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Coto

First Radio Telescope Test - Success!

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Turns out, my grandpa had these two satellite finders. One of them was one of those more expensive/sophisticated satellite finders (with a screen, tools to adjust proper elevation etc.), and one of those cheap common ones that beep when a signal is detected that every amateur radio astronomer knows about.

I tried connecting the LNB to the sophisticated one, but I didn't get any signal when pointing the dish at the sun (when the LNB's face seemed to get most sunlight). There were quite a few parameters that I needed to play with in order to get it working, so I decided to use the sophisticated satellite finder as a power source to the cheaper satellite finder, and after a bit (a lot!) of struggle trying to set everything up under the hot sun with mosquitos bothering me and cables getting unplugged, I noticed that pointing the dish to the sun made the satellite finder noisy! And it's definitely the sun, because turning the dish slightly away made the satellite finder noisy. At first I got thinking, because such a small dish would have a very wide beamwidth, and turning the dish a few degrees away shouldn't drop the signal to 0. But doing the calculations, I found out that at 11GHz, the beamwidth should be around 2.17º (assuming k=1 in Bw=k*λ/D), so I had to be a bit precise with the rotation.

Enough talking, check it out:

This is a very rough setup, just to confirm it's working. When all of the adapters arrive, I will connect the telescope to my HackRF, set it up on a proper mount etc., and get some proper data recorder!

 

- Coto

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Cut out 4 discs from aluminium foil about 25 mm in diameter. Stick them to random points on the inside of the dish and smooth them out so they form crude mirrors. They will reflect the sun to form a spot of light that will centre on the LNB. You can estimate from the spot's as to the correct focus position of the LNB. Its simple to then check that the sun is correctly positioned on the LNB.

 

Edited by Tomatobro
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Yes it's easily picking up the sun. Prop it against something and aim the lnb shadow slightly ahead of the sun and slightly higher about an inch. After a few minutes you should hear the sat meter increase as the sun drifts through.

Carl

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10 hours ago, Tomatobro said:

Cut out 4 discs from aluminium foil about 25 mm in diameter. Stick them to random points on the inside of the dish and smooth them out so they form crude mirrors. They will reflect the sun to form a spot of light that will centre on the LNB. You can estimate from the spot's as to the correct focus position of the LNB. Its simple to then check that the sun is correctly positioned on the LNB.

 

That’s a pretty good idea. But why 4? Won’t just 2 (placed at the ends of the diameter) do?

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On my large dish I have five.  In bright sunshine the reflected spots of light have to compete with that reflected from the dish surface.

Its also a good way to determine the accuracy of the dish profile in that all spots should converge to a single point.

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Update: Bias Tee and F-Type to SMA connector has arrived. I soldered the power wiring to the Bias Tee and gave it power. I decided to check how it works with a regular whip antenna, so I wrongfully plugged RF+DC to the HackRF and RF to the antenna. More here.

 

Tl;dr: Might have killed my SDR... :(

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16 hours ago, Coto said:

 so I wrongfully plugged RF+DC to the HackRF and RF to the antenna.

Tl;dr: Might have killed my SDR... :(

Sorry to hear that but I did warn you. 

Still, you are probably not going to be able to pick up much more than the sun and moon with this 12GHz setup and you can still do that just with the sat finder

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10 minutes ago, robin_astro said:

Still, you are probably not going to be able to pick up much more than the sun and moon with this 12GHz setup and you can still do that just with the sat finder

Yeah but I want to connect it to a receiver so I can get some "more proper" drift-scan data.

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A transit with 2 deg beam width will take ~20min so you could log that manually the old fashioned way with pen and paper (or typing into an excel spreadsheet) taking readings from your meter say every 15 sec.

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So I tried observing the moon with the same setup I used on the sun observation. Didn’t work.. After taking a look at the cabling, I noticed the end of the coax was not properly connected to the satellite finder (I had used duct tape to fix this, but apparently that didn’t last very long). Will try again soon.

As a side question, do I need to wait for a full moon (= more thermal radiation emission) to be able to observe the moon, or does it also work when it’s around, say, 35% (today’s illumination)?

