Purc 5000 5MHZ HSO moved to a GFB MSF5000

This forum is for the discussions targeted at converting various models of Motorola equipment to operate in the 900MHz Amateur Band.

Moderator: Queue Moderator

Post Reply
User avatar
Posts: 1125
Joined: Wed Oct 12, 2005 5:13 am

Purc 5000 5MHZ HSO moved to a GFB MSF5000

Post by fineshot1 »

Motorola Purc 5000 5MHZ HSO KXN1176AA moved to
a GFB MSF 5000 900Mhz cabinet requiring an HSO.

I tested the KXN1176AA connected to a 12.0VDC supply on the bench and a GD R2670B. Initially the oscillator output was about 180Hz low and drew 770mA. The frequency rapidly approached 5MHz and was within 30Hz in about three or four minutes. Right around this time the MSF synthesiser locked. The current then started dropping to around 250mA after a few more minutes. After 30 minutes the current was down to 180mA, and the output frequency had stabilized to exactly 5MHz varying once in awhile to + or - 1Hz.

This HSO Oscillator module KXN1176AA is referred to as A2500 in the schematic prints on page 8
of the Motorola Doc 68P81084E19(PURC 5000 Paging Synthesiser). Power is
delivered to A2500 from the TRN9812B HSO Power Regulator Board also shown
in the schematic. I fed the TRN9812B from the raw +15.8VDC from the bottom
TPN1186A power supplies TRN7242 power distribution board J603 which has nothing plugged into it. The left 4 pins are + + - - so I found a small molex connector that would slide on and cut off the original 2 pin connector from the PURC 5000 cable assembly and spliced that on and it all works perfectly
and I took the opportunity to install a 2A inline fuse in the power line to the regulator board. At one time after I powered up the cabinet the 2A fuse
blew while warming up so I changed it to a 3A and never had a problem after that and still not sure why that happened.

I acquired the Purc 5000 HSO and did this back in May 2011 and I have a GFB and have been waiting for Antenna work at a site which
never happened so while the cabinet was on the floor it seemed like the thing to do. I have pics but the regular MSF5000 is almost
the same thing so if you have seen the MSF5000 HSO then it is virtually the same.
John G
Posts: 215
Joined: Tue Nov 20, 2001 4:00 pm

Re: Purc 5000 5MHZ HSO moved to a GFB MSF5000

Post by John G »

I did pretty much the same thing with a KXN1130A UHSO I had obtained years ago. I had the whole shelf so I also had the regulator board. There are mounting tabs for the regulator board in the empty space where the oscillator fits. The only thing I had to improvise was the fine adjust. In the PURC, you have an electronic fine tune. There was an EEpot on the voltage regulator board but nothing to control it with on the MSF. So, I found a 10 turn, wirewound pot with a spec'ed temperature coefficient of 20 ppm per degree to replace the EEpot with. I got it from Mouser and it was a little pricey but I wanted good stability. After everything was mounted and adjusted, it holds the MSF to within 1 Hz, 2 at the most so far. I even tried turning it off for a while and it retraced perfectly which was a pleasant surprise. I only wish I had more. That KXN1130A is very nice. I guess next time i will change the jumpers for a 10 MHz reference and fit a rubidium source.
Posts: 911
Joined: Thu Dec 18, 2003 11:38 am

Re: Purc 5000 5MHZ HSO moved to a GFB MSF5000

Post by SlimBob »

Now to fit it with a "beacon" mode so that you don't have to read the error locally, but can transmit an unmodulated carrier... ;)
Post Reply

Return to “Converting Motorola Equipment to 900MHz Amateur”