A Panadapter for the yaesu FT-817 using the Funcube Dongle
An interesting new SDR receiver called the FUNcube Dongle recently went on sale in support of AMSAT-UK’s FUNcube satellite project. The unit is a self contained SDR receiver that can cover 64 MHz – 1700 MHz. It is USB based. Under Windows, it shows up as a sound card. No special drivers are needed. It works with most SDR software that supports I & Q. It includes an LNA, tuner and audio card built into a small package. The RF input is SMA. 96kHz is the quadrature sampling rate. Once the ADC’s decimation filter skirts have been taken into account, you have about 80kHz.
When I first saw the receiver, I thought of using it as a Panadapter for weak signal work with my 10 GHz and up gear. It would tune 144 MHz and 432 MHz which are the two IF’s I use with my transverters. One issue is that I would have to unhook my IF and connect the Dongle in its place. To transmit, I’d have to reconnect my IF. I could hook up RF switching but it was not the ideal situation. When the FUNCube was first shown at a N.E.W.S. meeting it was suggested that possibly it could be used by tapping the common IF in the rig used with a transverter. This intrigued me.
I looked into my FT-817 and saw that it used a common 68.33 MHz IF. This looked perfect as the FUNCube could tune that easily. Also being a common IF, it would be the same regardless of whether I used 144 or 432 MHz with the FT-817.
The first step was to identify a location to tap the common IF. In looking at the schematic, there is a point just before the first crystal filter (XF1001) that looked like a good candidate.