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1 hour ago, Coto said:

So I tried observing the moon with the same setup I used on the sun observation. Didn’t work.. After taking a look at the cabling, I noticed the end of the coax was not properly connected to the satellite finder (I had used duct tape to fix this, but apparently that didn’t last very long). Will try again soon.

As a side question, do I need to wait for a full moon (= more thermal radiation emission) to be able to observe the moon, or does it also work when it’s around, say, 35% (today’s illumination)?

The moon is a lot weaker than the sun and you don't need to wait on a full moon as the microwave radiation comes from just below its surface.

I would also go with the satmeter setup as you will see the beam and power level going through the target. I suspect if you were using a wide radio spectrum you would just see a rise in the noise level across the whole band.

A sat meter connected to an ADC is ideal something like a Dataq logger.

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2 hours ago, Carl Reade said:

The moon is a lot weaker than the sun and you don't need to wait on a full moon as the microwave radiation comes from just below its surface.

Can you elaborate? What do you mean by the radiation coming just below the surface of the moon?

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If the drawing represents what is in your SDR then its kind of hard to see how applying DC to the antenna input killed your radio.

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2 hours ago, Tomatobro said:

If the drawing represents what is in your SDR then its kind of hard to see how applying DC to the antenna input killed your radio.

Would have thought C64 would have offered protection?

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And the circuit seems to have a bias "T" built in so I cannot see that failing either so I agree that C64 would not pass  DC.

A post mortem would show what happened but regardless its probably not worth repairing.

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Is it actually dead or just deaf?  Maybe the bias T control circuit did not like 12v DC being applied to it (it is designed only to supply a few mA at 3.3V)  If it is running but just deaf,  snipping the inductor in the bias T (followed by also snipping the surge protecting zener diode) might be a simple step to see if it could be brought back to life.

Robin

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On 15/09/2018 at 20:49, Coto said:

 

As a side question, do I need to wait for a full moon (= more thermal radiation emission) to be able to observe the moon, or does it also work when it’s around, say, 35% (today’s illumination)?

Here are my observations with the same setup. Note the difference in voltage signal between sun and moon (~x40)

http://www.threehillsobservatory.co.uk/astro/radio_astronomy/radio_astronomy_1.htm

 At 12 GHZ there is little difference between a full or new moon 

Robin

 

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If Coto could get it to someone that understood and is equipped to deal with surface mount electronics then the components involved could be checked and lifted and results evaluated. The components would be easy to identify being close to the SMA connector.

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@Carl Reade & @Tomatobro : I showed this to my grandpa and uncle who know quite a lot about electronics and they also said C64 should be protecting it. So it’s either D1 or MOSFET that got killed. We’re going to try to remove that RF shield (which seems like a difficult thing to do) and see what’s going on in there. My uncle tested everything outside the RF shield and everything seems to be functioning properly, so we’ll have to somehow open the shield and see what’s going on under the hood.

I’ll forward Robin’s idea in case it helps them out somehow.

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He’s checked D1 and it seemed to be fine (I think he said there’s no short circuit), so it’s probably the MOSFET that’s presenting problems? Oddly, plugging it in doesn’t turn on any LED, and he doesn’t hear any sound (according to my uncle), even though I experienced it at home myself before dropping it off to him. Could something have broken while he was testing everything? He didn’t supply any huge voltage or anything, so I don’t know why the LEDs aren’t lighting up and no sound is coming out of the RF shield. It’s as if the USB isn’t plugged in at all...

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I dont know how the MOSFET bias T control switch would behave under these circumstances but if the full 12v  got through the MOSFET onto the main supply rail  it would likely have caused untold damage elsewhere.

Robin

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I’ve ordered a MOSFET transistor to replace the broken one. Hopefully that’ll do the trick.

But hey, full moon today! Let’s see if my dish can pick something up with the satellite finders. It did pick something up yetsterday, but turning it around often beeped as well. I checked with a satellite finder app and it looked like the moon fell right on the line of satellites, so I’ll try again in a few hours and update you with my results.

EDIT: Satellite finder needs charging... will try tomorrow.

Edited by Coto

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