[amsat-bb] FT736R cable

Greg D ko6th.greg at gmail.com
Tue Mar 24 05:12:27 UTC 2015

The FT-736R definitely has a serial interface, but it's not USB. It's 
the old style serial, aka "RS-232" or "Com port", except the signal 
levels are TTL (0-5v) instead of proper RS-232 (-12 to +12 usually).  
Actually it's +12 to -12, i.e. inverted in sense compared to TTL.  So 
one needs a level shift and invert, which is what the circuit is for, 
and that then needs to plug into a Serial port.

Most computers built in the last several years (decade?) don't have 
serial ports, having replaced them for peripheral attachments with USB 
ports.  Some computers have more USB ports than my car has cup holders.  
The difference is protocol - what information gets sent over the wires - 
and there USB is very different than simple Serial.  If your computer 
doesn't have a serial port, you need to buy a USB to Serial adapter, and 
then plug the referenced circuit into that.

What Daniel refers to on sites like eBay are essentially the combination 
the two parts.  They have a USB to RS-232 adapter, and the level 
shifter/inverter, all in one package.  Good deal if you don't feel like 
a soldering project, but, yes, watch out for the drivers.

Regarding the circuit, if your program only sends commands to the 736, 
and never reads information from the 736 (I don't know of any that do), 
then you can simplify the diagram to just R1 and Q1. Either way, I would 
recommend you add a small diode (1N4001 or 1N914) between the Base of Q1 
and ground (the Emitter pin), cathode at the Base, to protect Q1 from 
the negative swing of the RS-232 signal.

Good luck!

Greg  KO6TH

Daniel Cussen wrote:
> Here is the wiring of a serial interface
> http://www.mindspring.com/~n2wwd/html/body_doppler_compensation.html
> For usb to TTL  you need 5V TTL logic and presumably similar
> connections and baud rates.
> If you look on ebay you can see people selling them and the rig end
> needs the right connector, a 6 pin DIN.
> You connect the TX of the USB lead to the RX on the radio (pin3) and
> the output of the rig (pin 2) to the RX on the USB converter and pin 1
> to ground.
> You probably don't need the pin 6 connection as the converter will be
> supplied by the USB power.
> Make sure to get a USB cable with drivers available for your current
> operating system and ideally a common one so that drivers will be
> available in many years time for future systems.
> Ideally if you could afford it a fully isolated interface would be better.
> On 23/03/2015, ingejack at cox.net <ingejack at cox.net> wrote:
>> Need to know what USB cable that FT736R users  are using to connect their
>> computer and SATPC32 with. It calls for a RS232 TTL cable but need to know
>> what company and cable descrition they are using if possible., Thanks for
>> any help !!  Jack/KC7MG
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