Internal GPS Mod Tech Support/Q&A

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jonwienke

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VCC is 3.3V. Make sure your external module is OK with that supply voltage. Some modules are 3.3V only, some are 5V only and some are OK with either. Check your specs.

IMO it's a bad idea though. The internal mod works just fine, even in vehicles. Getting better reception isn't a very compelling reason to move the antenna outside the scanner. Even the Ladybird (the worst-performing module I've tested) has no trouble keeping satellite lock under the seat in a SUV parked in my carport, with the antenna sandwiched between the scanner and the floor. Given that Location Control only needs a location update every few miles or so, there isn't much justification to go external antenna for performance reasons.

As to the testing issue, I've done dozens of hours of testing. Every scanner I mod gets a minimum of 12 hours of test run with the GPS on to make sure that the GPS module and MAX3232 chip do not fail prematurely, and that sensitivity is not compromised by RFI when the GPS is running.

If you have questions about doing an internal mod, answering them is one of the stated purposes of this thread.
 

nick223

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The 996p2 pictures everyone's been seeing are my scanners. Jon does some great work and answers all your questions before, during and after the mod process. Communications are amazing with status reports, pictures and videos. If he has a question about anything before he goes forward he will send you a messaged with a mock up. Turn around time is fast too with nice shipping packaging back to you. Highly recommended. Thanks again [emoji106]
 

ResQguy

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Jon does some great work and answers all your questions before, during and after the mod process. Communications are amazing with status reports, pictures and videos. If he has a question about anything before he goes forward he will send you a messaged with a mock up. Turn around time is fast too with nice shipping packaging back to you. Highly recommended. Thanks again [emoji106]
Ditto. I sent my 436 to Jon and received it back in record time. It does exactly what I hoped it would do and I would enlist his handiwork again if needed.
 

jonwienke

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BDS GPS Dual-mode Module Flight Control Satellite ATGM336H Replacement NEO-M8N S | eBay
The actual module is even smaller than the Ladybird. Since the antenna is not attached to the module, it may fit inside the 436 without cutting open the back of the case. It outputs TTL, so the MAX3232 or some other TTL-to-RS232 converter is still required. This one also claimes to receive GLONASS and GPS.
I received my samples today, and initial testing is very positive. It maintains satellite lock in the safe drawer almost as well as the Reyax module, and testing for RFI indicates less than the GMouse. I will do further testing, but this may be the new default 436 module if it gets reception comparable to the GMouse, has less RFI to control, and doesn't require cutting the case for the antenna.
 

frazpo

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jonwienke

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The MAX3232 seems to be the only game in town for anything resembling a reasonable price.

The power tabs are connected on both sides and both ends of the board. Use whichever ones are convenient. You can pass power through the MAX3232 module to power the GPS. The data tabs are isolated from one side of the board to the other. You can have 2 bi-directional connections with one module, one on each side of the board. The modules have 2 quirks you MUST deal with to avoid smoke release:

1. Unused RS-232 inputs must be tied to Vcc.

2. The power supply must have a filter to prevent spikes, ringing, or keybounce on Vcc when the chip powers up.
 

frazpo

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If I am correct then the only unused input on the RS-232 side would be data in if I powered the GPS module through the converter.

What filter are you currently installing?
 

jonwienke

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There is an RS-232 input on each side of the board. Neither one is used for this application. A TTL input is connected to the data out on the GPS, and the RS-232 output (must be on the same side of the board as the TTL input used) is connected to the scanner.
 

frazpo

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There is an RS-232 input on each side of the board. Neither one is used for this application. A TTL input is connected to the data out on the GPS, and the RS-232 output (must be on the same side of the board as the TTL input used) is connected to the scanner.
OK thanks. Ive never seen the diagram for those so didn't know how it was configured, thanks.
 

jonwienke

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I've been doing some more testing on the ATGM336H GPS module, and the results are pretty impressive. The module itself draws between 30 and 35mA. It will keep a satellite lock in the safe cubby torture test (something only the Reyax and ATGM336H do), but unlike the Reyax module, it will not acquire a fix inside the safe from a cold start. Without adding any capacitors or ferrites or additional shielding, I used my SDR to sniff the ATGM336H for RFI from 25MHZ to 500MHz and couldn't find anything--a test that the GMouse and Ladybird both fail. Both the Ladybird and the GMouse require filtering to keep RFI at manageable levels, and both the GMouse and Ladybird induce audible artifacts when installed in a 436 and monitoring certain analog frequencies.

