[Elecraft] [P3] Ability to copy very weak signals

[Fred Jensen]

"Doing science with your P3"  Nice idea Al! [:-)  What actually gets 
delivered to our ears is signal plus noise.  At the "ear end" of the 
receive chain, there are things we can do to increase the ratio of
(s+n)/n by either decreasing n or increasing s, or both.

Several techniques in addition to reducing the BW will, to varying 
degrees, accomplish this:  The K3 AFX, RIT, RF/AF gain, inverting the 
phase of one headphone [my Heil Proset does this], moving one or both 
headphones forward on your head, or laying the headphones on the table 
face up on the desk can reduce or modify the noise and raise the ratio 
(s+n)/n as you perceive it with your ears.

I guess that headphones on the desk rather than on your ears forces the 
noise into the background to a greater extent than the desired signal, 
but I've never really heard a good explanation of why that works.

My hearing is admittedly significantly compromised but many hams tend to 
be in the older rather than younger population, and with birthdays 
passing, so does hearing.  On CW, judicious use of RIT can place the 
s-component at a peak in hearing acuity without modifying the 
n-component, raising the perceived (s+n)/n.

73,

Fred K6DGW
- Sparks NV DM09dn

- Northern California Contest Club
- CU in the Cal QSO Party 7-8 Oct 2017
- www.cqp.org

On 11/26/2016 9:43 PM, Al Lorona wrote:
>
> How are your 'ears'-- your ability to copy very weak CW signals?
>
> Here's a way to "measure" your ears. You'll need your panadapter set
> to a narrow span such as 2 kHz. Turn on averaging so that the noise
> flattens out to allow you to estimate the true level of the noise.
> Use a full-screen vertical scale of just a few dB to make it easy to
> measure small signals just above the noise.
>
> Whatever your noise floor is, when a signal creates a 3 dB "bump"
> above the noise floor, that means the signal and noise are equal
> (because if you add two equal powers you get twice the power, which
> is a 3 dB bump). We call this condition a "signal-to-noise ratio of 0
> dB".
>
> Now tune around the band to find very weak signals and see how much
> of a bump they make. Here are some rough rules of thumb, rounded off
> for simplicity:
>
> ++++TABLE DELETED, DID NOT SURVIVE THE REWRAP ON REPLY++++
>
> I listed some negative S/N ratios because I've heard of folks who can
> copy signals below the noise floor! That's crazy!
>
> In any case, this is a very approximate measurement, but it's fun
> having some idea how well you can actually copy CW at phenomenally
> low levels.