RS485 Noise on FM Transmission

[rwertz]

I changed over to LOR the week after Christmas last year. I noticed a pulsing buzz type sound on my FM radio signal. The level of noise was directly related to the number of changes in light states in my show. I had an extension wire on my FM transmitter antenna and it was ~ 1 foot from my CAT 5 line that ran to the controller. When I moved the CAT 5 line or the antenna extension the level of noise changed. I removed the antenna extension and moved the transmitter away from the CAT 5 and the noise was hardly noticeable.

Has anyone else had this issue and if so, were you able to do anything to prevent it? I have been looking at shielded CAT 5. I might be able to move the transmitter outside my garage and run the audio signal to it using shielded cable. Another possibility is to relocate the RS485 converter outside and run shielded RS232 cable to it.

Thanks

[Denny]

What FM transmitter are you using? I have a Ramsey FM25B. The first year I used it, I had the audio cable connecting it to the computer too close to an extension cord and got some noise, but when I moved the cable, it disappeared. What is the reason for the extension on your antenna? Is the signal too weak?

[rwertz]

So far, I’m using a C. Crane transmitter. The antenna extension was an attempt to get a better signal while still using a legal transmitter (but maybe not legal field strength). Since it was horizontal I wasn’t really that attached to the extension idea, and it only made a minor improvement.



I was able to significantly reduce the noise by relocating the transmitter and wires. But, once I knew what the noise was, I could still hear it on the transmission.

[Steve Constantino]

Here is something you can try. It mite make it worse or it may solve the noise problem or even no change at all. It worked for me.

What you need to do is try grounding the FM transmitter. Take a wire and run it from the audio input ground or the antenna's shield on the transmitter and the other end to what ever AC ground you can find at your audio source. example(pc power supply ground)

This mite help

Steve

[rwertz]

I hadn’t thought about grounding, probably because the C Crane has a plastic case. I’ll have to crack the case open and see if a ground point jumps out at me.

Thanks

[Steve Constantino]

You can try the audio ground or the DC power ground.

Steve

[Jeff 1S.A.H.D.]

I have a CCRANE and tried to copy what you are hearing,
Is the red light flashing during your show if so you may want to
try to lower the volume down maybe that is what you are hearing

don't hear a thing during the show a little noise when there is no sound playing

does it happen during the day or night
Because in my area there is a lot of day time interference


good luck


http://www.radio-locator.com/cgi-bin/vacant

Jeff

[rwertz]

I’m familiar with the red light and the distortion from over driving the input. My noise is definitely coming from the serial communications.

Here is a description of the worst case condition (with the CAT5 close to the transmitter antenna / audio lines): At the beginning of the song, when things are slow, you don’t even notice the noise at quiet points in the song. Once the light activity picks up, the noise is noticeable at moderate sound levels in the song. The noise level has a direct correlation to the light activity.

Once I put some distance between the CAT5 cable and the transmitter the noise was barely noticeable. If I didn’t already know where it was coming from, I’d probably blame it on normal interference.

If I keep everything separated, I’m sure most people wouldn’t even notice it. This is definitely not a show stopper. But I’d like to try to knock it down some more.

I only used LOR for a short period after Christmas. So I didn’t get to pursue these issues too far. I could always hope that next year’s configuration will make everything better. I’m just never that lucky.

Thanks everyone.

[Steve Constantino]

Did you try grounding it?

Steve

[rwertz]

Steve Constantino wrote:

Did you try grounding it?

Steve

Unfortunately, I’ll have to wait till I get set up for Christmas to try too much. The lights are all packed away and the PC has been returned to the family room to resume its life as an AIM terminal.

Although Halloween would be an excellent opportunity to work any bugs out before Christmas. We’ve got our eyes open for some pumpkin blowmolds.

Thanks

[Steve Saunders]

Just a thought, but have you tried isolating it by using different controllers 1 at a time?

-Steve

[rwertz]

I don’t think it’s caused by the controller. However, if it would be, it could be related to another issue I saw. Short (50 mS) pulses were getting missed and later I noticed on long fades the lights would cut in and out.

I believe I had fixed that by moving the controller power to a different outlet. By the time I moved the controller power I was done transmitting and just running an animation sequence. So I would have never noticed any improvement in the transmission noise.

Thanks

[RayNMesa]

Here is somthing else you may want to try RF Choke

[John]

You might be hearing the Triacs turning on and off in the controller.
This is a common problem with light dimmers in your house. They also use either SCR's or Triacs. Try this... take an portable AM radio and hold it near a light dimmer in your house. With the AM radio tuned to a dead area of the dial turn the dimmer slowly from off to full on. Listen to the buzzing sound you get as the dimmer goes from off to full bright. That's the same sound you will hear if a radio is near the lights or controller. Granted we are using FM Radio but the Triac noise can still find its way into your audio lines. Keeping the radio equipment and audio lines away from the CAT-5, light extension cords, and controllers is good practice.

[Richard Hamilton]

I see that this thread is a little old, yet the is a common one that new users may see, and it comes back to haunt prior users. Here's my 2 cents on transmitter noise.

Noise of any type will get into the transmitter in two ways... conducted (through the wires), and radiated (through the air). There are other terms to describe it, but you get the idea.

For conducted noise, many transmitters will get a 60-cycle hum that often comes through the low-voltage "wall-wart" that these transmitters have. One really good and easy way to solve this is to take the wire that comes out of the low voltage transformer (wall wart) and wrap it around the transformer with 5 or 6 tight loops and then tape it, tie-wrap, it, or hot-glue it in place. You will likely notice the hum to drop appreciably.

The other type of most common noise is as one person says above. It comes from the computer through a conducted or radiated means. Ways to solve this are to have more physical separation of the audio output line from the computer with the rest of the computer or other cables coming from the computer. Use a really good quality SHIELDED audio cable, not those cheap things that are packaged in with every electronic audio device you buy.

Sometime a small iron ferrite "doughnut" on the end of USB cables near the computer will greatly reduce interferrence conducted out of the computer.

Lastly, put the transmitter as far from the computer as you can (at least 3 feet).

Richard

[rwertz]

Follow up:

It looks like my noise originated from the Triacs as suggested above. I had a hard time conceiving this when it was suggested. But about a month ago I realized that my CAT5 control line was ran up the outside of the wall very close to the power run inside the wall for the outlet the controller was on.

Apparently the Triac noise was induced into the CAT5 control line (causing some erratic light behavior). Once the noise was on the CAT5 line, placing the transmitter anywhere near the CAT5 induced the noise into the transmitter and onto my transmission.

This year my power feeds come from a completely different direction. When I set up for Halloween I intentionally tried to avoid running the CAT5 near the power feeds for the controller. I have no noise on the FM transmission and also no erratic behavior on the lights.

Thanks everyone for your help.