Using Raspberry Pi GPIO

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2i0jmt
Posts: 65
Joined: Tue Apr 16, 2019 2:48 pm

Using Raspberry Pi GPIO

Post by 2i0jmt » Wed Apr 17, 2019 9:36 pm

Hey Folks

As I'm sure many folks know, we can generate a low-symbol rate DATV signal from the Raspberry Pi using one of its GPIO pins.

Of course, this uses nasty square waves so generates a lot of harmonics.

My question is, if I were to attach a good filter onto the GPIO output, would the signal be acceptable to use?

It wouldn't be the neatest signal in the world, but would it be legal?

Thanks

Jonny 2I0JMT

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G0NMY
Posts: 75
Joined: Wed Nov 11, 2009 6:10 pm

Re: Using Raspberry Pi GPIO

Post by G0NMY » Tue Apr 23, 2019 3:34 pm

The GPIO based transmission are only good for around the shack because they are such a low rf level and are not a clean transmission. You would not want to amplify such a signal without properly aligned filters.
That is why the Portsdown Project exists.
You seem to be concerned about legality, The amateur radio licence is all about experimentation so would it be legal? yes providing it doesnt cause interference to services outside the ham radio spectrum and fits the remit of your licence, ie power levels and other restrictions like not transmitting music or other copyrighted material etc.

Its also a given, that you would also not want to cause interference to your fellow hams within band, atleast not knowingly.
Its nice to see you are concerned about the legalities of your licence but experiment away that is the whole point of Ham Radio Just be aware that interference is possible and it is your responsibility to fix it. ;)
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2i0jmt
Posts: 65
Joined: Tue Apr 16, 2019 2:48 pm

Re: Using Raspberry Pi GPIO

Post by 2i0jmt » Wed Apr 24, 2019 11:43 pm

Thanks for the reply!

It's nice to hear of the experimentation mentality. Truth be told, I find it absolutely fascinating to be able to send DATV (Or any useable RF in general) from something that was not designed for it. As a radio experimenter, this is definitely one of the most interesting things to me.

I just off course don't want to do it in such a way that I cause trouble.

Filtering out of band harmonics is easy (LPF + BPF), but would anyone be able to provide any info on the feasibility of cleaning up the signal in band?

When doing SSB with pitx, the in-band fft actually looks pretty clean...at least as far as my rtl sdr can see!

I should add that this isn't a cost thing. You'll see in my other thread "My Plan" that I am going to purchase a LimeSDR Mini and do it properly with a clean signal. This experiment is separate from that :)

Thanks

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