I posted this on sonycreativesoftware forums and thought it might be addressed here too, since they are more on the software side:

Background info:
I recently rigged up an old Sony DV camera to record (DV pass-through) our church services to computer, and also use the AV out to send a signal to a TV in the nursery via an RF modulator & coax cable. Works great, and there is a zero budget so I'm mostly using things I have "lying around." I've produced videos to post online & get DVD's made for shut-ins - streaming live will be phase 3 or 4.

But now a few weeks into the venture I'm getting around to exploring the different ways I might get better sound. I hope to run mics on one channel through our mixer (from main/monitor out or something) and a room mic (aux out) on the other. Then in post-production I can work with the 2 tracks and mix/reassign as needed (Sony Sound Forge & Vegas Pro). That way sermon audio is crisp but I can bring up the room mic for laughs, amens, you suck*, etc. (*that's usually my wife )

The problem:
As soon as I plug a cable into the (stereo) mic-in jack I get multiple AM station broadcasts into the headphones on the camera. If I disconnect from the RF Modulator it goes back away, and using higher quality cables (XLR, 1/4 in, RCA) does not make a difference. So at this point I can either send the coax signal to the nursery TV (very important) or input better sound into the camera. The cable is only connected on the camera end so far, so it's not any of the other equip, and it still does it when I disconnect the coax from the modulator or DV from the computer.

This is the entire setup for troubleshooting purposes:
AC power via 2-prong transformer > RF modulator > AV cable to camera (on battery power) > shielded cable in mic jack

Absolutely nothing else connected other than headphones in the camera.

I get the same results (AM radio broadcast) with a variety of cables, and no broadcast until I plug a cable into in mic input.

I recognize the underlying reasons for the issue, and it appears any wires connected to the mic jack act as an antenna. What I'm wondering is if there is a filter/gate or something I can put in the system to nix the radio signal.

I've searched around and not found anyone with this issue, running AV out and converting it to coax at the same time as connecting a mic in cable. Any ideas?

Tell me there's a 1.98 RF filter at Radio Shack! (but don't lie, this is for the church..)

The cable is only connected on the camera end so far

This is probably where the problem is occuring.

The camera is running on battery and is thus not earthed. All it takes is a slightly dodgy solder joint anywhere in the connection string to turn the entire set up into an exceedingly efficient radio receiver/ demodulator, with a nice big amplifer in the shape of the mic in preamps.

Try connecting the other end of the mic in cable to the sound board o/p connection. If the ground on that is actually a ground it may stop the problem in it's tracks.

Else dive down to Radio Shack and buy a 50 cent ferrite torroid. Loop the mic in cable (at the camera end) through it about half a dozen times and secure tightly with electical tape.

That should strangle any RF at birth. You may find (depending on length of cable run) that you need to do the torrroid thing at both ends.

Given the nature of RF electrickery, it may be wise to follow suit on every other cable going into or out of the system (yes, power cords too), everything BUT the co - ax taking the modulated RF to the nursery (if one of the above hasn't nailed it).

You can buy "clamp on" ferrite RF killers designed for power cords and such, but as to whether they're available at RS, dunno.

Keep us posted.


CS

Thanks Chris, the ferrite may be the trick, I've used them with other issues. I'll hunt some down - now where did I see some last?... I know where I left some in a drawer 2 hours from here, lol.

As for other connections, they were all originally made but were taken out for troubleshooting. With the camera plugged into AC, mic cable connected to sound board or other devices, etc. the problem still occurred. I only removed them to reduce the variables.

You don't mention the specifics of the RF Modulator, is it a stand-alone modulator? You could try substituting a different one. For example you could use an old VHS VCR for this just as a test although it would probably be more likely to pick up radio than a stand-alone modulator that was working correctly.
I'd also use the shortest possible cables for all these connections and make sure all the cables have no problems with their wiring.
Are you reducing the level of your outputs from the mixer to the mic-level that the camcorder input will need?
If you must use a long audio cable run from the mixer to the camera, you may need to employ some additional items to keep the run balanced for the majority of the distance.
What to use would depend on the output connector you're using from the mixer.
For a different trouble-shooting approach than connecting and disconnecting pieces one at a time, I would probably hook it all up the way you hope for it to work and then substitute a different cable in place at each leg, one at a time. It may be a combo of items or cables causing the radio reception that will require switching something completely new into the total system to eliminate it.
Good luck with the chokes and with the whole project!

Thanks Jay, I just fooled with it some more, the ferrite cores unfortunately did nothing for the situation, and I realized the AV cable had one all along already :(

The RF modulator is a rinky-dink one for hooking up a vcr to tv, and I considered trying a few different ones including VCR's - but I found out tonight that it is not the root problem.

