Weirdly hacked RadioCom intercom system
A wireless intercom system fell to me to evaluate, and to make sure it would be compatible with other systems in use around our community. This one is a bit of a strange duck. It looks basically like the other vintage-early-oughties Telex BTR-200 class systems that have crossed my bench, but this is definitely a later revision on the concept and has a couple of immediately noticeable features.
[These are low-res images, but each is linked to a higher-res copy.]
The most obvious oddball thing is the white pushbutton switch, added to the beltpack in a decidedly homebrew sort of fashion, labeled "ISO". A bit of digging around hints that it's for a mode called "wireless talk-around", where the wireless-system beltpack users can converse among themselves without the audio going out to a connected wired system. It's not clear why this would be useful, but I suppose some venue operations wanted this functionality so it was evidently worthwhile enough to add.
Opening the beltpack reveals a small add-on board, kludged in with tape and hardwired to various circuit points around the unit. The "ISO" switch contact brings battery-positive straight into this via the orange wire.
Other than that, the innards look like an up-rev design of the TR-200 pack with the exact same case around it. For some reason the sex of the headset connectors is reversed, too. There's no real point in that as it makes this system incompatible with most other intercom parts, and the exact same piece of plastic is used to mount the XLR4 connector so it's not like it's saving any internal real estate.
A look inside the base station reveals the other end of the ISO hack, and it's fairly clear how it works after a little poking around. This seems to be some kind of add-on kit, with a rather sketchy approach to mounting the parts. It may be either a prototype for a higher-end system or an aftermarket kit with very limited distribution, but certainly not an official feature of this one. That's a guess from reading this product catalog, which was originally grabbed from here. The "talk around" feature is not mentioned anywhere for the BTR300.
And yet here it is, sort of, spliced in a somewhat brute-force fashion into this particular base station. The little add-on boards, possibly a commercial product intended for some other application, appear to implement a CTCSS tone of about 90 Hz. This gets superimposed on the talk audio from any beltpack channel that's using the ISO switch. Per-channel audio is tapped off at the connector headers on the receive board and sent to the block of decoders, where the tone on a channel triggers an analog switch to redirect the audio away from being sent to the general intercom channel. Instead, it is sent through its own little mixer [that little proto-board at the left] and piped directly into the transmit board so the rest of the headsets hear it. The white wires from the decoder are logic inputs to the switch daughterboard which handles redirection of any given channel. The switcher is brute-force wired into each channel's audio path by lifting resistors near the channel-enable pushbuttons and soldering to the connections, and the other add-on parts are simply *taped into* the box wherever there's convenient empty space. The daughterboard has "Currycomm" in the circuit etch, for which there is no findable information on the net -- other than some unrelated marketing company that talks about "communications", but certainly not this type.
So the whole setup has a very one-off or few-off feel to it, and it's not even engineered very well. The audio mixed via "ISO" mode is significantly louder than the normal path, which tends to lead to headset feedback in these systems -- maybe the designer thought that was a good idea to emphasize when the feature is being used, who knows. When the stock base station itself has a switch to either engage or isolate from an external wired intercom bus anyway, I can't quite see the merit of creating a "separate channel" on the fly per a user's choice -- and if they did want to do that, the ISO button is momentary and would have to be held down for the entire duration of the "private" conversation. What is so secret or inessential, that the rest of one's run crew shouldn't be hearing it?? And because the CTCSS decoders take a moment to sync up and assert the switch logic, beltpack audio *does* go to the main channel for an obvious quarter-second or so whenever an ISO is keyed -- letting everyone on the bus know that the wireless users are having their own conversation anyway. If an important directive needs to go out and the wireless users are gabbing away loudly in their own little enclave, they might easily miss it.
There's a little discussion about wireless talk-around in this forum thread, where users at some venues seem to favor the feature but don't really explain why. It doesn't really seem to be too common a thing, and almost certainly not needed for typical usage in our tech community. With the stock audio paths disrupted through the switch board in a way that's rather involved to repair, the easiest way to disable the "feature" is to remove the four audio taps at the receive board and be done with it. Leaving the beltpack switches installed would still send audio with the 90 Hz tone added to it, but it would just go via the normal path and sound about the same as using the normal talk switch.