"Control" Station for my Business

[Jurassic69]

Hey all,

So I manage a large cinema complex. We use about 30 MOT CP200's that operate on 4 channels, 2 of which use repeaters. I think we are somehwere in the 460mhz area. I am looking for a sort of "base station" where we can monitor all 4 channels and brodcast "all calls" to all 4 channels, or some combinations of the 4, at once with some type of alert tone preceeding. I would like to accomplish this and spend under $1k.

Any thoughts?

Thanks!

[RKG]

Step One: review your license and file for whatever changes would be required to authorized fixed stations.

Step Two: You could purchase a CDM1250 mobilie and program your four channels, with a scan feature. And most likely you could program your CDM to send QCII signals to your portables and program your portables to receive and act upon the QCII signals. However, you won't be able to simultaneously send or signal on all four channels with only one control station and one antenna.

Your budget may be a tad light. You should be able to get the CDM for under (just) $1K. You'll need an outside antenna, some coax, and someone to install it all for you. And you'll need someone to do the programming. $2.5-3.5K is more reasonable.

[kb4mdz]

How complex do you want to go? I agree with RKG that $1k is rather on the low side;

Perhaps very simplest would be 4 mobiles, 1 on each of the freqs, with power turned down, and one desk microphone and a switch arrangement to feed its audio to 1,2,3, or 4 mobiles simultaneously. Tho this might end up loading the microphone circuit too much, and reducing your resultant transmit audio; might need to do some sort of buffer circuit, 1 in & 4 out, to drive the microphone inputs of the radios properly.

Next step up in professionalism would be something like a CPI TRML, multi-line tone remote; handles up to 4 separate radios, & I see the brochure says it will do multi-select (so you can transmit on more than 1 channel simultaneously). But, we're talking some more bucks, in addition to the 4 radios. Another might be a Gai-Tronics IPE-2500 MLS; multi-line select. Similar idea to the CPI.

Have you talked to your local radio shop? Do you even HAVE a good (notice that qualifier) local radio shop?

[ILMRadioMan]

Is there any chance that the 2 non repeated channels are just the TX side of the repeater / RX side of the radio for a talkaround.

IF (a big IF) that is the case, then it would be easy.

Even if its not the case, and you have two completely separate freqs for the 2 non-repeated, this is what I would do to keep things cheap. (its gonna be dirty, but it would keep costs low)

Remember that in these things, the PTT is enabled when its grounded.

So I would get 4 accessory plugs for a CP200 (like those off a shoulder mic)

I would also get a cheap audio amp, anything with a MIC input.

I would wire the amp output into each of the TX audio wires of the accessory plug. I would have one mic into the amp.

I would then wire the PTT on the accessory to a Mic PTT switch, or anything that I can have switch on ground.

Then I would hook up 4 of my CP200s, one to each accessory plug and BOOM, PTT on keys the radios. Audio amp puts out enough audio power to give you a good level over the air.

When you are done, you can disconnect the CP200s and use them like normal until you need to call again.

And if you HAVE to have some tone, just get any old cheap tone generator on the amp input.

No need to buy radios that are just going to sit there and will only be used for these all-calls.



And if you DO get mobile/basestations, then concept will pretty much be the same thing.

Aux Audio in, Aux PTT.

Or you could go the REALLY cheap route and just key up 4 remote mics at the same time with each radio on a different channel

[ILMRadioMan]

And before anyone berates me on it, the guy said he wanted to keep costs below 1k, and pretty much any idea other than mine will be above 1k.

[w8jjr]

And still be FCC type accepted ???

[RKG]

Originally Posted by kb4mdz

How complex do you want to go? I agree with RKG that $1k is rather on the low side;

Perhaps very simplest would be 4 mobiles, 1 on each of the freqs, with power turned down, and one desk microphone and a switch arrangement to feed its audio to 1,2,3, or 4 mobiles simultaneously. Tho this might end up loading the microphone circuit too much, and reducing your resultant transmit audio; might need to do some sort of buffer circuit, 1 in & 4 out, to drive the microphone inputs of the radios properly.

Next step up in professionalism would be something like a CPI TRML, multi-line tone remote; handles up to 4 separate radios, & I see the brochure says it will do multi-select (so you can transmit on more than 1 channel simultaneously). But, we're talking some more bucks, in addition to the 4 radios. Another might be a Gai-Tronics IPE-2500 MLS; multi-line select. Similar idea to the CPI.

Have you talked to your local radio shop? Do you even HAVE a good (notice that qualifier) local radio shop?

The trouble with the 4-radios solution is that, after mourning the passage of the $1K budget, you have to worry about antenna separation. This means either four sticks vertically separated or a combiner/multicoupler set up, which (a) may be impossible, depending on freqs involved and (b) will put the late lamented budget into low earth orbit.

What I think might be more practical (this is not a public safety system) would be four channels with one control station. Channel allocation would be:

Ch 1: Ops A and Call/Alert
Ch 2: Ops B
Ch 3: Ops C
Ch 4: Ops D

where A, B, C and D are his various operations requiring communications within the group.

