Batboard

I asked about adding a mobile repeater to a fire department license and was told that there is a 2 watt power limit for repeater. Is this correct? I want to have a VHF inband mobile repeater that repeats portable radios into main VHF repeater back in town. I would like about 25 watts output on the mobile repeater. Is this possible?

Whoever told you this probably had in mind the "old" vehicular repeaters, by which a guy took an off-band portable out of the car in order to access, bi-directionally, the mobile in his car. These were licensed on 25 kHz channels on 12.5 kHz splits, and for that reason they were limited to 2 watts (which was all you needed because you weren't going to be that far away from the car).

For what you want to do, there is no a priori power limit (you'll still have to convince the coordinator that you need whatever power you're striking for, and they are getting pretty stingy), but you have to license as a new station. That means finding a frequency. And it probably means working on a true 12.5 kHz channel.

Be careful of the term "mobile repeater," since in FCC regs speak, it is likely to be confused with the term "mobile relay," which is what we think of as a repeater. What you really want is a temporary repeater with no fixed site but limited to the service area defined for your regular base station.

arlojanis wrote:I asked about adding a mobile repeater to a fire department license and was told that there is a 2 watt power limit for repeater. Is this correct? I want to have a VHF inband mobile repeater that repeats portable radios into main VHF repeater back in town. I would like about 25 watts output on the mobile repeater. Is this possible?

I would think that the OUTPUT of your mobile could be the same as what you are licensed for on your license for your main repeater pair. In other words the sames as what your other moblies are running. The input would be what you might be limited on I would think.

Cam

My suggestion is to research this carefully before proceeding. This is one area where it is pretty important to follow the rules because of the likelihood of causing interference to other licensed users on your frequency. Here are a few things to keep in mind:

Unlike a fixed repeater, your coverage area follows you around as you drive. This means that if you are at the edge of your coverage area, the output of your repeater could very easily extend well beyond the coverage area specified for a base station at a fixed location.

Unlike a standard mobile unit, the transmission duty cycle of a repeater may be very high. Instead of occasional transmissions typical of a mobile unit, a repeater could be transmitting nearly continuously in some cases. So what might be tolerable co-channel transmissions might become interference that would provoke others licensed on the frequency to complain.

If you look at your license, you will note that there are probably two or three station types listed... FBn licenses either a fixed base station or a fixed location repeater at a specified location, power level, and coverage area. MO licenses mobile units, either portable or installed in vehicles for operation within the coverage area. Several factors define mobile stations, but generally there can be no permanent fixed antenna installation. MOI licenses mobile itinerant operation. This type of operation is for temporary (Itinerant) use on shared frequencies, with no protection from other licensed users. These stations are generally allowed to operate at a location or in an area for no more than 30 days.

As you think about these operation types, you see that operating itinerant repeaters carries a lot of complications. Careful engineering, licensing, and preparation is required to do it successfully and legally.

Regards,

Sounds like you're talking about a "mobile extender". Some additional points to consider:

This system shows up on FCC Forms as "MO3". Frequency coordination is required, and in most cases, you get either a low powered 12.5 kHz splinter frequency, or you're relegated to a mobile-only channel.

A lot of the VHF fire systems we installed back in the day had to license local government channels in the 151 or 159 MHz range for MO3 systems. Since fire departments used the lower to middle 154 MHz channels almost exclusively, you needed several megs of tx/rx separation between the high powered mobile transmitting and the mobile repeater receiving the walkie-talkie to prevent interference. Even then, many installations required cavity or notch filters to work properly, especially where 100 watt mobiles were being used!

The preferred arrangement involved a UHF mobile repeater into a VHF high (or low) band mobile which worked fine and eliminated any problems between transmitters and receivers mounted in the same vehicle. The only customers who demanded an in-band system were those who wanted the MO3 walkie to also access other agencies that used VHF high band directly.

The mobile repeater is designed to extend the range of low powered portable radios. For example, anything the mobile unit hears will be rebroadcast through the MO3 radio. If the MO3 hears someone calling, it will key the mobile radio and pass the audio, then un-key the mobile when the carrier and correct PL tone are no longer present.

This sounds simple until you re-read the above paragraph. If the vehicle-mounted mobile is in "SCAN", the MO3 will repeat everything heard on every channel into the walkie-talkie. The mobile radio must be set up to either (a) "home" back to a pre-designated transmit channel -- usually what is selected as the transmit channel on the control head, or (b), go back to the last channel received and transmit there when the MO3 keys the mobile transmitter.

