Batboard

Hi,

I am looking for some ideas on upgrading the current system that is used at work.

The present system is a 40 watt VHF mobile radio on a 80' tower that attempts to cover approx. 110 square miles.

The dispatch center is 45 miles away and remotely connected via a phone line.

Needless to say there are problems.

The system needs to remain VHF.

Thanks, Eric

Well, what are the problems and what do you want to see that it doesn't do now?

I think you need to give more information on your system problem.

You're using a 40W mobile as a base station with some type of a remote adapter to interface the Telco line (RT2002) back to the dispatch console 45 miles away.

You have a 80 foot tower but no information on the antenna or feedline between the antenna and the base station. Is the antenna a ground plane 0 dB gain or some sort of a fiberglass 20' vertical or even a 4 element open face dipole arrangement on 20' mast pipe mounted at the top of the tower? If you can get close enough to the coaxial feedline with a tape measure, the diameter for RG-8 is 3/8", for LDF4 Heliax is 1/2" or LDF5 Heliax is 7/8".

Is the transmitter site located on a hill, flat terrain or in a valley? In fact what's the over terrain appear to be, flat or hilly. Is there a lot of foliage as in tall trees or pine trees? Does the radio coverage change beteen the summer and winter months?

Are there many tall building 4 stories or more, or buildings as in a metropolitan downtown area or are you servicing mostly in residental neighborhoods? Is the transmitter site close to any tall buildings higher than the antenna tower?

Is the transmitter site centrally located for the coverage area or off to one side, use a map to determine this question? Has your employer slowly increased his business coverage area throughout the years without taking into consideration his radio communications system?

While your attempting to talk or listen to dispatch, are you experiencing co-channel interference from other business users on the radio channel? Do you have a radio maintenance shop maintaining the radio equipment? And when was the last time the base station was serviced? Approximately how old in years is this radio equipment and system?

You did not state what the power output level of the mobiles are in watts and if they have 1/4 wave whips (18") or base loaded antennas (3' with a coil at the base of the mobile antenna) mounted on the vehicles.

Unfortunately I have more questions than answers on your system.

Dan

( Nail ) (hammer + Dan562 ) = ( Bang )



CHART

The vhf system appears over it's limit.
Has any one run the HAAT calculations.

There are many easy ways to correct this.
The HAAT gives a lot of help on what to do.

STEP ONE: What does the FCC license have for the tech parremitters. TX location, TX power, antenna hight, ERP, HAAT, ectra.


STEP TWO Did you do a test on the base station, TX power, freqq., dev., VSWR, and receiver sensitivity, receiver desense.




Did you do a co-channel look-up to see who else was out in your service aera.

Sorry for the delay and ambiguity, I appreciate your input.

What I was looking for was a very general idea of what is necessary for a simple system based on VHF in a 110 sq. mile city/suburban area.

Basically something to the effect of a real transmitter, a repeater, etc. and does not have to be in depth.

I am assuming someone out there has a similar coverage area.

This info is strictly for presentation at a meeting to demonstrate the inadequacy of the current radio set-up and to justify the need for improvements.

Thanks, Eric