From: Paul Keinanen on 10 May 2005 09:11:19 -0700

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.

But...there CAN be COUPLING there and that is, very
definitely, part of the layout. When mixed with
analog signals - as would be the case in a "radio" -
the layout can be critical.

In a PC, the signals are all around a few volts, thus the crosstalk
problems are not so bad.

Look again at the 3.3 V logic thresholds. :-)

In a radio receivers, the signal levels vary
from less than a microvolt to several volts, so the crosstalk issues
are much more demanding.

I will disagree on radio receivers on such wide dynamic
ranges. "Several volts" INTO a receiver front end?
No. Such levels aren't encountered in practical
locations and would, definitely, cause enough IM
that would create much distortion and spur products.

In radio transmitters, YES, but those stages can be
individually shielded and thus isolated...do NOT
need to be close to the control lines...or even need
control lines (in the case of an amplifier block).

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.

Not the case in practical RF structures done in
the last three decades. [been there, done that,
got lots of T-shirts] It is BETTER to have good
stripline and microstrip as opposed to "ordinary"
PC layout, but that isn't an absolute necessity.


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

That was cited solely as an example of something
that IS mature and used daily in radio-electronics
testing.

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).

IF and only if this SDR of the future NEEDS micro-
computer control...or even modular microcontroller
sub-systems.

Trying to use an EXISTING computer interface system
isn't always good because that system has worked for
a decade-plus. While automotive computer interface
system speeds are increasing with increasing control
demands, radios aren't quite vehicles. The control
needs aren't quite the same.

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.

I've had hands-in on earlier unmanned spacecraft but
understand the principles...which are similar to the
interface chips for things like USB adapters to work
with Serial or Parallel port peripherals with PCs.
One SOC (System On a Chip) that is essentially a
dedicated mircocontroler is all that is needed.
[FTDI makes those chips, Mouser sells them]

What you describe is more like an outgrowth of the
existing microcontroller adaptation to amateur
radio (and, more, to commercial radio) equipments.
The front panel controls are coupled (mostly) via
DC lines to the actual signal controls on PC boards
to reduce the mechanical complexity...which allows
greater freedom of layout and compactness.
[positive attributes for spacecraft as well]

My "ancient" Icom R-70 receiver has a central
microprocessor doing a great number of control
tasks...and does have some external control
capability through a rear connector. At about
two decades old, that's just one example of what
already existed - in radios - some time ago and
still does. Modern amateur transceivers usually
have two microcontrollers. Some of those allow
external control and a few are entirely controlled
externally. The basics have already been laid
down for the SDR system on what CAN work.

What is lacking is STANDARDIZATION. That can't be
worked out in newsgroups, but requires much more
organization...and willingness to compromise
(almost impossible in newsgroups, heh heh). See
any of the industrial standards (EIA, AES, etc.
in the USA) which are the first steps towards
making ANYTHING "plug and play." Example: The
Cannon "D" connector was on the market in the
early 1950s. A combination of factors made it a
practical connector line used in many electronic
things. Eventually, it became so common in the
USA that it was Standardized in shape, materials,
dimensions, etc., despite the original company
changing in corporate evolution. Wide use made
it "standard." The 25-pin and 9-pin D connectors
are on practically every PC today...as they were
in the beginning of the PC in 1981.

Standardization isn't anywhere close to reality
for SDR now. Nobody can seem to agree on WHAT
range of control is needed, let alone details of
the controlling interface signals. :-) That
might work itself out later.

On 10 May 2005 13:59:13 -0700, wrote:

From: Paul Keinanen on 10 May 2005 09:11:19 -0700

In a radio receivers, the signal levels vary
from less than a microvolt to several volts, so the crosstalk issues
are much more demanding.

I will disagree on radio receivers on such wide dynamic
ranges. "Several volts" INTO a receiver front end?
No. Such levels aren't encountered in practical
locations and would, definitely, cause enough IM
that would create much distortion and spur products.