My plan at this point is to use an ATGM336H in the next 436 mod I do, and do some testing to compare RFI between the GMouse and the ATGM336H. If that is favorable, then the GMouse and the Ladybird will be retired from the lineup, and replaced with the ATGM336H.
 

mancow

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I've been doing some more testing on the ATGM336H GPS module, and the results are pretty impressive. The module itself draws between 30 and 35mA. It will keep a satellite lock in the safe cubby torture test (something only the Reyax and ATGM336H do), but unlike the Reyax module, it will not acquire a fix inside the safe from a cold start. Without adding any capacitors or ferrites or additional shielding, I used my SDR to sniff the ATGM336H for RFI from 25MHZ to 500MHz and couldn't find anything--a test that the GMouse and Ladybird both fail. Both the Ladybird and the GMouse require filtering to keep RFI at manageable levels, and both the GMouse and Ladybird induce audible artifacts when installed in a 436 and monitoring certain analog frequencies.

My plan at this point is to use an ATGM336H in the next 436 mod I do, and do some testing to compare RFI between the GMouse and the ATGM336H. If that is favorable, then the GMouse and the Ladybird will be retired from the lineup, and replaced with the ATGM336H.
That right there looks like the answer to the HomePatrol installation difficulty. My problem was mainly having to remote mount the antenna and that meant carefully separating it from the board I used. I'm going to get one of these and try modding my second HomePatrol.

Thanks for the info.
 

jonwienke

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Here's some dimensions for you to play with:

Ladybird PA6C
16.0 x 16.0 x 6.6mm
Shielded enclosure and board is 2.2mm thick.

ATGM336H:
16.2 x 13.3 x 6.1mm
Board + shield is 3.8mm thick. Thickest point is where the antenna connector plugs into the board.Thickness is 5.3mm with antenna connector unplugged, where the backup battery mounts. If you soldered the antenna directly to the board, you could keep the 5.3mm max thickness.

Antenna is 6.2 x 20.8 x 6.3mm. Antenna coax is 70mm long and 1.3mm in diameter.

One correction: the ATGM336H receives BeiDou + GPS, not GLONASS + GPS.
 

mancow

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Here's some dimensions for you to play with:

Ladybird PA6C
16.0 x 16.0 x 6.6mm
Shielded enclosure and board is 2.2mm thick.

ATGM336H:
16.2 x 13.3 x 6.1mm
Board + shield is 3.8mm thick. Thickest point is where the antenna connector plugs into the board.Thickness is 5.3mm with antenna connector unplugged, where the backup battery mounts. If you soldered the antenna directly to the board, you could keep the 5.3mm max thickness.

Antenna is 6.2 x 20.8 x 6.3mm. Antenna coax is 70mm long and 1.3mm in diameter.

One correction: the ATGM336H receives BeiDou + GPS, not GLONASS + GPS.
Thanks, that helps a-lot. The antenna appears to be the same size as the one I removed from the 736 or whatever it was called board. If so then then it looks like the board would be just about as thick as the GPS antenna is wide. I use that as a gauge since I had it mounted sideways and it just barely fit between the two boards.
 

jonwienke

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The module board is slightly thinner than the antenna, even without removing the IPX antenna connector.

The antenna is 6.7mm thick, not 6.3mm.
 

nessnet

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Jon,

Any idea when you feel the ATGM336H will go 'into production'?
Also, the GLONASS question.

My apologies, I'm playing catch-up here.
It'd be nice to have GLONASS + GPS.
I suppose not necessary, but us darn engineers you know....
Are there any of the current rec'vrs you use GLONASS + GPS?
 

jonwienke

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If you'd like, you can be the first!
 

nessnet

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I still want to look into the GLONASS + GPS question, if possible before I jump.
Any capable of both modules you have / thinking of / are testing??
 

jonwienke

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The ATGM336H does BeiDou + GPS, so it receives 2 of the 3 major systems available.
 
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