[Elecraft] K3 auxbus support

[wayne burdick]

George,

Thanks for bringing up this important issue. (The information below 
will be added to the FAQ when we get it going.)

The K3 will provide backward compatibility with some, but not all K2 
auxBus peripherals. It will support the transverters and KRC2, but 
probably not the KAT100 or KPA100. If there's a way to make them work 
in the future we'll add support, but not in the first release of the 
transceiver, and probably not this year.

In general, K3 auxbus device control will be limited to receive-mode 
communications. This means we can detect and set up auxbus devices at 
power-up, as well as send them band-change commands.

Here's the reason for our hesitance to support transmit-mode auxbus 
devices, such as the KAT100 and KPA100:

Like most modern transceivers with extensive computer support, the K3 
is the nexus for many low-level I/O signals (soundcard inputs and 
outputs, panadapter output, external reference input, etc.). The 
location of all these signals is the KIO3 module. This is also where 
our "ACC" connector is that has the auxBus line.

Since the KPA100 and KAT100 make heavy use of the auxBus during 
transmit, there's the potential for RFI on these low-level signals 
lines during transmit at high power, through inadequate shielding, 
ground loops, or just proximity. It would take much more shielding, 
multilayer PC boards, and more complex internal and external cabling to 
ensure that this wasn't a problem. This would greatly increase the cost 
of the K3.

We'll review what devices we can control as we start to do more complex 
system tests.

73,
Wayne
N6KR

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