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Author Topic: 'Crosstalk' on UHF-R systems  (Read 4584 times)

Patrick Riley

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Re: 'Crosstalk' on UHF-R systems
« Reply #10 on: August 04, 2016, 07:21:10 pm »

That all makes sense. I am using WWB whenever possible. Sometimes the freqs are a lot farther apart than those two.

Sam

It sounds to me like you are experiencing intermods. If you are using WWB 6, there should never be a reason for you to coordinate your 8-24 mics on any other setting than the most robust setting, even in a crowded environment like Washington DC. Use the aluminum baking tins. They help a lot. :)
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brian maddox

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Re: 'Crosstalk' on UHF-R systems
« Reply #11 on: August 04, 2016, 09:19:46 pm »

Use the aluminum baking tins. They help a lot. :)

Use the tins Luke.....  :)

yeah a lot of crap happens when you put all the transmitters together.....
« Last Edit: August 04, 2016, 10:03:08 pm by Mac Kerr »
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Jason Glass

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Re: 'Crosstalk' on UHF-R systems
« Reply #12 on: August 05, 2016, 12:01:14 am »

I've been doing a lot of RF work recently, almost always using UHF-R and WWB 6 for frequency coordination and monitoring. I generally am having a pretty pleasant time, all things considered in this Washington DC crowded environment.

I have observed a problem occasionally where there will be RF and audio crosstalk between channels. I mean by this that two receivers will seem to pickup & meter audio from one transmitter. Transmitter A will be set to frequency X, and receiver A set to frequency X, and this will operate no problem. Receiver B will be set to frequency Y, yet still seem to meter RF and audio from transmitter B, with bad signal quality. I'm the past I written this off as frequencies too close or something, but I've now observed it many times when frequencies are multiple MHz away. This has happened when coordinating with WWB using a less than default exclusion threshold. It happened to me yesterday. I re-did all of my frequencies this morning using an even lower exclusion and 'robust' analysis, which I have not used before, and I've had good results. But, I've had good results loads of times with standard.

I would love to understand this phenomenon. Is this an intermodulation issue? I recently have been borrowing an RF explorer and was very interested to see how proximity affected the intermodulation, which I didn't realize happened to the extent that it does. Wouldn't WWB 6 be able to place frequencies far enough away to prevent this every time? Maybe it will better, in robust? Or is something else at work here?

As long as we are talking about WWB 6.... I've been setting the exclusion essentially as low as I can while acquiring the number of frequencies I require. Is this how you all are doing it?

Thank you!

Sam
Hi Samuel,

One thing that has not been mentioned here yet is the possibility that your system might be using too much RF amplification. Are your antennas the active type? Changing them to passive LPDA's could very well solve this problem.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Samuel Rees

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Re: 'Crosstalk' on UHF-R systems
« Reply #13 on: August 05, 2016, 07:33:25 am »

Hi Samuel,

One thing that has not been mentioned here yet is the possibility that your system might be using too much RF amplification. Are your antennas the active type? Changing them to passive LPDA's could very well solve this problem.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Interesting, I don't know anything about that, really. In this particular case I am using passive paddles. In other cases it's very possible I've misconfigured active antennas. Is it correct that active receive antennas should be set at '0' unless the coax cable is very long?
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Keith Broughton

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Re: 'Crosstalk' on UHF-R systems
« Reply #14 on: August 05, 2016, 09:13:44 am »

Interesting, I don't know anything about that, really. In this particular case I am using passive paddles. In other cases it's very possible I've misconfigured active antennas. Is it correct that active receive antennas should be set at '0' unless the coax cable is very long?
Yes.
Active antennas can cause problems when set to too much gain.
Also, your transmitters apart and away from the antennas, quite a bit away.
When you have all the transmitters on, do you get clean audio on all channels?
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Samuel Rees

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Re: 'Crosstalk' on UHF-R systems
« Reply #15 on: August 05, 2016, 01:33:36 pm »

Yes.
Active antennas can cause problems when set to too much gain.
Also, your transmitters apart and away from the antennas, quite a bit away.
When you have all the transmitters on, do you get clean audio on all channels?

Well, this has happened to me many times and I can't say what the exact situation was each time. It may be that everything would have been fine and I was only having issues because I had them next to each other on the table. Maybe had I deployed them without changing the freq it would have been fine, as the transmitters would never be that close. I'll have to experiment and report back.
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jason misterka

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Re: 'Crosstalk' on UHF-R systems
« Reply #16 on: August 07, 2016, 08:41:02 pm »

Well, this has happened to me many times and I can't say what the exact situation was each time. It may be that everything would have been fine and I was only having issues because I had them next to each other on the table. Maybe had I deployed them without changing the freq it would have been fine, as the transmitters would never be that close. I'll have to experiment and report back.

I have had a similar issue when working with transmitters (changing batteries, applying power locks etc)  directly underneath active paddles. 

Jason
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Keith Broughton

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Re: 'Crosstalk' on UHF-R systems
« Reply #17 on: August 08, 2016, 09:36:36 am »

I have had a similar issue when working with transmitters (changing batteries, applying power locks etc)  directly underneath active paddles. 

Jason
This is a common problem that most people don't think about.
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Samuel Rees

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Re: 'Crosstalk' on UHF-R systems
« Reply #18 on: August 08, 2016, 09:50:24 am »

This is a common problem that most people don't think about.

It sounds like I may be regularly experiencing intermod products from multiple sources. Not so much during show, but during testing on the desk. My transmitters are probably much too close to one another (lined up on the desk), AND very close the the receive antennas.

I'll try to work on these variables and I bet I'll have a better time. Thanks everyone!!!

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Scott Helmke

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Re: 'Crosstalk' on UHF-R systems
« Reply #19 on: August 08, 2016, 09:59:26 am »

I'll try to work on these variables and I bet I'll have a better time. Thanks everyone!!!

Also don't forget the baking pans!   8)
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