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Categories | Receivers: General Coverage | Funcube Help

Show all reviews of the Funcube

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KK7WM  Rating: 3/5 Jan 30, 2012 11:32  Send this review to a friend!
Best for experimenters  Time owned: 3 to 6 months
The Funcube Pro is a software defined radio contained in a USB dongle. The specified frequency coverage is 64 MHz - 1,700 MHz. However, there is a gap in coverage between 1,100 MHz and 1,270 MHz. On the other hand, most units will work down to about 55 MHz and up to over 2 GHz.

The Funcube Pro does not need USB drivers, but it is not a plug and play device. There are two main issues. One issue is that the set up information is scattered over several different documents, and assumes at least a little bit of background knowledge of SDR architectures and software. Another issue is that the unit has very high gain before the first mixer, and almost no RF filtering. As a result the front end is easily overloaded, which leads to desensitization and apparent deafness. Experienced users can work around the issues, but less experienced users who want a plug-and-play experience are likely to be disappointed.

Having used a Softrock and a FLEX-1500, I found the setup of the Funcube Pro to be reasonably easy. I went to the download page at funcubedongle.com and obtained the first three of David Barber's user guides. I then followed the instructions for downloading and installing the basic FCHid (Funcube human interface device) software, and confirmed that FCHid was communicating with the dongle. I then downloaded and set up the latest version of the Spectravue SDR software. This is downloaded from a different site than the one specified in the Spectravue user guide, but there is a link from the old site to the new site. After following the detailed instructions for setting up Spectravue the noise floor was 50 dB higher than I was expecting, and I could not receive anything. The cure was to change the microphone gain in Windows 7 from a setting of 100 down to 1. At this point the noise floor dropped to a reasonable value and I could receive several NOAA stations just above 162 MHz. (I could receive the nearest station, without any antenna all.) I could also receive local FM stations, but the audio was distorted because the spectrum of the signals of these stations is wider than the 80 kHz bandwidth of the Funcube Pro. Having established that everything was working, I did the frequency and I-Q adjustments. I then followed the step-by-step instructions on how to upgrade the FCHid firmware to a more recent version that provides greater functionality. The process went flawlessly.

In order to understand the overload problem it is necessary to know that the tuner chip used in the Funcube incorporates a low noise amplifier (LNA) that provides up to 30 dB of gain but has a noise figure of 4 dB, which is undesirably high for ham radio applications. The designers appear to have addressed this issue by adding a silicon MMIC amplifier that provides around 20 dB gain and lowers the noise figure to around 2.3 dB, which is much more respectable. However, there is now up to 50 dB of wideband RF gain before signals reach little CMOS mixers that provide up to 14 dB of additional gain! Using FCHid it is possible to set the gains of the LNA and mixer to lower values. I start off with 0 dB for the LNA and 4 dB (the lowest specifiable value) for the mixer, and only increase the gains when conditions warrant it. Relatively expert users will understand the interplay between antenna characteristics, narrow-band passive and active filtering, preamplification and passive attenuation. Less expert users may become frustrated trying to use the Funcube effectively.

There are a few other potential issues associated with noise pickup from computers (use a USB extension lead), mechanical stress on the SMA connector (use an SMA to connector-of-choice extension cable) and so on. The yahoo users group and the yahoo developers group for the Funcube are excellent sources of additional information. The yahoo users group contains more information and downloads than the funcubedongle.com web site.

Overall, I am very glad to have a Funcube to experiment with. It gives me coverage of frequencies that I want to be able to receive using an SDR system but without the costs associated with having several different narrow band converters. However, I can see why other people can have different reactions.  
Product is in production.
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