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Old 19-07-2021, 05:18 PM
Malewithatail (Peter)
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My first radio telescope.

Many years ago I acquired a 10 foot dish, designed and constructed a feed point, modified an old Pye ranger TV set (all valve) by retuning the sound IF strip to get max gain from the 5 stages (It was a fringe area set), connected it to the feed point, and was startled to hear the sun when I manually rotated it across the suns disk. That thrill has never left. Unfortunately, when we bugged out from Albion Park some 18 years ago, a 10 foot diameter dish was a little too big for the removalists to cope with !
With a piletier effect cooled feed, cooled to as close to absolute zero as possible, some very interesting work can indeed be done with a 1 meter or less diameter ex satellite dish. Be aware that most of the gain in a satellite system is in the LNB, or low noise block converter, the receiver is just a tunable IF stage and has a poor noise figure, as the satellites are quite powerful transmitters.
Indeed, Ham operators have been bouncing signals off the moon for decades, and are now doing the same with Venus and Mars as well. The technology gap between amateur's and professionals is getting smaller all the time.
Have a go, you can use a SDR or software defined radio dongle (TV usb stick), on the pc to do the tuning, and a standard LNB, with solid state Pielter cooling modules to better its noise figure.

Oh by the way Alex, gravity is a myth, the Earth sucks mate !
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Old 19-07-2021, 05:26 PM
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Peter we have to get one up and running...we have the gear just need to move it to the top of the to do list..I have a mount that will carry the dish...plus a peltie unit
Plus there are two dish on the roof here that may work.
We can put it in the small observatory.
Alex
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Old 19-07-2021, 09:22 PM
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Quote:
Originally Posted by Malewithatail View Post
With a piletier effect cooled feed, cooled to as close to absolute zero as possible, some very interesting work can indeed be done with a 1 meter or less diameter ex satellite dish.
How do you cool to Absolute Zero (K) or did you mean 0 degrees C or F?
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Old 20-07-2021, 06:39 AM
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Oh by the way Alex, gravity is a myth, the Earth sucks mate !

Love it.

Leon
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Old 20-07-2021, 08:25 PM
Malewithatail (Peter)
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How do you cool to Absolute Zero (K) or did you mean 0 degrees C or F?
Yes, as close to absolute zero as possible to reduce thermal noise as low as possible. Multiple, stacked pielter devices, commercially available from dead car/fridge/freezers, can be stacked one behind the other and are quite capable of getting to within a bugs whisker of absolute zero, or -273 degrees.
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Old 20-07-2021, 08:41 PM
Malewithatail (Peter)
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I too have been collecting the stuff to set something up, somewhere I have a professional super high frequency receiver that has a very low, for a 20 year old piece of gear, noise figure. Add a decent lnb and a 1 meter dish, and we could certainly tune into the cosmic background and other sources. Only 1 thing missing, well 2 actually, the usual time and of course money......
When I was at school, I designed and constructed a 4 bay, I think, stacked Yagi aerial system with 4 or could of been 6, 30 element Yagi's tuned to 220 megs I think. A homemade feed match, gamma type, was made to combine the aerials and by using the channel 10 Sydney tv station, I plotted the pattern of the array and fine tuned the individual aerials. Once again, I used an old (Valve tv sets were being scrapped all the time as solid state and color was coming in), tv set, another Pye, as they were fringe area sets and had 5 If stages, which originally were stagger tuned to give a wide bandwidth needed for the video signal. I retuned them to be narrow band, obviously totally destroying any chance of video reception, but improving the noise figure and sensitivity. I borrowed a Honeywell analogue chart recorder from the Wollongong TAFE college, or maybe the Wollongong Uni as my Dad worked there, and ran some charts of firstly thermal noise (for calibration), then some noise from the sun and other stars. I was a big thrill to pan the array, manually as I didn't have any money for motor driven stuff, and watch the pen move up the chart. Also, the automatic gain control in the tv chassis had to be disconnected as it tried to smooth out the response and I wanted a raw data set.
There used to be a astronomy club called the "Illawarra Astronomical Society" and it met in Boyong street, about 20 mins walk from home and I joined it when I was about 12 or so. I remember they built from scratch a 24 inch Newtonian telescope, but no one was interested in radio astronomy.
Will talk about a radio telescope when I see you mate.


