[time-nuts] smallest rubidium

[Jim Lux]

-----Original Message-----
>From: WB6BNQ <wb6bnq at cox.net>
>Sent: May 23, 2011 2:17 PM
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>Subject: Re: [time-nuts] smallest rubidium
>
>David,
>
>You should have said so in the first place.  Unless you are sure that the reference
>oscillator is the base for all the generated frequencies, it would not make sense to
>install a Rb source in the radio.  You are correct concerning most of the
>"so-called" higher stability options in that they are barely worth the price asked
>for them and only meet specs in a tightly controlled environment.
>


For a lot of HF radios, the TCXO performance required is such that the actual frequency be within 20 Hz of the displayed frequency (that's the NTIA standard).  20Hz comes from empirical tests of how close the frequency needs to be to not require a "clarifier" for intelligible speech on SSB.  (probably moderated, too, by what's easy and practical to do in a portable transceiver)
(http://www.ntia.doc.gov/osmhome/redbook/ed200801rev201009/M_9_10.pdf)

bear in mind that that there's two radios in this whole stackup, because the transmitter has comparable frequency accuracy as the receiver.  So the overall frequency uncertainty is on the order of 30 Hz (sqrt(2)*20 Hz).

Hitting a 0.5 ppm accuracy (15Hz out of 30 MHz) is a fairly challenging spec to meet over a wide temperature range.