Options for Unlicensed, Low-Power Paging?

[fogster]

I have in the back of my mind a little PC-based system for in-house paging. Is POCSAG legal on MURS? If not, are there other options for in-house paging, without requiring licensing? I'd want a watt or two to cover a fairly big indoor facility, but it's nothing worth trying to obtain a license for. (But at the same time, staying totally legal is important when it's being done for a client!)

[firefighter13669]

an intercom paging system would work

[fogster]

an intercom paging system would work

I don't follow what you mean. I'm looking for a wireless solution, and need to transmit text (due to noise). When you say "intercom," I'm envisioning a wired voice solution, neither of which I want... Am I misunderstanding what you're saying?

[Wowbagger]

I think he is implying you should stick with audio paging, rather than RF.

I don't think you are going to find many solutions that will allow you to push a watt of RF, for commercial purposes, using data signaling, without a license. Even assuming you do, getting cheap pagers on that frequency, whatever it is, is going to be hard.

What about going to a cellular text messaging solution? Or an 802.11b solution and some form of instant messaging on a PDA?

[k2hz]

Paging and digital emissions are allowed on MURS but finding a transmitter certified for MURS use and digital emissions may be a problem.

Here is some info from the FCC WTB website on MURS:


Permissible Communications

MURS stations may transmit voice or data signals as permitted in 47 CFR 95.631(j).
A MURS station may transmit any emission type listed in 47 CFR 95.631(j).
MURS frequencies may be used for remote control and telemetering functions. MURS transmitters may not be operated in the continuous carrier transmit mode.
MURS users shall take reasonable precautions to avoid causing harmful interference. This includes monitoring the transmitting frequency for communications in progress and such other measures as may be necessary to minimize the potential for causing interference.

Operating Restrictions

MURS stations are prohibited from operating as a repeater station or as a signal booster. This prohibition includes store-and-forward packet operation.
MURS stations are prohibited from interconnection with the public switched network. Interconnection Defined. Connection through automatic or manual means of multi-use radio stations with the facilities of the public switched telephone network to permit the transmission of messages or signals between points in the wireline or radio network of a public telephone company and persons served by multi-use radio stations. Wireline or radio circuits or links furnished by common carriers, which are used by licensees or other authorized persons for transmitter control (including dial-up transmitter control circuits) or as an integral part of an authorized, private, internal system of communication or as an integral part of dispatch point circuits in a multi-use radio station are not considered to be interconnection for purposes of this subpart.
The highest point of any MURS antenna must no be more than 18.3 meters (60 feet) above the ground or 6.10 meters (20 feet) above the highest point of the structure on which it is mounted.

[fogster]

I think he is implying you should stick with audio paging, rather than RF.

Ahh, I get it. The project I had in mind was actually for bowling alley mechanics. The place is currently using two-way radios, but the mechanics are surrounded by extremely noisy machines, so they're currently stuck with solutions like wearing earbuds under gunmuffs to hear, and for some reason, even with that they miss a fair amount of calls. It's mostly a one-way solution; the only time they really talk back is when they ask for a repeat. Hence my interest in a text-based solution.

What about going to a cellular text messaging solution? Or an 802.11b solution and some form of instant messaging on a PDA?

I've thought about Nextels, which would actually be ideal... Except that the "client" is a total tightwad. :rolleyes:

Even assuming you do, getting cheap pagers on that frequency, whatever it is, is going to be hard.

This is actually the one part of this idea I have under control. What inspired it was noticing that the set of used (but working!) VHF POCSAG pagers I picked up was still sitting in a box about a year later, with no real use. I believe they cover 151-159, hence my interest in using MURS.

Paging and digital emissions are allowed on MURS but finding a transmitter certified for MURS use and digital emissions may be a problem.

Pardon my ignorance: when a normal ol' MURS HT is "certified," does the cert mean that it's OK for MURS in general, or that it's approved specifically for FM use (only)? I've had good luck recovering data from an audio jack (and processing it at POCSAG) even after passing through the discriminator... So I thought about trying in reverse: dropping the data rate to 512 baud (it might see 30 pages sent in a day, to a whopping 2 pagers, so it's not like I need to keep that baud rate high to support everyone), and then, doing the same thing you do with a crappy TNC on a crappy ham rig: feed the output into the mic jack. Obviously this isn't as desirable as a radio with a dedicated FSK input, but I wonder whether this is legal or not on MURS?

MURS stations may transmit voice or data signals as permitted in 47 CFR 95.631(j).

Googling this reveals:

(j) A MURS transmitter must transmit only emission types A1D, A2B, A2D, A3E, F2B, F1D, F2D, F3E, G3E. Emission types A3E, F3E and G3E include selective calling or tone-operated squelch tones to establish or continue voice communications. MURS transmitters are prohibited from transmitting in the continuous carrier mode.

My understanding of the emission types is lacking... Would POCSAG fall as "F2D" (frequency-modulated, digital (subcarrier??), data/telemetry)?

MURS transmitters may not be operated in the continuous carrier transmit mode.

This would just be occasional transmissions... I assume this isn't getting at the same thing as the ham "no one-way transmissions" sort of thing, but rather, "You shall not run a transmitter 24/7..." type thing?

This includes monitoring the transmitting frequency for communications in progress and such other measures as may be necessary to minimize the potential for causing interference.

This part might be tricky... I had in mind that the user, who wouldn't be technically-oriented, would type in a message, hit Enter, and have it transmitted. I suppose I could just feed the audio through (and mute when transmitting!), but I can see them encountering static and turning it down. Would simply implementing BCLO work? (It's worth noting that this is for a place in the middle of nowhere, and it'd be in-building, so the odds of external interference are very slim... But I want to make sure that this would be totally legal in any event.)

[k2hz]

FCC acceptance of any transmitter is always for specific emission types. Most MURS units would be voice only. Digital generally requires a direct FM input to the exciter. It won't work attempting to just run a digital signal into the mic input.

There is no prohibition on one way transmission. What is prohibited is leaving the carrier on continuously or when no information is being sent.

Both licensed business paging and MURS require monitoring a shared channel before transmitting. This can be done with carrier sense from a monitor receiver inhibiting the transmitter until the channel is clear.

[CAPTLPOL]

Equipment that was certified prior to 2002 would be type accetped as long as it falls within the guidelines and is part 90 certified as well.

[Jason]

There are used peoplefinder base units out there, but they are are getting scarce, and the RSS and service cables are NLA and are also hard to source....

This should do the trick:

http://www.jtech.com

License free? Not likely youll get there from here, unless you have a local part 22 carrier just lease you some airtime. I think pagers are around $5/mo?

Sure seems easier than all that....