Batboard

I have been racking my brain in an attemtp to help improve my counties communications system with out breaking the bank and using our very precious and limited UHF RF as efficiently as possible. Simulcast is far to expensive for use and we do not have a reliable backbone to build it on. Multicast is not efficient use of our available RF and would not meet our needs.

Here is my question regarding what I called "Smartcast". Is there a way to have multiple UHF repeaters all on the same frequency and pl where the receivers are voted together. When the dispatcher goes to transmit rather than the dispatcher having to select the specific tower to transmit on the voter(or some other equipment) automatically selects the site based on which signal the voter chose and then transmitts on that tower site? Maybe I am missing something technical here but it seems that if I only transmit off one tower I should be okay. If I am totally out in left field please let me know or if there is a manufacturer that makes something that will do what I want please pass it along.

Thanks,

Mark

It's called transmitter steering and we use it for our MED8 system that has 3 transmitters and 8 receivers that are regionally placed around the county.

This configurationworks fine from Dispatch to Unit, but there is a flaw if you do unit to unit transmitting and they are seperated at distant locations and can't hear each others transmission sites.

My two bits worth:
I built a VHF IMTS mobile telephone system here in Honolulu about 30 years ago.

One feature was "transmitter steering" by the IMTS Spectra-Tac voting system. (IMTS=Improved Mobile Telephone System for you history buffs)

Worked perfectly in theory, very un satisfactory in practice.

The problem was that the voting system selects the site with the best signal to noise ratio, which has nothing to do with the received signal at the mobile.

Perhaps the "best site" was hit with some noise, at the same instant a distant site happened to have a good signal.

The solution was "sloppy cast" with directional transmit antennas.

That's got to be the first time I've ever heard "Down Voting" referred to as "Sloppy Cast!" I suspect one of the IMTS sites had the Sloppy-TAC Comparator and Transmitter Steering Unit Colocated with a Base Station's receiver.

My two bits worth:
This particular system, Radio Call, used Micor 100W IMTS stations, as well as some Motrac MTS 120W stations. IMTS Spectra Tac with Transmitter control chassis.
A Glenayre IMTS terminal controlled the system.

There was a satelite receiver on the roof of the office in Honolulu, which unfortunately also had a paging station 50KC from the receive freq.

My comments on the choice of this frequency in the first place are not suitable for print in this forum. This channel was NOT included in the RCC channels because of intermod. Would have been CH 15 mobile TX.

There were two transmitter sites, Mauna-Kapu, on Palehua ridge, which overlooks Honolulu, as well as on Mokapu, which is on the other side of the Koolau mountain range. This gives some terrain attenuation.

The transmitter sterering did not work as expected. Then there were spectra-tac issues due to sharing a telephone cable with a burglar alarm co, which used very high current pulses for signalling, another issue altogether.

The Telco MTS system on the big island used 3 sites with "Relay Race" voting. I think they used 50W GE Prog Line bases.
Kulani Cone, above Hilo, Okala on the Hamakua coast, the CO in Kailua-Kona.
There was enough terrain attenuation so there was very little interference between sites, plenty of dead spots.

Mark,

What you haven't supplied on this system coverage problem is the Subscriber units ... Portables and/or Mobiles; and RF Power Output levels. A voting comparator and TX steering units are only as good as the Infrastructure and Subscriber units within the original design. Since I have not been out to Conneticut in 12 years, I can't remember the lay of the land whether it's flat, rolling or very hilly and then I'm guessing which county this system might be located.

Are all the tower sites and antennas using the same dB Gain and Height Above Average Terrain / Above Sea Level? If you are using a +9 dB Gain antennas, the TX RF signal is being sent over the horizon and creating the umbrella effect on the closest Satellite receive signal therefore forcing the signal to be voted at a distant tower site.

Are any of the tower sites shadowed from each other?

Are all the repeaters the same, i.e. Micor, MSR2000, MSF5000, Quantar and/or MTR2000 or a mixture of stations?

Since your system has multiple tower sites, Does the Base Station TX RF signal overlap with one or more of the other tower sites?

As Bernie has stated, a Subscriber Portable keys up in Zone # 2, a Satellite receiver in Zone # 5 detects the strongest initial RF signal. The Specta-TAC comparator selects that tower site in conjunction sends the repeat audio and TRC to the TX Steering unit out to Zone # 5 tower site and the recovered audio to the Dispatch Console. In the meantime (a few microsecomds later) the comparator selects the Zone # 2 Satellite receiver but the TX Steering unit is unable to redirect the TRC signaling to the Zone # 2 tower site. Nobody knows which Satellite receiver site will detect the best initial RF signal on any system.

All Satellite receivers must be set up for the 20 dB Quieting level used in an "And Squelch" Analog configuration, to work correctly in a voting comparator system. If your system has Subscriber 4W Portables and 40W or higher RF power Mobiles, there's a minimum of +10 dB RF signal level that can cause the wrong receiver tower site to selected in the RF system coverage. Everything in your system has to be carefully analyzed before making the proper changes that you want.

Dan