[time-nuts] "Piezo Little Wonder" OCXO
richard at karlquist.com
Fri May 30 15:01:36 EDT 2008
Maybe it's the 2nd LO for a dual conversion receiver with IF's at 10.7
MHz and 455 kHz. 10.238 + 0.455 = 10.693
Rick Karlquist N6RK
Jim Lux wrote:
> At 10:37 AM 5/30/2008, you wrote:
>>I have two PIEZO 10.230 MHz crystal oscillators in the same style package
>>the 10811. But the oscillator in question is for 10.238 MHz.
> interesting.. is the 8kHz a deliberate offset? Is the manual tuning
> off to one end? Maybe they were using them in a scheme where instead
> of I/Q they did offset IF sampling.
>>----- Original Message -----
>>From: "Jim Lux" <James.P.Lux at jpl.nasa.gov>
>>To: "Discussion of precise time and frequency measurement"
>><time-nuts at febo.com>
>>Sent: Friday, May 30, 2008 12:47 PM
>>Subject: Re: [time-nuts] "Piezo Little Wonder" OCXO
>> > At 08:33 AM 5/30/2008, you wrote:
>> >>Early GPS receivers used a 10.23 MHz time base.
>> >>Probably related to 2^10-1.
>> > yep.. the chip rate for the C/A code is 1.023 Megachips/second, the P
>> > code is 10.23 Megachips/second, and the L1 frequency (1575.42) is
>> > exactly 154 times the 10.23 MHz, the L2 is 120 times.
>> > So you can see that having a 10.23 MHz oscillator is a handy thing in
>> > a GPS receiver, especially if you can discipline it with the received
>> > signal.
>> > These days, one might choose a reference oscillator somewhat higher,
>> > so that when you do your 1bit A/D of the signal, you get many
>> > samples/chip, and so that the signal directly aliases to somewhere
>> > convenient. A lot of receivers use a sampling clock such that you get
>> > 1 bit I and Q samples at a convenient sample rate. 4*10.23 would
>> > work nicely, eh? 40.92 MHz
>> >>Some GPS manufacturers approached HP about making
>> >>a 10811 on 10.23 MHz. There is a circuit modification
>> >>for 10.23 MHz and some crystals were made (I
>> >>have some somewhere). However, I don't believe
>> >>any 10.23 MHz 10811's were sold. This unit was
>> >>probably intended to meet the need not filled by HP.
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