Transmitting FM, AM, SSB, SSTV and FSQ with Just a Raspberry Pi (opens in new tab)

Right, but narrow passband filters are not that hard to make.

I see this as a way to get more experimenters to be hams. It also makes it much easier to demo explain / teach / get people excited about SDR and what you can do with them.

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."

For experimental Arduino and Rasberry Pi based RF apps, serviceable RF test equipment isn't as cost prohibitive as it once was. EG, Amazon has a PC-based 24MHz - 1.8 GHz RF spectrum analyzer by Touchstone for USD $80. The functional 100 MHz digital Rigol 1102E scope is useful when you're in EE-mode and still runs for $400. If feeling creative, Hantek arbitrary waveform generators hover around $160, and can use Tektronix software available online gratis, complete with GUI. Basic SainSmart USB PC-scopes with logic analyzer modules hover around $150 (watch circuit power output or you can fry your PC). None of these items are top of the line but they should get the job done at the Arduino or Rasberry Pi level.

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). $ $ :)

Its just a vritual machine.

Yeah, how...what is that?

More or less, it really helps if it's the right length (as posted near here). An easy way to make one is to calculate 246/Frequency for a 1/4 wave antenna. So around the two meter / 144 Mhz ham band: 246/144=1.5 feet. The example in the video he's at ~440 Mhz so : 246 / 440 = 0.6 feet ~6 1/2 inches. You can make a "ground plane antenna" with a connector and coat hanger wire that will improve both the reception and transmission. At 50 Mhz where lots of doorbell items are it would be 246/50: ~5 feet of wire. In which case you can go for 1/8 wave length, about 2' 7'.

Somewhere in the posts is a suggestion to build a lowpass filter and that will work. But the Pi puts off some pretty messy spectrum splatter, so before you build a good antenna take a few mins and build a narrow passband filter. It cuts the splatter below (like a lowpass) and above (like a highpass) your chosen frequency.

Better yet, go to QRZ.com and look up a ham in your area to help you out. We have parts in our vast inventory of supplies (aka junk box) to help you out.

If it doesn't have the right length, impedance, and possibly orientation it's going to be significantly less effective. Even at this scale it probably makes sense to distinguish a wire antenna from a wire on that basis.

For more powerful equipment getting the wrong wire geometry could melt your expensive setup and get you in trouble with the FCC, so it makes even more sense to tack on the word "antenna" to mean "I've thought about this chunk of metal outside the DC approximation."