Radio Cans

[ClaireL]

Just finished working at Grange Park Opera as DSM with a semi-duplex system (I think). I didn't set it up, and don't know the specific details, but I had a two-ring belt pack with one ring to wired comms and the other ring to one of the motorola channels. I could talk to both simultaneously, and talk over someone else on the motorola channel.

 

(Side note, the belt pack required a double-press on the mic button. And a very specific length of press and length of gap between said two presses. Which got very irritating in busy bits of the show. If anyone is ever involved in manufacturing/developing belt-packs, please don't do that :-) )

[mackerr]

I could talk to both simultaneously, and talk over someone else on the motorola channel.

 

 

It is very unlikely that you could talk over someone else on the Motorola channel. You might not have been aware of it on your pack, but the generally only 1 talker on a walkie talkie channel at a time.

 

Mac

[cedd]

It is very unlikely that you could talk over someone else on the Motorola channel. You might not have been aware of it on your pack, but the generally only 1 talker on a walkie talkie channel at a time.

Mac

 

Indeed. I wondered if it might have been some kind of trunked system, with priority assigned to the base station/mobile that was assigned to the comms system.

 

Paul's suggestion about knocking up a comms interface ties in with a project I've been trying to get off the ground recently. I now own a set of 6 Tait licensed (UK Business light) radios and am wanting an interface to a comms system. I tried building one using an attenuator and a sound-activated relay to key the hand held, but it kept getting itself into a feedback loop of keying itself with the "splat" at the end of the transmission pulling its' PTT back in again.

I've now decided to buy myself one of the cheap Baoafeng hand helds because they've got a VOX function which should do the job. I only need radio users to listen.

 

 

 

 

 

[ClaireL]

Thank you Mackerr for correcting what is clearly my faulty memory - were you there? Obviously I was imagining all the occasions when I clicked my radio channel mic on at the top of a standby/go sequence and left it open whilst receiving "Standing by" replies from various crew members via their radios.

[J Pearce]

Claire - are you saying you were on wired and could talk to wireless while receiving replies from the wireless? This would be the semi-duplex system Paul and I were discussing.

 

If you were also on wireless then generally only one wireless unit can talk at a time - unless something more complex has been set up, like some of the digital systems.

[mackerr]

Thank you Mackerr for correcting what is clearly my faulty memory - were you there? Obviously I was imagining all the occasions when I clicked my radio channel mic on at the top of a standby/go sequence and left it open whilst receiving "Standing by" replies from various crew members via their radios.

 

I wasn't there, but I have extensive experience with wireless comms and walkie talkies, and I work as an RF coordinator or comms lead on large productions. There are many wireless comms that are full duplex, meaning more than one person can talk on a channel at a time. This requires a base, and separate RF frequencies for the base to talk to the packs, and the packs to talk to the base with each pack on its own frequency. Motorola (walkie talkie) systems have one frequency per channel and everyone talks and listens on that same frequency, so only one can transmit at a time or there is severe interference that wipes out all communication on that channel.

 

Mac

[graemeftv]

Radio cans

 

television ob and studios for years! have been using the Motorola style walkie talkie radios , fully integrated with your hardwired users.

 

its simple and not impossible to build

 

followspots sound and lighting all on normal hardwired coms beltpacks

select few on walkie talkies

 

base station consists of

 

1 x motorola gm160 transmitting all the time on Freq 'A' - audio input is from the wired coms system

 

1 x motorola gm160 receiving all the time on Freq 'B' - audio output is fed into the wired coms system

 

walkie talkie (£20 from ebay rechargeable with 3 buttons - talk, volume channel select, simple and easy)

 

Walkie Talkie is programmed via usb and windows software so that it receives all the time on Freq 'A' and stage crew can hear all the wired comms all the time

 

walkie talkie is programmed to transmit using the push to talk button on a different freq 'B' which then lands this audio back into the wired coms system, this dialogue is then also present on the output of the wired coms system so gets repeated on the motorola gm160 base station on Freq 'A' so all other walkie talkie users can also hear there colleagues on a walkie talkie.

 

 

 

This is an industry standard setup in broadcast, and is used widely. its simple good range, cheap, add as many walkie talkies as you want. lots of manufactured base stations on the market raycom, riedel, prolink

 

if anyone needs any free help or advice feel free to contact me

[paulears]

It's a perfectly normal system - works extremely well, but can't be described as cheap. The old discontinued Raycom was fifteen hundred quid! The one I'm putting together would easily be that if I didn't already have them on the shelf. There's plenty of solutions - including the newer fully duplex systems, but cheap isn't the word I'd use!

