I found I need to frequently operate my main station from another location. I successfully got my Icom IC-7610 working using a combination of Icom’s RS-BA1 software for radio control and audio transport and TeamViewer to remote in to the PC at my station. It isn’t quite like being there, but it’s far better than not operating.
Much of that operating has been low power because I was
unable to turn on my 1999-vintage Acom 2000A amplifier remotely. I run M0YOM’s great AcomDirector utility to control the amplifier once it’s turned on, but that initial
turn-on task required a physical interface I lacked – or a physical journey to the main
station to push the button.
I bought Acom’s RP-ON product to fill that gap and allow full
remote control of the amplifier. I plugged it in, hooked it up to my computer,
and … nothing! What a disappointment! I tested the RS-232 connection to determine the viability of the
control lines and I verified the signals were indeed correct. I consulted the priceless
collective wisdom on the Acom-List@groups.io
email reflector. Replies were quick and helpful. Many thanks to WC2L, N6TV, and
K5WA for their advice that got this working!
Long story short: an extra 10k resistor across R3 fixed my
problem (see the attached figure). For the long story not as short, read on.
Upon examination of the circuit, it is very simple. When
either pin 6 or pin 8 on the RS-232 COM port goes high, it applies a voltage to the gate of Q1 to pull pin 5 on the RCU connector to ground. Pulling that pin 5 to ground
turns on the amp. C1 is (I assume) there to prevent short-term spurious signals
from activating pin 5.
The Acom Director software sets both DB9 COM port pins 6 and
8 high. I verified this in testing. This makes the voltage on Q1’s gate higher,
thus better ensuring a good ground for RCU pin 5. It’s important that the COM
port supplies enough voltage and current. Apparently, some USB-to-RS-232
converters do not fulfill this requirement. My particular situation uses a real
RS-232 COM port on the PC, so that’s not my issue.
When I analyzed the voltage divider, something seemed awry. It
has a 2.4k resistor from the gate to ground and a 10k resistor from the gate to
12v that is supplied by each COM port pin. With just one COM pin active, the
voltage on Q1’s gate would be (2.4/(2.4+10))*12 = 2.32v. Since Acom Director
sets both COM pins high, the 10k resistors are effectively in parallel,
yielding 5k total resistance. That will make the gate voltage (2.4/(2.4+5))*12
= 3.89v. I haven’t yet investigated whether that is insufficient to pull RCU pin 5
completely to ground, but I thought that might be the case.
The Acom-List members (WC2L especially) relayed the recommendation from Acom in Bulgaria to add parallel 10k resistors. This is mainly to help with USB adaptors, but it obviously was my problem too. Adding one more 10k resistor (now 3 in parallel) should set Q1’s gate voltage to (2.4/(2.4+3.33))*12 = 5.05v. I carefully soldered an extra 10k resistor across surface-mounted R3 (see photo). Voila! It worked! I haven’t yet measured the gate voltage to confirm my calculation.
I don’t know if adding yet another 10k across R2 will help.
It should theoretically bring the gate voltage to (2.4/(2.4+2.5))*12 = 5.877v,
but my fix works, so I’m not going further. I live by the folksy old adage, “If
it ain’t broke, don’t fix it.” It ain’t broke anymore! I am now a happy boy,
able to power up my 2000A remotely!
VY 73 de Glenn K3PP
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