Batboard

First off -- this is not my design....... I am looking for comments and/or input on the following configuration.

Two repeaters (uhf) will be installed on opposite ends of town. Both will have the same input and output freqs and dpl. One will be at the dispatch location where a voting system will be located and the other remoted and will be connected via hardwire (customer owned) to dispatch. The concept is to have the two repeater receivers connected to the voter and then select the stronger signal via the voter and send it back to the tx side to be repeated back out of that location. All of this will be connected to a zetron console. The repeater portion will be for mobile/portable to mobile/portable communications. And the dispatcher will get their rx audio from the voter via the rx side of the repeater and they will tx thru the tx side of the repeater (in other words they will not be using the repeater as a repeater).

I'm hoping I explained this enough for you to understand. I have my own opion on this set up but would like to hear from some of you.

Gary

They call that "Transmitter Steering".

What exactly is the reasoning for it? It isn't necessarily the best way to cover a large area. It depends. Can you describe the use of it a little more?

Hello,

Yes I am aware what they call it..........But the usual way that I have seen that done is by using regular base stations connected to the voting system. I have never seen it used to control the repeater. I'm not sure why they chose to do it this way. This is the design that someone is pushing. Like I said I have my opinions I'm looking for yours.

The town is about 7 sq miles with the dispatch at almost one end. Currently running a simplex uhf channel we get fairly good coverage (portables) some dead spots.

Gary

7 sqaure miles?? That is tiny!! You need two transmitters to cover that whole area? How is the base-to-mobile and base-to-portable performance from the one site you have now? I would think in a space of 7 square miles, it should be pretty damn good. How high are these antennas?

Unless there is a mounting in the middle or the dispatch antenna is like 10' off the ground, I can't see any reason for that second transmitter. The receiver and voter, yes.

It is called the poor man's simulcast.. transmitter steering. I have seen it done with multiple transmitters (8)

It is one step up from two seperate repeaters with the same freq, but different pl tones.

It covers an area that could otherwise be uncoverable with one transmitter. 7 sqaure miles seems a little ridiculous though.

To do this the "proper" way... ie simulcast involves alot more money. Goto http://www.simulcastsolutions.com and Ed has a bunch of info about the different ways to add coverage.

It makes sense that the dispatch will not be using the repeater since the receiver is right there. If you are going to key a transmitter, why go through two?

Howard

The only significant issue from a mobile standpoint is that units in "A" site's coverage area won't always hear traffic from the "b" TX site and vice versa. Most PS users (LE in particular) will complain about that, for various reasons.

I worked on a similar system with 12 stations, the only things I would do is make sure that the dispatch console cannot key more than one station at the same time, and that there is a way for dispatch to hear RX audio from the indiviual sites if your voter dies at 2 AM.

Speaking of voters, many of my (unfounded) trouble reports were from dispatchers who said "it isn't voting the right site, I know he was right under the XYZ tower", it is hard to convince non-technical personnel that S/N ratio is the sole criteria for voting and not location. Try to educate your people about this right up front.l

If you are presently getting pretty decent coverage with a "few dead spots", you might be better off putting the time, effort and $$ into
improving the present system instead of a major change.

7 square miles is not a very large area to cover, even with horrendous topography.

If the town is very hilly, you might want to thnk about antenna work, such as getting rid of high gain mobile antennas if they are used, and trying 1/4 wave antennas (they tend to fill in a lot better in lousy terrain.)

or tailor the base station antenna to the area by modifying the location, gain etc.

A common problem with "lousy coverage" in a small area is the use of too MUCH gain on the base station antenna.

We once had a p/s agency with DB-420 antennas at the top of the tower, and it wondered why it couldnt cover the town. Dropped the gain down (DB-201), and coverage improved from around 40% to around 95% .

Make sure the antenna system is presently performing as it is supposed to be... verify the feedline & connectors are up to spec, as well as the receiver and transmitter specs..

While steering works well when done right, I really think you would be much better off improving your present system... you know what your system strengths and weaknesses are now, no need to throw in a lot of variables at more $$.

just an opinion from an old fart!

73!

Mike in CT
KM1R

Receiver steering of multiple transmitters is an application that requires some very careful engineering if the results are to be satisfactory. At least one of the reasons is that a voting selector selects the "best" (or "better", if only two) receiver for processing the audio. This is not the same a selecting the "best" (or "better") site for transmitting, since at least in theory (and almost certainly in practice), it will be that though Site B's receiver gets the better audio, the unit that is transmitting into Site B's receiver would be able to hear Site A's transmitter well enough, but some of the other units may not be able to hear Site B's transmitter nearly as well. In short, because the coverage of a transmitter and a receiver (both co-located) are not the same, using receiver coverage as a surrogate for transmitter coverage can lead to some wrong answers.

I endorse Mike in CT's suggestion.

Hello All,

First I want to thank all of you who have responded so far, I agree with all of your comments. I have said most of what you have said to the powers to be and was looking for some addition support towards my comments with them. I should note that the topography is almost perfectly flat and the tallest building being the hospital at 4 stories.

Comments are still welcome

Thanks
Gary

Our town is almost the exact same size with the same topography. We have a Vhf repeater on the west side of town up about '75 running out of a 4 bay foded dipole antenna. We get county wide coverage with that system. It's even better than the county repeater at certain places.

What they are proposing sure seems like overkill to me. I don't see why you wouldn't have almost 100% coverage with what you have now. Have they considered a repeater to atleast extend the portable to portable operation?



mancow

GMC:

How high is the current UHF base trasmitter and what power & antenna gain if known? One site should cover that perfectly from base to mobile. A remote receiver on the other end for portable talk-back would probably make it complete.

i also endorse MikeInCT's opinion. Fine tune that current install, because 7sq mi is CAKE for a small base station to cover. And hell, your topography and landmarks do not sound like they are doing anything but help you. There has to be something else that is a-miss...like a nearby agency stompin all over you, or a bad antenna or poor tuning job that's hurting you more...if the powers that be are interested in doing massive changes, i'll trade you our 14 sq of hills for your 7sq mi of flatness...i'll even throw in a ridgeline down the middle and the busiest street in CT for you!

I'm goona have to agree with most other folks here, 7 square miles, no matter how ya lay it, doesn't warrant all that. A good base should cover most of it, a good repeater located well will do it better. for portable/portable and mobile to mobile.

Just make sure you don't have too much gain, I am fighting that with the powers that be now here, they have a 9db antenna on a mountaintop 2400 HAAT and wonder why areas of teh county get no coverage but you can get a great radio check 150 miles away

My two bits worth:
As was noted some dispatchers mistake voting indicators as a vehicle location system.
For the very same reason "Transmitter steering" via the voting comparator is a very dicy issue.
I have spent much time attempting to make a VHF IMTS steering system work. ( a long time ago)
Why is the site over the mountain selected rather than the one in Honolulu? Because the Honolulu receiver is being grossly desensed by a paging transmitter.
I must admit that Oahu Hawaii is anything but flat.
I think a decent repeater perhaps, with voting would be the solution, as suggested by other members.
Many customers discover after spending many thousands of dollars that 18 DB gain receiver preamps, and super high gain antennas do not solve all problems, and can actually degrade a system.

Dude, you said IMTS, I didnt know if anyone still knew what that was!

Nothing like the hum of an idle tone at 350 watts to keep you company on lonley nights up at the tower site.

Q