I completely agree..................I have a multitude of vias on all of my
boards, especially around the RF components. When a system has 80dB gain at
one frequency, it is just to easy to have things fly, otherwise.
On another note, I have completed the first pass of my quasi-synchronous
detector. Audio is very crisp, and since no PLL is involved, there is no
lock to lose. Basically, it consists of splitting the I.F. signal into to
paths...........one path feeds the input port of a Gilbert Cell mixer, while
the other path feeds the input of a high gain limiter. The clipped output of
the limiter feeds the LO port of the mixer, and the audio is taken from the
I.F. port of that same mixer.
It is interesting, when I compare it to the envelope detector output of the
receiver. While the envelope detector output exhibits distortion from the
selective fading mechanism, the quasi-sync detector output remains very
clean, all the way down to the .1uV lower system limit.
My next iteration will use a Philips SA637.................if this circuit
work out the way I expect it to, I will have a single chip solution for this
function. I just need to check the parameters of the LO input, low frequency
limit of the mixer, etc.

Pete

Telamon wrote in message
...
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

Hi Michael,
I finished the prototype this morning, and it does work
pretty well on low to medium level signals. On very strong signals, there is
a little bit of edginess on the modulation peaks.
As far as the NE602, you can feed the limited I.F. signal into pin 6, and
this works out pretty well.
My next iteration of this circuit will be one that uses a Philips SA637.

Pete

Michael Black wrote in message
om...
"Pete KE9OA" wrote in message
...
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

Do you actually need two ICs? The MC1496 datasheet talks of using
it as a "synchronous detector" but even mentions that an external
limiter is not needed so long as the signal level is sufficient.
I don't suppose that can work out with the 602?

For that matter, the variable gain stage in the MC1350 is
a "Gilbert cell" and it can be used as a mixer, albeit one
with a gain stage between it and the output pins. Could it
be better suited for a self-limiting "synchronous detector"?

I don't suppose the MC1330 which is the same scheme intended
for detector use in TV sets, is still available and suitable?

Michael