Once I had the initial problem, I took most variables out of the equation, so only the items listed here were connected:
AC power via 2-prong transformer > RF modulator > AV cable to camera (on battery power) > shielded cable in mic jack

However, tonight I discovered that it appears to be a signal carried through the RG6 coax, it was just that it was near enough to the RF modulator (though not connected anymore) to jump into it and through the AV cable to the camera.

So now I can do this, no other wired connections:

1. Camera on tripod using battery power, headphones plugged in, no other connections (just air and my body) > no AM radio heard
2. If I then plug any cable into the mic jack of the camera (other end not connected), I can hear the AM very faintly - tried a variety of cables & types
3. If I just touch the outside of the coax connector (which is the shield), then I get multiple AM stations in the headphones, clear as a bell.
4. If I then unplug the cable from the mic jack and still hold the coax, no AM radio at all.

The coax runs several hundred feet through the facility and is good quality, just ran it 2 wks ago. It could be getting a signal from many places.

It's becoming more of a brain teaser than anything, though I still want to broadcast to closed circuit TV while capturing video with proper sound input from the sound board.

I re-read Chris' post and realized that the long run of coax is not grounded anywhere. Tomorrow I'll put a ground on it along the line and see if that doesn't suck out the AM signal. That would be too simple! I had been contemplating why this isn't a problem with cable TV and was going to check with a cable tech, this might be the answer.

And I also realized that it would be a great place for one of our Florida lightning bolts to travel!

Been giving this some more thought.

As a matter of interest, what channel(s) is the RF modulator outputing (theoretically)?


CS

I've tried both ch. 3 & 4, the only 2 options. Same results.

I'm looking forward to grounding the cable later to see what happens, I'll post back.

If it's the former, I think I may know where the problem lies.


CS

Still not resolved, but here's the latest:

With the RF Modulator out of the picture for test purposes and only the coax cable which runs all over the facility (connected to 2 TV's along the way), I can get the AM signal with the camera on battery when I just touch the coax shield. - So that leads me to think the RF modulator might be a carrier of the AM signal, but not the cause.

But If I hook the RF modulator up and put a ground wire from the signal amplifier into the AC ground (power strip), it reduces the AM signal significantly but not completely. I can and did do all kinds of different connections but bottom line is if I connect to the ground in the power strip certain ways I can clear out about 75% of the AM signal.

The power strip is quite far from outside and/or a direct link to the ground, so I wonder if it would be better with a "clean" ground. This is all located in a balcony so running a plain ground wire to a rod or something isn't ideal for testing, but could be done permanently if I was sure it would work. I'm wondering if the ground wire on my cable box at home serves this sort of function as well as lighting arresting. Any cable techs out there?

btw I also tried a ground wire way down line on the coax into an electrical box ground wire, but it did nothing at all up in the balcony (too far I guess).

I'll keep fiddling with it, and use the built-in mic in the meantime. (remember the broadcast only happens when I try a cable in the mic-in jack)

the signal amplifier

What exactly are the specs for this thing?

I knew there had to be a RF amplifier somewhere in the sytem, either as part of the modulator or seperate. I take it it's a descrete standalone device?

Frequency range, gain, inbuilt filters etc etc?

The reason I'm so curious is I'm not entirely sure what you're hearing is AM radio stations.

Also, about this co - ax.

You've mentioned it feeds two tv's. How? By which I mean, have you/ they fitted in - line splitters to take feeds to correctly terminated 75ohm RF inputs?

Does all this co - ax have any other purpose? Is there an aerial and if so, how is it connected into the system?

OK, my suspicion(s).

I'm gonna guess that amp is a full band VHF amp working from channel 2 all the way up to channel 13. I'm also gonna guess it doesn't have a FM trap built in.

The two channels you mentioned (3 & 4) are @60 - 66 Mhz and 66 - 72 Mhz, respectively.

If the amp is a full band amp then it's amplifing everything between Channel 2 (54 - 60 Mhz) and channel 13 (210 - 216 Mhz).

It won't have escaped anyones notice that sitting slap bang in the middle of that range is the.............88 - 108 Mhz FM band.

Without a FM bandstop filter somewhere in the works, the slightest amount of FM that gets into that amp is going to whistle around that co - ax circuit till it hits an improperly terminated connection and set up standing waves all over the place.

You now have an exceedingly efficient FM transmitter.

