[amsat-bb] Sat Tracking and SatPC32 w/ICOM rig - CT-17 hardware mod needed

Bill Dzurilla billdz.geo at yahoo.com
Sun Apr 12 12:05:57 PDT 2009

This may be old news to many but perhaps will save a few hours of frustration for newcomers.

In my prior post about HRD Sat Tracking slowness with my Windows Vista computer, I reported there that ST was working very slowly with my Lenovo desktop running Windows Vista, but that it ran at normal speed with a laptop running Windows XP. However, the frequencies were not tracking properly -- the transmit frequency would "stick" as the receive frequency on my IC-7000.

It seems there is a hardware cause for this issue. After I gave up trying to get HRD Sat Tracking to work with the laptop, I downloaded SatPC32, another program that automatically sets transmit and receive frequency to account for doppler. The same "sticking" problem occurred with that program.

The ReadMe(Icom) in SatPC32 provides what appears to be an explanation for this issue:
With ICOM half duplex transceivers (IC-706MKIIG, IC-7000) hardware
handshaking must be installed to suspend computer control while the radio
is transmitting. Frequency changes are theoretically possible while the radio
is transmitting, but frequency errors will occur, i.e., the frequencies
of VFO A and VFO B will be exchanged.

Unfortunately there is no way to check the PTT state of the radio via
the CAT software. Therefore hardware handshaking is needed to prevent
writing to the radio while it is transmitting. On the radio side pin 7
of the ACC socket can be used for this purpose. The voltage at this pin
is approximately + 8.0 V while the radio is in RX mode. In TX mode the
voltage at pin 7 drops to 0.

Pin 7 of the ACC socket must be connected with the CTS pin of the
serial port on the PC side (pin 8 of the 9-pin, pin 5 of the 25-pin
RS232 cable connector). I have connected these pins via a diode
and a 5K resistor, see Acc_Com.jpg in this sub folder.


When the radio pulls down the voltage at pin 7 to 0, it signals the PC
not to send data. As soon as the radio is back in RX mode the frequencies
are updated by the program.

ATTENTION! There must be NO bridge between pins 7 and 8 of the 9-pin
(5 and 4 of the 25-pin) cable connector at the PC side! Otherwise the
voltage at Pin 8 (rsp.Pin 5) and therefore also at Pin 7 of the ACC
socket will be pulled down and the radio will be switched into transmit
mode. The sketches in the Icom sub folder provide this bridge. If it is
built in, please, remove it.

The 25-pin Connector at the ICOM CT-17 also provides a bridge between
pins 4 and 5 and other pins. The CTS pin of the cable connector at the
PC side must be connected only to Pin 7 of the ACC socket.
Thus, as I appreciate this, a standard ICOM CT-17 CAT cable will not work properly with SatPC32, and presumably not with HRD Sat Tracking either.

Can anyone confirm this? Does anyone sell modified CT-17 cables that will do the job?

73, Bill NZ5N 


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