View Full Version here: : Any Radio Astronomy enthusiasts?
31-05-2009, 06:37 PM
Hi all! After years of planning, I'm about to begin my multi-10-metre antenna RA array project in earnest!
The site is a large, fairly remote valley, at around 500m ASL, almost entirely surrounded by mountains, and essentially radio dead. (No TV, radio, cellular, etc.)
I'm starting with a single fully-steerable 10m diameter antenna - small enough to be doable, large enough (I hope) to be useful - but plan to add at least two more in the next few years.
If anybody is interested, I can "chronicle" progress with pics here, otherwise I'll just throw a page up for it on my website.
Any questions, criticism, suggestions or comments most welcome.
Cloudy skies! (Because radio astronomers don't even notice...) ;)
31-05-2009, 07:08 PM
Sounds interesting. Some pics would be good, also a link to a web site ?
01-06-2009, 07:17 AM
I would be more than interested in watching the progress of your work. Please keep us informed on how you are getting on.
01-06-2009, 09:10 AM
This sounds like a pretty ambitious project, definitely keep us informed!
10m isn't huge but plenty enough to do proper science with.
Are you building a dish or some sort of scoop?
I can see this getting expensive reallly quickly :)
01-06-2009, 12:07 PM
It's already expensive, and I'm barely past the prototyping stage! My wife is resigned to the fact that we'll never have any money. But that's what happens when you marry a man with a plan! :lol:
The antennae will actually be 12m diameter "dishes", but at first I'll be leaving the outer 2m circumference unilluminated. If I'm able to cover the outer portion later ("able"="afford it") then I will.
Luckily I get a discount on metal through the company I work for, and most of the key engineering will be done for me at cost by their mechanical fitters. I'm a comms tech so have that side covered. Lots of keen volunteers in these departments looking for interesting projects to waste their time on! :)
It's the little things which help: I'm mounting the antennae on railroad bogies and track which I get mostly gratis courtesy of some of the railroad enthusiast employees at the company! They are ex-railways staff and also members of a local train society!
Pictures of the site will be up sometime soon...
01-06-2009, 12:55 PM
It's a pretty big project to start from scratch. The ASNSW has a 12' (?) dish at Wiruna mounted on an equatorial platform. Ex CSIRO Mills cross at Fleurs.
About six years ago a receiver was used to look for Hydrogen noise around 1421 but I don't think the receiver was sensitive enough because nothing was seen or heard even looking at the Sun.
The project has not been revived yet but We are getting some better receivers and will probably try again in the future. I spoke to the project leader at the SPSP about reviving the project so we may have another go soon.
I personally am not into radio astronomy but I will probably provide some technical assistance and equipment.
01-06-2009, 05:51 PM
This has been a long time coming but worth the wait. And a man's gotta have a hobby, right? It sure beats sitting around at home watching 'Idol' shows or "Reality" TV and listening to my brain waste away to nothing... :lol:
Good luck with your own RA project, I look forward to updates about it!
23-06-2009, 10:01 AM
hey yes please keep me posted!
if you need any help gimme a shout .. love to see that baby working!
btw a 12ft dish should give a hunk of sun noise a 1421 so if that ANSNW dish cant hear any solar noise then there is something def amiss
23-06-2009, 10:02 AM
btw I just received my LNC and LNA from germany for the 8 GHz DSN
so look out for that too soon :)
24-06-2009, 10:50 AM
Could you please be more specific. I am not familiar with all those abrieviations.
25-06-2009, 11:54 AM
Hi guys. Sorry for the lack of further info but I've been flat out building and testing gear. The track surveying is completed and the sleepers are being delivered to the site ready to take the rails eventually. Details and pics to follow soon.
28-07-2009, 03:32 PM
Well Barry I think LNA is "Low Noise Amp" needed at the antenna. LNC could be Low Noise Cable, and DSN reminds me of the Deep Space Network that has antenna dish at Madrid, Goldstone and Tidbinbilla...
I hope your story is here on the forum, best of luck , Do the Bogey Wogey!
29-07-2009, 08:36 AM
Yes I know those abrieviations. I was having a dig at the prolification of technical terms using this form when they can be confused especially by people from older generations that used the same abrieviations and slang terms to describe totally different phenomena.
As an added reference there are a lot of terms used by the younger generation quite freely today that in my day were used to describe obscenities etc. and were not used in general company.
