[eagle] Re: Eagle 10 MHz Clock

Lyle Johnson kk7p at wavecable.com
Wed Apr 11 10:14:38 PDT 2007


Hello Bill!

> Good points about keeping the command receiver on 100% - no issue there. 
> But I think the matter is somewhat confused (at least for me) since I 
> believe the command receiver that John has designed is also the 
> data/analog receiver. I don't recall that being the case is the past 
> satellites. If command and data function stay combined, then that's all 
> the more reason for considering John's suggestion.

In the past, the "command receiver" used the same front end as the 
transponder receiver.  The difference was an IF tap that was then 
downconverted to baseband to drive a hardware command decoder.

Thus, all uplink that had command capability had receivers that were 
always on.

One rule learned the hard way is you *never* turn off a command 
receiver. It's also why command receivers, at least, were never 
frequency agile.  It's bad enough to recover a spacecraft if you are 
commanding it in the blind - it's even hardware if you have no idea 
where the receiver might be tuned.  So, we always used crystal 
oscillator/multipliers, or PLLS with pins-selection of dividers.  Using 
a serial-load PLL adds a lot of risk -- not sure what the reward is for 
the risk.

Not to say we need to always do what worked in the past, just that we 
should have compelling reasons to change things that relate to 
spacecraft safety and health.

73,

Lyle KK7P



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