Radio/RFI - Revision history

Admin at 05:52, 22 May 2016

2016-05-22T05:52:54Z

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			NOTE: This page has incorrect/outdated/wrong material on it. Use at your own risk.

	These notes use a web-based software defined radio to explore some concepts around radio - specifically, radio frequency interference (RFI).		These notes use a web-based software defined radio to explore some concepts around radio - specifically, radio frequency interference (RFI).

Admin: /* Voice Signals */

2016-05-22T05:50:43Z

Voice Signals

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	===Voice Signals===		===Voice Signals===

	Voice traffic is easy to spot, because it's always 3 ~~MHz~~ wide. This shows a whole bunch of voice signals on one side of the 40 meter band:		Voice traffic is easy to spot, because it's always 3 kHz wide. This shows a whole bunch of voice signals on one side of the 40 meter band:

	[[Image:VoiceWidth.png\|500px]]		[[Image:VoiceWidth.png\|500px]]

	A note on SSB, USB, and LSB: to transmit a voice signal, you use up 3 ~~MHz~~, but you have to pick a single frequency to transmit on, as your primary transmission frequency. The additional 3 ~~MHz~~ of bandwidth used can either be above or below the nominal frequency you're transmitting on. If it's above, you're using USB. If it's below, you're using LSB.		A note on SSB, USB, and LSB: to transmit a voice signal, you use up 3 kHz, but you have to pick a single frequency to transmit on, as your primary transmission frequency. The additional 3 kHz of bandwidth used can either be above or below the nominal frequency you're transmitting on. If it's above, you're using USB. If it's below, you're using LSB.

	Here's a tour of some voice signals on CW from the Hack Green WebSDR station, to give you an idea of what they sound and look like:		Here's a tour of some voice signals on 40 m from the Hack Green WebSDR station, to give you an idea of what they sound and look like:

	<embedvideo service="vimeo">https://vimeo.com/134893337</embedvideo>		<embedvideo service="vimeo">https://vimeo.com/134893337</embedvideo>

Admin: /* What Is RFI? */

2015-07-30T00:07:48Z

What Is RFI?

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	(photo from Wikimedia Commons)		(photo from Wikimedia Commons)

			(Also check out the [https://xkcd.com/273/ XKCD version] of the electromagnetic spectrum)

	This means there's a limited amount of space in the radio spectrum, with a lot of different applications that can use it. Which technologies use which frequencies depends on many factors. Among other things, it can be a function of the range required by the wireless transmissions - signals at higher frequencies dissipate their energy faster, and carry for a shorter distance. You wouldn't want to use a frequency for wireless internet that propagates for miles! Likewise long-range aircraft communication would need much different signal properties than a hands-free Bluetooth headset.		This means there's a limited amount of space in the radio spectrum, with a lot of different applications that can use it. Which technologies use which frequencies depends on many factors. Among other things, it can be a function of the range required by the wireless transmissions - signals at higher frequencies dissipate their energy faster, and carry for a shorter distance. You wouldn't want to use a frequency for wireless internet that propagates for miles! Likewise long-range aircraft communication would need much different signal properties than a hands-free Bluetooth headset.

Admin: /* What Is RFI? */

2015-07-30T00:07:18Z

What Is RFI?

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	(photo from Wikimedia Commons)		(photo from Wikimedia Commons)

	This means there's a limited amount of space in the radio spectrum, with a lot of different applications that can use it. Which technologies use which frequencies depends on many factors. ~~It's~~ a function of the ~~distance~~ required - ~~the~~ higher a ~~signal's frequency, the~~ shorter ~~its range~~. ~~And you don~~'t want to use a frequency for wireless internet that propagates for miles!		This means there's a limited amount of space in the radio spectrum, with a lot of different applications that can use it. Which technologies use which frequencies depends on many factors. Among other things, it can be a function of the range required by the wireless transmissions - signals at higher frequencies dissipate their energy faster, and carry for a shorter distance. You wouldn't want to use a frequency for wireless internet that propagates for miles! Likewise long-range aircraft communication would need much different signal properties than a hands-free Bluetooth headset.

	What this means is, each chunk of the frequency spectrum is allocated to a particular purpose. (~~This is what the~~ FCC regulates.) Some chunks are dedicated to amateur radio, some chunks are dedicated to wireless internet, some chunks are dedicated to aircraft radio broadcasts.		What this means is, each chunk of the frequency spectrum is allocated to a particular purpose. (The FCC regulates this.) Some chunks are dedicated to amateur radio, some chunks are dedicated to wireless internet, some chunks are dedicated to aircraft radio broadcasts.

