[Elecraft] [KX3] RS232 xcvr control when serial ports are occupied

[Don Wilhelm]

Steve,

Yes, since you are using both the KXUSB and the KXSER cables, a "Y" at 
the KXPA100 would serve you well.
If your magloop controller also attempts to transmit, you can remove the 
connection to pin 2 on the DE9 end of the KXSER cable (just remove the 
backshell and disconnect the wire).

RS-232 multiplexors are complicated devices and require the use of the 
full RS-232 bus (mainly DTR and CTS signals) to handle the handshaking 
signals.  The 3 conductor KX3/KXPA100 wiring will not provide the proper 
handshaking signals.
The handshaking signals are not provided from the data stream (as they 
are in Ethernet and other communications protocols), but from the 
explicit signals separate from TXD and RTS.

Note that the KX3 (and most other Elecraft products) rely only on TXD 
and RTS, which are reserved for data transmission only in the RS-232 
scheme of things.

73,
Don W3FPR

On 7/8/2018 4:56 PM, Stephen Rector wrote:
> Hi Don:
> 
> Yes - it occurred to me after sending the post that I might be able to create the split at the KXPA with a stereo Y-cable/connector. I am using a KXUSB to the computer, with a KXSER cable going from the the antenna controller to the KXPA. It is the KXUSB that presently has no place to connect to.
> 
> So - I think I can try a 3.5mm stereo y-junction at the KXPA. Hopefully impedances won't be an issue at 38400 baud...
> 
> I did look for RS232 multiplexers - they seem to exist for industrial applications. The documentation seemed to be sparse on the web.
> 
> Anyway - thanks for the pointer :)
> 
> 73,
> 
> Steve NU7B
> 
> 
>> On Jul 8, 2018, at 1:37 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
>>
>> Steve,
>>
>> Are you using the KXUSB to connect with the KXPA100/KX3, or are you using the KXSER with a real computer serial port or a USB to serial adapter?
>>
>> Since your magloop controller only 'sniffs', it means it should only listen and never try to transmit on the RS-232 signal lines.  If it only listens, there will be no collisons (RS-232 is not packet oriented, but an asynchronous communications system).
>>
>> If the magloop controller also transmits on the RS-232 bus, you will need some external device to act as "traffic cop" - note that RS-232 is a point to point system (unlike Ethernet and others) where there is one driver device and one receiver at each end.
>>
>> So yes, you can use a splitter - one with a 3.5mm stereo plug and two 3.5mm stereo jacks if using the KXUSB.
>> If you are using the KXSER cable instead, yes, you can connect a "Y" DB9 splitter to the DB9 end of the KXSER cable - the computer connects to one side and the magloop controller connects to the other side of the "Y".
>>
>> On 7/8/2018 3:31 PM, Stephen Rector via Elecraft wrote:
>>> Hy home station is a KX3 + KPXA100, and I can control the radio via the RS232 port on the KXPA. However, recently I added a Ciro Mazzoni magloop to the station, and its controller plugs in to the KXPA serial port to sniff for frequency information, allowing re-tuning on the fly. This leaves no RS232 port left for remote control of the radio.
>>> How do I modify this arrangement to add an extra serial port for KX3 control? My first thought is that, since the antenna controller just sniffs for data, I could add a DB-9 Y-cable to provide the extra port at the controller serial port location. However, packets could still collide ...does the protocol handle this? Is there some sort of multiplexer available?
> 
>