Steve wrote:
wrote:
I found this web page while looking for a nifty audio filter I found
last year.
At the very least it gives food for thought.
http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf
Terry
There are some helpful hints here, though I'm puzzled by the gripe this
fellow has with synchronous detection. I personally wouldn't spend a
lot of dough on any receiver that lacked it. I think a lot of people
are sour on synchronous detection because they've bought and/or used a
receiver that had a very poor implementation of it. When sync detection
is done right, as it is on Drake's R8B, then it will sometimes do more
to aid reception than all of these hints put together. But the good
news is that we don't have to choose between synchronous detection and
this fellow's helpful hints. We can have all of these tools at our
disposal.
Steve
My first expousre to SAM was with an AOR7030+. My first impression was
that
"great". That lead me down a long path toward building my own SAM+
outboard
detector. Along the way I had a chance to test a Kiwa, MAOP and the
Sherwood
SE-3. Both are good and both are much better then the AOR. I tried
several
designs and settled on a variation of Pete's AD607 SAM. Again at first
I was very impressed. However after using it for several months the
glammor started to dull.
For better then 99% of my AM listening, which in truth is a very small
part of my
SWL activity as I am into utility, I ofund the 3 OpAmp simple "improved
detector"
to be the equal or the match for any of the SAMs I had on hand. I was
not able
to compare the MAP or SE-3 for any extened period and while both are
great units,
they do have differences. On balance I like the sound quality of the
MAP over the SE3,
but I liked teh SE3's ability to track rapid, deep fades, espcially
with nearby AM
signals. I had my feet held to the fire for my posts about Dallas
Lankfords
observations about the utility of a sharp LP audio filter that chops
every thing above
~3 or 4KHz. Exact break point depends on individual choice.
Now that I have a R8B, I must admit that this is the best implentation
of a SAM
I have yet experienced. However in many situations it too can benefit
from the
AF LP filter.
Perhaps I expected too much from SAM detectors. They aren't magic and
are far
from perfect. The
home.worldnet.att.net/~wa1sov/technical/sync_det.html
page is no longer up, but Peter C. McNulty, WA1SOV, offered an
additional
OpAmp fitler design that was reported to allow the AD607 to fully
reject
unwanted signals via I and Q difference and summing. I don;t have my
printed
copy in front of me so I can't relate the math. The design appeard to
be valid,
and several other EEs agreed with his reasoning. However I was never
able to
get that part of the design to work. I wrote if off in part to the 50Hz
minimum
tuning step the R2000 offers. His design is clearly worthy of study and
I suspect
that for someone with more time it could be a winner.
At this point I am most interested in reducing the local RF noise,
improving my
antennas and getting to understand how to get the most from my phaser.
Oh,
and I am still after the Holly Grail" of a perfect 12V audio amp.
Terry