[eagle] Re: Eagle 10 MHz Clock

Jim Sanford wb4gcs at amsat.org
Wed Apr 11 18:03:04 PDT 2007


All:
All systems should be designed to fail gracefully upon loss of the 10MHz 
reference.  This was a key discussion in the UHF peer review.
This will be clarified when I get a chance to update the FRD, which is 
low priority right now, compared to getting test results on U RX.
73,
Jim
wb4gcs at amsat.org


Rick Hambly (W2GPS) wrote:

>Bill,
>
>s/c means SpaceCraft.
>
>It is a waste of time to design for operation without the 10 MHz satellite
>oscillator (it is not a clock). The design will simply need to be redone. On
>the other hand, if designs incorporate their own soft fail options, so much
>the better.
>
>I expect a design for the 10MHz satellite reference based on a design Tom
>and I have seen that includes its own soft fail redundancy. I will discuss
>this possibility with Tom soon.
>
>Rick
>W2GPS
>AMSAT LM2232
> 
>
>-----Original Message-----
>From: eagle-bounces at amsat.org [mailto:eagle-bounces at amsat.org] On Behalf Of
>Bill Ress
>Sent: Wednesday, April 11, 2007 1:17 PM
>To: K3IO at verizon.net
>Cc: EAGLE
>Subject: [eagle] Re: Eagle 10 MHz Clock
>
>Hi Tom,
>
>Thanks for your inputs.
>
>Do you have a time frame for your USO benefactor's commitment to the 
>program??
>
>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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>  
>
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