Batboard

I have been installing these really cool amplifiers for Nextel signals in buildings in our county with poor reception. See http://www.cellantenna.com/repeater/cae580.htm for more. We have one on the way for our new all steel and concrete (RF cocoon) fire station so Nextel conversations, even in the basement, wil be great.

But, we are also having troubles with our std UHF signal reaching our Minitors. We will have an antenna on the tower for the base radio so regular duplex use will be handled by the county-wide repeater setup. But it would be nice to have reliable pager reception in the building also. Does anyone know of a "amplifier" gismo like this for 460.575 (our receive side of the duplex)?

TIA
Greg

1. The devices you refer to are called "bi-directional amplifiers" (or "BDAs"), though the term "amplifier" is inapt because they are not true RF amplifiers, but rather a form of paired simplex repeaters that generate their own RF signals.

2. Yes, there are BDAs for LMR frequencies. Unlike the bandwide BDAs for cellumar and SMR, they are tuned for two specific frequencies (your input and output), and they require some pretty intensive engineering to achieve the needed in-building gain while preserving the donor-to-client RF separation. The best equipment comes from TxRx.

3. Not to start a fight, but under the authority of what license are you transmitting via the SMR BDAs? You don't have your own license, and the Nextel license doesn't cover your BDA without Nextel's approval (and, in fact, a large portion of the supposed Nextel-Public Safety "interference" is caused by the indiscriminate installation of such bandwide BDAs).

Not to start my usual nextel rant, but I find it amusing that you guys are making your cell phones work everywhere before your actual primary communications radio system.

I was not clear then. While Nextel is a highly used method of communicating, the primary radio system is still primary - all tucked it and handled by the stick on the tower and a really nice Motorola Simulcastinging system county wide. The station occupants will receive alerting and susequent dispatch through the PA system. The issue I am trying to tackle is personal Minitors and getting the dispatch stored in them if the guys are in one of the many RF dead zones in the new building.

And to RKG who said:

Not to start a fight, but under the authority of what license are you transmitting via the SMR BDAs? You don't have your own license, and the Nextel license doesn't cover your BDA without Nextel's approval (and, in fact, a large portion of the supposed Nextel-Public Safety "interference" is caused by the indiscriminate installation of such bandwide BDAs).

...

Yikes, I did not know this and the supplier does not ever mention this. I do know the transmitter is VERY low power and doesn't even reach outside the perimiter walls of the building (measured crudely by the cell phone sig strength mode).

No surprise that the manufacturer doesn't mention this; it would put them out of business. And similar units are being marketed to boat owners, using a donor antenna on the flybridge and the client antenna at deck level. The marine-oriented units are being sold out of a catelog and are user installed out of a box, with no engineering input and, even worse, using omnidirectional antennas for donor function, yet another violation of the rules on point-to-point transmission. Needless to say, these units are causing havoc, particularly when two or more of them installed on nearby vessels compete with one another and shut everyone within a mile or so out of cellular service.

Note that there are two -- sometimes four -- transmitters in a BDA. The client transmitter(s) are the low power units that broadcast from the client antennas mounted (usually above the suspended ceilings in the building). The donor transmitter(s) operate with more power, particularly within the primary lobe of the directional antenna that they are supposed to be used with, on input (and sometimes also the output) frequencies of the SMR system in question. It is these transmitters, operating on the input frequencies, that cause the public safety problems.

There are at least two licensing issues: first, an SMR subscriber only has privileges under the system operator's license, and if you look closely at your Nextel paperwork, you are extended privileges under Nextel's license only for Nextel-supplied subscriber equipment (i.e., the iDen handset). Second, the BDA, because it uses a fixed power supply and an antenna fixed to a structure, is technically a "base station" or "fixed station" and requires licensing as such.

As one would expect, the FCC has done virtually nothing to enforce the rules on BDAs, and Nextel (and Motorola), which are both leveraging the supposed public safety "interference" for their own purposes (more frequencies for Nextel and the sale of replacement iDen units for Motorola), have been remarkably quiet. I am aware, however, that some 800-based public safety agencies have come down on BDAs in a few situations.