Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
1–10 of 24 posts
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#2Awesome. Now, the critical question is: how to implement a proper filter and a HF afterburner? And can it do live streaming - i.e. use an USB/Pi-Shield soundcard with a Line-In or Mic input?
I could imagine this being a cheap platform for crisis regions where radio transmission channels are run by government (or not existing at all).
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#3I hope the spurious emissions aren't as bad as they look in the waterfall, because they're basically stomping all over the band and all the neighbouring bands and they're closely spaced enough that I'm not sure it'd be realistic to filter them all out. Is this even legal to use?
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#4I hope the spurious emissions aren't as bad as they look in the waterfall, because they're basically stomping all over the band and all the neighbouring bands and they're closely spaced enough that I'm not sure it'd be realistic to filter them all out. Is this even legal to use?
This is directly addressed in the article:
"Important Disclaimer: While the output power is very small, you should still take great care as the carrier is a square wave, and there is no filtering on the antenna output. So any transmissions will cause harmonics all across the spectrum – possibly interfering with life critical devices. A filter must be used if you actually plan on transmitting with any sort of range further than your room."
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#5I hope the spurious emissions aren't as bad as they look in the waterfall, because they're basically stomping all over the band and all the neighbouring bands and they're closely spaced enough that I'm not sure it'd be realistic to filter them all out. Is this even legal to use?
This is directly addressed in the article: "Important Disclaimer: While the output power is very small, you should still take great care as the carrier is a square wave, and there is no filtering on the antenna output. So any transmissions will cause harmonics all across the spectrum – possibly interfering with life critical devices. A filter must be used if you actually plan on transmitting with any sort of range fu…
Harmonics are trivial to filter - they're at multiples of the fundamental frequency, so 100MHz, 150MHz, and so on. You can just stick a lowpass filter on the output and it'll block all the harmonics because they're so far away from the fundamental. Unfortunately, the waterfall appears to show strong spurs every 30 Hz, and those would be ridiculously difficult to filter out. I think the normal solution is to design your transmitter so that it doesn't do that.
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#6Earlier quoted context omitted.
This is directly addressed in the article: "Important Disclaimer: While the output power is very small, you should still take great care as the carrier is a square wave, and there is no filtering on the antenna output. So any transmissions will cause harmonics all across the spectrum – possibly interfering with life critical devices. A filter must be used if you actually plan on transmitting with any sort of range fu…
Harmonics are trivial to filter - they're at multiples of the fundamental frequency, so 100MHz, 150MHz, and so on. You can just stick a lowpass filter on the output and it'll block all the harmonics because they're so far away from the fundamental. Unfortunately, the waterfall appears to show strong spurs every 30 Hz, and those would be ridiculously difficult to filter out. I think the normal solution is to design yo…
Given how regularly spaced they are they might be other channels (regular TV maybe?)
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#7Very cool, but please don't do this without a proper filter, you're spewing garbage all over the spectrum.
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#8Wow, bit banging radio? Neat idea. But there's gotta be USB SDR kits on the cheap, too, right?
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#9Wow, bit banging radio? Neat idea. But there's gotta be USB SDR kits on the cheap, too, right?
HackRF: https://greatscottgadgets.com/hackrf/ ~> $300
HackRF Blue: http://hackrfblue.com/ ~> $200
rad1o (HackRF from spare parts): https://events.ccc.de/2015/07/10/rad1o/ , http://hackaday.com/2015/07/12/cccamp-2015-rad1o-badge/ ~> $100?
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That would only give us half duplex. If we want to simultaneously transmit and receive, I guess we could add an RTL-SDR. ~> $10
Plus antenna(s). $ $ :)
Re: Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi
#10I am slightly confused by the screen-shot of an ubuntu OS with a windows XP desktop. :)