All subscribers would be programmed with all four channels and a 2-channel scan list: Priority 1 would be <SelChan> and the sole Non-Priority member would be Ch 1.

Users in B, C and D would be told: use your particular channel for normal operations, but dispatch won't hear you. If you need to talk to dispatch, shift to Ch. 1.

Now, program all radios for QC II, but as a practical matter you're only going to use the Group Call. Program the radios for a 4-6 sec Long B group call, but programmed the control station to send Long B for a longer interval (8-10 seconds).

The Group Call will be heard by all subscribers selected on Ch. 1, and it will be heard by most users on Chs. 2, 3 and 4 so long as those channels are not in use at the time the Long B is sent. (The extra time added to the dispatch-sent Long B accounts for the time required for the scanning subscribers to land on Ch. 1.) However, dispatcher must be alert to the fact that on any of Ch. 2, 3 or 4 that were in use when the Group Call was sent, the Group Call will likely not be heard. You deal with this either by repeating the Group Call on each channel sequentially or by requiring Ch. 2, 3 and 4 users to acknowledge the Group Call by voice on Ch. 1.

[Jurassic69]

Wow, thanks for all the input. Maybe I should give some more info. We use an authorized dealer/service provider named McDermott Communications co in Los Angeles (by LAX). Our 4 Channels are like this:

Channel 1: Operations (repeater)
Channel 2: Theatre Security
Channel 3: Mall Security and Operations (repeater)
Channel 4: Projectionists/Ops Tac

Now when we have something like a paramedic response, all 4 channels need to be notified. A show sell out, or almost any other "news" would be for channels 1, 2, & 4. I really would like to be able to have an "all call" tone that would just grab peoples attention who may not be using earpieces or have their radios down for some reason.

Using 4 seperate CP200's is not really cost effective, considering when we are busy on weekends, pretty much all radios are in use, so I would be buying 4 new CP200's. If I raise my budget to $1500, does anyone think that could help?

Thanks all!

[ILMRadioMan]

Originally Posted by Jurassic69

Using 4 seperate CP200's is not really cost effective, considering when we are busy on weekends, pretty much all radios are in use, so I would be buying 4 new CP200's. If I raise my budget to $1500, does anyone think that could help?

Thanks all!

Fair enough, but you are probably going to be buying 4 new radios regardless.

[stevelton]

Someone posted above that you would have to have lots of separation between the 4 antennas.
WHY?
The OP said the set-up would be used for paging out on all 4 channels at once, i.e. TRANSMITTING. If there is no receiving going on, there would not be any need to separate them. Having all the antennas 2 inches apart is not going to have any noticeable affect the signals.

[ILMRadioMan]

Originally Posted by stevelton

Someone posted above that you would have to have lots of separation between the 4 antennas.
WHY?
The OP said the set-up would be used for paging out on all 4 channels at once, i.e. TRANSMITTING. If there is no receiving going on, there would not be any need to separate them. Having all the antennas 2 inches apart is not going to have any noticeable affect the signals.

Steve,

You have your theory backwards.

Receiving is when seperation isnt an issue because there is no RF being generated.

When you are transmitting on an antenna that is "2 inches" away from another antenna, RF is going to feed into the other antenna.

You can actually take a wattmeter and measure it.

Take your wattmeter to the non-transmitting antenna. Place another antenna within close range. Transmit on the antenna without the wattmeter. Watch what happens to the wattmeter.

You will burn out multiple parts of the radio incredibly fast by doing this consistantly.


I wouldnt say you need a LOT of seperation, but it all depends on the antenna type and the amount of power you will be generating.

[RKG]

Moreover, he didn't say the hypothetical four control stations would only be used for simulcasting.

If you have four control stations and four antennas with only horizontal separation of less than 100-150 feet, then when you transmit on one radio you'll blitz the other three.

As a practical matter, the four antennas would have to be coaxial and vertically separated with not less than 10-20 feet between the base of one and the tip of the one below it.

[rescuecomm]

It would help to know the actual frequencies being used. One way would be setting the radios transmitting to the repeater to very low power to minimize intermod. The simplex channels could be wired through the speaker mic input using CAT cable and the radios widely separated from each other and the control point. This would require a power supply and antenna at each point. In the 460 band, mobile notch duplexers are fairly cheap and might be the answer to desense.

Bob

[RKG]

The issue isn't intermod, it is desense (or, perhaps, blowing up a receiver front end altogether).

As a practical matter, you will need between 75 and 100 dB of isolation between a transmitting antenna and any other in-band receiving antennas.

Using RFS Celcalc and an exemplar frequency of 460.0000, 200 feet of horizontal separation results in only 57 dB of isolation, while 25 feet of vertical separation gives you 71 dB of isolation.

The way you solve this in the real world is to put all of your receivers into a multicoupler and all of your transmitters into a combiner, and then mix the combiner and multicoupler outputs into a duplexer. This only works for repeated systems, does require an intermod study, and cannot be done for anything within a country mile of the OP's desired budget.

