Batboard

Greetings,

I have a question to pose as I am having an issue trying to lay this out.

We have a GE Master 3 repeater which we are currently using on a 155 freq for TX and a 156 freq for RX. Now the county is having some paging issues and we are worried that they will not be able to page our own members as it has happened already.
Now we have applied for the license and have been issued to page on 152 freq (which is also the county paging channel) at 100 watts. So while we are waiting for the budget to build a little bit more to purchase a base radio and paging terminal we want to be able to use the same transmitter.
Now we have paging capabilites in our portables but they are only 5 watts and will not reach that far as we want to be able to page all members within the village limits as well as a few miles out from the village limits.
Now we planned on using the imput of our repeater freq with a DIFFERENT DPL and have it repeat out on the paging channel. We have the license issue taken care of but we need help with the antenna set-up.

As of right now we have a GE Master 3 100 watts going into a duplexer and then going out to one antenna. Now in looking at how we want to do this it almost seems that we need two antennas and we can not get enought horizontal seperation between the two antennas so we could have one for tx and one rx. However the other issue with that is the tx and rx freq are way to close so we need something different.
We thought then lets put an antenna switch between the PA and the duplexer and have a seperate antenna when we page. Since the input to the repeater is 156 and the pagin freq is 152 we should be able to do this just to page. But concerns as to what if someone forgets to put it back, not to also mention the main thing we want with this set-up is to be able to do it without that kind of intervention.
So paging goes down with the county, one of the officers or myself find out, in turn we pick up our portables and send the page and advise the on-call crew to respond to the station.

So does anyone have any suggestions on how to accomplish this task with out some sort of human intervetion. IF we need to do it I guess we will have to but we would like it hassle free since not a lot of people on the service a radio savy.

HELP!

As most repeaters have a set of tuned filters to let them use a common antenna for repeater operation, your idea probably won't work. These tuned filters are very narrow in the change of frequency they can pass.

To put it bluntly, NO IT WON'T WORK. Bad idea, bad planning, poor system design. Do it the right way and use a different transmitter and antenna system.

If you said it, I missed what service this is for. In the fire and EMS service, the operation is covered by NFPA 1221. I have to tread carefully here as not all agencies have adopted the NFPA guidelines as how they operate. However, with that said, NFPA 1221 states that the dispatch should have an alternate means to dispatch calls and alert emergency personnel. I would have to go back and read it again, but that is the general gist.

What your talking about here is to use the same radio for both repeater and paging communications. What do you do if the repeater fails? How are you going to communicate? Not only have you lost voice, but you now have no way to page either.

You have at least thought about changing the frequency of the repeater. That too would be an issue if some radio shop figured a way to kluge this thing together. Maybe have a relay to switch out the cavities and use another antenna when paging. It all could be done, but you have created a monster and injected many more points of failure.

You didn't come right out and say it, but you have implied this is for public safety communications. Do all the people that live in town a favor. Do it the right way. Provide the radio system you need. Let it be built to standards and have the reliability it needs.

Jim



[quote="n9upc"]Greetings,

I have a question to pose as I am having an issue trying to lay this out.

We have a GE Master 3 repeater which we are currently using on a 155 freq for TX and a 156 freq for RX. Now the county is having some paging issues and we are worried that they will not be able to page our own members as it has happened already.
Now we have applied for the license and have been issued to page on 152 freq (which is also the county paging channel) at 100 watts.

HELP![/quote]

Jim I understand what you are talking about in regards to public safety and NFPA and all that.

No offense but I was just asking if anyone has every done this before. I realize the inportance of public safety communications. But this is not a common situation in this case!

Our repeater is used as secondary communications for internal agency issues. We do not use it as our main dispatch channel just to communicate within the service when someone is chatting on the fire channel uselessly and the simplex channels will not work.

The county PSAP does page us for all needs at this time. However, as of late they are having some serious paging issues. As a matter of fact one of the Ambulance and Fire Department in our coutny which spills over into the county north of us needs to be paged by that county since the county there mostly in can not even page them.

Now add the fact that the fire channel is always keying up on it's own 24/7. With this keying some comms also get walked over and they have a hard time hearing you or units talking to other units.

So what do we all do as EMS and Fire agencies in the county. Complain complain and complain. Now the answer we keep getting back is that they have /\/\ working on the problem all the time.

So if they have an issue paging us we which have had then we need to get out own back-up paging system. Therefore, we looked at using our repeater since it was 100 watts, can handle another channel, and we do not always have someone at the station 24/7.

