fun2audio Files

	Programs: fun2audio, funData

	The Funcube Dongle Pro+ (FCDPP) is the hardware front end
	for a software defined radio (SDR). FCDPP design details may
	be found at: http://uk.groups.yahoo.com/group/Fcdproplus/
	It was developed as part of the UK Amateur Radio Educational
	Satellite project: http://funcube.org.uk/. But the FCDPP may
	be used to receive transmissions in a wide frequency range 
	from 150kHz to 240 MHz and 420 MHz to 1.9GHz, including other
	satellite transmissions and all of the amateur radio (Ham)
	bands.

	The fun2audio and funData programs implement the data
	capture interface to the FCDPP. The device appears to the
	computer as an audio device. It mixes a selected rf signal
	down to baseband. The remaining modulation is then sampled
	with an A/D converter. It then delivers the resulting I/Q
	sample pairs via the two "stereo" channels of its USB
	interface. The samples are 16-bit signed little-endian
	integers. Sample pairs are delivered at the rate of 192kHz.

	The FCDPP frequency and signal gain are set using an
	existing program: qthid. Version 4.1 may be downloaded from
	sourceforge.net by entering qthid-4.1 in the site's
	Search window. This version implements the interface to the
	Pro+ dongle.

	The programs access the audio interface using functions
	from ALSA library: libasound. It is necessary to install
	the following packages to compile and run these programs:
	libasound2, libasound2-dev, alsa-utils. The alsa-utils
	package contains programs arecord and aplay that are needed
	to identify the audio ports used (see the program code for
	details).

	Both programs capture audio samples from the FCDPP device.
	Program fun2audio then outputs the samples to the host's
	audio port as a monaural (single) data stream. As such it
	performs as a "rudimentary" SDR radio. That is, it may be
	used to listen to CW and AM broadcast transmissions. But
	additional signal processing would be needed to demodulate
	FM and SSB signals (Project: add SSB demodulation to the
	program. Hint: consider using the Weaver method. Best for
	software implementation. Feel free to experiment!) 

	The FCDPP frequency and gain may be changed while program
	fun2audio is running. However, when a change takes place,
	the data stream in interrupted. This causes the interface
	to the host's audio port to report a data underrun error.
	Since there's nothing that can be done about this (the
	programs operate independently) the fun2audio program
	outputs a '.' character as an indication to the operator.

	Program funData simply outputs the received samples to its
	standard output port. At present the program runs for about
	five seconds before terminating. The stream may be captured
	for offline processing by redirecting it to a file. Various
	existing programs may then be used to process the data. For
	example the Audacity program may be used to read the file as
	a raw data file. The data may then be processed by the
	program's algorithms.

	The program code follows examples in document "Introduction
	to Sound Programming with ALSA" by Jeff Tranter, which is
	located at:
	http://www.linuxjournal.com/article/6735?page=0,1

	Specifically, Listings 3 and 4 were used. The article also
	provides excellent additional explanations.

	Antenna: A good antenna and shielded leadin are needed to
	get acceptable performance from the dongle. I started with
	a simple ten foot wire plugged into the dongle antenna port.
	I soon found that it was picking up noise from my desktop
	computer. So I then put up an outside "long wire" antenna. I
	got a one-hundred foot role of number 14 stranded and
	shielded copper wire (from Home Depot) and strung forty feet
	of it around my house (under the edge of the siding!) and
	connected it to the center lead of a ten-foot fifty ohm cable
	(from Radio Shack). I then connected the remaining sixty-foot
	role to the cable shield and just dropped the role to the
	ground (would be better to attach it to a ground rod). This
	antenna gives good performance over the Ham bands.

	Walter S. Heath
	(previously K8HGO in 1957!, when Sputnik was launched)
	walmarheath@comcast.net