David, (caution, long explanation)
I am not certain how the "Black Box TL115A" achieves a splitter
function, but if it does not have smarts to allow only one RS-232 device
at a time to transmit, it will not work properly.
Similarly, a simple "Y" splitter will not work.
To answer the "why" of the problem - look at the RS-232 switching
levels. The driver level for a logic 1 (mark) is at a negative voltage
while a logic 0 (space) is a positive voltage. The actual voltage can
range from +3 to +15 volts for a logic 0 and -15 to -3 volts for a logic 1.
Imagine what happens if one device tries to send a logic 0 while the
other device tries to send a logic 1. The voltages will "fight" with
one another and the result will be garbage.
For a "Black Box" to work properly, it must act as a 'traffic cop' to
allow only one device to transmit data at a time. That means the
'traffic cop' must control the DTR and CTS control lines - and that the
two devices must honor those control lines to indicate when to send.
The Elecraft KXPA100 only connects the TXD and RXD signals, which means
it cannot honor the DTR and CTS control signals. Your ATU may be
similar. In other words, there is no 'handshaking' to tell which device
can transmit data.
For purposes of the KXPA100 (and KX3 and PX3), neither your device nor a
splitter will function correctly.
The only device that will work on a single RS-232 port with the KXPA100
(or other gear) is the SteppIR controller or other gear that can be
configured to only listen to the data between the KXPA100 and the PC (it
never transmits data). In that case, a simple "Y" cable will suffice,
no more complex "traffic cop" device is needed.
You did not say what ATU you are trying to connect, so I can't say how
it applies to this situation. If it only listens to the data (either
has no driver on the DE-9 pin 2 signal [RXD] or disables that driver),
then it will work with a "Y" splitter cable, but otherwise it will
conflict with data sent from the KXPA100 to the PC.
73,
Don W3FPR
On 2/6/2017 10:12 PM, David Orman wrote:
Hi,
I picked up a modem splitter (Black Box TL115A) and tried to make this work
with no luck. If I connect my computer's output directly to the KXPA100
serial out cable, it works fine. If I connect the ATU to the KXPA100 serial
out, it works fine. If I put the splitter in place, even if I only just
connect the computer, I cannot communicate with the KXPA100. Same re: the
ATU. Connecting both does not work either. I did get these devices off eBay
(I was shipped two, actually) but neither appears to work - not sure if
this is faulty adapters or if this mechanism just doesn't work in general.
I only spent $10 on them, so it's no big loss, but I'd sure hate to go
spend $80 on the BCE model to have the same results.
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