Some of us have 100 watt mobiles with the ability to page that we purchased ourselves but we are not going to just hand our mobile over to them and say here. In addition we do not want to sell our mobiles to the service as we llike them and use them alot. (We have not bought any extra encoder either for our mobile. We use long tone as our main paging tone so we adjusted our singletone encoding feature of our Spectras for 8 seconds to trip our pagers.)

So therefore we were looking at other possible issues or answers to our problem. We did look at purchasing an antenna combiner system but wanted to see what some other alternatives are before we lay the cash down out on this combiner.

Hello John,

I've configured a specially modified GE Master III into a station with 2 Transmit Frequencies, 2 individual Receivers, the Repeater Receiver having Dual Digital Call Guard, the second receiver as a Monitor for the Paging Frequency with COR for Channel Busy (a FCC requiement) and additional Cavity Filters with a RF DPDT Relay and an automated Paging Terminal with a TELCO interface. I believe this can be accomplished with the necessary hardware and software scripting.

Please check your regular email for the BMP diagham.

Dan

We have been there, done this same type of 'dual freq.' station TX.
Using a seperate antenna and a RF bypass relay on the TX side, the receiver has a second PL code, and that changes the TX frequency and energises the RF bypass relay and everything returns to normal repeater when the receiver does not hear the second PL code.

I think the RF bypass relays are still available, used in some hi power stations to revert to battery backup at a lower power.

As for the 'monitor the paging freq.' requirements, the mobile 'listens' to the paging frequency prior to initating the page. Also the mobile will also have to give the FCC call sign to meet station identification rules. The station ID can be provided by a ID - 8 that only ID's on the dropout of the second PL code in the repeater receiver, a delay could be added in the ID-8 to make the seperation from the paging tone(s). ie; PAGE Tone, Voice, delay then station ID, transmitter drops out.

If your frequencies are close enough and the passes are wide enough on the duplexer it would work.

The CMED bases I work on are set up as full duplex (4 wire) tone remote control as well as have all 10 MED frequencies programmed in them. They all have duplexers on them and are able to run in repeater mode.

The med frequencies vary from 462.950-463.175/ 467.950-468.175, so they're pretty close. Going from 152-156MHz is not going to work unless you do some interesting things such as seperate RX and seperate antennas.

Kurt

Kurt,

If you go back and read N9UPC original post, it states the following information, "We have a GE Master 3 repeater which we are currently using on a 155 freq for TX and a 156 freq for RX" which could be either a 1 to 1.5 MHz Tx to Rx seperation unless I'm reading N9UPCs information incorrectly. He wants ADD a second Tx Freq of 152 MHz presenting a F1 Tx to F2 Tx of roughly 3 MHz seperation. I do not know any VHF Commercial Cavity Filters available in the market place that would cover this wide of a frequency spread between F1 Tx to F2 Tx and I've been in the two-way radio professional for 35 years.

On the other jand, the UHF MED Channels 462.950-463.175 MHz are only a 225 KHz Frequency Seperation from your Lowest to Highest Tx frequency RF Channels that you probably provide the Dispatch operation. In UHF Duplexers 225 KHz Tx to Tx is a "Walk in the Park" tuning them and your system has the standard 5 MHz between the Tx and Rx spread.

When approaching UPCs configuration, you need to have an open mind how this can be accomplished on one antenna system but not trying to incorporate only one set of Cavity Fikters or a Combiner system. One way to accomplish this design would ADD a RF Double Pole Double Throw Antenna Relay with a good set of 2 or 3 Notch Cavity Filters tuned to Pass the 152 MHz Tx Frequwncy and Reject the 156 MHz Rx Frequency. There would be parallell coaxial lines from the RF DPDT Coaxial Relay with one coaxial feed connecting the regular F1 Tx 155 MHz Cavity Filters and a second coaxial feed connecting the new F2 Tx 152 MHz Cavity Filters. I will recommend ADDING at least 2 Notch Cavity Filters tuned to Pass the 156 MHz Frequency and tuned to Reject the 152 MHz Frequency into the Receiver coaxial cable.

When Scrioting the special function in the software, remember to provide enough Delay Time 500 mS for the RF DPDT Antenna Relay to Pull-In or Drop-Out so there's NO RF on the Relay contacts otherwise you'll be presenting a High Impedence to the RF Power Amplifier stage causing pre-mature failures to the Transmitter and Burnt Contacts on the RF Relay.

Dan