Need GPS board for KS24361 aka RFTGu-O

[WPXS472]

The green "Active" light on my KS24361 GPSDO has stopped working. Meaning it is not on. The two alarm leds are on, indicating that it is not locked to GPS.
A cursory examination revealed nothing wrong. I suspect the Motorola GPS board has gone bad. I am not sure exactly which model it is. I believe it is an Oncore VP. I removed it from my now defunct Z3801. It was the only one out of several Oncore boards I had that worked. I have had a search for Motorola Oncore VP active on eBay for some time now with no results. Does anyone know of a readily available GPS board that would be a direct replacement? I have been told that it is possible to use another GPS board to supply the 1PPS that this board normally supplies, while leaving the old board in place for the controller to talk to. I don't think that would work in my case because it seems the existing board is no longer talking at all. I will investigate further with scope and voltmeter, but was hoping that I could find another of the proper boards and just plug it in. This unit does not come with a GPS board installed. I found directions on the internet on how to modify it to work. There was already a socket for the GPS board. It has been working fine for a couple of years now.

[ZigmundRat]

A brief reply before I fall asleep (again) and the tablet smacks me in the face (again) ...

I don’t know for sure but I bet you experienced the same problem I did.

I just completed the conversion of three RFTG-m-Rb units to stand alone operation. These Rb units were the ones of the pair without GPS, so I needed to add the Moto receiver. Seemed it should be pretty straightforward but... The problem is that the standard Moto GPS powers up in a silent mode and the RFTG doesn’t see it. 

I’ll post an update with details on the conversion in the next day or two. (I’ll need to take pics, collect docs, etc.) BTW, I used non-specific Oncore receivers that I had on hand.

[WPXS472]

Thanks for the reply. This thing has worked flawlessly for a couple of years, so I don't think this problem is the same as the one you had. I have numerous Oncore boards, even some NOS ones I picked up on eBay a few years back. Out of all of them, this was the only one that worked in my RFTGu-O. I had plans to interrupt the 1PPS line and substitute the 1PPS from something like a uBlox ZED-F9T. But, I think it requires a working GPS board prior to doing the mod.

[artag]

Dan Watson was working on an upgrade board to use with the KS24361. This is one of the later posts, where he was testing a Denuo GPS receiver on a carrier PCB. There may be later progress.

https://syncchannel.blogspot.com/2015/11/denuo-gps-hits-rev-b-dongles.html

[WPXS472]

I read that post. It appears to be from 2016, a while ago. There were several articles about intercepting the output of a newer, non Motorola, GPS board and translating the data on the fly to make it usable by the RFTG-0. That would be way beyond my capability unless offered in a kit form. The article mentions the Motorola UT+ board as being the correct one. I was under the impression that it was the VP board. I will add the UT+ to my eBay search. I have a hard time distinguishing the different Motorola boards apart. There are numbers, but nowhere does it ever say "Oncore VP", or "Oncore UT+" Most of the original Motorola documentation that existed on the web seems to have disappeared. I have been unable to find any actual, official documentation on the KS24361, and have read where several people flat out say that it isn't available.

[WPXS472]

I found what was supposed to be an Oncore UT+ on eBay and bought it. It arrived this morning, and looks exactly like the board that was in the RFTGu except for the orientation of the antenna connector, which poses no problems. I installed it and after several hours, it isn't locked, still get a "no GPS" indication. I am at a loss as to what to do next. I do have another RFTGu, as yet unmodified. I am thinking of trying to find the mod information and modifying this one too. That should tell me for sure whether it is the GPS boards, or the RFTGu itself that is bad.

[ZigmundRat]

Here's my solution. I've done this on three RFTGm-II-Rb units and all sync up correctly and the units report good values via the RFTG software. All are on frequency to within a few parts in 10^12. These three units do NOT all have the same Motorola receivers, but they are all similar Oncore types.

In the standard configuration, the OCXO half of the timing unit provides the PPS and certain GPS messages to the Rb unit. If we provide these messages and the PPS to the Rb unit will sync up and become GPS disciplined. These RFTGm-II-Rb units have the 2x5 footprint required by the Oncore receiver, and all that was required was to install the header and the stand-offs for the GPS board. The firmware on the Rb RFTG board does not know how to fully drive the GPS module, but it does listen to certain messages (which are normally provided by the OCXO half). Any standard Oncore module will power up in Motorola binary mode but will not automatically emit  messages - and this is the basic problem here. To solve this, we add a small micro-controller to configure the Oncore after power up.  I used an ATTINY85 board which turned out to be just the right size and pinout configuration to sit handily on the test connector at the side of the board. *Note: I did have to make one mod to the RFTG board - on the 5V there is a current limiting resistor by the header which I jumpered.*  The TX/RX of the micro is simply bridged onto the TX/RX of the Oncore/RFTG interface. It doesn't provide enough loading to interfere with the normal operation.

