On 9 May 2005 15:08:07 -0700, wrote:

From: Paul Keinanen on Sun,May 8 2005 11:54 pm

While a backplane would not be suitable for running the RF signals, it
would be a good idea to have a common control interface standard. This
might be some sort of serial interface or perhaps a CANbus interface
as used on some AMSAT satellites.

Who says a "backplane would not be suitable?" :-)
Those PC backplanes carry terribly broad spectra of
RF...from (literally) DC on up to the low microwaves.
No "perhaps" about it. Thing is, the layout can NOT
be done as if it were wire-wrap; i.e., in random
order of wire placement.

The PCI signals must run on transmission lines, since the receiver is
not activated by the for forward wave, which is reflected by the
mismatched end of transmission line and the receiver is only activated
by the combination of the forward and reflected wave. So indeed, the
layout is critical to get the signal through, even if no crosstalk
problems would exist.

With broadbanding anything,
every single adjacent trace becomes a COUPLER and
unwitting layouts can produce remarkable crosstalk
effects. Designers have known that for decades and
handle it...all kinds of Application Notes and info
out in public access available for anyone...just too
specialized for the "weekender" small-project
assembler hobbyist.

In a PC, the signals are all around a few volts, thus the crosstalk
problems are not so bad. In a radio receivers, the signal levels vary
from less than a microvolt to several volts, so the crosstalk issues
are much more demanding. Microstrip transmission lines would hardly be
enough, at least striplanes with grounded traces between the signal
conductors in the middle layer would be required, so the minimum would
be a 3 layer PCB.

The IEEE-488 is a mature standard for control and
interface for computer-controlled, interconnected
systems. Would be a bit TOO all-inclusive for a
special-purpose new design. The "interface" does
NOT have to be some kind of "new" thing used on the
latest whatever out in space.

The IEEE-488 requires a lot of signals and a complex handshaking, so
in practice, you would need an interface chip anyway.

The CANbus has been used in the automobile industry for more than a
decade. The CANbus has a nondestructive collision system, so this
makes it possible to have a true peer-to-peer communication system,
without complex protocols (such as token passing).

The AMSAT thing I was referring to is a standard PCB, with a size
about a D connector, with an interface chip on it and it has a few
digital signals. It is included in every module on the bigger AMSAT
birds. This bus structure greatly simplifies the wiring between
modules.

Paul OH3LWR