Carl Reade

1 hour ago, blinky said:

Good stuff. You should be able to get false colour in the settings as well.

Not bad at all. You will get passes like that and others will be a lot better.

1 hour ago, Alan White said:

A question gents, are you trying to get data from the satellites?

All this radio stuff is new to me, well this use is anyway.

Basically these satellites orbit constantly transmitting live weather pictures. So the aim is to wait for it to pass overhead, tune to it's frequency, decode the signal using software and produce a picture.

1 hour ago, blinky said:

Very nice!  What antenna/setup do you have?  And is there a way to know if its going to be a good pass or not in advance or is it luck?

Just a horizontal V and LNA. I used WXtrack software to look at the passes.

29 minutes ago, blinky said:

Ah, ok, see what you mean!  That's the setup I have.  Put the supplied dipole into a v shape and have it pointing north lying flat on a garden table outside the van with the LNA close to the antenna.  Is ther eother software or anything I should use?

Software is fine. To improve a quad helix or turnstile would help both not easy to build. Overall I found I generally I got one decent quality pass a day. Here are my decent ones.

1 minute ago, blinky said:

Hmm.... the online tutorial said to have bandwidth at about 36Khz

I was referring to your first post😀

On the weather one the best results I've had was using a horizontal V antenna and a LNA4ALL preamp and a decent pass helps a lot.

Looks way too narrow for station. Check if noise level changes when aerial connected. Would also widen the band to the max.

Nice webpage and concept. Just a couple of questions, points,

The user is going to need the co ords of the telescope to know when and what it will drift through.

Is the scope going to be Alt Az mounted in order to look at different locations of sky?

Maybe an idea to point users to software ie Stellarium in order to plan a scan request.

I take it you will be carrying out requests manually?

Carl

2 hours ago, Coto said:

Just installed G8FEK's L-Band radio astronomy LNA on a fixed 3.2m dish pointing 20 deg below zenith. Here is a first result:

(The square-ish blocks are due to data intervention (had to remove some RFI spikes))

Detecting the hydrogen line is nice and all, but what about multiple HI lines in a single observation? You already did this: 

And it's been done here, by an even smaller dish: http://blog.svenbrauch.de/2014/08/29/14204-mhz-hydrogen-line-there-it-is/ (my feed dimensions are identical too)

And these guys with a 3.1m dish seem to get amazing results with similar equipment: http://www.midem-drustvo.si/Journal papers/MIDEM_47(2017)2p113.pdf

Firstly, how can I distinguish hydrogen line emissions originating in the spiral arms of our galaxy, from other types of emissions (e.g. nebulae like Cas A, emissions with extragalactic origins etc.)?

Secondly, what does it take to see multiple lines in a single (averaged) spectrum? Is pointing an important factor I'm not considering? I've managed to do it with the 1.5m (up to 2 lines though) with little observing time (2 mins in this case):

I think it'd be interesting to see more than 1 or 2 hydrogen lines, proving we live in a spiral galaxy by a single plot. 😁

 

P.S.: My chain is Feed -> G8FEK LNA -> 3m LMR-400 coax -> 1m USB extension -> RTL-SDR (without the shield 😕) -> PC

Do you think it'd increase my S/N significantly if I inserted an in-line amp right after the LNA?

EDIT: Also, do you think it'd do any difference if I took an OFF measurement and then subtracted the ON data from the OFF data? (I don't believe I could extract anything else from this plot)

Glad to see your getting results. I don't think the line amp would be any advantage with only 3m of coax.

Yes pointing is important, depending where you point and arms in that direction. The above graph was a drift scan of Cassiopeia. If your getting a big jump and small bump it's safe to say Cygnus area has passed through the scope.

I use the off method for all the graphs that brings out the details and should give you results.

To seperate different objects would be difficult as the resolution of the small scope simply is not good enough and there is a lot of hydrogen up there.

Maybe using other frequencies than hydrogen would be useful to do this.

I have still to put the total power bit of the scope together to see if it works or not.