Look at a multitransmitter contest site with one transmitter on each
band, the voltage induced to the receiving antennas for other bands
can be quite large. Of course, in a competent receiver design only the
frequency band of interest is filtered out before processing. However,
if the antenna is connected directly to the backplane and the modules
do their own filtering, the large composite signal on the backplane
will radiate all around the system.

In non-contest sites large wire or log-periodic antennas can collect a
quite large signal voltage (in the order of 0 dBm, 220 mV or more).

Also if the final IF is within or below the receiver tuning range and
a diode ring mixer is used as the SSB demodulator with +7 or +17 dBm,
you must keep this BFO signal and harmonics from entering the front
end.

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).

IF and only if this SDR of the future NEEDS micro-
computer control...or even modular microcontroller
sub-systems.

Trying to use an EXISTING computer interface system
isn't always good because that system has worked for
a decade-plus. While automotive computer interface
system speeds are increasing with increasing control
demands, radios aren't quite vehicles. The control
needs aren't quite the same.

Even the SDR is going to need some switchable front end band pass
filters in order to survive in the hostile RF environment these days
with a lot of strong signals even in ordinary sites.

In transceivers, there would be several points that would need
switching.

I used the CANbus as an example, since the cable can be tens or
hundreds of meters long depending on speed and thus, it could be used
to control some internal points in a transceiver as well as wire all
devices in the ham shack as well as in the tower. For instance, the
same controller could control the antenna rotator, command the antenna
preamplifier to bypass mode, turn the transvertter into transmit mode,
select the VFO frequency for transmit (in split operation) and finally
turn the transmitter on.


examples of previous control systems deleted

The basics have already been laid
down for the SDR system on what CAN work.

What is lacking is STANDARDIZATION.

This is definitely a big problem.

That can't be worked out in newsgroups,

A newsgroup is a good place for open ended discussions between people
with experience in quite different fields. This can generate quite
different ideas (some useful, most less usable) than a "business as
usual" attitude. It is a good idea to have a lot of new ideas to chose
from than having no new ideas at all.

but requires much more organization...

Writing a formal specification may require some formal organisation,
but on the other hand quite a few successful RFCs in the IT sector are
written by a single person or a small group.

and willingness to compromise

That is the problem in formal committees, in which most delegates from
various vendors have large commercial interests in the subject and in
order to be able to produce even some kind of standard, all features
from various vendors are included. This makes the final standard hard
to implement properly or each manufacturer is implementing only a
subset of the complex standard and thus, there is no real guarantee
that two devices would actually communicate, even if both claim
compatibility with xxxx standard (remember the RS-232 "standard" :-).

Paul OH3LWR

From: Paul Keinanen on Wed,May 11 2005 12:13 am

On 10 May 2005 13:59:13 -0700, wrote:

From: Paul Keinanen on 10 May 2005 09:11:19 -0700

In a radio receivers, the signal levels vary
from less than a microvolt to several volts, so the crosstalk issues
are much more demanding.

I will disagree on radio receivers on such wide dynamic
ranges. "Several volts" INTO a receiver front end?
No. Such levels aren't encountered in practical
locations and would, definitely, cause enough IM
that would create much distortion and spur products.

Look at a multitransmitter contest site with one transmitter on each
band, the voltage induced to the receiving antennas for other bands
can be quite large.

In a production model receiver? Mais non. That's
not a design prerequisite, never was, not even with
the Rhode & Schwarz designs featuring very high
3rd IP specifications.

I've been IN such situations on aircraft installations
where the potential RFI was much stronger than in ham
DXpedition or Field Day setups. The work-arounds to
make the receivers operate is NOT a design criteria,
not in avionics-oriented design plans.

Of course, in a competent receiver design only the
frequency band of interest is filtered out before processing. However,
if the antenna is connected directly to the backplane and the modules
do their own filtering, the large composite signal on the backplane
will radiate all around the system.

Possibly, IF and only IF the antenna IS connected
to the "backplane" (or motherboard). Why must it be
so? Look at the PC. Sound cards have their audio
input (at microphone levels) on a separate connection).
No interference doing that.

