School Video News Cam IC Part Two

Camera Intercom Systems-Part Two

PART TWO

How Does Production Intercom Address Wireless?

First, all of our solutions involve augmenting or creating a cabled system with a few wireless stations. From thousands of telephone conversations about wireless over the years, our customers, when asked how many in their crew actually need to be wireless, have almost universally answered 2 or 3. Though the solutions we offer can go way out beyond 2 or 3, all of our assumptions have been based on 2 or 3. Here are our suggestions, going down the same list of system types.

AA. Simplex system with a Production Intercom twist:

Old friends and customers can skip this part. We’ve been doing this one for almost 20 years. Our AD913 permits a group of simplex transceivers to communicate, back and forth among them and with a cabled intercom system. It is simple to use and truly inexpensive. You’ll need as many portable transceivers as you have crew that need to be wireless, plus one. The AD913 connects to the cabled system just like it was another cabled beltpack. The combination of the AD913 and the extra transceiver connected to it becomes the base station for the wireless portion of your system. The extra transceiver is connected to the AD913 with a cable we’ll provide. When the roaming portable transceivers transmit, their signal is picked up by the transceiver that is part of your base, and fed into the cabled system by the AD913. The wireless portion of the system is still simplex, so we have to find a way to cause the base transceiver to transmit when cabled stations want to speak to the remote transceivers. This is done using the signal light system in the cabled portion of the system. Pressing and holding any signal light button (on the same circuit as the AD913) in the cabled system will cause the AD913 to switch the base transceiver into its transmit mode, and whatever communications traffic is on the cabled system will be heard at the remote transceivers. You’ll only have to adjust the levels in and out of the AD913 so that the transceivers are being heard at the same level as the cabled beltpacks, and the cabled beltpacks are being heard at the same level as the transceivers. It’s simple and quick to make these adjustments, which might not be required at all since every AD913 is set and tested at normal levels before it leaves the factory. All you have left to do is choose what headsets you want to use with the remote transceivers and the system is complete. We have a broad selection of headsets and lapel speaker/mics. It is not necessary to carry the transceiver around in your hand. Sling it around behind your back and use the in-line PTT switch on the headset cable.

The switch can hang on your belt, clip to a shirt pocket, or just be hanging in front of you. There are a huge number of headset styles and qualities to choose from.

BB. Full Duplex Systems:

Save your pennies. If we ever figure out how to build a full duplex system that is either better or less expensive (or both) than the products currently available, we’ll sure let everyone know about it.

CC. Half Duplex Systems:

The AD913 Simplex System discussed above has four or five legitimate knocks on it:

1. In the real world of performances, technical crew members are getting the information they need not only from instructions being transmitted specifically to one individual, but also by monitoring the general traffic on their intercom channel(s). They can’t do that in a simplex system.

2. The persons calling the show from master stations do want to reliably assume that the crew members on wireless are hearing them, and don’t want to have to remember to press a call light button to transmit all the time.

3. Using the call light to trigger transmit to the wireless crew, effectively makes the “call” function unusable for its original purpose. The light is going to be flashing on and off, all through the performance. If there are any signal devices like our Blazon strobes in the system, they too are going to be triggered unless they are isolated on their own circuit. (We’re about to announce a cure for that!!)

4. The noise often heard in the headphones (k-chzz) each time the base transceiver is keyed to transmit could be annoying.

5. Wireless crewmembers equipped with simplex transceivers must press their talk button to communicate back to the stations on the cabled system.

A half-duplex system can eliminate the first four problems and we would argue that the fifth is seldom a real issue. In fact, people calling the show, stage managers, lighting directors, etc., generally want crew members to keep their headset microphones turned off except when they need respond to a call, or need to report. (Some manufacturers actually offer an accessory that will permit the person calling the show to shut everyone’s microphone off.) But they do need to listen constantly.

