area?

Click to expand...

Thanks for the info.

Yes, we are using 418.00 MHz. The system uses mini transmitter and receiver modules from Linx corp. TXM418LR and RXM418LR. If you are interested, Digikey.com sells them. Our FCC id is TSQQUIK-FLAG.

I'm not sure how selective the receiver is, frequency-wise, but it is extremely sensitive. When testing the units, we can typically get over 600-700 feet away from the transmitter before the signal fades out.

If the prison (about 1/4 mile away) uses that frequency, that answers the question, but I'm curious what use they have that is transmitting continuously, since there has never been a time that I know of when the mobile home haulers haven't had a problem in the area.

Unfortunately, I don't have a spectrum analyzer to check it out.

Anyway, thanks again for the info.

I think you'll find that a lot of these short range consumer devices are Part 15 and have sloppy receivers and transmitters. Getting overwhelmed from strong nearby signals is a real possibility. Same thing happens with some garage door openers in the presence of high RF fields.

My unsolicited opinion...

Since the lights are "Part15", this applies...

This device complies with part 15 of the FCC rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

You state the issue clears up after you leave the area, you could get something like this...

RF Explorer WSUB1G | Location Sound

...and sniff around.

Only $130, I have one and I love it. It's not a lab quality instrument, but I understand its limitations and it serves my purpose quite well.

Thanks again for all the info.

MMCKENNA:
I just looked in the manual for the RXM-418-LR receiver, and it doesn't really give the bandwidth, unless "noise bandwidth" is the correct measurement (280KHz). The receiver is a superhet type with a PLL synthesized local osc. so it should have a reasonably narrow bandwidth. They use OOK modulation.

KEVIN C:
That spectrum analyzer looks interesting--I'll have to save up for one, but I wish it would cover lower bands as well as what bands it does do.
-----------------------
By the way, when I upgraded another product, (remote controllers for mobile home placement tractors), several years ago from the previous radio units to the Linx modules, I removed and saved the old units. They are 900MHz band 2-way short-range units designed to be an RS232 link, up to 19200 baud. Made by Comrad company. If anybody is interested, I just want to get rid of them cheap. They're collecting dust and taking up space on my shelves. Each pair was originally about $500.00 as opposed to the Linx units for $8.00 and $14.00 for TX and RX. They also were a LOT larger (about 5" by 3" by 1.25"), and only got about 4 hours on the battery pack. I had them modified by the factory for an external antenna rather than the wire whip that plugged in, and I added a data/power connector to match the rest of the transmitter and receiver units. They come in several different frequency pairs. I probably have at least 8-12 working pairs on hand.

If anybody is interested, I could scan the manual in and send it to you.

Yes, the Federal Correctional Institution in Sheridan is running a UHF trunked radio system. Here is a link to the system information:Federal Correctional Institution Sheridan Trunking System, Sheridan, Oregon - Scanner Frequencies

It would be possible the 418 MHz receivers are getting de-sensed by the control channel of the trunked system nearby.

- Chris

Theatronix said:

If the prison (about 1/4 mile away) uses that frequency, that answers the question, but I'm curious what use they have that is transmitting continuously, since there has never been a time that I know of when the mobile home haulers haven't had a problem in the area.

Click to expand...

Trunked systems constantly broadcast a signal on what's called a control channel. The radios of all the systems' users are parked on that frequency waiting for instructions from the controller. When someone pushes the button on their radio to talk, their radio sends a small bit of data to the controller that identifies it. The controller then sends instructions to that radio, along with all others that are on the same talk group or 'channel', to a separate radio frequency where the transmission actually takes place. This way many different user groups can communicate using a small pool of frequencies. This works because at any one instant only a small number of users are actually transmitting. All of this is orchestrated by the controller computer and is transparent to the users.

That system does not use 418 MHz, but its frequencies are close enough that it could certainly be causing problems for your equipment. You could try doing some drive-bys north-south, and east-west, past the facility and make notes on exactly where your problems start and stop. Map those points out and see if the results are consistent with the theory. Probably nothing you can do if it is the prison radio system. You could file a complaint with the FCC. They may come out to see if the system is compliant with the regs.

.