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davezap

What SDR are you all using?

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Hi all, first post here. 

I came across this forum while doing some research around hydrogen line observations. I am also quite interested in it and have read the 8 page topic on this board with interest. 

My background is in electronics so think I can assemble the RF chain. While I am not an RF expert I won't be putting a metal pole up the can ;) 

What I am really interested in is what SDR are people here using. I guess I mean in terms of the secondary software for doing FFT averaging should I pick one SDR over another based around it's support / drivers / API and so on?  I see lots of mentions everywhere for the RTL-SDR gear, but lets say I was willing to spend a little more money what do you think I should look at?

At this point in time I am kind of sitting between a SDR Play RSP1A or an AIRSPY R2. I am leaning more towards the RSP1A due to it's lower range (not that I need that for H-Line but perhaps for other things later) and 14bit ADC (vs 12bit on the AirSpy) and TCXO.

Love to hear your thoughts and experiences with some of these 'mid-range' radios, bad experiences and all.

Thanks

Dave

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Hi Dave,

 

The SDR you should get depends on what you want to achieve with it. SDRs differ in operating frequency ranges, bandwidth, sensitivity and so on. For the hydrogen line, the RTL-SDR is a fine option, that is very inexpensive and reliable, operating just fine at 1420 MHz, with a more-than-enough maximum bandwidth of 3.2 MHz (spectral line observations don't usually require more than 1 MHz of bandwidth).

 

If you're looking for a broader bandwidth (for continuous, pulsar observations etc.), then the SDRPlay, AirSpy, HackRF, LimeSDR [Mini] are all better options, each offering at least 10 MHz of bandwidth (look up each one's specifications and decide which one is the best deal for you). I personally just ordered the LimeSDR Mini, as I feel like it is definitely best option for me (and for most people in my opinion, especially amateur radio astronomers).

 

Maybe others can provide more useful info based on their experiences!

 

- Coto

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Hi Dave as I'm sure you've read I use a Nooelec dongle which is the cheapest probably on the market. It has no screening and no txco however it does work and has proved very reliable so anything else will be an improvement 😂

I would probably go for the RSP1 or duo for the reasons you stated.

My biggest nark is the lack of software that can display sub dB readings, increments of 0.2 dB for astro work. Spectravue can do it but is tied to the RF Space SDR 14. Hopefully the software will get better.

Carl

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26 minutes 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

I'd probably buy that, but I can't find a similar dish in Greece, and shipping would probably cost thousands to ship it from the US to Greece... :/

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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!

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I'll go and have a look at it tomorrow. From my basic understanding its a gregorian style dish. From the description 'tracking satellites' I'm going to guess it's setup for 4GHz+ but have little to base that on. 

I suppose I will be ripping out the feed and replacing it with my own one. 

Having said that 4.8m is huge and I can't imagine my neighbors will be much pleased with me :) pulling it apart, moving and setting up again looks like a big undertaking. 

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8 hours ago, davezap said:

I'll go and have a look at it tomorrow. From my basic understanding its a gregorian style dish. From the description 'tracking satellites' I'm going to guess it's setup for 4GHz+ but have little to base that on. 

 I suppose I will be ripping out the feed and replacing it with my own one. 

 Having said that 4.8m is huge and I can't imagine my neighbors will be much pleased with me :) pulling it apart, moving and setting up again looks like a big undertaking. 

I'm not sure if it's a Gregorian, but based on the image and POAM Electronics' dishes (they look like the one on the listing), I'd guess it's a Cassegrain antenna. The dish already looks far smooth enough for 1420 MHz, so you shouldn't have to worry about it.

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Hi again, went and had a look and pending some money changing hands it's a done deal.. OH dear god what have I done? :)

The primary reflector is actually 4.6m (not 4.8 as advertised), although I'm not complaining. The depth is 0.85m giving a focal point at 155cm where we find a concave (hence my thought it was a gregorian) secondary reflector, f/D=0.34. So at the target frequency of 1420MHz it's 20 wave lengths wide. Then if we take a punt on efficiency at 70% (although I have no idea) the overall gain would be about 35dB and that would be most welcome. The secondary itself is 550mm wide and 220mm deep and has been designed specifically for this dish so I'm assuming it's perfect.

I realize this has gone terribly off topic.

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4 hours ago, davezap said:

Hi again, went and had a look and pending some money changing hands it's a done deal.. OH dear god what have I done? :)

 The primary reflector is actually 4.6m (not 4.8 as advertised), although I'm not complaining. The depth is 0.85m giving a focal point at 155cm where we find a concave (hence my thought it was a gregorian) secondary reflector, f/D=0.34. So at the target frequency of 1420MHz it's 20 wave lengths wide. Then if we take a punt on efficiency at 70% (although I have no idea) the overall gain would be about 35dB and that would be most welcome. The secondary itself is 550mm wide and 220mm deep and has been designed specifically for this dish so I'm assuming it's perfect.

 I realize this has gone terribly off topic.

A large dish indeed! Is it motorized? Having rotors and being able to track an object is a huge plus.

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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!

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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 😉

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12 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!

Woah, that's an insane deal for the price I see on the page!

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