Radio Mic Recievers

[marc]

To make radio mic's work properly you have to be the devil,

 

Radio systems are the devils game,

 

Personal preference being receivers at the side of stage, I generally work on the less distance that you send the radio signal the less it can get messed up, line of site is good for me,

 

Yeah, yeah, it’s a radio wave and does not need line of site, but I fancy the odds better on line of site,

 

Any way to finish I offer my last comment,

 

Radio systems are the devils game,

 

Enough said? ;)

 

Mk

[vinny baby]

we are using some of the higher end Audio technica radio mics (£1500 a mic!!) and the range of signal is crap, I was always taught to have the reciever as close to the transmitter as possible.

 

we have our recievers located with the monitor guy, (havent droped out yet touch wood) who can monitor the signal, and the battery status. handy thing about the artiste elite range is that you can put power to the aerials to boost them. (I know that)

 

again im an LD not a soundie so im not 100% up on mics ;)

 

vince

[Bobbsy]

Well...it's actually the ANTENNAS that need to be as close as possible to the transmitters, not the receivers themselves.

 

I think some of the difference of opinion here may stem from differences in the equipment being used. With a properly specced, high-end system using proper antenna dividers, good cable, care over terminations, etc, there's no reason at all not to have the antennas near the stage, feeding receivers near the FOH position.

 

If, on the other hand, you're stuck with antennas on the back of each receiver, then I guess it makes sense to keep them near the stage.

 

And....RF is NOT the work of the devil...it just seems that way! The level of engineering required to make it work is high...but it IS engineering!

 

Bob

[vinny baby]

I was always taught to have the reciever as close to the transmitter as possible.

 

Well...it's actually the ANTENNAS that need to be as close as possible to the transmitters, not the receivers themselves

 

yes but on the other hand, the recieving is done by the antennas, so the reciever whether is being the antenna or the mic reciever (with antennas fixed to the rear of the unit) should be as close to the transmitter as possible.

 

vince

[paulears]

Not really Vince. Best is to consider the antennas as the 'capturing' device and the receiver as the 'decoding' device. The object of the two combined being to ensure the input to the receiver is presented with the best signal possible. RF drops off rapidly, following the inverse square law, so at double the distance, the signal has dropped to a quarter of what it was. If this is still plenty, then fine - the system still works. RF in a cable still gets weakers as it travels further, but much less than in free space. So, best practice is to have the capturing element as close to the transmitters as possible. If the antennas stick out of the receiver, then the receiver needs moving closer, if they can be remoted, then antennas close, receiver further away is best. The only caveat is that RF cable comes in many varieties. Some is thick and very low loss, some is thin and much worse. VHF generally gets attenuated less than UHF, but UHF allows antennas with gain. On this subject, people have mentioned amplifiers. In general, their purpose is to boost the antenna level so that losses in the cable don't matter too much. Their benefit when used at a distance is marginal. In effect, if the signal isn't there, the amp can't amplify it. It tries and although level goes up, the noise does too, tending to make the nasty surprise noises worse.

 

Aerials placed close in, high enough and away from obstacles, especially metalic ones, is always the best way. Diversity receivers work better with decent spacing too. The short distance as on the back of a receiver isn't really far enough apart to stop all dead spots or dropouts.

[Bobbsy]

Thanks paulears....good explanation!

 

The point I was trying to make is that, given the resources and skills, an RF system can and should be DESIGNED, not just purchased off the shelf.

 

The eirp of the transmitters is known, the gain of the antennae and the cable/connector/splitter network lossses can all be calculated. So long as you get the numbers right, remoting the recevers from the antennae should not be a problem.

 

As an example, I don't know of any professional TV studios where the antennai are not located in the studio itself and the receivers in audio control...which can be many tens of metres away.

 

You're also very right to stress the importance of separating the antennae for true diversity reception...this makes a huge difference.

 

Bob

[david.elsbury]

FWIW I have heard it said that it is a lot easier and more reliable to send balanced audio than it is to send RF a long distance.

 

In effect, if the signal isn't there, the amp can't amplify it. It tries and although level goes up, the noise does too, tending to make the nasty surprise noises worse.

True, so this is why if using antennas you should place them at the source, to line-drive the signal.

 

HTH some

David

[paulears]

The ironic thing about RF is that sometimes you spend more time stopping it getting where it shouldn't than making at appear at the right spot!

 

I've moved recently and the fire station next door wipes out ITV, I'm in a fringe area anyway and have to have a high gain aerial, that points STRAIGHT at their tower. Filters work, but the insertion loss spoils the picture. To make matters worse, it was me who installed the aerials on their tower 10 years ago, so any moans I may have make me a bit of a hypercrite. Sorry for going off one one, but I just attempted to watch a programme I'd recorded!

[colray]

I started out as an RF engineer working with flight avionic systems.

I think some basic principles would be handy here. I would hope we are talking UHF.

Getting the Tx to be as closely coupled with the antenna is a definite plus. Get the antenna as high as you can above the stage BUT as far from lighting components as practical. Never line up the polarization of the antenna or co-ax with mains cables. anything closer than 3m is asking for it.

Always use a diversity system and head amplification. Good idea to provide clean mains to the entire RF system. Be prepared (I mean Licensing) to change channels to avoid RF noise sources in the proximity. Be prepared to play with the polarization of the antennas to maximise the I/p signal.

Remember most Co-ax cables even the expensive ones from Canford leak RF and that is both ways. Take care how the coax is installed. changes of directions should only be gentle curves because if the inner core moves fractionally to close to the brade then you will create an impedance change which will cause unexpected phase shifts and loss of signal. Again don't run the coax anywhere close to mains cables. Do not leave co ax as a coil. even 1 turn of co ax will act as one side of a transformer!!

As for the Rx, site where ever is operationally prudent for you. I always have it FOH for small events or at big events at the monitor mix control desk.

[Djbarryblue]

We use 17 Radio mics on avarge a week and all of our recivers are at the sound desk so we can monitor them we keep spare mic heads and batteries down at the dsm s desk for emergencys and a spar belt back.

 

We have never had any problems with this. We have spoke about running anntenas down to the stage but as it works they way we have got it for a few years why change it now.

 

Barry