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 know...........it seems that the more you learn, the more you realize how
much you just don't know.
On another note..................I am working on a quasi-sync detector, so I
should be able to build the prototype unit up this Monday. Basically, it
consists of a limiting amplifier (MC1350) feeding the squared up I.F. signal
into the LO input of an NE602. The unconditioned I.F. signal it fed both to
the input of the limiting amplifier and to the RF input of the NE602. It
should be interesting.
I've been meaning to get around to these things for the past couple of
years..........I'm glad that this radio project came along.

Pete

Telamon wrote in message
...
In article
,
"Pete KE9OA" wrote:

snip

I think I understand what you are describing here but I need more
detail to be sure.

What this consists of is removing the resonator from the oscillator
circuit, leaving only the feedback capacitors (collpits circuit)
intact. Next, you connect a network analyzer to this input poing of
the circuit, and set it up for a Smith Chart response, viewing the
S11 parameters. The trace you are interested in is the Unity Gain
Circle. In the frequency region where the circuit will function as an
oscillator, you will see a bit of negative resistance. As you adjust
the value of Cequiv of the feedback capacitors, you will see this
region mover around. In this way, you can optimize the circuit,
seeing the changes in the imaginary terms. Another cool thing about
this technique is that you predict whether or not the circuit will
have a monotonic response (VCOs) This negative resistance should be
very smooth; if there a small squiggly loops in the response, the
response will not be monotonic. In other words, if you were working
with a VCO, and you had a tuning voltage of 2 to 5V, as you increse
the voltage from 2 to 5V, the frequency of the VCO should increase at
a rate determined by its KV characteristic. If this isn't the case,
for example, suppose you start out with a tuning voltage of 2V; you
will be starting at frequency F. As you increase the tune voltage,
the frequency should now be (F+X), but what can happen at some tuning
voltages is that you actually see the frequency decrease slightly,
only to increase again as you continue to increase the tuning
voltage. In other words, you can have two different tuning voltages
that can invoke the same frequency from the VCO! Can you imaging
trying to design a predictable PLL when this happens?

Using the network analyzer to measure the reactance of the feedback
circuit looks like a good way to characterize its response.

If the VCO described above was used as part of a PLL it would lead to
jitter problems.

Oh, one more thing........................about those board
resonances that we were talking about. There was one microwave
synthesizer board that I was characterizing for spurs several years
back. All of the spurs were below -70dBc, but as soon as the unit was
installed into the enclosure, the 3rd harmonic rose to -30dBc. This
board was mounted on bosses in about 15 different places. I
discovered that when I loosened one of the mounting screws in the
middle of the PC board, and adjusted the tension on the screw, I
could use it like a trimmer to null the harmonic down to the original
level. I never did figure out what was going on, and we eventually
decided to place a piece of Kapton tape on the underside of the
board, and use a nylon screw in this location. I did try that RF
absorbing foam, and even that didn't work. I do realize that this
really wasn't a cure..............an old friend of mine put it
perfectly; a problem board is like a water ballon. If you push into
the balloon at one point, it bulges out in another direction. In like
manner, a simple change to change a resonance in one point of the
board can cause another resonance in another part of the board, if
the board isn't designed properly. Unfortunately, sometimes these
problems don't show up until it is too late. Thanks for the input!

You had the board working by itself and you then screwed it to a metal
frame, which provided additional ground paths between different parts of
the board. Apparently that middle spot was either a noisy part of the
board or the sensitive part of the board.

You changed the impedance of the path by adjusting the screw. I¹ll bet
the spur got worse as the screw was tightened lowering the impedance of
the new problem path.

The problem was the new conductive path not radiated which is why the
lossey foam did not help.

Using the insulated screw is similar to dividing power or return planes
in a board. You are directing noise currents so they aren¹t a problem.
I¹ve seen notches in posts and plates from world-class manufactures of
test equipment for the same reason. Sometimes it¹s the only thing you
can do to solve a coupling problem.