Here’s how it works. After looking at the available products and prices, we chose to use a professional quality, off-the-shelf, ICOM repeater with some special preparatory modifications and connect it to the cabled intercom system through our new HD903 half-duplex adapter using a custom DB25 cable. The HD903 takes care of matching the audio ‘out’ level from the repeater to the audio ‘in’ level of the cabled system and the reverse.

Plug a standard intercom cable (2-conductor shielded with male and female 3-pin XLR-type plugs) into the back of the HD903 and into any convenient jack in the cabled system. It could be a special run from the cabled system’s master station but it does not have to be. An available loop-through jack on the back of any belt pack would do just as well.

The remote transceivers can be any high quality UHF portables that have been programmed to operate on the frequencies set up on the repeater. If you choose our ICOM portables, we can do all this for you.

When you activate the repeater, any transceiver on the chosen frequency will hear the uninterrupted audio from the cabled system and the other portables. Press the talk button on the portable transceiver and you will be heard on the cabled system and by the other portables.

The receive side of a repeater, to which the cabled system is always connected, is inherently noisier than the audio on our cabled systems, so the HD903 has a circuit to eliminate that noise.

If you don’t already have a cabled system you can run 5 belt packs directly off 3-pin XLR jack on the back of the HD903. This will require that you connect the small power supply that comes with the HD903. If you already have a cabled system, the HD903 will be powered by your intercom power supply.

Because you will be using conventional portable transceivers, all of the accessories and gadgets made for them can be used, from lapel mounted speaker mics to concealed earspeaker/microphone combinations like those used by the secret service. The batteries available for these transceivers have capacities as high as 1800mAh and will operate at 4 watts output for as long as 14 hours. Since you’ll probably be operating at 1 watt, battery life becomes a non-issue. Should one of your portables be damaged, lost or stolen, a replacement can be easily found. Any two-way radio shop in any town should be able to solve your problem. When it’s not performance time you have a very powerful repeater based system to coordinate setup, teardown, or sending somebody out for a pizza.

All of the points regarding FCC licensing, etc. in section AA above, dealing with straight simplex systems, also applies here. It’s more than worth it to properly license your transceivers. You will get protection from others in your area using the same frequencies. You will be able to use the full power of your transceivers, including the repeater, which will give you far more coverage and reliability of communications than any other system discussed here. And you’ll be cooperating in the campaign to share those precious frequencies in the most efficient way. Oh, and you won’t get a nasty letter from the FCC.

Huge changes are coming in the availability of frequencies and in the spacing between frequencies required by the FCC. The spacing between frequencies is going to be cut in half, for the third time (from 25 to 12.5 to 6.25), and only the best transceivers are going to be able to operate without slopping over onto the adjacent frequencies. Those that can’t will soon be unusable. The bottom portion of VHF television channels (2 through 6) is going to disappear within the next couple of years, and the top half (7 through 13) not long after. This, and the advent of high definition TV, is going to result in massive reallocations of frequencies. The ICOM portables, and the repeater that we are recommending, are already engineered with that in mind.

The half-duplex system isn’t perfect. We believe that the only serious drawback is the fact that only one portable can be successfully transmitting at a time. If you’ve ever joined in a multi-party conference call, you might not consider that such a disadvantage. What does happen? If two, or more, portables try to transmit at the same time and one of them has a more favorable position vis-à-vis the repeater’s receive antenna, that portable will win the competition. In the unlikely situation where two portables are in exactly the same relative position, and both start transmitting at the same moment, the repeater may alternate back and forth between the two creating a jumble. In practice it’s not much of a problem for crews who are familiar with one another and where a voluntary protocol evolves. If it does become troublesome and you are using ICOM portables we can program them and the repeater to implement a ‘busy channel lockout’ feature. When any of the portables begin to transmit, the others, when they press the transmit button, will get a beep/beep/ beep tone indicting that the channel is in use. This is simply a programming function. There is no hardware involved. We don’t do it to all of them because we have learned from 20 years of selling our AD913 system that it’s just not much of a problem for most of our users.