minimizing RF in wireless mics

[Stitch333]

Anyone have any good suggestions?

[Matt Biermann]

1 - Make sure you have the newest models (expensive, but there are only so many frequencies and everyone is using them up).

2 - Make sure there is a clear line-of-sight between Tran. and Rec.

3 - Avoid structures and items that diffuse your signal like metal doorways, exit signs, weird wiring configurations in walls and ceiling (if you know where they are), wifi hubs and other wireless units.

4 - On that note, keep multiple wireless units away from each other.

5 - Position your Rec. antennas in an "L" or "V" formation (especially with true-diversity systems).

6 - Don't exceed the distance limitations as specified by your unit's manufacturer.

[JEGG]

If you've got a bad surface-like a bad wall-hit it straight on, and not at an angle if possible.

[Jim vanBergen]

Originally Posted by Stitch333

Anyone have any good suggestions?

What problems are you experiencing?

What models and type of transmitters are you using?

What is the distance from receiver (Rx) to transmitter (Tx)?

-ALWAYS use fresh, new batteries.

-Use directional antennaes (shark fins) and active antennaes if you are in harsh RF areas and more than 15-20 feet from Tx to Rx. Using whips can be VERY dangerous.

-Use the highest quality cable, RG8, 50 Ohm, and the shortest run. Don't let your antennae cables get coiled or you will have huge issues.

-Get the best S/N from the mic thru the transmitter and out from the receiver. The RX is line level; use that gain. Make sure you select a mic element that is right for the source- lavs come in various sensitivities, which makes a HUGE difference.

Hope this helps!

JvB

[Mr P]

To repeat others here, without more details of the issues encountered it's difficult to give specific advice.

That said, I have found the following resources valuable:

The free Wireless guide that Lectrosonics publishes.
Lectrosonics, Inc-Wireless Microphone Systems Guide

On the Audio Systems Group website, Jim Brown has a number of useful articles on Wireless systems.

Go to the ProSoundWeb SR forums and search for messages by Henry Cohen. Search the TheatreSound archives for the same.

There are also a number of articles that can be found in the AES library, though these aren't free. Given the above resources, they are also probably redundant to some degree.
Vear & Spurling - Wireless Microphone Systems, an Overview. 2003
Somers - Obtaining the best performance from Wireless Micrphones. 1992
Frese - Wireless Microphone Systems with a High Channel Density. 1992

Jim, are you able to elaborate on just how much signal loss might be expected from a coiled cable? I guess I end up with one of two coils or LMR400 about 2ft in diameter relatively often. I don't normally have trouble getting systems to work, but maybe I can make them work a little better.

Matt, I have no memory of seeing a range specification in any wireless manual. Given the number of variables in system configuration and environmental RF conditions I would treat any such specification as nominal at best, and mostly worthless.

[Jim vanBergen]

Originally Posted by Mr P

Jim, are you able to elaborate on just how much signal loss might be expected from a coiled cable? I guess I end up with one of two coils or LMR400 about 2ft in diameter relatively often. I don't normally have trouble getting systems to work, but maybe I can make them work a little better.

Both Henry Cohen and Jim Brown have told me personally that RG8 or similar high quality antenna cable needed to be stretched out and not coiled as coiling would not only hinder transmission but could also, depending on the tightness of the coil, actually have the effect of reflecting signal back down away from the receiver. Perhaps I am simplifying this, but I see significant improvement in my systems by 1) testing the cable in advance of shows on an IFR to insure the connectors and cable are good, 2) stretching out the cable when in use, and 3) testing the best paddle positions for ideal coverage on each set-up . When I've used 50' or 100' loops or bundles, I have seen a loss of 6-9dB on the receiver itself- so it was easy to see the light!

I test the paddles in a) vertical/horizontal axis (one in each), b) widely spaced vertical pairs, and c) same plane/different height as well as vertical/horizontal axis.

Hope this helps!

JvB

[Mr P]

Originally Posted by Jim vanBergen

Both Henry Cohen and Jim Brown have told me personally that RG8 or similar high quality antenna cable needed to be stretched out and not coiled as coiling would not only hinder transmission but could also, depending on the tightness of the coil, actually have the effect of reflecting signal back down away from the receiver. Perhaps I am simplifying this, but I see significant improvement in my systems by 1) testing the cable in advance of shows on an IFR to insure the connectors and cable are good, 2) stretching out the cable when in use, and 3) testing the best paddle positions for ideal coverage on each set-up . When I've used 50' or 100' loops or bundles, I have seen a loss of 6-9dB on the receiver itself- so it was easy to see the light!

I will try this tomorrow on an IEM system I am using that could use a little extra range.

I'd like to know about the IFR, and which tests you perform. Futhermore, for cable that is either part of rental stock or sees alot or touring how often would you recommend the cable be tested?

I tour with a small theatre show that tours our own RF cable - precisely because too many places provide us with 3532s coupled with nothing but 60' RG58 cables - makes it very hard to get clean reception at 300' and beyond. I wonder if we should find a local audio house (System Sound maybe) or RF specialist that can test the cables between tours.

Cheers,

Phillip

[Jim vanBergen]

You're tx'ing IEMs a distance of 300'? I hope to god you're using helicals, and not shark fins!

