This one has me stumped.. I am running around 10 watts AM here and the studios LCD computer monitor is somehow picking up RF. I see interference lines go through the screen moving up the monitor slowly much like you'd see on old TV sets when something was screwing with the signal. It's not too noticeable and the interference seems to fade in and out on the screen.
I am still able to see everything on the monitor fine but if I pull up a large bright image I can see those lines move through it darkening the image where the lines are.
The odd part is I have tried RF chokes on the power cable, on the video input cable. I have tried different wall plugs. Nothing seems to work. I took a field strength meter and put it next to the monitor and it's not too strong of an RF field around it; nothing any other device can't handle fine.
Part of me thinks maybe something internal on this monitor is clocked close to the frequency I broadcast on?
It's an Acer X171 older 17" LCD.
Any ideas how to fix this? The more power I run the worse the lines go through it. I'd like to up my RF power but am almost afraid my computer monitor will go up in smoke if I do
I've seen monitors do this in the computer shop i work in. try taking the monitor to another location that isn't close to your equipment. if the monitor is your problem then im not sure what you can do because we just recycle them at that point. you could try shielding the VGA cable with some pipe.
Remember that "radiation film" touted to reduce Xrays from CRT monitors? It's a conductive film with a few megs of resistance and if placed over your LCD and grounded, it may attenuate enough RF coming through the screen (the back and sides are usually well shielded enough).
Not much you can do if you tried all the chokes and filters. It's internal and caused by beat frequency interference. About the only thing you can do further is relocate things or simply put up with the harringbone lines...that old familiar term used for the old CRT's..is the same thing here with LCD monitors.
You think that's annoying...thank goodness these computer monitors are not plasma. Altitude makes those things jitter and spatter with the same visual effect.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Last night I tried just about everything to remove the problem. I wonder if the interference is somehow carrying up the power cord since while taking a field strength meter I am getting a high reading around the wall outlets. That alone doesn't make sense to me because near the transmitter there is absolutely no RF getting into the power outlet. To confirm this I tried running the transmitter off of pure DC and same result. This leads me to believe that the house wiring is just so cheap or long that it's picking up the RF like an antenna. I never had this issue at the previous place I lived. Well I will try choking off the power cord itself going into my monitor and see if that helps. I know there is stray RF hanging around my studio equipment, but it is NOT because it's connected to the transmitter. I can completely remove the audio cord going from the studios computer and mixing board from the transmitter and I still get RF floating around the audio and power cable cords. However it's so little that it doesn't effect any equipment besides this computer monitor. The transmitter is about 15 feet away from all of the other equipment. It probably doesn't help I have the ATU indoors rather than outside. Ugh this is giving me a headache
By the way I will let you guys know if I figure it out. To make matters more complicated the interference seems to come and go like it has a mind of its own.
I wonder if the interference is somehow carrying up the power cord since while taking a field strength meter I am getting a high reading around the wall outlets. It probably doesn't help I have the ATU indoors rather than outside. Ugh this is giving me a headache
Ahh. With the ATU unit indoors, then it is most likely an issue of RF being inductively coupled onto the power wiring inside, in turn can cause the monitor problem.
Basically acting like a carrier current system in the house, and possibly feeding down the power lines into nearby homes as well.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Well I will try a filter like that, however I don't sense any RF on the power cord from my transmitter using a field strength meter. I ran my meter along the power cord from the TX right up to the outlet and zilch. However in a room or two or more away I can pick up the RF on the lines like it's an antenna.
As said on the LCD monitor I can run the sniffer wire right up to the monitor from the outlet and pick up RF.
I am thinking something is screwy with the wall wiring here. I never had these issues in my old home. Both places are manufactured mobile "trailer" homes. This place is much newer and I suspect uses aluminum wiring rather than copper like the old place. I question if that has some odd effect.
You mentioned the place is newer than the previous. A manufactured mobile home. Comparing to the previous home, what are the outer walls on the newer home made of, and where is your transmitting antenna in relation to the position of the newer home?
It may be that your previous residence had adequate shielding within the walls, perhaps all the wiring was in conduits which were grounded, and the type of wiring.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Well one dumb problem fixed... My stereo was also having a nasty issue of RF getting into it. I use this stereo as the studio monitor and I doubt the designers ever had in mind that it would be used this close to a high powered AM transmitter. After hooking up the linear amp and increasing my power the hum coming through the stereo was unbearable. On the back of the stereo there is preamp outs and amp in jacks for left and right. There is a U connector going from the in RCA to the out RCA jack. Well I had no idea that the ground also needed to be connected between the two jacks. Replacing the U shaped piece of metal with actual quality RCA cables solved the hum issue with that. Now I hear nothing getting into the stereo except on the phono inputs which I don't use anyways.
The monitor is still an issue. I guess it's something I will have to live with. It's not so terrible that I can't stand looking at the screen but it is rather annoying watching the slanted lines bounce around to the modulation. I'm going to connect a LPF to the transmitter and see if that helps. The only strong harmonic I pick up is on 3220Kc (1610Kc*2). I wonder if that happens to be close to some kind of synch frequency the monitor uses.
If I ever figure it out I will post about it.
It's funny how with the extra power I am running now how the RF gets into shit I would have never expected it to. Well when I start hearing the toaster oven play music then I know it's time to back off the power
Well those loop thru pre amp outs and power amp input ports are using the chassis ground for the ground path. What solved the problem there was that you shielded the + path with RCA cables with a ground shield around the + wire. Those "U" shaped loops have no shielding around them, and in the presence of high level RF, will act like antennas and inject the RF right into the power amp input!
It's possible there could be a data buss clocked at or near 3Mhz within the monitor and is getting the TX's 2nd. No doubt you have changed frequencies and noticed on certain ones, the bars are not there, and then return on other frequencies.
The LPF should help some if the TX did not have one to start. But depending upon how much power your running, it may only help a little, but a little is better than nothing!
The time to start noticing there is a bit too much RF inside rather than outside at the antenna is when that toaster starts imprinting musical notes and waveforms on your toast!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Finally all this time later I have a clue as to what is going on. I noticed today after repositioning the monitors cable that there was a strange dull line on the right side going vertical from top to bottom. Getting angered I started double and triple checking that the cables were tight and suddenly when pressing my hand against the back of the monitors connector I notice the line went away.
So this gave me the idea to fire up the AM transmitter for a moment just to see if this had anything to do with my problem and low and behold the stupid scrolling RF interference lines were almost gone, or would come back by wiggling the connector.
Tonight looks like my job will be opening the monitor and checking the soldering. I have a funny feeling the actual connector has a bad grounding either on the pins or the actual outer sleeve.
This will be so nice if this solves it. You guys have no idea how annoying it is to broadcast and see translucent lines run down your LCD monitor that come and go at random times.
Sometimes I just have to move the monitor cable about an inch or so and the lines go away. Haven't seen those lines lately but they do pop back a little now and then.
Home computer monitors were not really designed to work in a high level RF environment!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Sometimes I just have to move the monitor cable about an inch or so and the lines go away. Haven't seen those lines lately but they do pop back a little now and then.
Home computer monitors were not really designed to work in a high level RF environment!
Peace!
Yeah I noticed when I increased the transmitter power that the lines are still there but no where near as bad now. I will have to open the monitor and see what's up. A better cable couldn't hurt either.
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