Radio Microphone Woes

[Yorkie]

Scenario: Church with three radio microphones:

1) TOA UHF Tie Clip (from about 2007) - Channel 69 or 70, set to use Ch 70.

2) Trantec S2000 VHF Handheld (from about 1995)

3) Beyer VHF Tie Clip (from about 1990)

 

Until November 2011, the Beyer reciever was mounted in a plywood cabinet (with its antennae coming through holes in the top) and the other receivers were put next to the cabinet on the floor. All three situated inside the pulpit, which is a three-and-a-half sided timber construction. In November we put the other receivers inside the cabinet so they wouldn't need to be got out and put away every Sunday. Since then (we think) there have been some problems.

 

The parish doesn't have any pubs/clubs/bingo halls/shops/community centre; the mics have never previously received interference. The system is unmanned; the mixer is in the cabinet (with the loop amp) and the radio microphones are controlled by turning them on and off.

 

The problems:

 

1) The TOA system occasionally drops out at random, but usally only for 10-20 seconds. It's not the batteries; I've tested it with new procells. It is used at most 15m away from the receiver, and the only things blocking the line between the transmitter and receiver are the plywood cabinet, the timber pulpit and people in the choir.

 

2) The Trantec system sometimes outputs a 'static' sound when the mic is switched off but the reciever is on. It only has an unbalanced output. The mic doesn't have a mute facility.

 

3) The Beyer system has a couple of issues - I replaced the mic a couple of years ago, resoldering it into the LEMO connector but this crackles when flexed; more heatshrink is probably the easiest way to cure this. The other issue is that it creates a thump when turned on; is this just a feature of an old radio mic designed to be muted at a mixer?

 

Are issues 1 and 2 likely to be due to the proximity of the receivers? Could issue 2 be due to the proximity of the loop amp and the unbalanced cable or is this normal for a radio system, or just an old radio system? Is Issue 3 normal for an old mic?

 

 

In the worst case, the church will replace these microphones. If the new receivers are to be installed in close proximity in a wooden (definitely not metal!) cabinet, should they require an external antenna? For a budget option I have suggested ch70 Sennheiser Freeports, but with the caveat that they are not robust, don't have a mute button and cannot have an external antenna. The existing TOA mic doesn't thump when turned on, is this an advantage of all newer systems? EW100 G3's would be a better buy if they can stretch the budget significantly - or should I be looking for second hand G2's ?

 

Unfortunately having an operator for the system is an unrealistic prospect.

[Bazz339]

Have you put the the receivers back where they were and tried them?

Were there drop out problems before you moved them?

 

I have used the S2000s in several church installations with no problems other than periodic breaks in the mics/aerials. The problem you are having with that sounds like squelch or mute on the receiver.

 

Have a look at the back of the unit. As far as I recall there are two adjustements, one for output volume (leave alone) and the other for squelch or mute, turn that up a bit. It sets a minimum level of radio reception below which the unit mutes automatically. Do not turn it up too much or you might get drop out of the signal when the mic is in use.

 

Likewise the mute/squelch on the TOA might be set too high and muting the receiver prematurely.

 

Is the Beyer Tie clip non-diversity? I.E 1 aerial? If it is don't bother with it too much, replace it. Beyer radio mics (some at least) used to be made by Trantec. Again it might be the setting of the mute/squelch on that.

 

Also the mic transmitters might be causing interference with the other receivers if one is on and the others off.

 

The Sennheiser Freeport units and Trantec S4.4 and I think 4.16 can put an audible click on the system when switched on.

[Yorkie]

I think they've turning the squlech down on the TOA, I originally set it at half way and I believe they tried it later at about 25%, unfortunately I'm not there very often so descriptions about issues or whether or not things have been tried are at best second hand by when they reach me.

 

The Beyer system is trantec built and diversity, but it has a pair of solid antenna that are fixed going vertically from the back of the receiver, which make it a pain to rackmount and I'm wondering if it's worth the hassle.

 

What I mostly don't know is if sticking a pile of different receivers next to each other in a cabinet is going to prevent them from working?

[timsabre]

We use the Senn freeports in a very similar situation, they very occasionally make a soft click when switched on/off "live" but mostly are silent. They are good value for money for a church in my opinion.

 

As Bazz says your trantec problem sounds like something's opening the squelch on the receiver - I have had central heating thermostats do this to me. Fluorescent lights being switched on is another one. Look around for something that might be sparking periodically.

 

I think turning the squelch down makes it more likely to cut out - try turning it to 75%.

 

Sometimes radio mic receivers can be really sensitive to positioning, move them a foot to the left and they work much better/worse due to nulls in the radio signal as it bounces off stuff. I would try moving them back to the original position. Stacking them shouldn't be a problem in itself.

[Yorkie]

Oh dear... The heating stat is about a metre away from the receivers and the front of the church has about 20 fluorescent tubes.

[timsabre]

Oh dear... The heating stat is about a metre away from the receivers and the front of the church has about 20 fluorescent tubes.

 

Should be easy to test then!!! They aren't gonna be turning the fluorescents on and off during a service though...it's all the starters flicking on and off that causes the trouble. You can check if it's the thermostat cycling.

[Bazz339]

 

I think turning the squelch down makes it more likely to cut out - try turning it to 75%.

 

 

Probably just a difference of terminology.

 

To clarify by turning the squelch up, I mean the level of RF required to un -mute is greater, therefore if the level of the TX output dips, it might fall below the level required to keep the RX un-muted and

therefore the audio may drop out. Turning the squelch up to 75% may exascerbate this problem. Turn it down too much and the problems with interference will almost certainly increase when the transmitter is off.

 

It may be RF from other transmitters that is causing the interference.

 

Whether receivers interfere with each other I do not know. I was certainly told many years ago that they did, whether that has changed with modern systems I do not know.

[paulears]

With the same type, then any leakage (local oscillator?) will probably not cause any issues - but harmonics of these can sometimes bite. Some older VHF receivers had an output up in the UHF band. Local aerials, sticking out of the rack could 'hear it', but remote aerials couldn't - it had gone, by the time it reached them.