[time-nuts] Frequency comparison

[Bob Camp]

Hi

If you mix the RB and GPS down with a mixer you eventually will run into a
problem. 

As you set them both very close to frequency, the output is a noisy DC
signal rather than a sine wave. Since each source can drift either up or
down for a short period of time, it can be hard to tell what's going on with
a zero crossing detector. It is much better to capture the output voltage
with a strip chart or the digital equivalent. 

Bob 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Raj
Sent: Monday, February 08, 2010 10:34 AM
To: danrae at verizon.net; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency comparison

Hi Dan,

        Low tech. Yes! IMHO I think its easier for my mind to track an
analog indication of Delta-V. I am more analog oriented.. my son OTOH may be
able to read a last digit flickering digital display better than me!.

I am other wise thinking of a DIY gizmo: 

        Mix two signals in an SBL1 or Eq. 
        Take the phase/DC IF difference out
        Make a zero crossing detector or similar
        Timimg the event. Wait for the event in other words!
        Twiddle the preset again and see what happens.

        The human mind does a lot more processing than the above with an
analog display..

Cheers
Raj, vu2zap

>Raj wrote:
>>
>>I was thinking of feeding two 10 Mhz signals to two ports of a SBL-1 or
similar and taking the DC
>>output at the IF port into an opamp or analog meter. This was visually
easier to adjust the drift between two frequencies by just watching the
needle move. A stationary needle over a couple of hours would be the best!
>>
>>  
>Raj, I did exactly this but with an old chart recorder attached to the
mixer IF port.  This allows one to leave the room and not have to watch for
hours or days.   I was able to adjust my -hp- rubidium unit this way against
gps to better than one cycle per day.
>
>Low tech but effective.
>
>Dan
>
>
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.

-- 
Raj, VU2ZAP
Bangalore, India. 


_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.