Well, we use IFR Com120B, which is an uber-expensive IFR-- to test all RF gear. When you test antenna cable on a spectrum analyzer, it allows to check for any minimal loss, internal nicks, etc, and shows you serious loss- like the 6dB you get with a bad connector crimp. A regular cable checker won't do this, but it would be insane to buy a high end frequency spectrum analyzer for a few stops- you could buy new cable for every single stop for less money! If you are using one of the bigger rental shops, they should be doing this for you every time the gear comes back in the shop. Masque Sound, Sound Associates, PRG Audio- this kind of rental shop does this automatically, or the specialized RF rental providers, like - Professional Wireless, Production Radio Rentals, CP Communications, Wireless First - these guys are specialists in RF.

You should not have to test your antenna cable between jumps if you take care of it. I have seen tours go out with cable and come back four years later with the cable in excellent condition...of course, these are sitdowns, not one-nighters.

My own personal spectrum analyzer is a little ProTek 3201, which ran me under 2k, because it's smalll and does the job onsite...but can't do a serious cable test.

Hope this helps!

JvB

Originally Posted by Mr P

I will try this tomorrow on an IEM system I am using that could use a little extra range.

I'd like to know about the IFR, and which tests you perform. Futhermore, for cable that is either part of rental stock or sees alot or touring how often would you recommend the cable be tested?

I tour with a small theatre show that tours our own RF cable - precisely because too many places provide us with 3532s coupled with nothing but 60' RG58 cables - makes it very hard to get clean reception at 300' and beyond. I wonder if we should find a local audio house (System Sound maybe) or RF specialist that can test the cables between tours.

Cheers,

Phillip

[Mr P]

Originally Posted by Jim vanBergen

You're tx'ing IEMs a distance of 300'? I hope to god you're using helicals, and not shark fins!

Sadly not. And the IEM reception is sketchy out there. Fortunately the actors don't spend too much time that far away.

Unfortunately despite a technical rider that very clearly asks for Helical or YAGI antennas, often we have to make do with LPDAs. This is a side effect of presenting at a lot of arts festivals (that are typically budget stripped), and with production companies who are not used to unusual RF requirements (such as very long range).

Normally it is not to much to get the mic's clean at that distance. Thankfully, as thats what the audience hears. The actors never go anywhere I can't get clean reception.

One sweet day my company will pony up the cash for some Helicals, a scanner, and IAS.

Back to the subject at hand. I straightened the remaining LMR400 on the IEM Tx out for tonights show. My limited polling of the actors proved inconclusive.

The Protek unit appears to be out of production, without a new equivalent. Do you have any experiences with portable scanners that are currently in production?

Thanks,

Phillip

[Jim vanBergen]

Originally Posted by Mr P

The Protek unit appears to be out of production, without a new equivalent. Do you have any experiences with portable scanners that are currently in production?

Thanks,

Phillip

Sorry, was unuaware the ProTek is no longer made.
We're supplying our new guys with the TTi units...

http://www.tti-test.com/psa/rf-spectrum-analyzer.htmw...

They do a nice job, the display blows mine out of the water. Different approach in terms of how to find something, and once I got used to using an earbud instead ofthe built in speaker for listening to the RF response, I was quite happy with this.

Sounds like you have a hard time on the road. Good luck, brother!

JvB

[drpro]

Another great product made in Australia is by WinRadio, WR-G33WSM. This is a hardware/software based sprectrum analyzer. I have one and it has been great on sets were there are multiple radios working and just to see the spaces in the RF spectrum. Less than $1k in the US.

David

[John Willett]

Originally Posted by Jim vanBergen

-Use the highest quality cable, RG8, 75ohm, and the shortest run.

Agreed on quality - BUT - every radiomic. I know user 50-Ohm cable. 75-Ohm cable is for video.

Unless it's a very odd radiomic. you must use 50-Ohm cable.

The thin stuff is RG58 - the signal loss down this cable is about 5dB every 10-metres at around 850MHz - so keep it SHORT.

The better cable is RG213 - this is about 1/2" thick - but the insertion loss is only about 2dB per 10-metres at around 850MHz so you can go longer.

I hope this helps.

But *DON'T* use 75-Ohm cable.

[Jim vanBergen]

John, thanks for the correction. You're absolutley right, 50 Ohm is for antennae cable such as RG8 or RG213 and smaller diameter RG-58 for internal distribution racks between antennae hubs and receivers; 75 ohm is for video runs ONLY on standard RG-59.

DOH.

Thanks for keeping me accurate & honest. I have corrected my earlier post.

JvB

[John Willett]

Originally Posted by Jim vanBergen

John, thanks for the correction. You're absolutley right, 50 Ohm is for antennae cable such as RG8 or RG213 and smaller diameter RG-58 for internal distribution racks between antennae hubs and receivers; 75 ohm is for video runs ONLY on standard RG-59.

DOH.

Thanks for keeping me accurate & honest. I have corrected my earlier post.

JvB

No probs - part of my job is advising on radio systems, so this is what I know......

[Mr P]

You can't use 75ohm cable? Have y'all read this article by JB...

http://www.audiosystemsgroup.com/Whi...eless_Mics.pdf

The winradio system can be quite handy. It can also interface directly with Shure's Wireless Workbench software. The front end of the winradio system is not as solid as the UHF-R system, and is more prone to displaying intermod products on the frequency scan.

JvB: Thanks for the info.

On another note. I have to get some wireless systems working in Singapore in the morning. Does anyone have a good reference for licensed transmitters working there?

I have found this so far:
Singapore TV: Television Stations and Channels

Cheers,

Phillip