15-09-2009, 01:36 PM
Noted you are having a go at Radio Astronomy, I should be able to help you get off the ground, I have been at it for some 15 years, and ran a phase switched interferometer (2 x 20 foot dishes) getting fantastic results, this was at a time when there was no UHF TV in this area, but with the advent of it every frequency around 600 Mhz. was occupied (I used 625 Mhz. got sources down to 1 Jy) things are even worse now and the Hydrogen Line at 1420.405 is blotted out with the second harmonic of the 710 Mhz. digital TV, anyway enough of my woes.
With a single dish I would suggest trying the Hydrogen Line, construct/buy a receiver and LNA you will get fantastic results (I did with a 12 foot dish) or for a start use any equipment/receiver to hand, that is made for AM reception and add a square law detector (diode) to the Audio Out, build/buy a DC amplifier/integrator (the integrator bit absorbes sky Etc. noise, and smooths things out) use "Skypipe" or Picolog as a recording program on your computer, and yes youll need an A/D converter after the DC Amp. into the computer, lots of info. at Down East Microwave on the internet.
BTW- LNA= Low noise amplifier
LNC/LNB= Low noise downconverter (has an inbuilt L.O. Mix. I.F. Amp.) ,
Hope this is useful, Pix. available.............cheers....... Jim
15-09-2009, 03:24 PM
Thanks for that info. I am not really into radio astronomy but there is a section in the ASNSW that has 12' dish at Wiruna and some other gear but it has not been used for some time. The dish needs some attention now having been out in the weather without maintenance for some years and I was hoping to get the group active again by providing some equipment and technical knowledge. I believe there is receiver and LNA somewhwere but I have not seen it. I have an old HP 8555 spectrum analyser that will look at that frequency with a noise floor of -117 dbm. What it needs is a good LNA at the antenna.
Back in the early 60's I had a friend who worked at Fleurs on the old Mills Cross. He used to tell me about what was going on there. The dish we have is one of the old dishes from the Mills Cross.
06-10-2009, 07:50 PM
Hi all, a quick update. Heavy snow caused a halt for a while and then a couple of rainstorms washed out the road into the valley, so I took a break for a while! But now things are back on track literally. I'll upload some pictures later.
08-10-2009, 11:43 AM
One of the limiting factors in this exercise will be the overall noise figure (NF) of your detection system. NF is the additional noise over theoretical minimum that the receiving system adds to the detection process.
Note NF is independent of detection bandwidth.
A spectrum analyser, especially older ones has a typical noise figure of 25 dB, hence a Low Noise Pre-amplifier (LNA) will be absolutely essential. The overall noise figure of a detection system is determined by the NF of the first amplifier in the chain (not the gain of that amplifier). You will be looking for an overall noise figure of less than 3dB. Problem with LNAs are that while being very sensitive, they can get easily 'swamped' by signals that are too large. The swamping signals are most often not the ones you are searching for. The resulting intermodulation caused by the overdriving of your LNA can produce spurious and misleading results. Hence it is important to limit the bandpass right at the front-end to be as narrow as possible around the 1421 MHzyou are interested in.
My expertise runs out about there, but I'm guessing that the limiting of bandpass is carried out in the feed horn or waveguide in front of the LNA.
13-10-2009, 06:18 PM
I would be looking for 1dB or better (read less!) noise figure (NF) for an LNA. There are designs/kits around that will give you this with up to 35dB gain. With these gains, however, there is the potential for instability, but they can be tweaked into submission - perhaps with slightly less gain, say 30dB should be achievable. Some of these LNAs may use a low noise FET input stage followed by one or more MAR/ERA type amp ICs. These FETs are capable of NF < 1dB in a well designed and layed-out circuit!
While the NF of a receiver's 1st stage is of primary importance, don't forget that the gain of this stage also largely determines the contribution of the NF of the successive stage(s). For example, in a 2-stage receiver (LNA + Rx front end) with gains G1 and G2, noise factors (the 'un-logged' version of NF) of F1 and F2, for the respective stages, the net noise factor of the receiver is
Fnet = F1 + (F2-1)/G1
So, if the gain G1 (in this case the LNA's gain) is too low, then the contribution from the 2nd stage becomes more significant.
Care should be used if adding passive filtering to band-limit the signal. There is usually insertion loss with accompanying NF, so should be added down-stream in the receiver chain where its NF will be less significant. Yes, perhaps rely on the bandpass characteristic of the antenna/feed system.
Unfortunately, with radio astronomy, as with optical astronomy, you really need to get away from interferring sources - whether it be other radio sources, or urban light pollution!
Cheers & good luck :)
vBulletin® v3.8.7, Copyright ©2000-2013, vBulletin Solutions, Inc.