In either case, there's a learning curve with your fire personnel. Unless you go back to the last channel received, you can hear but not talk to everyone you monitor when the vehicle radio is scanning. You'd have to walk back to the mobile and physically change the channel on the radio control head to change the channel the MO3 will talk on.

There are also interference problems that will occur if you have more than one mobile repeater. If Engine 1 and Engine 2 both have mobile repeaters , but both trucks end up at the same scene (or at two different calls within a half mile of each other), then each walkie-talkie may key up BOTH MO3 units, causing both mobiles to retransmit the same message at the same time from two different locations.

You can "fix" the problem by using different PL's on every MO3 radio, or you can use different operating frequencies for each MO3 -- assuming the FCC and frequency coordinators can find lots of in-band channels for you to use. But then you have to assign certain walkies to certain trucks exclusively (because they won't activate the other truck's repeater) or you need multi-channel walkies that can transmit a different PL on each channel, then you select the channel by what truck you're wanting to repeat through!

Or you can purchase a PAC-RT type mobile repeater (a Motorola trade name) which includes the electronic circuitry that 'senses' the presence of other MO3 stations in the area and automatically shuts other units down. It's very expensive (about $3K per vehicle, if I recall correctly) and not a totally fool-proof system.

And speaking of PL, there used to be a hard and fast rule that the mobile repeaters MUST USE a different PL than the mobile radio will transmit. I don't know if that's still true with the latest equipment ...

I believe the MO3 system is still restricted to 2 watts, but most only use 2 watts on the portable. To "balance" the receive and transmit range, most vehicular mounted units are normally set at about 0.8 watts. Anyway, just some things to keep in mind when you're engineering mobile repeaters into your radio system.

Hope this helps.

OK, here is one... What about an IN Band for 800 Mhz? we have a small 2 man PD here that is part of the county 800 trunked system. THey are on the frindge, hard to get out with the portable. getting another repeater pair, or trunked talk group is out of the question, can a 1/2 watt from the portable, into a maxtrac type receiver over to the trunked radio work? ( RICK or similar setup) the car radio is on the trunk, if you put the receiver radio antenna at the front of the car, even mounte dupside down at the front to give the most distance, and you have the 45mhz split on the freq's....the mobile transmits on the repeater input freq, while the receiver and portable is receiving/transmitting on ( any) output freq with low power and it's on PL/DPL?

Now what about getting lic for a freq in the right band? what does it take for a small town to get one? it's so small a freq from another 800 system outside the county should work right? with the portable and the receiver/rick transmitting so little power it should not travel far right? no disruption of other systems I would think.

any Ideas?

The PAC RTs I handled were .25w out on the MO3 freq. I had one working with my Syntor X on the ham bands. The Syntor X was on 2m and the PAC RT was on a 446.xxx freq.

The PAC RT transmitted and received on the same frequency and had switching circuitry so it would stop and "listen" for the MO3 portable every X seconds. Thus if the mobile was working through a repeater with a longish tail, the MO3 could pick up and transmit without waiting for the tail to drop on the main repeater.

I always preferred calling the setup I had on the ham band in my car a "remote base." That better describes the true function I think. But alas, "remote base" is not defined anywhere. It used to be in Part 97, but is no longer.

The biggest problem of this setup, aside from running down the car battery, was that as far as I could ever learn, the PAC retransmitted everything back to the MO3 that was on the channel the Syntor X was monitoring. The audio was taken from the Syntor X ahead of the PL decoder, so having the Syntor X programmed for PL squelch didn't matter. The PAC retransmitted everything.

Now I've always thought that was pretty dumb, so I've always left open the possibility that I had something set up incorrectly. But the couple of guys who helped me get it all working were in agreement that that's the way the original PAC RT worked. It was also one of the reasons I pulled the PAC RT from my system.

I don't know much about the legalities on the public safety band, but plenty of fire depts use the things. It can't be THAT tough to do legally.

Good luck.

dfc2 wrote:OK, here is one... What about an IN Band for 800 Mhz? We have a small 2 man PD here that is part of the county 800 trunked system. They are on the fringe, hard to get out with the portable...

The BEST solution I ever saw for that mess, short of having the county install a satellite receiver on the 800 system in that town, was to install a UHF PAC-PL unit (not PAC-RT, but very similar) at a fixed location with a really good outside base station 12 dB antenna and a tower. License it as an FB2 fixed repeater, and then give the cops a UHF walkie to carry when outside the car.

The officer marks out on a call using the vehicle mounted 800 radio, but carries the UHF portable when inside the house. The UHF PAC-PL is connected to a control station on the 800 system and repeats all radio traffic on the talkgroup, just like a small fixed repeater. The portables pick up the UHF signal from the tower in town, and the officers can access the county 800 system from anywhere in the city limits -- with or without a cruiser nearby.