[graemeftv]

motorola gm350 radios are £50 each online 2 units required to make a base station. most radio suppliers will program them for you before shipping

1 x 12v 5amp psu - £15

 

Here is a unit already available off the shelf from riedel at prob £2000 or more

but proves the concept

 

 

[paulears]

I didn't think they could cope with the duty cycle, but seems they actually can, but just get a tad warm. Not seen them for fifty quid yet, but for that money .............?

[dmxlights]

I have built ham radio repeaters from 2 radios back to back and also cross band ie vhf to uhf, uhf to vhf. both fully duplex. Its not hard to interface radios with a cans system at all. If I had some here as in belt packs or master station. I know I could do up an interface no problem.

 

For local shows that we do sound and lighting for we also provid Icom radios for coms and never had any problem with them as of yet. I get 3 shows from them with no problem at all. I will be giving my radios an over hall and good check up soon and renumbering them as I have added a few more.

 

I have them numbered for a reson so each user is to make sure their radio is turned off at the end of each show and they are to blame if the radio is flat for the next show they are using them on and cannot swap them around with an other user. The batteries are also number to match th radio.

[cedd]

What are the licensing situations in some of the above circumstances? If people are using UK Business Light then the license doesn't allow for any music to be broadcast (so no show feed if it includes music) and the license also says it should be single frequency only operation without use of a base station.

Of course all of that goes out of the window if you're properly licensed for a site specific duplex system, but I thought it worth mentioning.

Interestingly I had a conversation with a colleague who used to work for Ofcom about my plans to build a vox operated line input for my TAIT hand portables (for just the above reason - to get wired comms on to my radios) and he said he would consider such a set to be a base station once it was wired to a DC supply and an external line input. There's nothing in the licence to clarify this, but as an Ofcom investigating officer this was his take on it.

I did have a fair bit of hassle building my system. I used a commercially bought vox relay (sound operated relay from CPC) with the input wired via DC isolation to the mic input (its' input was designed for an electret mic, as was my radio). I then had a pad and isolation transformer across the mic input coming from the line out of the comms system. The PTT pulled in fine, but wouldn't then drop out again, or worse it'd get stuck in a feedback loop of off & on. Never had time to get to the bottom of it, but one day I might revisit the project.

[Tom]

motorola gm350 radios are £50 each online 2 units required to make a base station. most radio suppliers will program them for you before shipping

1 x 12v 5amp psu - £15

 

Here is a unit already available off the shelf from riedel at prob £2000 or more

but proves the concept

 

Graeme - Had a look at the Reidel site but couldn't see these units. Also, the GM series is now discontinued so hard to find. I can find DM equivalents, but only at the £200 each mark plus the PSU.

can you provide some links to your suppliers please.

 

Does anybody have one of these systems good to go for a hire next week - inc wire comms.

 

T

[paulears]

Cedd - I suppose of you bought one, you'd license it with a technically assigned frequency, or if hiring, park it on one of the duplex hire channels. I didn't think the music clause was still all licenses as it's gone from PMSE and the broadcasters talkback and cue channels always have music on them. Checking my suppliers license, it's still there, however! I suppose that leaves it as a PMSE assigned license venue specific? Although the music content is really leakage into the comms isn't it - it's not like it's a radio link for the music.

[cedd]

It's a difficult one to know for sure. Sadly with Ofcom's documentation it's all very generic (remembering it covers everything from hospitals and airports through to taxis and school lunch staff). It's also very difficult to get hold of anybody technical to discuss any issues or questions. Getting put through to Baldock (or having the direct number is the only way to get somebody technical, and that only really happens if it's safety critical). Our needs are very specific and a lot of what we do legitimately in our trade may in others be seen as dodgy (taxi firms have been done for broadcasting their own mini radio station over their channels before, whereas music content on our show feed is essential to our work in some cases).

 

I think the overriding thing with Ofcom these days is simply that, if you behave, don't cause interference and are properly licensed then they're probably going to leave you alone. It's blatant disregard for power output, licensing and generally being a nuisance that they're actively going out and tackling. They don't have the resources they used to (a team of 4 or 5 guys covering Yorkshire is now one guy covering the north east of England - top bloke though.