Batboard

Our department operates on a VHF frequency simplex which works well for most applications. A few larger industrial buildings and one hospital building cause extreme issues with radio communications. Portables can't be eard by other portables inside and outside apparatus cant hear the radios either. It varies from each position in the buidling getting better or worse. Hospital security does run a uhf repeater with pretty good success.

We expermented with a pyramid repeater and the cdm1550 in the truck. The result was dissapointing, but not suprising: if we can't get out on the current channel then trying to get out to the repeater on a same band channel did not work any better.

Currently I have reached my level of expertiese on a solution. A suggestion has arisen to put the pyramid-CDM repeater on the roof with a base antenna. Another is a "leaky" antenna of some type in the building. Our prefered method is some type of system that we can take along with us to any other building or facility for future use, and it is eisier than getting buy in to numerous building owners and an ever shrinking FD budget. Other ideas would be to cross band, but now we would use uhf radios for only a hand full of applications. Additionally it needs to be public safety oriented and the operation should be VERY simple (firemen and radio technology seldom mix).

Do any of the radio gurus on here have a suggestion as to the best way to solve this problem?

Several different options... I would suggest contacting a good local radio dealer for assistance.

There are local towns that are starting to enact ordinances that require public safety radio systems work inside new construction buildings before the are approved for a CO. It becomes the building constructor's responsibility to install whatever is necessary to make sure public safety radios work inside. Most places are only doing this for new construction. It doesn't help for existing buildings, but could help down the road. Something to look into.

With the exception of the radiating coax, these suggestions are to help the radio signal from the outside get in the building and getting the signal from the inside the building to the outside. They will not help portable to portable coverage inside the building. The active and passive systems will help all VHF communications and if PD is on same band should also help them with in building communications. If they are on the same band, chances are they are having the same type of problems. If you contact PD, they may be willing to share some of the costs with your FD if solutions will help them as well.

1. You said you tried a Pyramid repeater on the same band? VHF? You may find UHF will leave the building better. Try a Pyramid repeater on UHF connected to the CDM in the truck.

2. Passive antenna system with antenna in building. High gain antenna on outside, short piece of low loss cable and high gain antenna inside.

3. Passive antenna system with leaky coax inside building. High gain antenna outside building. Inside building run radiating leaky coax such as Andrews radiax. This cable can be run down the length of the building with a high gain antenna on the far end.

4. Active antenna system. Similar to above but uses a powered amplifier between the outside and inside antenna. Active BDAs (Bi Directional Amplifier) are not too popular for VHF because of high costs.

These are some suggestions. There are even more things that can be done, including switch operations to UHF. Installing a repeater system, installing receivers for the repeater inside or near the buildings with problem areas. Install repeaters on the buildings. A big problem with using a repeater mounted on a building for fire operations, is the repeater may fail especially if the building is on fire :/

Good Luck,
John L.
Sparta NJ

Very soon the multi band Thales Liberty Harris One and Motorola APX radios will be available. Perhaps using those would solve your problem. There is some info here on Batlabs about those radios.

WCHija wrote:Very soon the multi band Thales Liberty Harris One and Motorola APX radios will be available. Perhaps using those would solve your problem. There is some info here on Batlabs about those radios.

Only if you have talk-out coverage on one of the bands other than VHF that you're struggling with...

Multiband "interoperable" radios don't solve coverage issues when the necessary infrastructure is inadequate or missing...

As far as options, UHF seems to work better for talk out in large buildings than VHF, at least locally. The use of a VHF Pyramid repeater with your VHF CDM is likely causing some amount of desense unless you're operating a high end duplexer with sufficient isolation - just because your Pyramid is on 170.x MHz doesn't mean it isn't receiving desense from your 151.x MHz operation...

What I meant was to use a few of the multi band radios to cross band repeat to a UHF V/R, which then talks out on your VHF CDM.

WCHija wrote:What I meant was to use a few of the multi band radios to cross band repeat to a UHF V/R, which then talks out on your VHF CDM.

I agree that there is a possibility of using multiband radios in the future, however, crossband repeating between bands has not been identified as a planned possible feature on either the Thales or Moto.

rrfd43 wrote:...an ever shrinking FD budget...

Dale Earnhardt wrote:http://mrtmag.com/iwce/news/p25-radios-thales-0228/
...with a cost of approximately $4000 to $6000 per device...

Either way, with the price tag upwards of several thousand per unit, it's unlikely this option will fall within the budget constraints of the OP.

As you seem to know, the basic problem you are having is due to the frequency. Here is what is happening: (apologies if this sounds oversimplified) since most buildings are made of materials that shield RF pretty well, the primary way for signals to get in and out of the building is for the wavelength of the signals to be small enough to easily pass through the openings (doors and windows) and then propagate down the hallways. At VHF, the wavelength is large enough (about 6 feet) that these openings are too small for very much signal to get through. UHF and 800 MHz work better because the wavelength is shorter (2 feet or less) making it so the signals can make it through the doors, windows, and hallways. Of course, if you are in a metal enclosed room or in the concrete reenforced basement, good luck to you on any band.

Using a vehicular repeater like a Pyramid on UHF and connecting it to the VHF radio in the vehicle makes it so you can operate on a higher frequency with your handhelds and thus get the signals in and out of the building better (assuming you get enough signal out of the mobile repeater). This, of course, means having two collections of handhelds unless, as others have suggested, you buy multiband radios.

The UHF repeater solution will work only as good as handhelds can talk, so if you want to experiment, get a couple of UHF handhelds. Send one person in the building with VHF and UHF handhelds and have another person out on the street to talk to. You can go to different places in the building and compare the coverage on the two bands. If you can't talk on UHF under these circumstances, there is no point in buying the vehicular repeaters on UHF.

Fireman's law of RF: The radios work the worst where you need them the most

Thanks, this is what I am looking for. Got a few ways to go here...I'll let you know what we try. Please add any additional information that may help with thought processes.....it helps prove / disprove ideas and gives an nother angle to look at the problem.