Hello Tony,
Multipsk tends to show a slightly higher SNR with certain modes, but the
values are still within 2db. I took a few screenshots that show Multipsk and
PathSim working together connected via VAC (see attached).
Thanks for 5 attachments. I think I had a bit of chance as I don't think to be
as precise as 2 dB (perhaps +/- 2 to 5 dB according to the modes).
If the AWGN source is enabled then Gaussian white noise can be added to the
input signal in order to simulate various SNR ratios. A SNR of 0 means that
the input signal rms level is equal to the noise rms level as measured through
the 3KHz bandpass filter
I agree with the definition (which is not always the standard, JT65 suppose a
2.5 or 2.7 KHz).
73
Patrick
- Original Message -
From: Tony
To: digitalradio@yahoogroups.com
Cc: F6CTE Lindecker
Sent: Sunday, November 01, 2009 11:29 PM
Subject: Re: [digitalradio] Message ID in multipsk [5 Attachments]
[Attachment(s) from Tony included below]
Patrick,
It certainly seems difficult to precisely measure digital mode SNR so thank
you for explaining that. I think the PC sound card method is accurate enough to
show the relative difference between modes and more importantly, the digital
mode path simulations and SNR tests seem to correlate well with on-air
performance.
In Multipsk when it is possible I evaluate the S/N by measuring the signal
energy in its band and noise in the reminder of the band (or part of it).
After normalization to a 3 KHz noise bandwidth, I display the
result (which is not very precise).
I'm not sure if I mentioned this before, but I noticed that Multipsk SNR
figures compared well with PathSim when the two programs were linked together
during my SNR testing (white noise only).
Multipsk tends to show a slightly higher SNR with certain modes, but the
values are still within 2db. I took a few screenshots that show Multipsk and
PathSim working together connected via VAC (see attached).
Moe Wheatley describes the SNR method used in the PathSim docs:
If the AWGN source is enabled then Gaussian white noise can be added to the
input signal in order to simulate various SNR ratios. An SNR of 0 means that
the input signal rms level is equal to the noise rms level as measured through
the 3KHz bandpass filter
Thanks for all Patrick.
Tony -K2MO
- Original Message -
From: Patrick Lindecker f6...@free.fr
To: digitalradio@yahoogroups.com
Sent: Sunday, November 01, 2009 5:09 AM
Subject: Re: [digitalradio] Message ID in multipsk
Hello Tony,
What software are you using to determine the SNR decode level?
What i do is adding noise so as to reach a S/N=-15 dB. Then I see if it
works (decode or not). According to the result, I will try -14 or -16 dB etc...
In Multipsk when it is possible I evaluate the S/N by measuring the signal
energy in its band and noise in the reminder of the band (or part of it). After
normalization to a 3 KHz noise bandwidth, I display the result (which is not
very precise).
There are other methods (based on correlations and hypothesis) as with
Olivia and JT65 but they are neither very precise.
For example, you could evaluate the S/N according to the phase jitter in
PSK mode (the more the phase moves randomly, the lower the S/N ratio is), but
this would work only in good ionospheric conditions.
73
Patrick
- Original Message -
From: Tony
To: digitalradio@yahoogroups.com
Sent: Sunday, November 01, 2009 12:44 AM
Subject: Re: [digitalradio] Message ID in multipsk
Patrick,
I think you are right about the burst characteristics of the mode and the
way the PathSim software handles this. Seems logical since our SNR tests have
been consistent with other modes.
I have an audio editor that has the capability of adding white noise, but
it doesn't indicate the SNR once the mode audio is mixed.
I mix signal and noise at digital level before the analogical transform
and then I see at what level I can
decode.
What software are you using to determine the SNR decode level?
Tony -K2MO
Attachment(s) from Tony
5 of 5 Photo(s)
SNR.jpgSNR_PSK31.jpgSNR_MFSK16.jpgSNR_RTTY.jpgSNR_CALLID.jpg
