[App_rpt-users] App_rpt-users Digest, Vol 83, Issue 43

[Chris HIll/K7AZ]

Would removing R67 in the RTCM help?

Sent from my dumb-smart DROID...

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>Today's Topics:
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>   1. Re: Garmin GPS18x no longer compatible with RTCM (Joe Bennett)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Thu, 28 Jan 2016 20:01:20 -0600
>From: Joe Bennett <aprs at ka3nam.com>
>To: app_rpt-users at ohnosec.org
>Subject: Re: [App_rpt-users] Garmin GPS18x no longer compatible with
>	RTCM
>Message-ID:
>	<CAD+1-48xN03rzJQNaedmJ3qZ8u6Jg87Qvq8ot44jPHWRAvVRww at mail.gmail.com>
>Content-Type: text/plain; charset=UTF-8
>
>I really doubt that a level converter will add enough timing skew to
>amount to anything. The jitter you see on the internet will greatly
>outweigh the skew of a level converter by orders of magnitude...
>
>
>-Joe
>KA3NAM
>
>On Tue, Jan 26, 2016 at 1:44 PM, James Cizek <james.m.cizek at gmail.com> wrote:
>> Hi folks,
>>
>> Wanted to get this out to you before anyone else bought one thinking they
>> would work (since this model is specifically called out in the RTCM docs).
>>
>> When using a GPS with a Micro-node RTCM for voting,  you need to find one
>> that has a 5 volt Pulse-per-second output.  The Garmin lines that is
>> recommended (GPS 18X, 18X lvc, etc...)
>> NO LONGER do this!
>>
>> This is what I got back from Garmin:
>>
>> Mr. Cizek,
>>
>>
>>
>> I was just told there was a design change with the GPS 18x LVC. The PPS
>> signal voltage is now 3V. This was something we were not told until today.
>> We will be making the changes to the online Technical Specifications to
>> reflect this change.
>>
>> I do apologize for the inconvenience. This was a change we were not informed
>> of.
>>
>>
>> So this line of GPS's will *NOT* work with an RTCM any longer.  Talking to
>> Mark at Micro-node, there is a voltage divider in the RTCM dropping the 5
>> volt to 3.3 volt to be compatible with the CPU.  With only 3 volts on the
>> incoming line, there isn't enough making it to the CPU to trigger a state
>> change and you will get "PPS Timeout" errors and be unable to achieve GPS
>> lock.
>>
>>
>> I am not sure what kind of timing skew a level converter would introduce, so
>> it's probably a better bet to just get a GPS that has a 5 volt line (Trimble
>> Thunderbolt or the similar).
>>
>>
>> There may be a possibility of removing or modifying the voltage divider
>> inside as well, but without schematics, and unless you have SMD capable
>> gear, it's unlikely that that is a good solution.
>>
>>
>> Just wanted to let folks know so they don't repeat the brain damage I just
>> went through figuring this out :)
>>
>>
>> 73
>>
>> James
>>
>> KI0KN
>>
>>
>>
>>
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>End of App_rpt-users Digest, Vol 83, Issue 43
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