You may find you need something like this on the I/P of the amplifier to can that FM before it can cause chaos:

http://www.tinlee.com/PDF/CR7%20FM%2040.pdf

On the other hand, it could all be a gigantic red herring, there's already a bandstop in place or the amp is only a single tuneable channel so couldn't possibly be the culprit.

Interesting theory tho'.


CS

Thanks again Chris, I always admire persistence!

I'll check the components and give you more detailed info later.

The big thing is the radio signal still comes in when the coax is not even connected to the RF modulator or the amp. I hooked back into the amp because it had a proper ground lug on it.

Downline the coax is run through one splitter (I'll check the specs 500- 2150 MHz I think) and then to 2 normal TV's via their coax jacks. It runs through several buildings and past/alongside various wiring.

If it comes to it, I'll disconnect various places along the coax line to minimize more variables, as I have in the balcony.

The broadcasts appear to be AM talk radio, but I've not listened for station identification yet.

OK you made me go over and root around again (good thing I live next door).

2 stations I heard were AM 1320 and AM 1460 (Jacksonville, FL, where I am)

I removed all splitters & cable connections, and hear radio in headphones if I:
- have a cable in the 1/8 mic jack of the camera (but not if I remove it)
AND touch the shield of the UNconnected coax (but way less radio if I also touch ground)
- either have camera on battery, or AC power
- either have AV connected to RF modulator, or not
- no other wires touching the camera
- nothing connected to coax other than the fact that it touches plenty of things in its run
- I believe only 2 cable connectors in the run of several hundred feet

fwiw the amplifier (not connected above) is:
Electroline EDA 2400 drop amp, + 7dB on 4 lines
specs say 5-42 54-1000 MHz 6kv
- but the issue happens whether it is in the system or not (& unpowered)

fwiw the cheapo RF modulator is (again, not connected above):
Radio Shack #15-1214

fwiw the only splitter besides the amp is (again, not connected above):
marked DSV 50
labeled 5-2300 MHz

I'll post a drawing next

Andrew, do you have a multimeter?

Can you measure both the AC & DC voltage between the live and ground input pins on that modulator, then the I/P ground to a "true" earth (or as close as you can get)?

I'm assuming it's got two inputs, one each for composite and audio, either will do.

Can you tell me whether the modulator has an internal or external power supply, and if external, what's the rated voltage?

The second experiment: can you connect a cable to the mic in (any cable that will fit, as long as you can get to the other end of it and it produces radio in the headphones).

If the headphones have radio, try shorting each audio channel live pin on the mic in cable to the ground connector.

Does either or both kill the radio?

As you haven't been using external mic's up to now (I'm implying that from earlier posts) where has your audio been coming from? The "on camera" mic?


CS

Yeah, I'll check with a meter tomorrow.

So far I've been using a shotgun mic on the hot shoe. Everything's fine with all connected until I try a mic cable. No different if I connect it in a variety of ways to the sound board.

I'm leaning toward a clean ground to the shield of the coax as the key, the ground I'm using (to a power strip) is the only thing that changes the issue.

I made a wonderful drawing of me when I have the issue, all other variables out of the system. If I disconnect the mic cable OR let go of the coax, all is silent. If I touch ground 75% or so of sound is reduced.

What's it been connected to if not the mic in connector?

You got XLR connectors as well as a stereo 2.5 mm socket?

Do you switch to XLR via a menu or a switch?

Do the on - boards work without radio and get cut out by plugging in a stereo mic cable to the 2.5 socket?

Confused.


CS

btw the reason I don't trust the ground in the power strip is that it is plugged into other strips and the whole AV booth is on ONE outlet. Mixer, equipment, etc is connected to many new and old inputs and outputs strung all over, remote amps, etc.

All in a 60 yr old church building with lots of modifications...

No telling what all ground goes to or is fed by!

High on my list is to crawl in the (scary) space under the balcony floor and add some more AC circuits, lol

The shotgun mic is powered by and sends the signal through the hot shoe, which automatically disconnects the built in mics.

If you plug into the 1/8 mic jack, it automatically cuts off the other sound inputs.

Unfortunately this camera does not have xlr inputs, just a stereo 1/8in socket. I have tried an xlr adapter right at the socket to xlr cable, but still had the issue.

I have one cheap mic with a hard wired 1/8" mono cable, and it is the only thing I've plugged in that does not produce radio signals (if you listen real careful you might hear some)

Both the built in mics and shotgun mic produce clean sound (no radio)

What a mess!

Suprised anything works at all.

Well, sure sounds like there's a major earthing problem (I was going to say "somewhere" but it sounds like it's probably "everywhere").

However, if the on boards work fine, the shotgun works fine and even that mono mic works fine-ish, sounds like there's an issue with that 1/8" stereo jack itself.