13 hours ago, Coto said:

Yes... I did a lot of experiments. I think I'll install the Pi under the dish (whose reflecting surface acts as a shield reflecting the Pi's interference away into the Earth's ground). I tried that and the RFI went away (at least sufficiently enough). I think it'll still cover it with aluminum foil or something.

 

P.S.: Do you know if G8FEK's L-Band Radio astronomy LNA is waterproof, or will I need to put it in a project box?

Yea PI needs to be shielded or away from the rest of electronics.

Not sure if the LNA is water proof so I boxed mine and sealed all the connectors.

2 hours ago, Coto said:

Well, I tried covering the entire box with aluminum foil, making sure it touches the antenna's ground, but I still get RFI... Why is that?

Is the PI on?

54 minutes ago, Coto said:

So I guess my question is, where does this energy go? Like the Pi emits radiation, it is picked up by the foil (as an antenna?) and transferred to the feedhorn's ground? Where does the energy go from there? Does it get radiated outwards (into the sky and also into the dish reflector as well)? Where exactly does this energy go?

You want to be doing two things.

All of your RF chain should be shielded in metal enclosures. There's not much point in having shielded coax with the line amp open to RFI. So in the RF chain it's to keep RFI out. That would leave RFI only getting in from the antenna and where filters come in.

With the PI your trying to keep its RFI in an enclosed area so it's not interfering with anything else. Bit like a microwave oven.

So doing both greatly reduces the PI and external sources interfering with the signal your after.

However another issue is cabling which can carry RFI so cables ie USB should also have a ferrite core on as well.

Computers simply are not screened for RF.

Amplifiers are dumb if they see it in their range they will amplify it, hence the use of filters.

13 hours ago, Coto said:

Separating the Pi out of the box would be quite problematic for me as I had already planned everything to nicely sit in a box... Also, putting it a few meters away would also be susceptible to interfering with my dish. I think I'd still need to make a faraday cage for. Currently planning to try this with my current box, although I'm not so sure how it should be done... Do I just cover the whole box with aluminum foil? Do I then need to connect this aluminum foil anywhere (as a ground/redirecting all the EM energy the Pi emits elsewhere away from the dish)?

A metal box would be ideal. You could line the box in foil and attach the RF ground to it and also foil up the pi seperate, ideally the pi would be best away from the RF amps. Be a matter of testing.

4 hours ago, Coto said:

So after a bit of investigating, it is indeed the RPI causing all this RFI, and not the power supply I was suspecting. Also, it seems like the in-line amp and the bandpass filter just don't seem to work. I really don't know what I'm doing wrong, but as soon as I insert the in-line amp after the LNA, I see no HI line. Same goes for the hydrogen filter: I insert it after the LNA, no HI line. It's as if the in-line amp and the HI filter are acting as attenuators... I'm not sure. Either way, using the LNA alone works fine for me so I'll go with that (I made a fine observation last night).

 

As for the interfering Pi, I'll try wrapping the project box in aluminum foil (forming a faraday cage) and making sure the aluminum foil makes contact with the feedhorn's ground (the waveguide side = the N-type connector's outer "shell"). If this doesn't help I'll have to get the Pi out of the box and put it away elsewhere, or maybe change it's CPU clock speed (cause it's originally rated at 1.4 GHz...).

I think you will need to move the PI away from the rest. Not sure what's going on with the line amp and filter perhaps a power issue when they are in the chain. Could it be that the LNA isn't getting power when they are connected?

I prefer the satellite inline amps as they and the LNA are just fed off the coax.

Keep posting your results.

2 hours ago, Coto said:

Why? The Pi gets pretty hot and you think could make the LNA noisy? (I don't think that's the case - they aren't in contact so it's not like the LNA would feel very warm or something)

LNAs always work better cool. It's more RF interference from the PI I was thinking of.