--
Telamon
Ventura, California

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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Pete KE9OA wrote:

I know...........it seems that the more you learn, the more you realize how
much you just don't know.
On another note..................I am working on a quasi-sync detector, so I
should be able to build the prototype unit up this Monday. Basically, it
consists of a limiting amplifier (MC1350) feeding the squared up I.F. signal
into the LO input of an NE602. The unconditioned I.F. signal it fed both to
the input of the limiting amplifier and to the RF input of the NE602. It
should be interesting.
I've been meaning to get around to these things for the past couple of
years..........I'm glad that this radio project came along.

Pete

That should work when the signal is strong enough to keep it locked but
I think it would be prone to losing lock when the signal fades. I wonder
if the sync' in the R75 is actually a quasi design?

BTW- How do you breadboard your circuits?


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I just do a quick layout with a CAD program, and print out the artwork on a
transparency. This gives me the tool I need to expose photosensitized
boards.
I wonder about that R75 circuit. For all of the time that I have had that
receiver, I have never used the sync detect mode. I don't even use it on my
SW8 or my AOR7030. I know that many folks like this function, so it is a
worthwhile thing to design into the receiver.
I am not sure how well this circuit will lock, so it may just be a first
pass at most. Still, signals won't be fading into the noise floor of the
system; the atmospherics will be the determining factor.


Pete

starman wrote in message
...
Pete KE9OA wrote:

I know...........it seems that the more you learn, the more you realize
how
much you just don't know.
On another note..................I am working on a quasi-sync detector,
so I
should be able to build the prototype unit up this Monday. Basically, it
consists of a limiting amplifier (MC1350) feeding the squared up I.F.
signal
into the LO input of an NE602. The unconditioned I.F. signal it fed both
to
the input of the limiting amplifier and to the RF input of the NE602. It
should be interesting.
I've been meaning to get around to these things for the past couple of
years..........I'm glad that this radio project came along.

Pete

That should work when the signal is strong enough to keep it locked but
I think it would be prone to losing lock when the signal fades. I wonder
if the sync' in the R75 is actually a quasi design?

BTW- How do you breadboard your circuits?


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In article ,
Pete KE9OA wrote:
I just do a quick layout with a CAD program, and print out the artwork on a

Would you please tell us which one?

Thanks in advance, and 73,

Geoff.

--
Geoffrey S. Mendelson 972-54-608-069
Icq/AIM Uin: 2661079 MSN IM: (Not for email)

said:


I have never used the sync detect mode. I don't even use it on my
SW8 or my AOR7030. I know that many folks like this function, so it is a
worthwhile thing to design into the receiver.
I am not sure how well this circuit will lock, so it may just be a first
pass at most. Still, signals won't be fading into the noise floor of the
system; the atmospherics will be the determining factor.



In my opinion, a synch detector that keeps losing lock on problem signals is
useless. Like another poster in this thread said, if you can't design a good
synch detector (apparently it's not easy to do considering that ICOM can't seem
to do it), I would rather have manual ECSS ability (SSB mode with an extremely
fine tuning (preferably analog) knob)).

I don't know if I would exactly call it useless -- synch detectors can speed
up the process of tuning. However I agree that nothing beats the
fine-tuning knob (not a button!) / human ear combination for really nailing
down a signal.

-- Stinger
--
"RFCOMMSYS" wrote in message
...
In my opinion, a synch detector that keeps losing lock on problem signals
is
useless. Like another poster in this thread said, if you can't design a
good
synch detector (apparently it's not easy to do considering that ICOM can't
seem
to do it), I would rather have manual ECSS ability (SSB mode with an
extremely
fine tuning (preferably analog) knob)).

In article , starman
wrote:

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?

We were discussing what had to be done to prevent board features from
becoming resonant structures on the board and yes at 3 to 30 MHz it's
much less likely due to propagational effects alone but still possible.
If a trace on the board is not closely associated with a ground plane
then its impedance is high and can look more like a lumped inductor than
a transmission line. If the following input to the next device or
circuit has enough capacitance it could resonate anywhere in the HF
spectrum. There are other reasons for via spacing like tying ground
planes together so they look unified electrically. One goal dictating
via density in board design is to make the RF return current path for a
device on the board as small as possible.

--
Telamon
Ventura, California

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