[time-nuts] Frequency comparison

Stan, W1LE stanw1le at verizon.net
Sun Feb 7 15:41:29 UTC 2010

Hello Raj,

Welcome to the Net.

Watching waveshapes on a Oscilloscope and comparing drifts can be 
interesting for a few days.
Then it is like watching then grass grow.

Alternative methods can show frequency difference much easier.

Consider the TRACOR model 527E frequency difference meter, obsolete but 
still available on Ebay.
This instrument will compare 2 reference  sources, your Rb and the GPSDO 
and uses an
analog or a digital meter to display the difference to 1 part in 10**11

Consider a modern LORAN C receiver like the Stanford Research Systems 
model FS700
to compare the Cs reference at the LORAN C transmitter station to your 
local references.

Consider the AUSTRON model 2200 LORAN C Timing receiver  or the 2200F 
Frequency Monitor.
For comparison of the Cs reference at the LORAN C transmitter to your 
local references.

Making this comparison between a local LORAN C, Cs based reference, and 
will show the GPSDO to vary between 10**9 thru 10**13 in the short term.
The LORAN C receivers can show the frequency difference as a numerical 
value on the display.
That drift was informative to watch.

Your equipment needs really depend on the accuracies you need/desire.

Probably the next big step is to get a working Cs reference to calibrate 
your Rb.

Here in the US, LORAN-C is obsolete and will be terminated this year,
some southerly TX stations earlier, some later.

Lotsa LORAN C equipment may become available on Ebay or at other auctions.

My records show LORAN C available from Saudi Arabia easterly thru to the 
I have not heard any word on their longevity.

Please be careful, chasing frequency accuracy can be an expensive obsession.

Stan, W1LE     Cape Cod     FN41sr

Raj wrote:
> Hi! all Time-Nuts,
>         For a newbie like myself at GPSDO & Rb oscillators etc. what method of frequency comparison would you gurus recommend ? Any articles on this subject ? 
>         Available test instruments are: Scopes digital & Analog, counters with 0.01 Hz display at 10 Mhz (HP & Racall-Dana).
>         Currently I am comparing the phase between two 10 Mhz and adjusting for the lowest drift visually on the scope and phase drift on the Racall-Dana 1992.
>         Your suggestions I would like to use for calibrating the Rb oscillator with a GPSDO.
> Regards

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