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Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

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Re: Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

#11

Post by Neywiny »

mikewarot wrote: post #10
Neywiny wrote: post #7

Earlier quoted context omitted.

Not sure I understand the I/Q comment. What would the phase shifter do to the signal? Just overlap I on top of Q?

If you only have a real signal, you're going to have to delay it 90 degrees to get the imaginary part before you do any frequency shift or filtering if you want to avoid image frequencies, negative frequencies, etc. Digital Signal processing is far easier if you have a complex signal. Without it, any frequency shift results in 4 output frequencies, f1+f2, f1-f2, f2-f1, and -(f1+f2), it gets geometric quite quickly. T…

I understand that. Why do you think this isn't already a good IQ stream? The max2830 has the 90 degree hybrid built in (like every IQ demodulator I've ever seen)

Re: Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

#12

Post by IgorPartola »

Neywiny wrote: post #6
IgorPartola wrote: post #5

Stupid question: what can you actually do with SDR? Everything I have seen talks about things like listening to telemetry from satellites or power meters which is cool but also not that interesting in a practical sense. Is there more to it than that?

I think there are a few ways to approach this question as an engineer that makes SDRs professionally (in a group, not just me, I'm not magic). I could probably fill a decent sized book with all I've learned of practical applications but I'll focus on a few high level points. The real reason is flexibility. Let's say you have a product that receives your specified signal at your specified frequency. Something like a c…

That makes a lot of sense. In industrial applications or when designing products I can see why it would give you all the flexibility.

I should have phrased my question a bit better: why is it so popular in the hobby space? Reading power meters seems like it would get boring real fast.

Re: Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

#13

Post by mikewarot »

Neywiny wrote: post #11
mikewarot wrote: post #10

Earlier quoted context omitted.

If you only have a real signal, you're going to have to delay it 90 degrees to get the imaginary part before you do any frequency shift or filtering if you want to avoid image frequencies, negative frequencies, etc. Digital Signal processing is far easier if you have a complex signal. Without it, any frequency shift results in 4 output frequencies, f1+f2, f1-f2, f2-f1, and -(f1+f2), it gets geometric quite quickly. T…

I understand that. Why do you think this isn't already a good IQ stream? The max2830 has the 90 degree hybrid built in (like every IQ demodulator I've ever seen)

Because at baseband they go around the max2830. A 90 degree hybrid for 100 khz all the way to 25 mhz isn't going to be small, so I can see why they didn't include it.

Re: Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

#14

Post by Neywiny »

mikewarot wrote: post #13
Neywiny wrote: post #11

Earlier quoted context omitted.

I understand that. Why do you think this isn't already a good IQ stream? The max2830 has the 90 degree hybrid built in (like every IQ demodulator I've ever seen)

Because at baseband they go around the max2830. A 90 degree hybrid for 100 khz all the way to 25 mhz isn't going to be small, so I can see why they didn't include it.

Ah. I missed that. But you wouldn't put a filter, you'd do what's called digital downconversion or DDC. This is doing the IQ demodulation in software. It's not a phase shift, it's a different type of block.

Re: Fobos SDR: High-Quality Radio for Hobbyists, Researchers and Professionals

#15

Post by Neywiny »

IgorPartola wrote: post #12
Neywiny wrote: post #6

Earlier quoted context omitted.

I think there are a few ways to approach this question as an engineer that makes SDRs professionally (in a group, not just me, I'm not magic). I could probably fill a decent sized book with all I've learned of practical applications but I'll focus on a few high level points. The real reason is flexibility. Let's say you have a product that receives your specified signal at your specified frequency. Something like a c…

That makes a lot of sense. In industrial applications or when designing products I can see why it would give you all the flexibility. I should have phrased my question a bit better: why is it so popular in the hobby space? Reading power meters seems like it would get boring real fast.

Another good question. I don't super understand a lot of the "I downloaded a software, bought a radio, and look it works". But I do like, for example, things like [1]. The reverse engineering side, the legal hacking side, that's where it gets interesting. The Flipper Zero is a great example of that, though I've never used one.

Another example I thought of on the industrial side is old NASA equipment like in the curiousmarc series. Any time they change anything, even frequency by a small amount, it involves effort like swapping out crystals and tuning filters and junk. In SDR, it's just a variable.

[1] https://www.washingtonpost.com/news/speaking-of-science/wp/2...

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