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
