Batboard

So I am on the job now for a month and started to make a block diagram of the PSAP/Dispatch center. This layout is questionable in my mind... is this typical?

7 "channels" (all vhf conventional)
Countywide
NLEC
SAR
Fire dispatch
Hear
State 2
FERN

2 Zetron 4010 consoles for 2 dispatch positions. 99.99% time there is only one dispatcher on duty.

3 antennas (2 6db and 1 3db) omnis

One Decibel products 6 position receive combiner

5 mtr2000 Rx only radios

2 mtr2000 rx/tx radios

The two rx/tx radios are on the 6db antennas

The one 3db antenna is connected to the combiner and the 5 rx only MTRs

Each console controls one of the tx/rx MTRs. The tx mtrs can transmit on any of the 7 channels (controlled by the console) and listens to one channel (Console 1 mtr listens to state 2, Console 2 mtr listens to NLEC)


The premise of the design (Shootin darts here) is that all 7 channels are able to be heard at all times.

Problem 1:
When console 1 transmits on any channel, console 2 then loses rx on state 2, when console 2 transmits, console 1 loses rx on NLEC.

Problem 2:
All antennas are on the same tower (6dbs are on legs on of tower about 18" apart) and the 3db is on top (about 12" from the tips of the other antennas). Frequencies are as follows
COUNTYWIDE 159.1500
State 2 154.6950
Lake, Fireground - A 154.1750
NLEEC 155.4750
Hear 155.3400
MRA 155.1600
FERN I 154.2800
All transmit is at 100w. Some of the channels are darn close. Why bother putting in seperate receivers if you are not going to manage the desense?

It seems to me that putting in two MTRs in scan would have accomplished this at a much lower cost. If they wanted to do this right, a tx/rx combiner, 1 antenna, 7 seperate receivers and 2 seperate transmitters would have been the right way to go. As an FYI, This is an ALL NEW install, none of the existing equipment was utilized.

Hope I made this understandable. I am just walking into this. A large Colorado Moto Dealer did this install in 2002.

Howard

Perhaps they don’t care too much about the desense problem since there is only one dispatcher on duty at a time. If they ever get busy enough for two dispatchers, they obviously will have to rethink their setup. It looks like they only wanted the second position as a spare. No doubt someone was convinced that this is what was needed and could afford.

It still is a level above having a Radio Shack scanner and monitor antenna in there. I have seen that in some places providing the same functionality with the addition of more intermod.

Nand.

My two bits worth:
It is amazing what one may find when the only specs given when the bid went out was "low bid wins".

Rule #1 in public safety dispatch: Never use scan.

With a "scanning" remote radio you have no idea what channel it stops on, and when it does stop scan and there is activity on other channels, you loose that activity. With seperate receivers you always can monitor each seperate channel.

To add to Alan's comment, separate Rcvrs also allow simultaneous recording.....

I'd run several multi-channel bases for TX with invidual receivers for all channels, dump the scan setup, combine the TX antennas and use tuned cavities to isolate the rx.

Apco25... that is how it SHOULD have been done. Pre-Me (only on th job one month) that is what WAS done....

As for peoples comments about scan.. yeah I know... but if they were going to do a half azz system, they might of saved some money while they were doing it. Just boggles the mind what a Motorola dealer would do....

To me it simply looks that there was no money available to do it right.

They have the best equipment, just not all the needed items.

Nand.

Howard,

Who ever system designed your present configuration were a few french fries short of a happy meal. You didn't mention the height of the tower the antennas are mounted on and if there's any vertical seperation between the Tx and Rx antennas.

If this tower is 140 to 160' tall (but I'm deathly afraid your going to tell me it's only 50 feet high), you could get a tower company to lower one of the Tx antennas (10-20 Feet) to provide better isolation and less front end overload. I'd bet the MTR2000 stations and separate MTR2000 receivers don't have the pre-selector option either.

Every time I think about (the future having) two dispatchers at the consoles keyed up on their respective frequencies ... all I can visualize them doing is jamming each other but hey, it's wireless.

Dan

It sounds like a small PSAP/Dispatch. I would guess that the VHF combining/interference protection problem would be complex. Given the expense of project it is possible that it was out of the financial reach of a smaller agency.

Then comes the question as to how much multitasking can a disaptcher handle? If only one disptacher is at the boards is it worth the cost of the dispatcher being able to hear all other VHF channels when talking on just one?

Now, no, I wouldn't have designed it that way but my agency is large enough and financially healthy enough that I have the resources to do VHF combining and interference protection.

What would I do? I'm betting that NLEC, FREN, SAR and some of the others are rarely used in transmitt. I would protect their Law Main and Fire Main (I'm guessing that EMS runs on Fire) against each other. If they are control stations I would put an Rx antenna at the top, a Tx at the bottom, and combine both their Rx onto one, and both their Tx on the other. If they are simplex I would put Law at the top, fire at the bottom, and pass/reject them against each other. I would leave the others on separate antennas as backup in event of the loss of either one of the combined stations. Yes, it isn't perfect but it may meet their requirement.

Good Luck,

We have not seen dispatch radios with scan.
We have not seen any dispatchers with bought
company suppied scanners.

Like it was stated public safety is # 1.here.
We are in canada and we are not that backwards.

The system you named here looks like it was made for only
the one dispatcher and the second radio is when the first
radio fails. To use two at the same time is BAD.

raymond345 wrote: Re: Well Nand yes you are in Eastearn Canada "BUT"

We have not seen dispatch radios with scan.
We have not seen any dispatchers with bought company suppied scanners.

Like it was stated public safety is # 1.here.
We are in canada and we are not that backwards.

The system you named here looks like it was made for only the one dispatcher and the second radio is when the first radio fails. To use two at the same time is BAD.

Eastern Canada??? Not that it matters, but I am just south of Ottawa; the capital of Eastern Canada. Or is that the Capital of all of Canada?

It was in one of the previous Ottawa fire dispatch centres that they were using a Radio Shack type scanner before the whole city switched over to trunking. And since as you suggest, you apparently don’t get to see too much from your Northern Ontario location, I provided some links for you that show that some agencies do use scanning. It is all a matter of economics. I’m sure they wished that they had the money to do better.

As for the rest of your post, you didn’t say anything that others and I didn’t already suggested, that they likely didn’t have the funds to do it right, but wanted at least a spare seat.

http://www.zetron.com/pages/english/realw/7018.html

http://www.crucom.com/con1.htm

Nand.