Camera to RF Modulator picks up AM radio

[Chris Soucy]

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

[Andrew Marshall]

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

[Andrew Marshall]

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)

[Chris Soucy]

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

[Steve House]

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.

[Andrew Marshall]

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"

[Andrew Marshall]

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!

[Greg Bellotte]

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.

[Andrew Marshall]

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...

[Chris Soucy]

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

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/wirele...der_vk82a.html

[Andrew Marshall]

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!

[Chris Soucy]

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

[Andrew Marshall]

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.

[Chris Soucy]

You winning or not?


CS

[Marty Welk]

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?