This lead is also used for cloning data between 2 FT-847's and is shown on the Make a Yaesu cloning cable page. If you have other Yaesu radios that use a "Null Modem Cable" you may wish to make Yaesu Null Modem CAT cable instead which is fully configured. Other Yaesu radios use a "Standard Serial Cable". To be sure which one you require check your manual, if it states "Null Modem" then this is the one, if it states "Standard Serial" then go to the Yaesu Standard Serial CAT Cable page.
I will only deal with a 9 pin serial port here as the 25 pin serial ports "died out" a while ago. If people ask I will add the 25 pin connection at a later date.
I made one of these leads a while ago for a local chap who was wondering why a null modem cable (as is stated in the manual) was so expensive (£6 plus, depending on where you look). I've also had a couple of emails about this lead too.
It only took me a couple of minutes to make up after a root through my junk box for the bits (I have loads of old PC stuff). I also made one recently for the Club (again my junk box supplied the bits) so the FT-847 can interface with a laptop and, using Ham Radio Deluxe software, can put a voice to the frequency etc.
A proper PC Null Modem cable comes fully wired but a check of the FT-847 schematic shows that only the Data Rx, Data TX and Ground are connected, the Data TX at one end is connected to the Data RX at the other end, making a cross over lead. See the diagram for details.
Simply solder one wire to pin 2 on P1 and pin 3 on P2. Repeat with the other wire, using the, as yet, unused pin 2 (P2) and pin 3 (P1).
If you have a 3 core plus shield cable, solder the 3rd wire to pin 5 on each plug and solder the shield to each plugs' metal casing.
If you have a 2 core plus shield cable, use the shield for the pin 5 connection.
After checking the soldering is good and there are no shorts or stray whiskers, assemble the shrouds around the plugs and you're ready to go.
I've also been asked how to modify this cable to use it on a PC with a USB port and no serial port.
Short of purchasing or building a USB to Serial adaptor I have no other remedy.
I can report that the USB to Serial adaptor using the Prolific Chipset works well with this, although Windows 7 had a problem installing the adaptor until I visited the Prolific website and downloaded the latest drivers.