On Wed, 26 Jan 2005 16:09:34 -0800, "Caveat Lector"
wrote:

Military and Ham operators operate this way and claim a SUBJECTIVE increase
in signal to noise over that of a wide open receiver.

This has been true back when I taught it to my students in the Navy.

Technically this
should not be true, Signal to noise ratio should not be reduced by
decreasing receiver gain

Oh but it should. AGC will compress differences, thus lowering the
subjective ratio in comparison to a non-AGC perception. However, the
fluctuation of all signals will be wider. Myself, I've never been
afraid of automatic circuits, but often I find they are marginal to my
interests and for weak signal detection, I follow the conventions
you've offered.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 26 Jan 2005 16:09:34 -0800, "Caveat Lector"
wrote:
Try turning the AGC off, turn the RF Gain way down and the AF Gain up
considerably. Then advance the RF gain until the signal is just copyable in
head phones. Repeat for the two antenna conditions. Make sure your audio
levels are equal.

Military and Ham operators operate this way and claim a SUBJECTIVE
increase
in signal to noise over that of a wide open receiver.

RC wrote This has been true back when I taught it to my students in the
Navy.

CL writes -- Indeed Richard -- I learned this while in the US Navy in the
50's


CL wrote Technically this
should not be true, Signal to noise ratio should not be reduced by
decreasing receiver gain

CL Writes Here I was comparing S/N ratio with a wide open receiver to a
reduced RF Gain receiver -- both with no AGC. The S/N ratio should be the
same.


RC wrote Oh but it should. AGC will compress differences, thus lowering
the
subjective ratio in comparison to a non-AGC perception. However, the
fluctuation of all signals will be wider. Myself, I've never been
afraid of automatic circuits, but often I find they are marginal to my
interests and for weak signal detection, I follow the conventions
you've offered.

CL writes Ah yes AGC can cloud the issue -- using fast AGC can provide a
greater amplification of the noise (between words) than the signal (if the
signal is strong enough)

But on the other hand AGC can be a big noise reducer if used properly.
Tune in a strong SSB signal on 40M or 80M, with fast or no AGC -- assess the
noise between words. Now use slow AGC and listen to a greatly reduced noise
level (between words)

That is why I advised the original poster to use no AGC when assessing the
two different antenna conditions

But I agree -- use AGC as appropriate.

New operators are inclined to set the RF Gain to max, to read the S-meter.
But the technique of increased AF Gain and reduced RF Gain with no AGC is
used by many experienced ops. Disadvantage is, of course, when a big gun
jumps on the frequency while you are set for no AGC -- ouch my ears. Maybe a
small price to pay in order to pull out that weak one.

Also for weak signal detection, listening with headphones can make a big
difference in comprehension as compared to listening to a speaker. Using the
above techniques and head phones, top notch CW operators can copy code even
when the signal is about the same as the noise.

I can't do this though (;-(
old ears I guess (;-)

--
73 es gd DX -- Caveat Lector

On Thu, 27 Jan 2005 08:11:34 -0800, "Caveat Lector"
wrote:

Also for weak signal detection, listening with headphones can make a big
difference in comprehension as compared to listening to a speaker. Using the
above techniques and head phones, top notch CW operators can copy code even
when the signal is about the same as the noise.

I can't do this though (;-(
old ears I guess (;-)

Hi OM,

Well, back when I was in college physics (before the flood), my
professor put me and a buddy on a task to build the perfect detector.
It correlates perfectly with your advice to use headphones.

He had us build a Synchronous Detector (not a simple device to
construct from tubes and at 455 KHz). Some may be familiar with this
form of detection, and yet they may be ignorant of its best
implementation. For others, this kind of detector is also found in
color TV detection and color information separation. Often the block
diagramming or circuitry is described in terms of I and Q paths. I
won't go into the particulars of design, but I will offer that these
two separate paths when broken out to separate Audio channels, and
then fed to stereo head phones, they offer an unique signal hearing
experience.

Basically, the entire two channel system is completed by the brain
combining phases and providing a perception of the wanted signal being
"heard" in the middle of your skull, while interfering off-frequency
signals are perceive off to one side or the other. In a sense, you
hear an enhanced signal through phase reinforcement.

73's
Richard Clark, KB7QHC

Ah indeed Richard -- some Ham DXers use stereo headphones where the
earpieces are out of phase.

--
Caveat Lector



"Richard Clark" wrote in message
...
On Thu, 27 Jan 2005 08:11:34 -0800, "Caveat Lector"
wrote:

Also for weak signal detection, listening with headphones can make a big
difference in comprehension as compared to listening to a speaker. Using
the
above techniques and head phones, top notch CW operators can copy code
even
when the signal is about the same as the noise.

I can't do this though (;-(
old ears I guess (;-)

Hi OM,

Well, back when I was in college physics (before the flood), my
professor put me and a buddy on a task to build the perfect detector.
It correlates perfectly with your advice to use headphones.

He had us build a Synchronous Detector (not a simple device to
construct from tubes and at 455 KHz). Some may be familiar with this
form of detection, and yet they may be ignorant of its best
implementation. For others, this kind of detector is also found in
color TV detection and color information separation. Often the block
diagramming or circuitry is described in terms of I and Q paths. I
won't go into the particulars of design, but I will offer that these
two separate paths when broken out to separate Audio channels, and
then fed to stereo head phones, they offer an unique signal hearing
experience.

Basically, the entire two channel system is completed by the brain
combining phases and providing a perception of the wanted signal being
"heard" in the middle of your skull, while interfering off-frequency
signals are perceive off to one side or the other. In a sense, you
hear an enhanced signal through phase reinforcement.

73's
Richard Clark, KB7QHC