You are right......................that would make too large of a spacing,
so common sense applies here. Every half inch or so is ok, except around the
RF components, where you might want to drop the vias more densely.

starman wrote in message
...
Pete KE9OA wrote:

I usually go for less than one tenth of a wavelength for maximum spacing
between vias. I never lay out the vias on a grid. This is one of the
things
I learned at one of the EMI/EMC classes I took at when I was working at
Rockwell-Collins. I understand that different folks have different
approaches to board design, and these different approaches do work well,
my
approach has been ok, with boards I have been designing well up to 5GHz.
I
do need to state that I am not the foremost expert in this field; I am
just
a simple soul that is scratching the surface of the RF realm!

Given that the highest HF frequency is 30-Mhz, then 1/10 wavelength
would be about 1-meter. This is much larger than the circuit boards in a
radio like the R8, so how important would it be to adhere to the 1/10
wavelength rule for grounding an HF board?


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I'll start counting vias on my R8B when I can't get to sleep. :-)
Seriously, I'm going to experiment with removing some of the PC board
ground screws to see what happens to certain 'birdies' that I have
identified.

Pete KE9OA wrote:

You are right......................that would make too large of a spacing,
so common sense applies here. Every half inch or so is ok, except around the
RF components, where you might want to drop the vias more densely.

starman wrote in message
...
Pete KE9OA wrote:

I usually go for less than one tenth of a wavelength for maximum spacing
between vias. I never lay out the vias on a grid. This is one of the
things
I learned at one of the EMI/EMC classes I took at when I was working at
Rockwell-Collins. I understand that different folks have different
approaches to board design, and these different approaches do work well,
my
approach has been ok, with boards I have been designing well up to 5GHz.
I
do need to state that I am not the foremost expert in this field; I am
just
a simple soul that is scratching the surface of the RF realm!

Given that the highest HF frequency is 30-Mhz, then 1/10 wavelength
would be about 1-meter. This is much larger than the circuit boards in a
radio like the R8, so how important would it be to adhere to the 1/10
wavelength rule for grounding an HF board?


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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

In article , starman
wrote:

I'll start counting vias on my R8B when I can't get to sleep. :-)
Seriously, I'm going to experiment with removing some of the PC board
ground screws to see what happens to certain 'birdies' that I have
identified.

snip

I own an R8B, as you know. Looking around inside it looks to me that
the main problem is no isolation between the digital and analog RF
portions of the harnessing to the front panel. The wires are all
talking to each other in that area of the radio. The analog / RF
controls are fewer than the digital so I would focus on those using
either electrical shielding or maybe common mode choke would be a
better approach. The electrical shield would most likely have to be
grounded on both ends to work well. You could try choking the analog /
RF cables since they mostly carry DC control voltages near the RF
board.

I noticed a few kluges in the radio in the way of not connecting the
coax shield at one end between different boards in the radio in what
looks like the main RF board and synthesizer board. The designer must
have been trying to keep noise from the synthesizer board ground from
getting onto the RF board ground. A transformer would have been a
better approach than leaving the ground dangling at one end. The untied
shield is still in proximity of the RF board components due the shield
ending just before the connector and it will radiate to that point of
course. You could try choking this coax cable around half its length of
the before it gets nears the RF board.

To get a feel of what is happening you can tune the radio to a birdie
and grasp the wiring by the insulation or move the cables around a bit
to see if level changes.

--
Telamon
Ventura, California