[SC.LUG] RE: [SC.LUG]Radio Telescopes = was ISPs

[Ian Molton]

On Thu, 14 Aug 2003 06:59:20 -0000
"Martyn Kinder" <martyn@czd.org.uk> wrote:

> <: How can that be?
> 
> z= sqrt(C sqd x L sqd)
> 
> ie Frequency independent - these are passive components. Active
> devices vary their L & C components depending on the frequency

How can an LC circuit be passive? I thought that was a tuned circuit?

> <: Still cant visualise it :-(
> 
> You can see it on a SA. But thats the way it is....

so does the added frequency come out as strong as the subtracted one? or
weaker?

> <: Whereabouts do you live?
> 
> Haslington


> <: And where did you get an SA? I'd love one...
> <:
> Bought it S/H from Telford Electronic Distribution  about 6 years ago
> - totally underused and really needs aligning

Know anywhere I could get one? I use a prog I wrote to do FFTs on my
soundcards input ;-)

> <: unsurprisingly, optical astronomy uses a similar degree of accuracy
> <: (relative to the wavelength). I keep meaning to try and make a
> mirror<: but never get around to it:(
> 
> Funny that - same here..

Thats it, Im calling pilkington to get two 4" discs of annealed glass.

> <: > <: surely if we can get pointed at the same source, then we
> <: > <: could find the
> <: > <: correct distance by simply moving one antenna until the
> <: > <: signal strength
> <: > <: peaked?
> <: > <:
> <: > <: we could practise on the sun or moon ;-)
> It may feasible if we were on a perfect E-W direction - however, the
> element of N-S and difference in altitude would make it difficult if
> not impossible, but I think that this is the lesser of the problems.
> 
> <: But would my idea work? simply moving the dishes within a known
> range<: until the mixed signal peaks?
> 
> If you are looking at two random noise sources, how would you know
> they have peaked.?

theres no 'phased' noise from a nearby source?

> But I think that is a function of the GPS receiver with a damping
> effect rather than the knowing your exact position,

Nah. the gps is too old to have stuff like that on it.

> Locking the receivers is absolutely essential. Imagine that you are
> only 10Hz out. That means that every 1/10 second your mixed signals
> will max and totally cancel each other out. The absolute frequency
> doesn't matter, but they do neeed to be identical.

Yes, but consider that the signal is being sampled by a computer. the
samplerate is dictated by a quartz crystal in a warm box. its garaunteed
to be a few Hz out. So even with perfectly locked receivers we would
still have the same problem. 

We will *need* to find a way to lock the computers clock so it can take
accurate samples.

Hm. on locking receivers, perhaps it would be better to build a
dedicated GPS locked receiver AND DAC (forget usign the PC soundcard)
then we're sampling digital data only and the computer doesnt need
ultimate lock... Can one buy GPS locked frequency sources- ie. without a
GPS in?

> Locking receivers is essential.. but not the hardest part.

Ok. but we need to lock or some how synchronise the rest of the sampling
chain too. 

> <: Do you have the address to subscribe to? I tried to before
> <: and ended up on a list with about 3 posts a year.
> <:
> Can't remember - but you will get in on the SARA website.

Thats where I found the last list I subscribed to :)

> <: On another note, I have attacked 3 of my LNBs tonight and hopefully
> <: should soon have 2 10GHz active aerials and one mixer/amp.
> <: (waiting for
> <: dremel battery to charge)

Well, one LNB converted, one to go...

> <: Oh, and could you do me a favour and quote in a standard way, if
> <: possible? I find your replies very hard to read :(
> 
> Sure - What is your definition of  standard?

LOL ;-)

Well, firstly, signature at the bottom, alleviating the need for a 'see
below...' at the top ;-)

secondly, '> ' is the standard quote character, but if you want to use
': ' thats fine. two character quotes are a pain though because it looks
like two people replied with single quotes.

Also, try to put a newline either side of the text you insert.

Time to mod LNB number two...

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