[time-nuts] filtering a 10Mhz frequency standard?

shalimr9 at gmail.com shalimr9 at gmail.com
Tue Dec 13 17:08:41 EST 2011


If your concern is harmonics, the best combination is a low pass filter that cuts high enough to have no (or negligible) group delay at 10 MHz, and one or more notch filters for the harmonics, as many as necessary to get the attenuation you desire.

These filters should have no measurable effect on the fundamental.

If you have phase noise or spurs near the carrier, you need a cleanup PLL with a good crystal and a narrow BW. 

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: gary <lists at lazygranch.com>
Sender: time-nuts-bounces at febo.com
Date: Tue, 13 Dec 2011 13:27:54 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] filtering a 10Mhz frequency standard?

If you are going to buffer the output, why does the filter have to be 
passive? Did I miss something here? Today 10MHz is in the realm of 
active filters. [Hey, not that I made an active filter at 10MHz.]

Sensitivity is a function of the denominator. The only advantage to a 
LPF over a BPF is the BPF has to be centered at 10MHz, while you could 
bump the corner of the LPF to a higher frequency so there is less 
sensitivity at 10MHz This presumes you are only getting rid of harmonics 
and not spurs.

For lowest component sensitivity, leap frog designs are best. But in 
continuous time designs, they require many op amps per pole.

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