Re: K3S NR


Bob McGraw - K4TAX
 

Why not just reduce the audio level via the computer CODEC level and be done with it?   That doesn't affect the receiver performance.

Agreed on the NB works well.

73

Bob, K4TAX

On 8/25/2019 9:12 PM, Carl Moreschi wrote:
For best results on FT8, you should set AGC to OFF, and adjust RF gain for a 30 db signal in WSJT with no signal being received.  If some signals push the signal above 80 db, you may need to lower the RF gain some.

WSJT does all the work here so let it do its job.

Also, NB can help but certainly not NR.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 8/25/2019 10:06 PM, Bob McGraw - K4TAX wrote:
Jim:

You might give the ATTN and RF Gain some work to do.   With information
provided by a highly respected ham and one that evaluates a lot of
radios, in a conversation and discussion we had at the Huntsville
hamfest a couple of years ago,  he suggested that most hams use too much
RF Gain for typical band conditions.   In his words, for legacy
receivers such as the K3 series and other like radios the optimum
receiver performance occurs when the no signal band noise is some 10 dB
above the receiver noise floor.

How does one accomplish this in as much as we have no control over
receiver noise floor?   The solution is then to attenuate the signal and
noise arriving at the antenna input.  The attenuator and RF gain is used
as a step in this direction.

To do a bit of math;  the noise floor of the K3 series radio is
typically about -127 dBm.  This is equivalent of S-0.   Now at our QTH
with the antenna of choice the no signal band noise is S-4 or -103 dBm.
The difference between the two values is 24 dB.  Now to have the noise
appear 10 dB above the noise floor is should be at a level of -117
dBm.   The optimum level is then a difference of -117 dBm {RX noise
floor + 10 dB}  minus -103 dBm or 14 dB.  Thus 15 dB of attenuation
brings the configuration to within 1 dB of the optimum receiver noise
floor to band noise.

In some cases, additional signal / noise reduction is needed in the case
where the no signal band noise is higher.   Again an example: Noise
floor is -127 dBm,  No signal band noise is S-7 or -85 dBm. Thus the
different is 32 dB minus our desired 10 dB.   Here we need RF gain
reduction of 17 dB or about 3 S units, plus 15 dB of attenuation.

Once the method is applied, we then find that signals pop out of the
noise.  And in this case the actual receiver noise only adds about 0.5
dB to the total noise value.  I've tried it on several receivers
including my K3S, my Tentec Eagle, my Tentec Omni VII and my KW
TS-590S.   It really does work.   It is just difficult to get past the
mental notion that more gain is needed to hear weak signals. Where in
practice, less noise is required to hear weak signals.

73

Bob, K4TAX


On 8/25/2019 8:06 PM, Jim Denneny wrote:
Thanks Bob.  I will stick with TXDATA & NB
Jim K7EG

Join Elecraft-K3@groups.io to automatically receive all group messages.