Short of stripping it out and cleaning all the contacts and checking solder joints, not sure I have a solution if it's the culprit (apart from the earths).

A squirt from a proprietry contact cleaner (CRC 2 - 22?) might sort it but I won't hold my breath.

I'll stay tuned for the next exciting episode.

CS

Step outside and see if there are some transmitter towers within a block or two of the church. Seriously, it sounds like you may well be in an area where the station's signal strength is so high that it just barrels its way through the relatively poorly shielded consumer electronics.

Another thought ... you've said you hear the stations in your headphones but are they getting into the sound that sent to the remote TVs in the nursery etc or sent to your recorder? It could be that just the headphones are affected and if so, maybe you can just live with it.

Well I'm not bored.

Actually it is probably not the jack, the same thing happens with 2 different cameras.

I will clean it just in case both cameras have sticky/dirty sockets.

It appears the cable out the other end of the camera just allows a component in the camera to act as a receiver/diode.

I'm not up on all the workings in radio receiver, but I know just to get the signal it does not take much: HowStuffWorks "How Radio Works" (http://www.howstuffworks.com/radio9.htm)

I don't see any towers nearby, and the broadcast goes through to the TV as well as the recording.

For now we will continue to record without using external audio.

I'm thinking just the right thing on the coax or mic line will squash the signal, I'll be glad when I find it!

sounds like you are pretty close to the AM transmitters (not studios). call the two stations to see where they are and how much power they radiate (ask for the chief engineer, he can tell you straight away). i'll bet they radiate at least 10,000 watts and you are within 5 miles of them.

that being said, unterminated (read-unCONNECTED) wire picks up RF like you wouldn't believe, or maybe you do now. :-) you said that grounding your coax solves 75% of the problem--in a 60 yr old building I would not assume that ground connections are that great, if grounded at all. i'd be running my own heavy gauge ground wire to a freshly driven ground stake of at least 10 feet into earth before i made any further adjustments.

after you properly ground the coax, you are likely to find a hum in the audio/video-i'm assuming that your modulator has unbalanced RCA connections. a transformer (radio shack "ground-loop eliminator") will fix this problem for the audio, and offer further RF rejection. you may find that transformer isolating the camera audio input helpful as well, although its one of those things that you won't know until you try it.

Thanks Greg,

Yes I realize the un-terminated wires pick up well, but these also pick up well when terminated on all ends. So far the only ground loop I got in all the variations and experimenting was when I grounded the coax in 2 places as a test.

Yes I suspect the stations are broadcasting strong and I'm not too far from downtown. I agree about the questionable grounding and encouraged by the one at the booth being the only thing that helped. I will probably drive a ground rod and hook it up to coax only as my next step.

Then I'll see if I need transformers on the many unbalanced components...

to see any way forward that doesn't involve spending money, so how's this for a bit of lateral thinking.

Why not find the cheapest (and I mean super el cheapo) AV sender/ receiver set that will offer suitable quality, plug the transmitter directly into the camera and the receiver into the modulator - hey presto, no need to ground anything, no ground loops and that mile or two of aerial co - ax is taken out of the picture entirely.

You can leave all your dodgy wiring be (probably the safest thing to do) and just get on with it.

Probably want to put snap on inductors on both power supplies but other than that, easy peasy.

Work out cheaper than fitting every (yes, every) cable involved with these:

Snap-Together Ferrite Choke Core - RadioShack.com (http://www.radioshack.com/product/index.jsp?productId=2103222)

I'm still thinking, but this sounds a winner.


CS

PS: Checked out RS for same but they seem awfully expensive, best other deal I've found so far:

http://www.x10.com/promotions/wireless_video_sender_vk82a.html

Thanks again Chris,

I got some of the ferrite cores from RS the other day (after the sales dude trying to act like I was not smart enough to know what I was looking for, because HE hadn't heard of them, lol). I have some heavy duty ones somewhere, I'll find them later.

The video sender is something I've considered, my father-in-law has a proprietary one for his old Sony camera, it would work with the older of 2 cameras I'm fiddling with. It might be better to just get a new one, I believe they work different anyway.

I'll keep "plugging away" at this until all is peachy and I am recording with stunning sound!

You could have let me feel like a clever clogs for a little while longer, just as I was thinking I'd dragged my IQ somewhere North of my shoe size................. you go and say you got there first!

Oh well, can't win 'em all, I guess.

Still sounds like a plan to me, and the only one that practically guarantees success, well, as far as killing this talkback radio is concerned, anyway.

Keep us posted with your "plugging away".

