External GPS Engine/Antenna Help

[nathandclements]

I've been searching around and I've seen a lot of mods for various GPS antennas, internal or external, for various scanners but none of them (that I could find) help with what I'm specifically looking for. I have had several vehicles with external NMO mount GPS antennas, and I have a whole box of them that I've gotten from surplus auctions. I have one for my Toughbook, one for DVR, etc. I am doing another vehicle build soon and was operating under the impression I could just plug one of these antennas into my 996P2. Most of the antennas have an SMA connection. Then I saw that my scanner has the stupid DB9 connector.

So my question is - is there a way to add an SMA connection for my GPS antenna? It seems to me, from what I've read, that there is no internal GPS engine in the scanner, and that it's expecting an NMEA string through the serial port? If that is indeed the case, does anyone know of a GPS engine with an antenna connection I can connect to? What options do I have?

 

[nathandclements]

So after doing a bunch of research and finding some more helpful threads, I was able to find the pinout for the DB9. Then I ordered this uBlox GPS chip from amazon. Amazon.com: DIYmall 6M GPS Module with EEPROM for MWC/AeroQuad with Antenna for Arduino Flight Control Aircraft: GPS & Navigation

Then I ran into another issue. Apparently there are 2 types of serial data, TTL and I guess... regular? One is 3V signal, the other is 5V signal. This GPS chip is 3V, and the scanner is looking for 5V signal, so it wouldn't work.

So I got this adapter: Amazon.com: DIYmall 6M GPS Module with EEPROM for MWC/AeroQuad with Antenna for Arduino Flight Control Aircraft: GPS & Navigation

It's supposed to convert one level to the other, but it still doesn't work.

So finally just for science, I ordered one of these: Amazon.com: GlobalSat BR-355 BR-355 Serial GPS Receiver: Home Audio & Theater

I opened it up, de-soldered the internal antenna and soldered a new antenna connection. It works great! And it's 5V signal level. But I'm still annoyed I haven't gotten it to work the other way with the other chip yet.

 

[KE5MC]

Looks like your 1st and 2nd link point to the same device. If the correct second link has a schematic like the 1st that would be helpful.
Mike

 

[a417]

Then I ran into another issue. Apparently there are 2 types of serial data, TTL and I guess... regular? One is 3V signal, the other is 5V signal. This GPS chip is 3V, and the scanner is looking for 5V signal, so it wouldn't work.

RS232 serial vs TTL are the two big serial protocols (yes, im intentionally leaving RS485 out of this). The latter being most prevalent on computers thru the late 90s with the DE-9 connectors (that many people mistakenly refer to as DB-9 (addt'l info found here)) on the rear, and TTL being a lower voltage (3.3v - 'CMOS level') & (5v 'TTL level') essentially chip to chip logic level.

Here is a good sparkfun article on the differences between RS232 & TTL

What you need to effectively convert 5v to 3.3v signals is something like this, which I frequently use when I have to breadboard a programming interface for an older radio (that i'm probably only going to program once) that has a signal level requirement that I don't have. That and the infamous MAX3232 RS232 to TTL level converter and you can pretty much breadboard whatever you need with a couple of jumpers.

 

[KE5MC]

Looks like he needs to up-convert 3.3 to 5.