10 way Sennhieser G3 system

[Mr Steve]

Hello,

 

We have a 10 way, home built, Sennheiser G3 system of ew100. Two ASA1s are connected together to cover 8 ways of G3, with A1031u omni paddles. I had been told that to connect the 3rd ASA1 for the 9th and 10th G3s I can use a BNC t-piece to split the input from the A1031us to the 3rd ASA because it "works well in practice".

 

Is anyone else operating a system like this with T-piece splits in the real world, or am I likely to run in to problems down the road?

[boswell]

Before we sent our Ch69 kit back, we had 8 ew100 (pre G1) all linked with 'T' splits and fed from the standard supplied senn aerial

No problems. Try it and see, not much to lose it it don't work, 50R Tee splits are cheap

HTH

[chelgrian]

Hello,

 

We have a 10 way, home built, Sennheiser G3 system of ew100. Two ASA1s are connected together to cover 8 ways of G3, with A1031u omni paddles. I had been told that to connect the 3rd ASA1 for the 9th and 10th G3s I can use a BNC t-piece to split the input from the A1031us to the 3rd ASA because it "works well in practice".

 

Is anyone else operating a system like this with T-piece splits in the real world, or am I likely to run in to problems down the road?

 

The answer is you *might* eventually run in to problems down the road. You are effectively creating a Y shaped transmission line. Due to inevitable impedance mismatches between the line and the termination you always get some reflection these reflections interfer with each other. If you attach the T-Piece directly to the back of the first ASA100 attach the antenna to once side and the shortest possible run of coax from the other side to the ASA100 for the 9th and 10th one then you will minimise the effect.

 

However as always the only way is to try. The G3 100 series now has sound check mode so you can put all of the receivers into that turn all your beltpacks on and get people to walk around. If you also record all of the sound outputs into a DAW at the same time then you can listen for RF based audio problems. Unfortunately the 100 series doesn't have Ethernet sockets to support WSM so you can't remote monitor them in that way.

 

However if it doesn't work a second pair of A1031s for the 9th and 10th mics is only around 200 pounds.

 

I see you are based on Cambridge, out of interest is this system in a venue in Cambridge and if so which one?

[Mr Steve]

Thanks. I had overlooked soundcheck mode. I will test the setup out and see how we get on.

 

Chelgrian - it's not a pro venue.

[Rob_Beech]

It's not something I could do as it wouldn't be acceptable for hire stock, but in practice it does work, it's unlikely to cause any issues at all. Just make sure you get the right one. Introducing anything based around 75ohms into the circuit will pretty much destroy everything.

[david.elsbury]

Introducing anything based around 75ohms into the circuit will pretty much destroy everything.

Could you please expand on this? My understanding (based on reading what Henry Cohen, a US based radio specialist who deals in our industry quite a bit, says) is that the input impedance of the radio RX's is between 50-75 ohms anyway, and so the use of more easily available 75ohm splitters, and chunkier cheaper coaxial cable, doesn't make an appreciable difference- a bigger problem is multiple connections and joins, resulting in reflections and signal degradation.

 

David

[timd]

From my research previously, and my thread from a while ago, the power loss due to reflections at the 50/75R boundary are negligible, and if you're using a long length of cable to the antennae, you might actually be better off using 75R cable since it typically has substantially lower losses, being designed for the minimal signal voltages in sat comms.

 

Tim

[paulears]

I'm firmly with Tim. RF problems with radio systems such as these are rarely related to signal level, but loss of signal - hence why remote aerials are so successful. The loss of thin,flexible cable is quite high, but stick a paddle or any aerial really, on the end, up in the air, close to the transmitters and system reliability is pretty well assured. For years, we persisted with the view that 50Ohm cable and connectors was for radio systems, and 75Ohm was video. There was also the 'fact' that plugging a 50Ohm BNC into a 75Ohm socket wrecked it. Pretty well all this is now just history. Diversity systems in many typical scenarios are pretty pointless. If the transmitter is in a dead zone,it's in a dead zone for both aerial fitted on a typical 19" panel - remote just one of these to an aerial up in the air, and watch the A B lights - the panel one rarely comes on.

 

Back in the 80s I had a spell working in radio - links for gas platforms off the coast, with feeders that you could hang a PAR64 from! However, once inside the rack,distribution was by BNC and TNC. With the short runs, it was perfectly suitable.

 

I still had in the store a few 4 way passive TNC splitters. I tried these on a radio rack instead of the 'proper' splitter and they were fine. 4.5dB through loss on each and hardly any change to the meters - their range is pretty huge, and small drops in signal really don't matter.

 

If anyone cares to try a proper test, they'll find that when a moving drop out happens, signal (on a 1 to 10 scale) doesn't go from 7 to 6, it goes from 7 to nothing - and no amount of gain in a splitter will make no signal into something useful. This is also why those people who use their racks FOH find plenty of signal, but any drop out areas are real black holes, RF wise - neither aerial get signal. Lots of people tour paddles and 20m lengths of thin cable. Look up the loss at 800MHz of this kind of cable - it's a lot, but it works!

 

A T-split with a short length of cable will make no practical difference whatsoever - and the results won't change if you move the system somewhere else. A proper splitter is a neat convenient (and expensive) way to distribute signals, but it's not really something technically clever - A television amplified splitter, designed to amplify and distribute RF on the same frequencies, works just as well for all practical purposes. Fair enough, they're wide open for 21-68, so provide no filtering,which purpose designed radio mic splitters do, but their design philosophy is the same.

 

I've never seen any documented reason for avoiding passive splits - we are not trying to amplify amazingly weak and distant signals - we're talking 20-50mW accross the distance you can throw a battery - field strength is many times higher than what comes out of my TV feeder - it's just that things get in the way, and we have to use aerial systems that aren't very good, so a 180 degree turn on stage places a damp salty blob of water between the transmitter and receiver, and spreading your aerials means there's a better chance of one having line of sight.

[Bobbsy]

I'm going to agree with 90% of what Paul said.

 

The difference between 50 and 75 ohm connector and cables is pretty small in grand scheme of things. Similarly, you can generally get away with a few T pieces (though I would plan that as a stopgap solution in an emergency rather than design it into a system.

 

I'm also a firm believer in getting the paddle antennae as close to the action as possible and using good low loss cable in a longer run to get the signal back to the receivers. I was lucky in this regard...working in TV we tended to have reels of high quality stuff that I could "borrow" the odd 20 metres of....

 

However, the one area that I suggest caution on is the use of cheap active splitters designed for CATV use. I've seen some of these that introduced phase errors that caused quite bad dropouts. Worse, the fault was hard to figure out until I borrowed some expensive test gear for the weekend since signal levels etc. all looked good.

[chelgrian]

If the transmitter is in a dead zone,it's in a dead zone for both aerial fitted on a typical 19" panel - remote just one of these to an aerial up in the air, and watch the A B lights - the panel one rarely comes on.

 

Sadly we are unlikely to see much advance in the technology used. There are a whole variety of things that could be done with spread spectrum, mimo and efficient encoding schemes.

 

There are 'digital' systems on the market such as Sony DWX, Zaxcom, AKG DSR but their doesn't seem to be much information about about their air interfaces.

[Mr Steve]

Well, in my scenario all connectors and cable are 50ohm RG58 type, and the antenna cable run to the omni paddles is under 5m, so things should be fine from what I have read here, thanks.