In non-contest sites large wire or log-periodic antennas can collect a
quite large signal voltage (in the order of 0 dBm, 220 mV or more).

Perhaps, but that still isn't a design criterion for
present-day ham receivers.

Also if the final IF is within or below the receiver tuning range and
a diode ring mixer is used as the SSB demodulator with +7 or +17 dBm,
you must keep this BFO signal and harmonics from entering the front
end.

Yes...but that was a problem a half century ago, too! :-)


Even the SDR is going to need some switchable front end band pass
filters in order to survive in the hostile RF environment these days
with a lot of strong signals even in ordinary sites.

Diode switching. My two-decade old Icom R-70 has that
to select approximate octave-bandwidth bandpass filters
to cover 50 KHz to 30 MHz. Has its own little PCB,
probably because every single L, C, diode, and resistor
is included on that board...no shielding except from
the side wall of the cabinet and part of the cast frame.

I've had that little receiver within a city block from
AM BC station KMPC running 50 KW into its towers. Worked
fine with a temporary long-wire antenna despite the RF
around that station.

In transceivers, there would be several points that would need
switching.

Of course. That's what was done two decades ago.

I used the CANbus as an example, since the cable can be tens or
hundreds of meters long depending on speed and thus, it could be used
to control some internal points in a transceiver as well as wire all
devices in the ham shack as well as in the tower. For instance, the
same controller could control the antenna rotator, command the antenna
preamplifier to bypass mode, turn the transvertter into transmit mode,
select the VFO frequency for transmit (in split operation) and finally
turn the transmitter on.

Right, no problem...except for the individual ham
installer who then has to set up the "program" to
do all those things. Can they? :-)

I think a better approach is something like SGC does
in their automatic antenna tuners. They add a
frequency meter function to their tuner micro-
controller, a small section of Flash memory to
hold data, measure an RF input, adjust the coupler
switches to compensate for VSWR, then record that
data in memory. Any future frequency close to the
recorded memory can use the same settings.

Near-ultimate in modularity is thus achieved. Needs
only DC power to operate and doesn't care what kind
of transmitter is connected to it...as long as its in
specification for power and frequency. Absolutely
"plug-and-play!" :-)


What is lacking is STANDARDIZATION.

This is definitely a big problem.

Yes and no. :-) It's like a recipe for "tiger
soup:" "First, you have to catch a tiger..."

In a similar way, there must be SOME idea of
what kind of control range, modulation, etc.,
etc. would be expected...and for what radio
service. The FCC in the USA can't yet come to
grips on that, nor has industry made much
progress outside of their own product lines.

Right now, it is more like Pandora's Box.


That can't be worked out in newsgroups,

A newsgroup is a good place for open ended discussions between people
with experience in quite different fields.

I agree. But, like the infamous "John Smith,"
it can be infiltrated with someone who doesn't
have either the experience or the courage to
use his/her real name. Raises the noise
level enough to make some go QRT for a while.


Writing a formal specification may require some formal organisation,
but on the other hand quite a few successful RFCs in the IT sector are
written by a single person or a small group.

Ahem...that INDUSTRY specification is going to
range considerably farther than some small group
within one company. As to IT (Information
Technology), I've not seen ANY industry-wide
softwares which extend beyond corporate levels
and that's been for the last three decades.
LANGUAGES not counted there.

and willingness to compromise

That is the problem in formal committees, in which most delegates from
various vendors have large commercial interests in the subject and in
order to be able to produce even some kind of standard, all features
from various vendors are included.

I'll just cite the ARINC standards which are
generally used internationally for all civil
avionics, from radio to radar, radionavigation
systems. ALL the interfaces to every avionics
box and the physical shape and mountings. NOT
a big commercial venture in terms of profit.
If you've been able to read the verbatim minutes
of ARINC meetings (I have), then you would see
that it can be done.

ARINC = Aeronautical Radio INCorporated, once a
radio communications provider for airlines,
later evolving into a combined industry-government
central standards organization for civil avionics.
[they have a website, BTW, but the documents are
horribly expensive now...]