The difference between a PAC-RT and a PAC-PL unit is the sensing circuit that determines if another PAC-RT unit is in the area and transmitting. Since there will only be one PAC unit in the system, there is no need for the additional cost. PAC-PL is the low cost version of the PAC-RT ... it only looks for the correct PL tone to activate.

The above mentioned system worked very well, as it allowed officers to be on foot or at home with a UHF portable and still have local access (through the PAC-PL and the 800 MHz control station) to the county system.

You could mount the UHF PAC-PL or PAC-RT unit in a cruiser for greater mobility, but when the car was turned off, out of service, or 15 miles away transporting a prisoner to jail, you lost all portable communication.

In any case, just a solution I knew about that worked well for the customer.

OK, another idea? If we use one of the lic freq's from the 800 system, and cause no interfearance with the system, can we use on of the freq's as an input into a mobile relay? any other coordination required? we are lic for the freq's. we have the county system set up with a type 2 TG's and fill in conventional repeaters, and tac freq's are car to car and portable to portable, and use the same freq's as the conventional repeaters. How about on eo f the type 2 freq's, use a maxtrac with 2-4 freq's so it can be changed when needed to avoid the control channel????? no problem on the car battery, they are only out 2-3 times a week, but need to be heard when they are out. looking for a cheep way to fix the problem.

any Ideas?

The BEST solution I ever saw for that mess, short of having the county install a satellite receiver on the 800 system in that town, was to install a UHF PAC-PL unit (not PAC-RT, but very similar) at a fixed location with a really good outside base station 12 dB antenna and a tower. License it as an FB2 fixed repeater, and then give the cops a UHF walkie to carry when outside the car.




**** Well Nothing is going to get installed. If the problem is to be solved it is up to the small town PD. and they don't have the money for that.


so either we come up with a fix like I have outlined or somthing similar, or it does not get fixed. minimal equipment, and no new portables. they only have one portable as it is.

To add more information, when the firemen are out in the county, they can hear the main repeater OK. They have a problem transmitting back to town. This is because the portables are on their belt or in their pockets. No antenna height. They want a R1225 repeater mounted in one of the trucks so that it can relay their transmissions to the main repeater back in town.

Hello.

The FCC will not allow a mobile extender with the input or output at 800MHz.
There is no type accepted equipment for this class of service at 800MHz.
Why is anybodys guess.

Cowthief wrote:Hello.

The FCC will not allow a mobile extender with the input or output at 800MHz.
There is no type accepted equipment for this class of service at 800MHz.
Why is anybodys guess.

Hrm. AL DPS uses a 859MHz extender, iirc.

Hello.

Motorola told the state of Texas no such thing was available.
Perhaps they were trying to peddle the trunking thing over anything that would have made sense.

Cowthief wrote:Hello.

Motorola told the state of Texas no such thing was available.
Perhaps they were trying to peddle the trunking thing over anything that would have made sense.

AL DPS also uses GE radios and repeaters.

Cowthief wrote:Hello.

The FCC will not allow a mobile extender with the input or output at 800MHz.
There is no type accepted equipment for this class of service at 800MHz.
Why is anybodys guess.

I thought there was a PAC RT ( form another company, not Moto) that was on 800? Can't recall the company, but I hear they make a good product?

DFC2

Not to go off topic (they do interface with /\/\ mobiles ), but the Pyramid SVR200s are available in VHF, UHF 700,800, and 900MHz versions.

HumHead wrote:Not to go off topic (they do interface with /\/\ mobiles ), but the Pyramid SVR200s are available in VHF, UHF 700,800, and 900MHz versions.

Yep, that was the one I was thinking, so is it legal or not to use one on an 800 trunked system? we are talking very low power, and not close to anyone else. is a Lic needed to run it using another freq form the trunked syste.....again as lone as it does not interfear with other users or the controller......


I would be suprised if the mechanics of it did not work..... I have a ear piece on my portable, and when I trnasmit on my mobile I can hear myself, no overload or anything......same princible right? low power mobile hooked to a higher ( 15-30 watts) power mobile. the portable talking to the car, received on a maxtrac programmed for simplex, then a rick ( or similar thing) over to the trunked system, either with another trunked maxtrac, or it interfaced with a trunked mobile. should be fine right? the split on the 800 freq's is 45 mhz so should be fine...Mount the antenna's at either end of the car. but what about the legal side?????? can I do this with the current licens? or do I need to get a lic for either the simplex freq or entire trunked system for the village?


can somone give me direction?