	It's important - particularly in that last example - that different applications and devices don't interfere with each other. It could be disastrous if a company started selling microwaves and refrigerators that created interference on a frequency critical for infrastructure, like an aircraft communications channel. So the concept of radio frequency interference is a very important one.		It's important - particularly in that last example - that different applications and devices don't interfere with each other. It could be disastrous if a company started selling microwaves and refrigerators that created interference on a frequency critical for infrastructure, like an aircraft communications channel. So the concept of radio frequency interference is a very important one.

Admin at 00:05, 30 July 2015

2015-07-30T00:05:08Z

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	~~Today we're going to~~ use a web-based software defined radio to explore some concepts around radio - specifically, radio frequency interference (RFI).		These notes use a web-based software defined radio to explore some concepts around radio - specifically, radio frequency interference (RFI).

	=What Is RFI?=		=What Is RFI?=

Admin: /* RFI All Around Us */

2015-07-29T23:58:22Z

RFI All Around Us

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	Here's an excellent deep dive into RFI around the home: http://randombio.com/interference.html		Here's an excellent deep dive into RFI around the home: http://randombio.com/interference.html

			=HackRF One=

			While these WebSDR stations are fun to listen to, it would also be nice to listen in on more frequencies, and do so locally.

			Enter the HackRF One. With a HackRF One and a good antenna, you can replicate this process with a much wider range of signals. I'm currently assembling some notes on exploring the radio frequency spectrum with the HackRF, so stand by for more...

	[[Category:Radio]]		[[Category:Radio]]
	[[Category:Ham Radio]]		[[Category:Ham Radio]]
	[[Category:Electronics]]		[[Category:Electronics]]

Admin: /* RFI All Around Us */

2015-07-29T23:52:46Z

RFI All Around Us

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	[[Category:Ham Radio]]		[[Category:Ham Radio]]
	[[Category:Electronics]]		[[Category:Electronics]]
	~~[[Category:Circuits]]~~

Admin: /* Interference */

2015-07-29T23:50:47Z

Interference

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	[[Image:InterferenceHorizontal2.png\|500px]]		[[Image:InterferenceHorizontal2.png\|500px]]

	~~This type of interference~~

	=RFI All Around Us=		=RFI All Around Us=

Admin: /* RFI All Around Us */

2015-07-29T23:44:07Z

RFI All Around Us

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	You can find RFI anywhere and everywhere. Even when there are no electronic circuits around, there are many natural forces creating electromagnetic waves. Our man-made environment just serves to increases the abundance of noise on different frequencies.		You can find RFI anywhere and everywhere. Even when there are no electronic circuits around, there are many natural forces creating electromagnetic waves. Our man-made environment just serves to increases the abundance of noise on different frequencies.

			<!--
	Here's an example of the kind of noise you can find all around. I flicked on a handheld 2 meter transciever, and scanned the band listening for signals.		Here's an example of the kind of noise you can find all around. I flicked on a handheld 2 meter transciever, and scanned the band listening for signals.
			-->

	Here's an excellent deep dive into RFI around the home: http://randombio.com/interference.html		Here's an excellent deep dive into RFI around the home: http://randombio.com/interference.html

Admin: /* Visualizing RFI */

2015-07-29T23:43:51Z

Visualizing RFI

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	[[Image:InterferenceProtocol.png\|500px]]		[[Image:InterferenceProtocol.png\|500px]]

			Finally, there are horizontal interference signals. The first one is actually sweeping upward through the entire band: see how it drifts downward (moving in time) as it sweeps through the frequencies?

			[[Image:InterferenceHorizontal1.png\|500px]]

			And the second horizontal interference signals are thick bands that show up occasionally:

			[[Image:InterferenceHorizontal2.png\|500px]]

			This type of interference

			=RFI All Around Us=

			You can find RFI anywhere and everywhere. Even when there are no electronic circuits around, there are many natural forces creating electromagnetic waves. Our man-made environment just serves to increases the abundance of noise on different frequencies.

			Here's an example of the kind of noise you can find all around. I flicked on a handheld 2 meter transciever, and scanned the band listening for signals.

			Here's an excellent deep dive into RFI around the home: http://randombio.com/interference.html

	[[Category:Radio]]		[[Category:Radio]]