I've been promissing myself that I'd convert my FT-847 to DRM use for a few years but with DRM broadcasts here in the US only being available in the early evening when I'm tied up with family matters there seemed to be little point.
However, RCI recently announced that they would be transmitting programmes throughout the month of December (2006) from 1500UTC until their normal shutdown time of 0000UTC; a whopping nine hours of programming every day! Where's my soldering iron?
A while back I ordered a cople of 455KHz-12KHz down convertors from I5XWW with a view to doing this job. These convertors use a freely available design found in a number of places on the Net. Frankly for the amount I5XWW charges for these pre-built boards it's not worth the hassle of building a convertor on a project board. I paid $15 each for them!
OK, lets get down to it. On a clean work surface (not like mine) remove both the covers from your FT-847 and place it upside down on the bench with the sockets facing you. If like mine your's is a stock radio then you will have a vacant space on the upper left quadrant. This space is earmarked for the installation of the optional CW filter. This is where we are going to install the board.
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Next make sure you have the following items;
As you can see from the picture on the right this mod is very simple and there is plenty of working space inside the 847. Lets start by mounting the convertor. I used a strip of double sided tape. Now lets tap the 455KHz IF. Locate the 8 pin IC just below the vertical SSB filter. Solder one leg of your 22pF cap to pin 2 of this IC. Pin 2 is the second pin from the right on the top row in this orientation. Next prepare a length of coax. Connect the center to the open end of the 22pF cap and the sheild to pin 4 of the chip (top row, left most pin). Be sure to check your work for solder splashes and shorts etc. Also make certain that the new parts will not come adrift and cause damage. Connect the other end of this coax to the 455KHz input of the convertor. In my case this was the top left 2 pins. |
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Take the hookup wire and attach one end to the screw terminal with the red wire on the right of the board. I used the one above the fuse. Connect the other end to the convertors power connection.
Now comes the hard bit. We have to find a space to mount the connector. As you'll see there isn't much room on the back panel and so I drilled a small hole and passed the coax cable through thus allowing the connector to hang out the back. Connect the RCA socket to the end of the cable that hangs ot of the radio. Connect the other end to the convertor output pins.
That's pretty much it. Before putting your radio back together again, fire it up to check everything is OK. You'll also have to set the output level so that there's enough to drive your sound card.
Below are pictures of the work and also of the relevant DReaM software screens. Click here for a log file and here for a sample of decoded audio.
© & ® Mark A Phillips, G7LTT 1995-2006
