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RE: Radios for 1.2 GHz operation



On Sun, 6 Jul 2003, Assi Friedman wrote:

> This could be easily compensated for by opening up the receiver bandwidth.
> Since most ground stations have a very high uplink margin, the increase in
> noise bandwidth is insignificant. This has been done on several spacecraft
> in the past on higher frequency uplinks. As a matter of fact, the Israeli
> Techsat has several uplinks in the L-Band which were used with good results.
> Assi 4x1kx/kk7kx

I'd be curious if they were synchronous or asychronous and at what
baudrade and deviation, etc.  I did not mean to imply at all that a 1.2
GHz  digital uplink wont work, I was cautioning against thinking that
a typical 3 KHz deviation FM narrowband off-the-shelf 9600 baud AX.25
system in a 15 KHz channel would work "normally"... when I said:

> I would think that command via 9600 baud uplink at 1.2 GHz is not a
> generally good idea because of the HIGH Doppler rate.  You will be
> transmitting in the blind hoping to get into the middle of the Satellite
> uplink receiver.  Even at 435 MHz this is a skill.  At 1.2 GHz, this
> problem is 3 times worse.
>
> You can reduce the problem somewhat by making the IF bandwidth of the 1.2
> GHz receiver very wide so that tuning is not so critical, but then you
> have just reduced the link budget.  But on the groun dyou have strong
> transmitters so that helps.  Just remember to consider all these things...
>
> de WB4APR@amsat.org, Bob
>
> PCsat WEB  page     http://www.ew.usna.edu/~bruninga/pcsat.html

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