Batboard

FOLKS
I work at an agency where in certain areas of the town we have very poor to no portable coverage. The portable units can hear dispatch but they cant get in to the system. Obviously the best solution would be to add a reciever in the area but the town is rural and in addition to not having any utilities in the area there are issues with suitable locations being state conservation land and thus that opens up another can of worms.
I was looking at the pyramid svr200's and in theory they seem like a possible solution to the problem, BUT the agency is on UHF (460.2xxx) and the portables do work in other areas so we would not want to use a vhf portable in a x-band situation we would want to keep the uhf port talking to the uhf backbone, thus we would want IN-band uhf to uhf
I know we will be looking at alot of critical issues trying to implament this not only antenna spacing, notch filters,licensing a simplex channel as far away as possible from the main freq. The mobile units are currently cdm1250 40w uhf units with quater waves on the trunk lids.
I am looking for any feedback from those of you who may have such a system, thise of you that may have tryied and failed as well as anybody with experience with the pyramid product and how they work in such an in-band application

thanks in advance for any feedback/imput

It is not a good plan to use in band PAC-RT type operation. With that said, you still have a chance to make
it work. Remember that at the 450 band, your radio system uses 5 MHz spacing between TX and RX channels
when using a repeater. This starts to provide some isolation to work with.

The other issue that will crop it's ugly head to the surface, is just how much of a spread you can get with
your current UHF portables. I would start looking at the radio specs for the portables you currently have.
Find out just how far they can spread and now you have a base line on which to start figuring out just
how you could design your PAC-RT system.

Under normal use of the Motorola and the old GE PAC-RT type units, these operate on a simplex frequency.
The reason for the simplex operation is for a multitude of reasons. One is that they are designed to support
multiple unit operation. Like if a single unit is already on and a second unit drives up and gets turned on.
The new unit sends a singnal over the PAC-RT simplex channel that turns off all and any other unit in range.
This is to ensure that only one unit is functional in a given area to reduce interference.

Also in normal operation, the PAC-RT unit may be re-transmitting the mobile RX audio. The PAC-RT unit
will actually go into RX every so many seconds to listen for the portable. This allows the portable to
have priority to the operation. Like the mobile is in RX scan and the portable needs to make a transmission
back to the dispatch on the priority channel. With the PAC-RT going into the listen mode for the small
time duration while it is sending audio from the mobile radio, the portable can maintain control and be
able to make a transmission.

Bear in mind that not all the PAC-RT units are configured this way, but this is the normal type of operation.

Anyway, now that I have rambled on, you need to look at a frequency that the portable can operate on
and not be blocked by normal use of the mobile. Like if you have a 462 repeater system, the mobile will
TX on 468.xxxx. So in this case, I would look at a frequency down at the bottom of the band for the
PAC-RT operation. Something near the 450 end would be the best choice.

Hope you work it out and can get a channel through coordination.

Jim

Radiogeek97 wrote:FOLKS
I work at an agency where in certain areas of the town we have very poor to no portable coverage. The portable units can hear dispatch but they cant get in to the system. Obviously the best solution would be to add a reciever in the area but the town is rural and in addition to not having any utilities in the area there are issues with suitable locations being state conservation land and thus that opens up another can of worms.
I was looking at the pyramid svr200's and in theory they seem like a possible solution to the problem, BUT the agency is on UHF (460.2xxx) and the portables do work in other areas so we would not want to use a vhf portable in a x-band situation we would want to keep the uhf port talking to the uhf backbone, thus we would want IN-band uhf to uhf
I know we will be looking at alot of critical issues trying to implament this not only antenna spacing, notch filters,licensing a simplex channel as far away as possible from the main freq. The mobile units are currently cdm1250 40w uhf units with quater waves on the trunk lids.
I am looking for any feedback from those of you who may have such a system, thise of you that may have tryied and failed as well as anybody with experience with the pyramid product and how they work in such an in-band application

thanks in advance for any feedback/imput

jim
the portables are mt2000's and soon we will have 10 or so xts2500's so i think we are ok as far as the spread IF we can get coordination to give us a simplex freq in the 450's Do you have any experience with these units needing some kind of filter to notch out the freqs? also any imput on antenna type and or placement for the mobile and pac/rt unit?

The magic numbers here are how much isolation you can muster. The more the better. I would look
at using a 1/4 wave whip for the PAC-RT. Your probably using a 5/8 antenna for the normal mobile
462 unit. Try and put as much space between them.

As a last resort, you could always add a notch cavity to the PAC-RT antenna line for the repeater
input frequency the mobile normally uses. I wouldn't go to this unless you have a problem with
noise and desense while using the PAC-RT package.

Jim

Radiogeek97 wrote:jim
the portables are mt2000's and soon we will have 10 or so xts2500's so i think we are ok as far as the spread IF we can get coordination to give us a simplex freq in the 450's Do you have any experience with these units needing some kind of filter to notch out the freqs? also any imput on antenna type and or placement for the mobile and pac/rt unit?

jim

actually the mobiles just use 1/4 wave do you think i should have them changed to 5/8th? As far as separation goes I assume that both horizontal and vertical separation would be most advantageous. Do you think putting the pac-rt antenna behind the grille would work? the mobiles have their antenna locations either on the center of the roof or on the trunk lid. So you think if i can get a freq far enough away from the 460.2xxx main freq that I wont need a notch filter? The mobiles are putting out 40w @ 460.2xxx


thanks
john

Why would you want to put the PAC-RT antenna behind the grill? The intent
is to be away from the mobile with a portable and still be able to use the mobile
radio to get back to the dispatcher. Mounting the antenna in the grill will
just kill your range and make the coverage very directive.

If your worried about picking the wrong location for the antennas, they make
some fine mag mounts that will let you try all sorts of location attemps until
you fine the ideal locations. Just make sure you use decent coax cable on
your antennas to keep unwanted radiation down. Don't use regular RG-58
coax. At least try to use some double shielded cable.

Jim

Radiogeek97 wrote:jim

actually the mobiles just use 1/4 wave do you think i should have them changed to 5/8th? As far as separation goes I assume that both horizontal and vertical separation would be most advantageous. Do you think putting the pac-rt antenna behind the grille would work? the mobiles have their antenna locations either on the center of the roof or on the trunk lid. So you think if i can get a freq far enough away from the 460.2xxx main freq that I wont need a notch filter? The mobiles are putting out 40w @ 460.2xxx


thanks
john

jim
the reason i was asking about behind the grille as a location is because i was trying to get as much horizontal and vertical antenna separation as possible. I know its not an ideal loction but thats why I asked the question.