Good luck.


CS

lol, I gave you more than a whole hour though!

Good ideas, I'm looking forward to this thread having the final solution at the end. Then I want to read it!

The interesting thing is I still don't find information about this when I google. So maybe it is something more unique to our facility, like we wrapped the coax around some equipment in the basement or something.

At one point I completely disconnected the coax about 2/3 of the way down the line with no difference. Maybe for curiosity I'll cut it back further to see how long of a run it takes to get what I currently have in signal. I'll do that when I get bored maybe.

You winning or not?


CS

sounds like you have made yourself a "crystal" radio about 2 times over.
anywhere you are even if your not by a station, any long wire is a Antenna, picking up waves of (radio) energy out of the air and converting it into ac power. with "amplitude modulation" AM radio stuff this AC power would be sound.
) ) ) ) | ( ( (
.)))))) | ((((
) ) ) ) | ( ( (

~~~~|===========================|~~~~
. . . . .^ ^ ^ ^ ^ ^ Energy waves ^ ^ ^ - Output

ok so i just like drawing pictures :-)

of course on your crystal radio, you also have an extra pre-amp a compressor probably (the auto volume control) and an amplfyer too :-) making it about 10 times worse.

WHEN you have it as bad as you have it now, the first thing you must do is determine the grounding wrappped around the signal wire. Lift that ground at either end , have poor shielding around the signal wire, or even improperly used signal connections at either end.
ferrites would be the final step after you had stuff correct in the rest of the setup, perfect for a pro application where everything else it correct.

me thinks that you are Sooo far back in this problem as the grounds around the signal wire itself are lifted, unterminated, or they just suck, and your pic shows them unterminated. Not that they need to be sent TO ground, although that can work, but that the connectors at the ends arent connected TO the ground wire , or sheild around the wire, or a termination point.

____________________ Ground
____________________Signal
____________________Ground

To test a wire , and its ground connections:
get a continuity meter out, you know an OHMS meter, connect the meter to both ends of the Ground on any of these wires, and read how many total ohms it is from the metal on one side to the metal on the other.

=|)=============================|)=
|----------ohm meter----------------------|

=|)=============================|)=
. |----------ohm meter-------------------|

Now your going to say , but but but, i cant pull the wire out.
then you add another wire loose through the hall and down the stairs, and across , bringing the signal back to the beginning (to the first one). Then test both wires at one time.
the reading you get from ground to ground, or signal wire to signal wire , should be in Ohms, like 3-50ohms not Kohms or Mohms which would indicate a disconnection somewhere.

it wouldnt be uncommon for coax to have connectors with incomplete connected grounds, for mic wires to use simple twisted pairs with minimal sheilding, or that a coax has broken down over time , a mouse has it for lunch, and just isnt connecting well or the internal plastic is breaking down.

when you mentioned that these wires might be wrapped around equiptment, it reminded me of all the things we tried to get a signal on the crystal radio :-) like metal pipes, wraping it around stuff instead of straight, making directional loops, in that case we (of course) wanted the signal. And YES we also used House GROUND wires to collect the AM signal from the house wiring which was a big antenna of itself, even though it was grounded once.

Like was already mentioned the ends of the wires really have to be "terminated" somewhere, besides, or the outer Ground Sheilding Wire , will be the antenna itself too.

____________________ Ground
____________________|)
____________________|) Terminate (usually with resistance, or with a device that will have termination usually) Cap it off :-)

Your picture shows that you SHOULD have a perfect antenna going, without having terminated or "grounded out" your antennas anywhere, sooo you have made a perfect radio so far, which is exactally the opposite of what you want to solve?

Well not quite a perfect crystal radio yet - I can't tune it to just one station! Maybe I'll add a tuner, one of the clear stations is the local Catholic Radio Network - I wonder how my Presbyterian members would like hearing that on our video recordings?

I had a busy week so haven't been able to pursue this more. I hope to pick it back up this week, but may be too busy again... Thx for the ideas, the radio signals come in whether the cables are terminated into a variety of equipment or not, and whether I switch around cables. I did put a resistive cap on the coax, no change either. Coax is brand new but you never know...

The ground to a questionable power strip (coax shield to electrical ground) is the only thing that has made one difference so far, and it is significant. I have a new ground rod I want to drive and hook up for a clean ground, I'll see what that does next.

This AM we had electrical problems instead: one phase out and another browning out & back with "variable" voltage. nice. Had to do church without the sound system, heat, and 1/2 the lights anyway. Fortunately I got a new shotgun mic for my other camera this week so we recorded on battery power. Projector and all had clean power so that worked at least.