Help, I'm diagonally parked in a parallel universe !
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Old 20-07-2021, 10:30 PM
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Originally Posted by Malewithatail View Post
Yes, as close to absolute zero as possible to reduce thermal noise as low as possible. Multiple, stacked pielter devices, commercially available from dead car/fridge/freezers, can be stacked one behind the other and are quite capable of getting to within a bugs whisker of absolute zero, or -273 degrees.
I am not sure of your calculations but Peltier devices are non-linear, they are primarily designed to work more efficient in high heat until thermal runaway takes hold but their efficiency falls dramatically at about -50 degrees C. After that point the molecules in the semiconductor region delta T bottoms out at 2 degrees per Peltier module.

I have an experiment on my bench now using up to 3 Peltier devices and I can already see from my results that it will get nowhere near the level of cooling.

The lowest I have ever seen it go is when using an ethanol mix radiator where the Peltier device is cooling the liquid in the radiator to about -100 degrees but it would be impractical for astrophotography as the camera would fail the function.
The same would apply to most electronic devices as most are rated to only work down to -40 to -70 for consumer applications. Industrial down to -100, space-based are specially made to withstand the harsh environment.

Already with 2 devices, I get a DT of 50 degrees on an open bench environment. I expect I will get a DT of up to 70 after placing it in an enclosure which is my next task.

Anyway, good luck with getting down that low.
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Old 21-07-2021, 08:30 PM
Malewithatail (Peter)
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The device I saw was 8 off 80 watt pielter devices, clamped together with the cold junction of one in contact with the hot junction of the other, in series thermally, and connected in series electrically to 72 volts dc at 8 amps, giving a device of about 600 watts. They quoted that it got down to a few degrees K.
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Old 23-07-2021, 08:09 PM
Malewithatail (Peter)
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The device I saw was 8 off 80 watt pielter devices, clamped together with the cold junction of one in contact with the hot junction of the other, in series thermally, and connected in series electrically to 72 volts dc at 8 amps, giving a device of about 600 watts. They quoted that it got down to a few degrees K. I'm trying to find the reference, before the internet was around.
I also tried a GEX 34 germanium diode, in the focal point of a 1 meter ex tv dish I scrounged (This would have been over 50 years ago, when I was 1 teenager), and fed that into a audio amp, basically ,making a crystal set that operated at microwaves frequencies, much like the early Police radar detectors. Sun noise was no problems, but the interference from terrestrial radars from ships at Port Kembla wiped out the detector regularly.
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Old 24-07-2021, 11:43 AM
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I have started looking for cheap Peltier devices on the net...when I dont want them they are very cheap..that is the price I want to pay ...anyways I will buy a six pack ( if the right price, maybe more) and stick them together and see what can be achieved...for fun ... If cheap enough I would like a batch to put on the chimney to see in practice what current could be harvested..as heat will produce current but not knowing how to apply the formula I have no idea of what one could expect...once you have some numbers you could work out how many to produce useful current...and the good thing is there would be plenty of heat available..heat that is normally wasted.
But as you say bolting them together is going to see a huge power bill
Alex
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Old 24-07-2021, 11:02 PM
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You two Tabulam lads need to contact the local Amateur (Ham) Radio Club -SARC in Lismore. Their web page is at;

https://sarc.org.au/

I know they have one member who lives at Tabulam and there are several members (including me) involved in building 21cm receivers with an American research group.

If you have a shortwave radio tune to 3.604Mhz 6.30am on week days NSW time.
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Old 25-07-2021, 07:58 AM
Malewithatail (Peter)
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Sarc

Yes I know SARC well, also being a ham operator. Some years ago, work kept me busy as well as trying to be self sufficient on the farm, time was at a premium, and that, coupled with my belief that if you belong to an organization, its up to you to support it, I didn't renew my membership. Its the same with the local apiarist association, that I'm the President of, I believe in supporting the groups you are in, the RFS as well.
This extends to web groups that I belong to, such as ausprep and the east Texas preparation group, and of course, ice in space. I try to blog regularly.
Thanks for the info re the 21 cm receivers, we will chase it up.

Last edited by Malewithatail; 25-07-2021 at 08:38 AM.
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Old 25-07-2021, 08:54 AM
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Ok Peter, having re-read your posts I now realise that I didn't comprehend your level of expertise.

Sorry to have wasted your time
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Old 25-07-2021, 06:57 PM
Malewithatail (Peter)
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You've not wasted my time mate, I am always open to new ideas, that's how we learn so don't feel bad about it. Its nice to have discussions.
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Old 11-08-2021, 09:53 PM
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If you have a shortwave radio tune to 3.604Mhz 6.30am on week days NSW time.

I'll be listening .....!!
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