[time-nuts] Test WWV timecube against Cesium, Rubidium, MASER or other precision time (UT-1) metrology

Bill Hawkins bill.iaxs at pobox.com
Thu Dec 7 16:29:01 EST 2017

One way to compare any WWV receiver to a local standard is to use the
PPS output of a standard against the PPS tick modulated on WWV. The tick
is five cycles of a one KHz signal derived from the master frequency.

It will be a bit tricky to determine the onset of the first cycle amid
the noise on shortwave radio. A computation that determined that there
were just 5 cycles and worked backwards to determine the timestamp of
the beginning or middle of the tick could then allow calculation of the
offset between the standard PPS and the tick. Limit of accuracy might be
100 microseconds. 

Years ago, I had a standard calibrator made by Lavoie that had a vacuum
tube WWV receiver. IIRC, the WWV carrier caused a circular sweep on a 2
inch CRT. The sine wave from a standard modulated the intensity of the
circular trace, so that a bright half moon appeared on the CRT and
rotated at the error rate between the two frequencies. On several
evenings the dominant signal varied between WWV and WWVH (identified by
the voice broadcasts). Here in Minneapolis the phase difference between
the two stations was about 180 degrees, causing the bright arc on the
CRT to change sides.

So yes, this could be interesting for a hobbyist, but it won't add
anything to Science.
A MASER is overkill. Heck, so are Rubidium and Caesium.
A naked crystal will be rock solid compared to received WWV.

OTOH, NTP has marvelous mathematical tricks to reduce Internet
propagation delay.
A scheme to reduce varying atmospheric delay would be useful, if there
weren't much better ways to get a standard frequency.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Patrick
Sent: Thursday, December 07, 2017 7:48 AM

Hello Friends,

I am picking up locally a couple of vintage analog Radio Shack SW time
cube radios, 70s vintage, 3 switchable SW frequencies.  Two types, the
one pictured and a Radio Shack model also that has WWV and Weather
channel VHF frequencies.
I am interested in an accurate bench test to compare the analog
shortwave radios time reporting hopefully UT-1 against other available
references.  For accuracy, and
repeatability.   Could eventually add an SDR to the mix, too.
The 5,10,15 mhz radios obviously are subject to the WWV Ft Collins site,
propagation distance delays, somewhat calculable, and the vagaries of
Ionospheric propagation, and, propagation delays between the antenna and
the measured tap point to the seconds ticks of WWV.   I have some
microwave professionals, who are also hams here in Auburn who may enjoy
doing a bench test, with published results, etc.  But wonder if anyone
else would be interested in borrowing a RS Timecube radio (and/or use an
SDR) and designing an accurate bench test against available modern
We are talking probably HUGE  UT-1 errors compared to what this group
plays with, and that is OK but I think still a worthwhile test,
especially if the errors using available and cheap equipment are
predictable, and repeatable.

----- %< ----- [snip of microwave stuff]

Best, 73,   Pat Barthelow AA6EG
apol <apolloeme at gmail.com>loeme at gmail.com

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