A number of people have responded to my mailing requesting further details.
A few others responded pointing me to
www.dk9ip.de/DK9IPprojects/DK9IPdecod/dk9ipdecod.html and to
www.qsl.net/k0bx/ where information can be found on a similar mod for the
TS850. I guess this just goes to show that most things in life have already
been done! You just need to know where to find the details!
For those that asked I will describe the mod I have done. A look at the
above URLs will also be worthwhile.
My initial idea was to try to find a source of 4-bit parralel band data
(Yaesu style) within the 870. It doesn't exist as the 870 ships band data
around inside the radio in serial form. Of course this data has to be
decoded for the purpose of switching the selector relays in the Final filter
circuit. This job is done by IC1 on the Final filter board (TC9174F).
What I decided to do was to bring out 6 buffered switching lines for the six
HF contest bands to facilitate automatic switching of my Array Solutions Six
Pack and my six band Dunestars. I don't need lines for 30/17/12m but these
can be available for anyone that does.
I mounted a piece of .1 inch pitch strip board about 3/4 inch square on a
DB9 female connector. I did this by wedging the edge of the strip board
between the two horizontal sets of pins on the DB9 such that pins 1-5 of the
DB9 lined up on the centre 5 tracks of the 7 track wide strip board. Pins
1-5 were then soldered to the board. Pins 6 & 9 were wired with short wire
links to tracks at either edge of the board. I connected 6 npn switching
transistor collectors, one to each of pins 1-6 of the DB9 and all six
emitters were taken to ground. The bases of each of the transistors were
taken via a 5k6 1/4W resistor towards the back edge of the strip board to
which I attached a piece of ribbon cable.
I connected the other end of the ribbon cable to the collectors of Q10, 11,
12, 14, 15, 16 on the foil side of the Final filter board which can be
located top centre of the radio under a removable metal plate. The filter
board must be removed to make the connections. Connection is relatively
easy as Kenwood have located spare pads close and connected to the
collectors of these devices. In order to make the mod neat I didn't worry
about which of pins 1-6 on the DB9 related to which band. It turned out in
my case to be 1=20, 2=160, 3=80, 4=15, 5-40 & 6=10m. I used BC337
transistors which are good for switching up to 45V at close to an amp.
I removed the external auto ATU connector, which for me is redundant and
mounted my DB9 in its place. Anyone not wishing to remove this could
possibly feed the ribbon cable out at the back just under the case top.
I claim no rocket science here. This is just a simple mod that solves what
for me has been a significant shortcoming in the use of my Kenwood TS870 for
contesting. I pass it on to you for what it is worth.
73 and good contesting
Bob 5B4AGN, P3F, ZC4ZM
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