Batboard

The company I work for uses a 506MHz private trunked radio system. It appears that any time it's foggy, the radio system just stops working. Before, the radios would come in scratchy, and today they're not working at all. We use CDM1550LS radios. Is this an equipment problem or what? Has anyone experienced this before?

This is for a school bus company, and lack of radios is not a good thing with over 160 buses.

Any help appreciated!

Could be just a coverage issue. Where is the system tower located? How far from the tower were you located?

Do other buses have issues or is it just yours? Has a tech checked both the buses and the system?

George

Are you using microwave for the site backhaul to the system controller?

Mike-

Define 'stops working'.

Do you get an out of range indication, or does the system go into failsoft?
A little more system info is needed too.


Off the top, I'd agree with RKG - this sounds like M/W signal fade, but if it's a single site system without a M/W link, that wouldn't be it.

The tower is located about 15 miles from our office, on one of the highest points in central NJ, on top of a 250 foot tower. We have used the system as far north as New York City and as far south as Philadelphia. This problem affects all of the buses. The only people who could talk were located about 5 miles or so from the tower. This system, to my knowlege, has no failsoft. It's either all or nothing. We can't even go onto simplex.

A little more info on the system can be found here:

http://www.atl-coast.com/

We use the tower marked in the purple circle under the services button.

I'm just looking to see if this is a common issue with this type of system or frequencies, I may suggest to the company for a different carrier or just try to purchase a private repeater for us alltogether.

My guess is that its an LTR system.

500 MHz can behave weird sometimes.

With that many units, a customer owned system is a good option.
(160 units x what $12.00 per radio? = $1920.00 per month)

Even here in Southern CA the most expensive site rental is $600 per box per month.

Get two YG / FB8 (unshared, exclusive) UHF channels and construct your own LTR system.

And LEASE the equipment! I am not licensed to give tax advice, but I understand there are benefits. This also helps with the initial cost of the repeaters controllers and licensing. b

Well, we already have the equipment. We use a combination of CDM1550LS units and some model of Johnson radios. An LTR system is a bit overkill imho for a school bus company, I think one repeater pair and a simplex channel would be sufficient for out operations.

Anyone have any rough ideas how much it would cost for a 500MHz conventional repeater and setup costs?

As another noted, without more details about the nature of the problem, it is hard to form much of an opinion. In general, fog does not fade UHF signals, and if you're operating from a single site, my suggestion about microwave fading probably doesn't apply.

You stimulated my curiosity, however, with your reference to 506 mHz. That is TV channel 20, and it is authorized for land mobile radio by Part 90, subpart L. It is only authorized for base stations within 50 miles of a point in Philadelphia (39-56-58.4N 75-09-19.6W). The regs go on to provide:

"Mobile units shall be operated within 48 km. (30 mi.) of their associated base station or stations. Such units may not be operated above aircraft in flight . . . . Base and control stations shall be located a minimum of 1.6 km. (1 mi.) from local televisino stations operating on UHF TV channels seprated by 2, 3, 4, 5, 7, and 8 TV channels from the television channel in which the base station will operate."

47 C.F.R. sec. 90.305.

I cannot tell from the Atlantic Coast web cite where the transmitter for the purple system is located, but it appears to be Long Beach, N.J. That is more than 50 miles from the cited point in Philadelphia (which cuts through West Freehold and Englishtown, but does not extend as far as Freehold itself).

I cannot explain the correlation to fog, but I wonder if it is possible that you are getting interference from TV stations in the UHF-TV ch. 22-30 range? I also wonder if you're trying to get more out of this system than it was designed (or under the regs could be designed) to provide?

The REAL benefit to a trunked system is frequency protection. There is no way to protect yourself with a standard UHF license.

The 500 MHz channels in your area have be auctioned the highest bidder by the FCC. So you will have to look the regular UHF business pool.

LTR controllers are not that expensive ($1500.00 for a Zetron) and in the long run the bus company will be saving tons of $ not have to pay for air time

601 wrote: Anyone have any rough ideas how much it would cost for a 500MHz conventional repeater and setup costs?

As far as Motorola goes you have two choises...

Quantar Limited $10,000.00 ea

CDR700 (Two CDMs as a repeater) $2800.00 ea

Antennas and duplexers may not be need if the site has a community antenna system.

SORRY no MTR2000 above 500 MHz

="motisking" SORRY no MTR2000 above 500 MHz

Oops...

No MTR2000 above 470 MHz.[/quote]

motisking wrote: As far as Motorola goes you have two choises...

Quantar Limited $10,000.00 ea

CDR700 (Two CDMs as a repeater) $2800.00 ea

SORRY no MTR2000 above 470 MHz

Another option is the RKR1225 19" rack mountable repeater. I am personally not very fond of this units for your type of application.

