[time-nuts] smallest rubidium

[Dr. David Kirkby]

On 05/23/11 10:44 PM, Jim Lux wrote:
>
>
>
> -----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.
>>

I believe the reference is the best for all the frequencies that are used, so 
there would be some advantage in a rubidium, but I think they are going to be 
too big. I'd hard to know what size this is, but I'm guess very roughly I have 
about 25 x 25 mm. But that's only from looking at manual and comparing it to the 
size of a tuning knob!!

The spec of the TCXO, that is a rare option (SO-1) is:

Oscillator frequency: 20 MHz
Frequency stability long term: +/- 10^-6 / year
Temperature stability +/- 10^-7 (-10 to +50 deg C)
Adjustment range +/- 60 Hz.
Weight 25 g
Output: more than 0 dBm into 50 Ohms.


There's no way this will be used anywhere near -50 deg C. I should think the 
coldest it would ever get would be +10 deg C, and that would be unlikely.

Looking at the service manual for this transceiver

http://www.g8wrb.org/data/Kenwood/TS-940S/TS-940S_Service_Manual_revised_edition.pdf

it appears one needs to remove about a dozen components from a PCB board if 
installing this option, then solder the TCXO in the place of those components.


> 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.


Bearing in mind this is going to be used at room temperature and since inside a 
piece of equipment it will be above room temperature, do you think achieving 
better than the above specs will be easy? I guess it should be. But whilst I'm 
putting one osciallator, I might as well put the best I can fit. I guess its 
only a matter of time before a 20 MHz oscillator with sine wave output comes up 
on eBay.

Dave
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