[aprssig] RE: D710 standalone control head!

Darryl Smith Darryl at radio-active.net.au
Mon Oct 1 16:19:35 CDT 2007

G'Day All. 

Unfortunately I missed the DCC in person - I left my decision not to go
until about 7 days before the event, but in the end I needed to stay home to
look after a sick relative who has just been through cancer treatment... 

I have a few guesses with regard to this product. Kenwood has a fairly
reasonable control protocol through the data connector of their radios. I
found this out when I decoded the protocols for the D7/D700, and I have used
this in the past for some consulting work. There is no reason why a 2m/70cm
radio cannot be built without any display, and with only external control
via something like the D710 control head. 

Of course the Kenwood control protocol is probably not ideal operating at
only 9600 bps. For responsiveness I would probably want a bit faster, but
that is not to say it would not work. It was interesting that Kenwood did
not bother releasing the protocol until I had reverse engineered it (with
some help from some other hams)

I have never actually got around to looking at the data between the D700
control head and the main unit. I have just looked at the
KENWOOD_TMD700AE_MAINTENANCE_MANUAL which I have as a PDF, and it told me a
few things. The control head IC 4 connects to the main unit IC 604 via a
UART. I am guessing that this is an RS232 connection. I have not seen a
schematic, but buffers are being used (IC1/2 in the control head). The
buffers seem to be just comparators, so some level shifting would be needed
to go to RS-232 levels.  

I would be inclined to suspect that the D700 uses the kenwood protocol that
we know about for the control head, except for one problem - as far as I can
tell there is no command to turn the unit on and off with the standard
protocol. So this might be missing. The other issues are sending volume and
squelch to the main unit, and also showing GPS data at the same time as
signal levels. This gets messy with the known protocol. 

I am guessing that the D700 has its own protocol for talking between control
head and main unit. So here is the question - how would the D710 be
controlling the main radio - if it does. 

I am guessing something like high frequency tones on the TX and RX signals
to the radio, modulated with RS232. Since Ham Radio only has a limited voice
bandwidth, if you had a 38 KHz oscillator, and turned this on and off
depending on if the RS232 was high or low, this should not affect anything
at all. It would be compatible with just about any other equipment out there

I guess the first thing to do is to actually get access to this new radio
for a few days with a CRO :-)


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