2 hours ago, Coto said:

Gonna try some troubleshooting soon when I get back to my dish. Just a question that came up to my mind: I installed the LNA a little bit too deep into the box, so the SMA male to male connector wasn't long enough to reach my feed's connector. Is it wrong that I used 2x right-angled SMA connectors before reaching my feed's SMA to N-Type connector? Could the loss of these connectors be significant enough to degrade the signal strength of the hydrogen line that I would otherwise be able to detect without these connectors, or am I just being paranoid? 😛

Hi shouldn't make any difference, however not so sure about having a PI so close to the amps but that will just need testing.

3 hours ago, Coto said:

I'll check with to see if power increases once I plug/remove the first stage LNA. As soon as I remove the feedhorn from the LNA, the spikes disappear. I assume the LNA (if it doesn't get any power) can still pass the signal to the in-line amp without amplifying it. (the in-line definitely gets power since I see its LED light up)

No there would be no signal your looking for just random stuff whatever the circuit board metal would pickup, like a bit of tin foil at the end of the RF chain.

A volt meter at the LNA will reveal all.

7 hours ago, Coto said:

Well, I connected it to the feed, tried a 30 min observation while MW is right in the beam, nothing... 😕

First thing I would check is voltage getting to the LNA and all connections good.

1 hour ago, Coto said:

"What sort of supply is it?"

It's just a 10 Amp 12V AC to DC converter (taking power from the plug).

 

"I would also suspect the simple wire antenna was it grounded?"

What do you mean by "grounded"? It's just a wire attached to the center hole of the SMA port of the LNA (all the spikes go away if I remove the wire antenna).

There's your answer it's the wire. The spikes would remain if it was the power supply.

Try it with the feed horn. I would stick to what works adding a wire is a random element.

If you change something keep the rest the same. It makes life easier.

What sort of supply is it?

I would also suspect the simple wire antenna was it grounded?

Was the pi on for the first time?

Suspect everything that changed since your last successful detection not just the filter. 

No the FFT won't deal with that.

Carl

3 hours ago, Coto said:

Essentially because I want to be able to observe from to 1300~1700 MHz if I want to (e.g. for solar observations etc.), and not limit myself to the filter. Right now I've placed everything in a box, and I'm controlling everything remotely using a raspberry pi (more detailed updates soon), but I cannot be opening the box, removing the filter and placing it back in afterwards for every single observation... Any ideas regarding a simple electrical workaround for this?

EDIT: This is my current setup: 

Maybe I could power the blue in-line amp directly from 12V DC and connect the + of the blue in-line amp to the LNA? Then it's just a matter of adding a switch go directly through the filter VS go "around" it?

Hi yes you could do that however the switch and wiring would become part of the RF chain on the filter and be susceptible to interference.

Best thing to do is remove it if not required and just power the line amp and LNA with a plus wire.

Looking forward to the Pi plan.

Carl

Short answer no.

That would mean the voltage going both ways and bypassing the biastee circuit and dead SDR!

Why bypass the filter it's only a benefit to the system?

Carl

47 minutes ago, Coto said:

So just to be clear, I should simply solder the `+` (next to GND) on my in-line amp to the center power pin on my LNA, and both will get powered up fine (with no worries of over-the-limit voltage reaches or any other concerns)?

Hi, yes + to centre pin. 12 Volts and enough current to supply both and your good.

6 hours ago, davezap said:

Yes it's motorized. I see concrete pouring in my future.  The guy was also getting rid of a rack full of equipment so I scored a 9kHz to 22 GHz spectrum analyser (second hand probably worth what I paid for the dish), GPS disciplined reference, RF Switch / controllers, a down converter of some description, various network switches, and a couple of Custom PCs to run it all.  So far a good deal I think, now I just need to remove the dish, now that is going to be an exercise!

Sounds good yea the analyser will be well worth it. Lots of concrete and pictures of the dish mounts before dismantling 😉

1 hour ago, davezap said:

I guess as a beginner either are fine and many are getting results with cheaper SDRs ( like the two of you ) . I might take a punt on the RSP1A. 

But how about this dish that is selling local to me! It's quite a beast. But where to put it, that's the question.

https://trademe.nz/marketplace/business-farming-industry/other/listing/2149700381

You could do some serious RA with that!