radio astronomy

Ian Molton spyro at armlinux.org
Fri Jun 14 15:48:07 PDT 2002


On Fri, 14 Jun 2002 21:25:07 +0100
Chris Lingard <chris at stockwith.co.uk> wrote:

> Ian Molton wrote:

> 10GHz is near an amateur band so you will find plenty of designs
> at rsgb.org or arrl.com.  What sort of bandwidth would you want?

I havent the foggiest. whaty sort of bandwidth does radio astronomy use?
;-)

> But how are you going to steer it?  Equitorial mount and geared
> down motor.  Loud grinding noises from Ian's home

This is the 'easy' bit. Its a cunning plan to use the huge stepper
motors and optical shaft encoders I have lying around ;-)

I assume an 'equatorial' mount is one with a plane parallel to the earth
and the 'scope would pivot up / down from it and swivel round?

> Get a multi mode receiver and use it as a tunable IF.

A what now?

>  Feed the
> output, via analogue to digital,  to a comms port; and write a
> driver for the port.

I was going to feed the analogue into my much underused sound cards
input...

> Write some patern recognising software, then sit back and wait.

easy ;-)

My problem is I havent the first CLUE about RF electronics, let alone
IF. all I know is Im going to need some EXPENSIVE transistors and be
VERY careful about signal routing and shielding...

what exactly IS bandwidth? (no, I dont mean in the sense of 'how fast is
my cable'.

as I understand it, if I have a 900MHz carrier and modulate it with a
5KHz signal, I not only alter the amlitude, but also the frequency,
causing it to deviate either side of the 900MHz carrier, although I dont
fully understand WHY changing the amplitude affects the frequency...

and if altering the amplitude alters the frequency, surely the reverse
is true?

so, surely then, amplitude modulation and frequency modulation are /the
same thing/ ?

Also, what /is/ a down converter? how does it work?

if I have a 10GHz band to observe, and beat it against a 10GHz
oscillator, then a 10.001MHz signal would resolve to a 0.001MHz signal?

so, to observe the 10GHz band with (is this the right term) a bandwidth
of 100MHz, I should beat it against a 10GHz osc. and low pass filter it
so I lose anything above 50MHz ?

Is that a down conversion or direct conversion?
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