Radio mic distro amp.

[Ynot]

We don't seem to have too much in the BR on actual distro amps, and my mind's been drifting towards adding one to our radio mic rack.

 

Anyone have any recommendations?

 

Would like actual experienced responses, please - not "I've Googled this one and it looks good on paper..."

We run between 10 and 14 mics (Senn EW100, mix of G1 and G2) on our licenced freq's.

[gareth]

We use Sennheiser distro amps in our many racks of radio receivers, and get good results. Will pop next door into the old projection room (which is where they live!) after this show, and find a model number for you.

[Ynot]

We use Sennheiser distro amps in our many racks of radio receivers, and get good results. Will pop next door into the old projection room (which is where they live!) after this show, and find a model number for you.

Cheers Gareth.

;)

[gareth]

The rack I just opened up has an ASP2 distro amp in it - I'm sure the others are the same. Couldn't tell you offhand whether those are compatible with your EW100s - but will check tomorrow with the man who knows about these things! (Aw, come on, I'm a lampy! I don't know about radio mics! ;))

[Rob_Beech]

Yes they are. They also supply power with the correct PSU, generally sold separately may I add.

 

4 per ASP2, or 8 non diversity. Unless you have 2, etc etc.

 

Very good units, s'what I use aswell.

[jason.fallon]

If your going for the ASP2s which are fine, and using the passive antennae with the boosters, make sure you get the boosters for the appropriate frequency band. The Splitter and antennae are not band sensitive, just the boosters (Which are well worth getting)

[Rob_Beech]

Don't fully agree. Boosters are well worth getting and using when they need to be used. Sometimes they can have negative effects.

 

Overmodulation is caused when the mics are too close to the receivers. With the boosters in place this can sometimes "boost" the problem.

 

It's also worth noting that you must keep the wiring neat in the back of racks. power cables crossing over RF cables multiple times can sometimes cause issue.

[Lamplighter]

Overmodulation is caused when the mics are too close to the receivers. With the boosters in place this can sometimes "boost" the problem.

 

It's also worth noting that you must keep the wiring neat in the back of racks. power cables crossing over RF cables multiple times can sometimes cause issue.

 

Being pedantic, overmodulation is caused by the transmitter being overdriven, eg too much audio, usually due to incorrect adjustment or fault. Intermodulation is the effect when two or more transmitters interact and produce unwanted frequencies and this can certainly be caused or made worse by overloading boosters, but is just as often due to direct breakthrough, receiver overload or a poorly designed frequency plan.

The effects of untidy wireing are less of a problem particularly with decent RF cable ( double screened) I have had far more cases of unwanted interference where the cables are neatly loomed but single screened than where the power and RF leads are loosely intermingled. This covers installations from microwatts to kilowatts. I would advocate tidy wireing but it doesn't need overdoing.

Brian

[jason.fallon]

Don't fully agree. Boosters are well worth getting and using when they need to be used. Sometimes they can have negative effects.

 

The only time Ive got negative effects from the boosters is if I am literally holding the transmitter beside the antenna, otherwise they make a very substansial difference to my ew300s. Enables me to op from furthur away and still have racks beside me so no more money spent on a NET1 to substitute.

 

It would be nice if they had an active directional antenna available though. Less stuff to plug in. I'm digressing now though...

[Rob_Beech]

On page 36 of the Manual for the 300 series G2 we see a bullet point that says

 

* TO avoid overmodulating the receiver,observe a minimum distance of 5m between transmitting and receiving antennas.

 

Though Brian is correct, decent cabling is more important. As with anything really. You wouldn't use rubbish cable for the AF, so don't do it for the RF.

 

 

 

To add :

 

Jason, very true, I use all 300 series, and have the boosters on all channels. I find its very rare I need to use the external antenna and a pair of standard ones on the front of the rack is good for well over 50m. That said I have never run them at FOH. Only on the stage, so I'm minimising the risk.

[Bobbsy]

Boosters, probably more properly known as RF amplifiers, have their place. As long as they're designed into your link budget and placed at the proper place in the chain they can help compensate for RF losses due to cable runs, connectors and splitters as well as simple distance between transmitter and receiver.

 

However, two points on their use. First, the ones chosen have to be of a sufficient quality not to add any unwanted noise or phase instability into your system. Second, you're always better off placing the boosters right at the antenna, not at the end of the cable from the antenna to the receiver. Once the signal is degraded, adding a booster will also amplify any noise present in the chain. Think of it like audio. If you "boost" a mic level signal to line level at source, you can then run it down a long length of cable without any appreciable noise. However, if you run a low level mic signal a long way, to the point where there is noise on the audio, adding an amplifier at the mixer end just makes a poor signal a louder poor signal. Purists will see that my analogy is a bit stretched, but it's basically what's going on.

 

As for antenna dividers, let me add a recommendation for the old Sony AN-820A which I used for many years of flawless work. It allowed me to do a couple of things...first it would combine up to 4 antennae, allowing me to scatter them around the theatre as appropriate to get coverage of those "difficult" scenes. Second, it gave me 4 outputs per "side" of a diversity system plus a "cascade" feature so I could use multiple dividers if required. The AN820 was stupidly expensive (and is no longer the current model) but if you see one cheap on eBay, snap it up.

 

Bob

[paulears]

In fact, Sennheiser's use of 'overmodulation' is probably just an attempt to use language most likely to be understood(ish).

 

Moving a transmitter closer to a receiver on a different frequency introduces de-sensitisation. The very strong RF on a channel close to the one you are attempting to receive on effectively saturates the front end of the receiver circuit, making it very 'deaf' - so the wanted signal from the distant receiver just isn't received at all. With narrow band receivers used for communications, a device such as a resonant cavity filter is used. These are very selective filters, designed to put a sharp notch in the received frequencies, just where the strong unwanted signal is - rather like an audio graphic. They're not really suitable for wider band systems as their design is not quite right - attempts to widen the bandwidth reduce it's efficiency - and, the things are quite large. Tuning them is also a mechanical task, involving expensive kit and they don't travel very well.

 

I suspect that many problems with noisy RF in radio mic systems are likely to be due to de-sense, rather than a real lack of RF energy. After all, many people have few problems with receivers at the mix position. RF is lower, much lower - but it still works. With receivers on stage the RF levels on the meters are higher, but every now and again one goes hissy. I've always reckoned it's more likely that somebody just got closer to the receive aerials (especially when remote ones are not being used) and wiped out the weaker people across the stage. Inverse square law applies to RF too, so somebody just a few feet from your receivers can play havoc - but because everyone is looking to the person who's pack must be the problem, the random element of other people doesn't get paid attention to - and you try it under controlled conditions and the problem channel is fine. Next show, it dies again at the same point - then you notice Joe Bloggs in the wings leaning against the receiver rack watching the show, just like he does at that moment each show.

 

Perhaps worth a thought next time you have problems - wide spaced receive aerials, high up make de-sense issues much less common.

[BlueShift]

I tend to use the Shure UA844 Distros - mainly because they are active, not passive. These have worked well with everything I have tried them with and are not frequency sensitive, simply add input filters for your particular band and you are away.

 

Thanks,