[eagle] Re: Eagle 10 MHz Clock

Bill Ress bill at hsmicrowave.com
Wed Apr 11 10:16:57 PDT 2007

Hi Tom,

Thanks for your inputs.

Do you have a time frame for your USO benefactor's commitment to the 

We're designing based on 10 MHz reference assumptions and that leaves 
me, at least,  with an empty feeling. Since over 10 subsystems will use 
this reference, it would be great to get this block defined.

As you know John has already designed for operating without the 10 MHz 
satellite clock and I'm also doing the same.

Oh - - - help with out Tom. You used "s/c ranging" in you one of your 
recent posts. The "s/c" stands for what??? S and C transponders??

Regards...Bill - N6GHz

Tom Clark, K3IO wrote:
> Bill Ress wrote:
>> (snip)
>> If indeed the clock is used by all LO's it is important that the LO 
>> designers know the reference's characteristics so that synthesis schemes 
>> and loop bandwidths can be better defined.
> Assume that it is a low noise crystal. Signals will come from an N-port
> driver that is a part of the USO. A good standard level will be 0 dBm
> into 50 ohms (although it could be a tad higher -- like up to 1V RMS =
> +13 dBm if really needed).
> I would suggest that each user system could use the precision reference
> if it is available, but should switch over to an internal oscillator if 
> the precision source goes away. This is the way most counters, spectrum
> analyzers, etc work and it permits a good, simple "fail soft" option.
>> With that in mind, can you Tom, 1) determine what the specs of the 
>> $ystem USO might be (or point me to a place when I might deduce them), 
>> and 2) what's a realistic time frame for deciding if that $ugar 
>> daddy/mommy comes through with a commitment? We not only have to get a 
>> handle on the 10 MHz oscillator but the RF distribution circuitry after it.
>> In regards to the RF distribution circuitry, I count 8 users of the 10 
>> Mhz clock. Help me out here if I missed one....
>> 1) V Transmitter
>> 2) U Receiver (maybe two?)
>> 3) L Receivers (two)
>> 4) S Transmitter
>> 5) S2 Receiver
>> 6) C Transmitter
>> 7) IHU
>> 8) Spare (for X or K beacon or a "contributing" customer)
> As Lyle mentioned, all the DSP widgets need the reference signal also.
> For precise ranging it is likely that some really tight special DSP code
> will be loaded into the DSP engines for maximum accuracy. This will be
> to ensure the flattest possible phase response thru the system (the
> group delay tau is measured as d(phase)/d(freq) over the however wide
> the passband can be).
> Thinking of obtaining the best possible accuracy, we may want to do U/V
> and a microwave pair simultaneously to provide a calibration of the
> ionosphere; the one-way group delay thru the ionosphere varies as 1/f²
> and has a magnitude ~2M at S-band.
> 73, Tom

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