Receiver or What?

[KG4LHQ]

Hello,

Local Police Department I work for is trying to increase their communications system better. When they use a handheld it is very hard for the dispatch center to copy their transmissions. The sergeant of the department asked me what could be done to make it better.

His budget is about 10,000 dollars for this project.

I suggested to him that he gets a receiver and install it at either a water tower, or a tower at their city hall. I also suggested to him that since the receiver would then be getting the signal to send to the repeater that they need to do some testing in the area just talking on a portable radio back to their city hall to see what kind of coverage they will have with this receiver.

He advised his tower at City Hall is about 80 feet in the air with a Elevation of about 650 - 700 feet.

Am I pointing him in the right direction and do you have anything else to recommend for this project. - Once again his budget is about 10,000 for this project.

[kb4mdz]

Yes, John, you are going in the right direction. First, tho, what is the form of their current communictions system? Repeater? Simplex base? Radio close to dispatch, or far away?

I'm gonna hazard a guess that you'll be looking at a 'voted receiver' system; two or several receivers scattered around the coverage area, the voter decides the best one & feeds to to dispatch and repeater. I've been involved in putting in several voters by JPS communications, (http://www.jps.com), and they are really sweet units.

Give us more details of what type system, how big an area, freqs, etc. & the members of the board can give you enough information to be dangerous!

Chuk Gleason
Cary, NC

[Motoman]

I know this sounds stupid, but check if the portables are putting out their full RF, sometimes they may have been tuned down to low pwr. If they are at full pwr, check what "Is full pwr" in the radios, and think of possiably upgrading the radios. Jus a thought.

[nmfire10]

Before you buy ANYTHING, have someone who knows what they are doing do a complete PM and test on all the equipment. You might very well find a pre-existing condition causing the lack of coverge. If there is a problem with the antenna, coax, connectors, lighting supressors, etc, it will kill your performance. There could of course also be problems with the actual receiver, like when you put it on a service monitor and it takes 4mV to break squelch....

I would also ensure your portables are up to snuff. Although it is unlikely that ALL of them are defunct, a good once over sure couldn't hurt.

After all your existing equipment is determined to be in good working order, it is time to look into remote receivers. If the water tower or town hall are in the area you have coverage problems, that is perfect. You sure can test it... climb up there with a portable and see what you can hear on the input (or do it on direct).

You also need to concider a few things:

1. You'll need a voter. A new JPS SNV-12 with 2 line cards is about $4,000 and it does everything short of cooking you eggs in the morning. You might be able to find a refurbished GE voter for 1/4 of the price and it will probably do you just fine. There's also the DigiTAC voter from Mother /\/\ but I really don't have any experience with them so I'll keep my mouth shut about them.

2. You'll need a radio to use as a receiver. Kenwood TKR-750 repeaters make very nice receviers in my opinion. They do everything under the sun out of the box and even have OTA DTMF control now. Pretty much any radio that can generate a COR signal will do. It just needs to have audio characteristics similar to the main receiver. Slap a JPS PTG-10 status tone generator on it and your good to gol

3. You'll need a way to get the audio from the remote site to the voter at dispatch. You could lease a telephone pair. This is probably the most common but is very expensive with monthly rates and you are at the mercy of the morons at the phone company. You also lose your radio when someone jackass takes out a telephone pole. You can use point-to-point microwave. This has a very expensive startup cost but there is no monthly fee. You also have the capacity to add more than one audio path between the site and dispatch or send data. Lastly, you can use a point-to-point link on UHF or 900Mhz. You lose the supervision of the link with this since you won't have a constantly connected status tone.

Good luck!

[kb4mdz]

Well, nmfire10 and motoman have the better initial idea; what SHOULD the system be doing?

This is where a lot of things can happen; systems don't get PMed properly, or at all, or whatever, and each portion of the system degrades a bit, and the net effect is a general loss of capability, without any one thing being truly 'broken.'

Basics to check:

Base station Receiver sensitivity, (direct, and what is called 'site sensitivity' - how well the receiver receives while connected to an outside antenna).

Transmitter power, freq. error, and modulation.

Same for the user's units; portables, mobiles.

Antenna & antenna line quality - forward & reflected power at the base station, and a frequency sweep of the line and antenna, if you can get it. Can show up problems like lossy line, where say 90% of your power gets absorbed thru the bad transmission line, and a bad antenna that reflects 50% of any power that hits it, and then that reflection is attenuated by 90% on the way back to your wattmeter. Hmmmm, 100 Watts out, minus 90% equals 10 watts to the antenna, have of that reflected back is 5 watts, then 90% of that is lost - leaves you with 0.5 watts reflected power, using just a wattmeter. Look good, no?? NO!!

Yeah, that's why it's worth it to have a professional; unfortunately, there are a lot of people calling themselves professional, who still don't know their own from a horse's patoot. (names have been changed to protect the guilty) That's where you, the educated consumer, come in.

It'd be a shame, and embarassing to boot, to spend $10K on 'fixing' the wrong problem.

[KG4LHQ]

Our system is regular maintained by the Motorola Company. All portables check out to snuff. They are using TK-280s. Its just the area that their in isn't the greatest in the world..... That police departments city hall is about 700 feet above sea level and they have a 60 foot tower in the air beside their city hall. I have a feeling if a receiver would be put there or sometype of system their communications would improve greatly

Our main city we don't have any problems on our system we currently have with the main police department that I dispatch for. Its the other city - the city that is having problems isn't that huge of a city they just want to be able to talk and you know officer safety.

Can't a receiver just receive the signal then transmit it to the input side of the repeater on our F1.

Program the mobiles and portables to receive on the same frequency but transmit on the receiver frequency at their city hall.... Or is that not how it works?

[nmfire10]

You could do that. You would have to put a repeater at city hall or the water tower. You would have to apply for a license for the repeater and buy the neccessary equipment. Then you're going to have to reprogram every radio in the fleet. Then you need to educate everyone to change the channels which is inconvinient and possibly dangerous if they forget to change it back. You'll also have some front-end clipping due to the delay from all the steps:

Portable --> receiver --> transmitter --> receiver --> dispatch

You'll have an inherent delay, where as a system linked by microwave or phone line would have far less of a delay. The only thing you gaining here is not buying a voter and paying for phone lines... Trust me, the repeater equipment and licensing fees will probably make up for it. Your buying transmitter equipment to build an unsupervised link. I think it's too much of a sacrifice. If you're going to do it, do it right the first time