Dial Up Modem for ASTRO Connections

ASTROMODAT · Post by **ASTROMODAT** » Wed Dec 11, 2002 1:38 pm

The Motorola approved methodology to connect an ASTRO Quantar repeater to a DIU is via a very expensive 4-wire circuit, such as a 3002 Private Line (with C5 conditioning preferred). The ASTRO modems are connected at both ends (Quantar repeater and the DIU) and a 9.6 kb/s full duplex connection is the result.

Why can't one simply install a 9600 baud modem, programmed to operate in the full duplex mode, at each end via standard dial up POTS lines at each end? One of these modems would call the other modem, which would auto answer and then connect to establish the circuit. Of course, these dial up connections would remain up 7/24. (Note: I have recently tested such a connection, and my phone company does not tear down the connection after too long of a time. I have flat rate and after one week of 7/24 connection, both modems are still up and running, so this is not a problem.)

The issue is that this would save over $1,000 per month.

Yes, I know that a conditioned Private Line makes Motorola happy with regards to being bullet proof reliable at 9600 baud, and Yes, a dial up connection is not as robust a connection as a PL. The dial up connection may take data hits from time to time. For an E911 type of environment, I can understand wanting to have the best there is. But, for my business to pay more than $1,000 per month for a 4-wire circuit versus a dial up connection, I would be happy to accept the occassional outages that might result from excessive data hits, and the like, with the dial up arrangement.

Does anyone know if it would be technically feasible to use full duplex 9600 baud generic modems, via dial up POTS phone lines at each end, to support a sufficient communications path for connecting an ASTRO Quantar to a DIU? Would I be best off to try to discuss this with someone at the MARC in Chicago and/or Dallas that have may have experimented with this, or a similar, approach?

Larry

Post by **xmo** » Wed Dec 11, 2002 1:46 pm

Assuming you used external modems - maybe you could go dial-up - BUT - why not get a Quantar control station at your office and no phone line at all???

You would still have all the APCO features - and at $10k per year for the 4-wire ckt. - the payback would be less than 2 years. Not only that - if you loose the repeater - power outage - equipment failure - whatever - your local Quanter could talk to your birds simplex.

Post by **xmo** » Wed Dec 11, 2002 2:10 pm

Also - If you configure the system with a Quantar control station - you can go with V.24 links at the office end - thus saving the cost of the Astro modems - plus the Quantar repeater not only does not need any modem - it doesn't even need a wire line board. That deletion credit will lower the cost even more - make your payback just over a year.

ASTROMODAT · Post by **ASTROMODAT** » Wed Dec 11, 2002 2:44 pm

Xmo, if the dial up arrangement works, it is dirt cheap and I have a hard-wired connection between my office and the remote Quantar---usually superior to an RF link. Anyways, I'm not sure if there is a clear RF path to the Quantar from my business location.

As to a Quantar control station, what exactly is this? Would this be a Quantar voice base station at my office location that also is ASTRO data capable, and sends ASTRO commands over-the-air, as well as ASTRO digital and analog voice? What option do you specify on a Quantar base to turn it into an ASTRO control station? Does this entail a DSS-III data station?

Would your suggestion of an ASTRO Quantar control station also support a DIU 3000, with encryption and MRTI options, at my office?

Still seems like it would be substantially cheaper to go the dial up modem route because I've got residential rates in my house at $20 per month, and commercial POTS at the Quantar site, at $50 per month (versus $1,100 per month for a 4-wire PL). The extra Quantar would cost $15,000+, so it seems like it would be worth pursuing the dial up modem approach. Then again, I HATE haywiring stuff---always costs more in the end and something invariably does not work. Do you know how I'd go about hooking up an external modem to the Quantar repeater and the DIU? Any advice as to who I might ber able to contact on this for details?

Thanks!

Larry

Post by **xmo** » Wed Dec 11, 2002 7:49 pm

First - you have to remember that unless you want this system to be 100% digital, you will need a 4-wire voice phone line between the DIU and the repeater. If you use the Motorola modems, that is the only line you need for analog voice, digital voice and remote control.

If you use external modems, you need TWO 4-wire lines (or one 4-wire line and your dial up) [I thought you said earlier you already have one 4-wire line in place to the repeater site.]

A Quantar control station is just a Quantar with an antenna relay option. You would hook the MRTI to the DIU and the DIU to the control station. The Quantar control station would be cheaper than the price you now have for a repeater because there is no duplexer needed. The repeater would be cheaper because of omitting the wire line and V.24. The two of them might cost $25K vs. maybe $15k for the full tilt repeater with duplexer, wireline and modem. Remember you are saving the cost of the modem at the DIU end also. The phone line savings should make this an attractive option.

Sounds like you need a system engineer to be involved in this project...

ASTROMODAT · Post by **ASTROMODAT** » Wed Dec 11, 2002 8:33 pm

Xmo, why 2 modems? One full duplex 9600 baud modem will support 9.6 kb/s TX and 9.6 kb/s RX simultaneously/FULL duplex. So, why do I need 2 modems?

Regarding a control station, how do you execute commands to the Quantar repeater over the air, for instance Set up/Knock down?

Larry