NMEA 0183 GPS Buffer

journey on · Posted: Sun Mar 19, 2006 11:07 am Post subject: NMEA 0183 GPS Buffer

Every new piece of electronics I get has a NMEA 0183 input for GPS, and the !@#$ GPS output only buffers two (TTL) loads. Does anybody know where there's a cheap buffer?

I've found several: $300, or made in England. All I need is a digital buffer. Radio Shack? Help.

Boris

flapbreaker · Posted: Sun Mar 19, 2006 7:12 pm Post subject:

I don't know anything about buffering NMEA. I'm not even sure what the problem is. Are you talking about a multiplexer? If so Raymarine sells one for $200 It basically lets you connect more than one "talker" together and multiple "listeners".

Almas Only · Posted: Sun Mar 19, 2006 7:49 pm Post subject:

I'm curious, too, and wondering what kind of setup you have that requires buffering?

Sneaks · Posted: Sun Mar 19, 2006 8:18 pm Post subject:

Boris, maybe it's the difference between an engineer and a tech, but I've paralleled TTL NEMA outputs to three separate inputs before, and in spite of the specs that say "maximum of two", they've worked just fine.

You have nothing to lose by trying.

Don

Almas Only · Posted: Sun Mar 19, 2006 10:23 pm Post subject:

I see that some manufacturers indicate the spec is that a talker should have the power to talk to 2 listeners, but the following indicates 4, rather than 2, as the NMEA standard:

http://www.shipmodul.com/en/multiplexer.html

This higher number would be consistent with having 3 work fine, so long as they just listen.

journey on · Posted: Mon Mar 20, 2006 12:30 pm Post subject:

wow, I'm impressed by the help. I do appreciate that.

I'll either try loading up the radar/gps output with three "listeners" or buy a buffer, which I found for $130. If I get a buffer, I'm sure that the GPS NMEA driver will not be overloaded and blow. Being a design engineer, I want margin (sound familiar?)

Boris

Almas Only · Posted: Mon Mar 20, 2006 7:04 pm Post subject:

Let us know how you finally get it set up, and what the results are. It would be interesting to switch back and forth between buffered and non-buffered, and see if there's any difference in performance.

tpbrady · Posted: Mon Mar 20, 2006 10:07 pm Post subject:

I'm not entirely positive, but NMEA is a broadcast just like television. The effect of adding listeners is like adding televisions in your house. Pretty soon the signal or picture gets unusable. The buffer is really an amplifier (may also be termed a repeater) that replaces the signal lost due to splitting.

I don't think you will blow anything. It will just stop working as a result of signal being too low.