[time-nuts] time-nuts Digest, Vol 76, Issue 109

[neilsan at tpg.com.au]

Hi Chris
You have received plenty of comments regarding the measurement and problems using the zero Hz 
zero beat method.

Here is the very successful method used here for many years. 

Use any good SSB receiver in the CW mode. This will give you correct freq readout with an audio 
offset commonly set to 600Hz (but usually selectable). Now you need a stable 600 Hz reference to 
beat with the measured signal. For rough measurements I use an audio sig gen, a pair of 
headphones or speaker then adjust the relative levels to provide the best beat. You can easily 
determine sub Hz differences providing your devices are stable. I use an IC706 with 1 Hz tuning 
resolution selected.
If the IC706 30 MHz oscillator is locked to GPS then the frequency display will be very close as not 
all of the internal frequencies are derived from the 30 MHz ref osc. This error can be 
calibrated out against a known freq.
The audio reference can be derived from your local standard in which case 1 KHz may be more 
convenient. Various refinements can be added to this effective low cost method such as an 
analogue meter etc.

For checking osc drift and the like a program such as Spectran provides a very convenient tool 
where you can use the Spectran cusor to measure accurate freq differences in the audio range.
73 Neil VK2EI

 > -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Chris Albertson
> Sent: Sunday, November 28, 2010 11:42 PM
> To: jfor at quik.com; Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] If there a FAQ
> 
> WWV at 10MHz is not bad at all.   My current "system" is a cheap
> $0.75 10Mhz crystal tuned with a screwdriver on a veritable trimmer
> capacitor.  I know I can zero-beat  it by ear and get within a couple Hz
> out of 10MHz.  That is better then 1E-6 simply by hand, ear and
> screwdriver.
> No computer.
> 
> The trouble with a 60Khz signal is that a two cycle error gives
> a 1 in 30K error,
> 
> I'm just looking to use it as a frequency standard, not caring at all
> about
> the
> data they transmit
> 
> I figure my first upgrade is to replace the crystal with a temperature
> compensated oscilator chip.   Now to go find one.
> 
> -- 
> =====
> Chris Albertson
> Redondo Beach, California