First to get the header and stand-offs installed:


Next is the Oncore module installed, with a pigtail going to a front panel antenna connector.


ATTINY85 board with machine pin socket soldered on for connection to RFTG


ATTINY85 back side - I used PB2 and PB3 for the serial pins


ATTINY85 mounted and connected. It sits nicely here and cannot come loose after the enclosure is closed up.


Crude and simple ATTINY code. LED activity is not tightly controlled and is just used to identify where in the process things are and to indicate it's still running.

Code: [Select]

  #include <Arduino.h>
  #include <SoftSerial.h>
  #include <TinyPinChange.h>

  #define LEDPIN 1

  byte disauto[] {0x40,0x40,0x45,0x61,0x00,0x24,0x0d,0x0a}; // @@Ea disable auto output, polled mode
  byte enauto[] {0x40,0x40,0x45,0x61,0x01,0x25,0x0d,0x0a}; // @@Ea enable auto output, 1 second interval
  byte setGPStime[] {0x40,0x40,0x41,0x77,0x00,0x36,0x0d,0x0a}; // @@Aw set to GPS time (not UTC)
  byte disposhold[] {0x40,0x40,0x41,0x74,0x00,0x35,0x0d,0x0a}; // @@At disable position hold mode
  byte elev104[] {0x40,0x40,0x41,0x67,0x0A,0x2C,0x0d,0x0a}; // @@Ag set elevation angle to 10
  byte productid[] {0x40,0x40,0x43,0x6a,0x29,0x0d,0x0a};      // @@Cj get product string
  byte getvissats[]  {0x40,0x40,0x42,0x62,0x00,0x20,0x0d,0x0A}; // @@Bb get visible sat status

  SoftSerial mySerial(2, 3); // RX, TX
  unsigned long i = 0;
  int state = 0;
  void setup()
  {
      pinMode(LEDPIN, OUTPUT); //LED on Model A  or Pro
      // Give the GPS a chance to power up... about 8 seconds
      for (i = 0; i<20; i++) {
      digitalWrite(LEDPIN, HIGH);
      delay(200);
      digitalWrite(LEDPIN, LOW);
      delay(200);
    }

    mySerial.begin(9600);
    mySerial.write(disauto,sizeof(disauto));        // Turn off auto output for now
    delay(5000);
    mySerial.write(productid,sizeof(productid));    // Product ID string
    delay(1000);
    mySerial.write(enauto,sizeof(enauto));          // Enable enauto
    delay(1000);
    mySerial.write(setGPStime,sizeof(setGPStime));  // Set to GPS time
    delay(1000);
    mySerial.write(disposhold,sizeof(disposhold));  // Disable position hold mode
    delay(1000);
    mySerial.write(elev104,sizeof(elev104));        // Set elevation angle to 10
    delay(1000);
    mySerial.write(getvissats,sizeof(getvissats));  // Get visible sat status
    delay(1000);
    i = 0;
    state = 0;
  }
 
  void loop()
  {
    // toggle led to show still alive
    // send the messages at specified intervals

    if (i == 0) {
      /* do stuff the first time */
      delay(1000);
      i++;
    }
    else if (i % 6 == 0) {                           // Every 6 seconds
      mySerial.write(getvissats,sizeof(getvissats)); // Report sat signals
      delay(1000);
      i++;
    }
    else if (i % 30 == 0) {                          // Every 30 secs
      mySerial.write(setGPStime,sizeof(setGPStime)); // Set to GPS time
      delay(1000);
      i++;   
    }
    else if (i == 900) {                             // Every 15 min
      mySerial.write(enauto,sizeof(enauto));         // Enable enauto - just in case
      delay(1000);
      i = 1;                                         // Reset the counter, but not to zero
    }
    else {
      digitalWrite(LEDPIN, (state) ? HIGH : LOW);
      state = !state;
      delay(1000);
      i++;
    }
  }


That's about all there is to it. You could use any micro you want really, it's just a matter of getting it in the enclosure to make it self contained. It should also be possible to do this outboard using the J5 Interface connector but I wanted a self contained solution.

Hope it helps. Cheers!