I would think there would be a problem getting a channel or two in that range but I my be wrong.

Cam22 wrote:I would think there would be a problem getting a channel or two in that range but I my be wrong.

450-469 MHz
or
506-512 MHz

Quote-"The REAL benefit to a trunked system is frequency protection. There is no way to protect yourself with a standard UHF license. "

Dont kid yourself!

The only real protection is to get an FB8 designation. And that doesnt guarantee a clear channel.

If you own the system, have a conventional repeater controller installed on one of the repeaters and reprogram the mobiles. The trunking system makes it hard to hear the interference thats probably present, due to the design. (probably why the trunking system was used) 506 megs 200 feet up? What kind of heliax on the tower? Better be at least inch and a quarter, or the loss could be significant.

Does the system come up if someone drives close to the tower and keys up, during the "outage" ?

In reading the other post closer, I see that you dont own the system.
Complain! You guys are paying alot to use the system.

If you are going to consider owning a system-
LTR will do you no good if there is only one user group. It needs a clear home channel, and if you have only one group using the system, all you need is a clear channel.

Dont skimp on the product. Make shure whatever you use is 100% duty cycle. Ive heard little 20 bus yards lock a channel down for the duration of their runs.

Your 1550's are fine. Trunking or conventional. If you are using ignition sense and have big relays on the vehicles, make shure you spike protect the ignition sense lines. Motorola is supplying kits to the dealers for this. These radios dont like bing spiked at all.


School Busses? License for PW not IG.

chpalmer wrote: A) Complain! You guys are paying alot to use the system.

B) If you are going to consider owning a system-
LTR will do you no good if there is only one user group. It needs a clear home channel, and if you have only one group using the system, all you need is a clear channel.

C) School Busses? License for PW not IG.

A) Yes complain

B) LTR WILL do good. It will provide an "exclusive" area of operation. You can not do this with out licensing for trunking. Currently the FCC is rewarding radio users for efficient use of spectrum (i.e.: trunking) by providing these protected service areas. With a 160+ buses a separate group for say MAINT and/or EVENT for special events and/or EMERGENCY would add some benefits I am sure.

C) A school bus company is a business. A school district bus operation on the other hand would qualify for PS freqs.

That’s my $0.02 worth.

Doing Groups that way would make use of the trunking system. But it would have to be more than two groups to make it worth the money, because one of two channels could just be assigned to each of the two groups, conventionally.

YG or Trunking on a license does nothing to protect you, trust me, we've been fighting this battle. Another company stuck a taxi cab service on the same freq as our only high 460 channel at the time, 2000 feet higher than us. The cab co was unlicensed so easy to fix. So we YG'd the channel and got an fb6 hoping to protect it. Now everyone is licensing it for their mountain top systems, and we have no recourse. We have a trunked system now but all our conventional customers are still their till they get tired of the other repeaters coming up at will and interfering with their conversations. Can you say loooong tail.

find a freq and fb8 it. Then you can key up whenever you want without having to worry about others coming on the channel. You can still use it conventionally if you want.

And still- School busses can license for public safety freqs, which might be easier to find in your area.

I think i may know whats up, but I could be wrong. It sounds as if your LTR trunking provider's system is constructed poorly. Get your SMR to check all connectors exposed to outside weathering. I used to work for an SMR which had the same issue of the system performance becoming downright crappy/unusable during cloudy/rainstorms and could not believe that they were even able to sell it as a service since it rains in south florida everyday at 2PM. It turns out water gets into the coax transmission line and hinders and severely degragates the performance of the system. The older the cabling, usually the more perceptable the system was to this problem. Where the connector fits on to the coax was the point of entry.

Finally someone talked about the problem. I agree whole heartedly the tower has coax or antenna problem that is allowing water to hose up the antenna system. The fact that it works from 5 miles out tells me that this is an antenna or trasmision line problem and likely has nothing to do wiht the fact that it is on a UHF LTR. Tell your service provider this is not aceptable.

Believe it or not some old systems still used nitrogen pressured lines. If they are check the site, should be a pressure guage in the radio shack. We had many problems with this type of set up and went to 7/8" heliax. Problem solved.

My two bits worth:
Sound like a problem on the receive side of the system:
Some possible problems:
Bad antenna, fractured radome allowing water to enter, drain plug not removed on invertable antenna, water in jumper cable, water in tower top amp, water in main transmission cable.
These problems are often caused by gallant hunters using the tower for target practice.
Defective multi coupler amplifier.

By all means bring the problem up with the SMR operator, as this will cost them revenue when they loose customers.

I have seen all of these problems at one time or another. Fortunately not all on the same system.