Comms/radios

[MrBoomal]

Hello all,

 

Could someone give me a definitive guide to the technical differences between a comms system and a two way radio system.

 

I have been asked to list the pros and cons of each.

 

Thank you all.

[RGSD]

Comms System -

 

A comms system is wired and therefore you can only move as far as the cable reaches, This could have safety implications if it is used around automation or across walkways. Comms systems come in two types, series - where if one set is disconnected - the others will go off or in a spider form where every set is unique.

 

You can get wireless comms systems but these are limited to the amount of users who can talk at once - this can be overcome by being able to allow an unlimited amount of users to 'listen only'. Wireless comms systems also incorporate an unlimited amount of wired comms systems so the wireless users and wired users can talk to each other.

 

Two way radios -

 

Two way radios generally only allow one person to talk at once restricting the amount of talk over the airwaves. This can be useful to be sure that a message is clear but if another user presses the talk button the message can be 'keyed' which distorts the transmission. Two way radio systems can be joined to wired comms for both transmission and receive.

[MrBoomal]

It would be a wireless comms system.

 

This is for a funding application.

 

It would be a like for like comparison. I.e both systems would be wireless with headsets.

 

 

edited for clarity.

[tolley1466]

I wish I could get some funding for Wireless comms :)

[RGSD]

Generally the only reason to get 2 way radio (Motorolla for instance) Is for the distance - Motorollas can travel further distances than wireless comms without having boosters or remote antennas.

 

For example - in a theatre, there would be more need for a comms set for the ability to all talk at once (not usually a large amount of sets) and the need for remote antennas to use the system in other parts of the building. In Festivals or large outdoor events, the radios are more viable as they transmit over further distances as well as needing large amounts of people to be able to use the transmit and receive functions.

 

So in short its all about how many people need to use the system and what the distances/RF obstacles are involved.

[paulears]

Hmm

2 way radios are semi-duplex or simplex - using one frequency, or two separate ones, but they can transmit OR receive at a time - so usually you press a button to talk, or use a nasty vox auto transmit - where as soon as it hears a sound, it shifts into transmit. On top of this, audio quality is limited - not a lot below 250Hz and nothing much up the top either - just the frequencies in speech that cut through.

 

Typical theatre typ comms allows full duplex - you can hear and speak at the same time without any effort. They're usually better quality too. Most are cabled, but some wireless versions exist, but are very expensive.

 

People like the TV outside broadcast companies use a combination of both. Production talkback is on a duplex system to those people who need it, while it's also continuously transmitted on a single comms frequency to walkie-talie style radios fitted with headsets. Most users do not need to talk very often, but when they do, they prod the button and their transmission is sent to the comms system via a separate receiver.

 

So you've got plenty of choices, all have advantages and disadvantages. Much depends on what you exactly need to do. Simplex radio, using a single frequency is the worst system because you have to prod a button, and you will talk over each other if you hit the button at the same time as another user. In addition, you can't butt in - you have to wait until somebody lets go of the button - meaning it's not too much good for cueing.

 

Semi-duplex with a repeater base station give better range, as the receive/tx aerials can be high up, meaning as long as your weak signal can be heard by the repeater, it can be re-broadcast to everyone else. Much more reliable - still only one person at a time though.

 

Wireless proper duplex comms can be just used as if it has wires and is open to everyone - BUT is the most expensive.

 

Simplex or semi-duplex walkie talkies are a real pain for theatre use. Cabled systems are very reliable. Wireless works, but there will be dead spots if you push distance, or are working in RF dodgy venues - as in those with steel skins, plenty of screening and possibly even other users trying to share available spectrum.

[duncanborrowman]

To add to that. Wireless Duplex is great for a Theatre auditorium, but don't expect it to go through walls.

 

The best place to start is what exactly do you want to do....

[lxdad]

Might I suggest having a look here:

 

http://www.riedel.net/

 

And here:

 

http://www.clearcom.com/

 

Buying anything else would be a mistake in my opinion.

 

Both those companies have good UK dealers who can help you put your document together.

 

LXDad

[JohnMac]

Remember that a wirebased comms system can be used anywhere. any time. :)

 

Radio systems will produce strong electromagnetic fields when transmitting, these can cause your lighting desk, computers, sound equipment to crash. :)

 

Regards

 

John Mac.

[osal]

we use both wireless and wired comms inked together at work for the flex of being able to go the distance etc

 

advantage to this is easy for everyone to talk

 

however when working with some of the schools I work at I prefer 2 way radios as it seams to minimise the chat to essential

[duncanborrowman]

In 20 years plus in broadcast I have never known a radio crash other kit. In my opinion for radios I would use motorolas. For theatre wireless I would use Altair and for wired either Tecpro for cheaper end or RTS for real flexibility.

[Neil Hampson]

I have never seen a radio cause anything to crash, however I have seen the effects of RFI from a radio, standing in the rack room below a power station control room where all the old chart recorders and measurement instruments live, press the PTT and watch all the charts fly off the scale for a split second. not so much of a problem in the new digital age, but a lot of big plants in the power, and the oil & chemical industry are using some very old instrumentation kit to control the plants. One oil refinery I know if is using a pneumatic control system built in the 1940's to run a critical part of the plant. it can't be ripped out and replaced because nobody knows exactly what it does or how it works anymore to replicate it.

[GridGirl]

The only thing I've ever seen a radio crash is a stopwatch - our Motorolas used to reset the stopwatch if you keyed them up within about 30cm of it! Never had any problems with lighting or sound gear though.

[cedd]

I guess it all depends on power levels. I doubt a PMR handheld would cause much in the way of RFI, however on a site licensed system (such as the ones I use at work) you're able to radiate quite a decent output power (5W in our case). I can key my handheld next to my computer monitor and watch the image be pulled a good 3 or 4 inches to the side. I too have seen servogor chart recorders go full scale when a handheld is keyed next to them.

 

I would say that festival sites or very large venues, where a license is held, are far more likely to feel the effects of a handheld crashing a piece of equipment than a small theatre running PMR (max ERP 500mW).

 

An interesting thing to consider though is that a normal GSM phone has a maximum ERP of 2W, so far more than a PMR446 handheld. Yet I know many lighting engineers who sit their phone on the desk during a gig. I wonder if they'd let a handheld radio near their desk. Arguably the frequencies are different (around 900Mhz) but the effect of such a high power transmission is going to be largely the same.

 

Of course if the desk and handheld radio are EMC certified then it shouldn't be a problem.........

[dbuckley]

Try keying a Motorola up next to a RCD - most of the older ones will open...