[ILMRadioMan]

Originally Posted by RKG

The issue isn't intermod, it is desense (or, perhaps, blowing up a receiver front end altogether).

As a practical matter, you will need between 75 and 100 dB of isolation between a transmitting antenna and any other in-band receiving antennas.

Using RFS Celcalc and an exemplar frequency of 460.0000, 200 feet of horizontal separation results in only 57 dB of isolation, while 25 feet of vertical separation gives you 71 dB of isolation.

The way you solve this in the real world is to put all of your receivers into a multicoupler and all of your transmitters into a combiner, and then mix the combiner and multicoupler outputs into a duplexer. This only works for repeated systems, does require an intermod study, and cannot be done for anything within a country mile of the OP's desired budget.

There again lies my solution

Low power output, with a little distance between portables, for a quick simulcast, then disconnect and back to normal operation.

Therefore there is no constant transmitting of close proximity for any desense problems. (Or future intermod problems either)

And it would all fall relatively close to OPs budget.

[RKG]

Originally Posted by ILMRadioMan

There again lies my solution

Low power output, with a little distance between portables, for a quick simulcast, then disconnect and back to normal operation.

Therefore there is no constant transmitting of close proximity for any desense problems. (Or future intermod problems either)

And it would all fall relatively close to OPs budget.

I think you miss the point: receiver desense (or blast into death) is not a function of simulcasting, but rather of ordinary use (one of four radios transmitting and the other three receiving).

[ILMRadioMan]

Originally Posted by RKG

I think you miss the point: receiver desense (or blast into death) is not a function of simulcasting, but rather of ordinary use (one of four radios transmitting and the other three receiving).

I dont miss the point. I realize that.

I was following suit with your last remark "being within a country mile of whats within the OPs budget".

Either requirements need to change, or budget needs to change.

But you make excellent points.

[RKG]

Originally Posted by ILMRadioMan

I dont miss the point. I realize that.

I was following suit with your last remark "being within a country mile of whats within the OPs budget".

Either requirements need to change, or budget needs to change.

But you make excellent points.

My apologies; I misunderstood the thrust of your comment.

Note, however, that the OP appears to be using simplex channels, which precludes use of a combiner-plus-multicoupler-into-duplexer approach.

[Mike_G_D]

If all radios would be transmitting at the same time as the OP would ideally like then that should mean that all radios would have their respective receivers disengaged at the same time so the issue of receiver desense and potential damage would "theoretically" and "ideally" be negated. "Ideally" some form of single PTT mic-to-multi-radio setup with a switch to allow choices of radio 1, 2, 3, 4, and "all" could be used. When only one radio is chosen the others would be powered off (a remote power switch tied into the circuit for all radios). "Ideally", when in the "all" mode, the circuit "should" key and unkey all radios simultaneously so "ideally" their should be no problem (as far as the receivers go). Nevertheless, I would try very hard to keep the radios at the lowest power effectively possible and separated as best possible (and I am assuming that 4 available handhelds would be used for this).

Now, here is another suggestion that should be as simple and perhaps more so and will definitely not hurt the radios. If there is some way to use these radios in a remote mode or to get a unit that has that capability you could prerecord the announcement (tape or digital loop, etc.) and then have the remote controlled radio transmit sequentially on each channel with the prerecorded message. Obviously this is not a true simultaneous broadcast but, unless the message is very long, it may do almost as well.

This way, you only have one radio and the record/playback device and controlling circuit/device. Such a box should be relatively easily designed and built provided the radio's remote protocol is available. Depending on the model, maybe such devices are already available commercially.

Obviously, the radio in question would have to have remote capability to change channels, switch between transmit and receive, and have auxiliary audio input. The special "broadcast box" would, in turn, have the capability to record an "all call" message and subsequently (upon completion of the recording or at a command by the operator) engage the radio's transmitter on each channel sequentially for the length of the recorded message after which time it would reset and be ready for the next use.

I see no technical reason for this approach to be outside of the OP's budget with the possible exception of the cost of the remote-able radio.

-Mike

[kayn1n32008]

Jurassic69
"Control" Station for my Business
Hey all,

So I manage a large cinema complex. We use about 30 MOT CP200's that operate on 4 channels, 2 of which use repeaters. I think we are somehwere in the 460mhz area. I am looking for a sort of "base station" where we can monitor all 4 channels and brodcast "all calls" to all 4 channels, or some combinations of the 4, at once with some type of alert tone preceeding. I would like to accomplish this and spend under $1k.

Any thoughts?

Thanks!

So rereading the OP, jurrasic wants to RX on all channels and TX all calls... so i guess desense is not much of an issue if all 4 radios are transmitting AT THE SAME TIME, and really at 4w how much antenna seperation do you really need??? i have had 2 Vhf GP-300 with in 18in of each other , one Tx the other Rx 0.600Mhz away and had no issues with desense (the repeater was atleast 3 miles away). wanting to do this for under 1k is the hardest part, but the poster that had the idea to link 4 ht to a common mic, with a selector switch for 1, 2, 3, 4, and all is probably on the right track for Jurassics buget.