[ntp:questions] Re: Any Spectracom hackers out there?

David L. Mills mills at udel.edu
Sun Oct 24 19:15:36 UTC 2004


I bought four 8170s in early 1981. I donated one of them to the Boston 
computer museum, one was stolen and I still have the other two. However, 
they have become useless because the UPS units in the computer room lay 
town a vicious 60-kHz QRM, even at the outdoor antenna site above a 
nearby building. I have a Netclock/2 at home doing reasonably well.

I have seen the little bumps you see, but I'm not sure it is loss of 
phase lock. That's a pretty stiff loop and the crystal is not that bad. 
Spectracom tells me the rock is good to 6 PPM. I assume you have a Rb of 
the variable kind, but you might be stuck like my Rb at 10MHz, which is 
kinda awkward if I remember the circuit diagram.

Before the UPSes killed the 8170s they got sick due to a on-channel 
buzzsaw RFI conducted by the power lines. I took a portable receiver all 
over town trying to find the source, but couldn't pin it down reliably. 
My guess is that it is coming from some switching supply at the Chrysler 
plant in town. Once upon a time before the displays got clean the 
problem was harmonics from TV picture tubes.

Watch out for motorboats; the radio has a whole lotta gain, so your 
external connections have to be seriously decoupled.

Two of my 8170s were rebuilt by Spectracom with the same interface as 
the Netclock/2. Yours might or might not have been modified. I don't 
remember all the mods, but I don't think they affected the RF circuitry.


John Ackermann N8UR wrote:
> I'm planning to try some experimental mods on a Spectracom 8170 WWVB 
> clock and wonder if anyone out there has done (or considered) something 
> similar.  Please contact me off-list so we don't bore everyone else...
> My hope is to remove the several millisecond jump and consequent long 
> recovery time when the receiver momentarily loses lock, which seems to 
> happen every couple of days.
> The 8170 phase locks a 10MHz crystal to the WWVB signal, dividing that 
> down to 1pps for the on-time signal.  It then decodes the WWVB timecode, 
> and shifts (delays or advances) the 1pps in 100us steps in a slow PLL to 
> stay on the mark.
> My thought is to replace the phaselocked 10MHz signal with an external 
> oscillator (in my case, an Rb standard that's monitored against LORAN-C) 
> to avoid the bump that happens when the cheap 10MHz crystal in the 8170 
> loses lock and free runs for a few minutes.
> Spectracom had an option to automatically switch to an external 
> reference when the WWVB signal was lost, but I'm wondering if it would 
> work to use the external clock all the time, since the Rb is kept within 
> a few parts in 10e-12 of LORAN (and is also checked against GPS every so 
> often).
> Just curious if anyone else has looked into this.
> Thanks,
> John N8UR
> jra at febo.com

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