Thank you for reporting from Brasil,
What is your receive equipment.
Here i am using Pi-A+ with DXpatrol only, antenna helix 6tr /60cm offset dish for transmit beacon H/24
Have a nice day.
73' Rene F6BIR JN19cf 50km north of Paris
I am using an unmodified Octagon LNBF, 1.2m offset parabolic reflector, RTL-SDR V3, SDR Radio, and wsjt-x.
QO-100 is at 5.8 degrees of elevation at my QTH.
73, Edson PY2SDR
I'm running a beacon wspr on the NB QO100, the frequency carrier is 10489.568Mcs, the power output is around 50mw in a 6tr helix antenna/80cm offset dish, the TX is a raspberry device PI_A+, her clock is locked GPSDO, the WSPRPI software generates on 28.069500Mcs a WSPR msg , wich is sent to a locked DXPatrol up-converter input, the output is connected to the helix antenna without any amplifier.
What could be the right freq to use and also how could we report the spot from the listened beacon on wsprnet.org knowing that there is no band know for QO100
Actually I use 2400,068Mhz working frequency in WSJT-X to spot the datas , this band is unknow by wsprnet.org but it spot my datas.
You can watch my spots : http://wsprnet.org/olddb?mode=…r&findreporter=&sort=date
Received your WSPR signal at GG56tv!
73, Edson PY2SDR
Forgive me but maybe there is a basic misunderstanding.
I don't know the details of your experiment. I don't know how you organized it. I am talking about JT digital systems in general and how they try to decode a message. I tried and tried again to delete that blessed archive file and the various programs, not only that of K1Jt but also the derivatives, become more "deaf" without that file. It is an experiment that anyone can replicate. And if after deleting that file, disconnect the Internet as well, you will have other surprises.
Lucio, I think you haven't read what I wrote, I do not use wsjt-x or any derivative. Perhaps there is a basic misunderstanding indeed.
be patient and look for this file, however it is called. ALLCALL.TXT OR ALL.TXT, CALL3.TXT
You don't seem to believe me. Not sure what else to say besides what I have already said.
The problem is known and lies in the operation of the program. In the directory C:\users\user\AppData\Local\WSJT-X\ there is an file: "ALL.TXT".
This file contains all the calls and messages previously received.
The first time the program decodes a signal it must necessarily receive the whole message correctly. Let's say the signal is at -20 dB. Subsequently, the program is able to receive a lower signal from the same station since the part of the message that possibly did not receive well reconstructs it thanks to the local archive contained, in fact, in the file: "ALL.TXT"
200324_115645 10489.540 Rx FT8 -20 0.9 1401 CQ PY4ZBZ GH70
Subsequently PY4ZBZ reduces its signal by 3 dB but the program correctly receives only the blue part of the message.
200324_115645 10489.540 Rx FT8 -24 0.9 1401 CQ PY4ZBZ GH70
Here the program goes fishing in the archive and tries to reconstruct the missing part of the message. The same was used 30 years ago with QSOs via EME. You knew in advance who was on the other side and it was enough to receive only a few characters to consider the QSO valid.
For me it is a half cheat but this is it.
Delete the file "ALL.TXT" and you will see the -24, -23 etc disappear
That does not apply to the experiment since I am not using the decoder with deep search enabled.
Hence no way to break the minus 24...
Thank you for the initiative and for investigating with K1JT.
Proposed next step once the FT8 QRPp will be completed : Nuke the minus 24 dB with a WSPR challenge !
Hmmmmmmm... You are giving me ideas!
Would you like to do some tests with WSPR?
I have exchanged a couple of emails with Joe K1JT about the QRPp experiment and the -24 dB limit for the FT8 decoder. The following are Joe's remarks.
By convention all SNRs reported by the software package WSJT-X are
measured in a standard reference noise bandwidth of 2500 Hz.
Detailed measurements of FT8 sensitivity in various simulated
propagation conditions are summarized in a graph posted on the WSJT web site here:
This plot was made by generating 1000 simulated FT8 signals at each
specified SNR, subjecting them to simulated propagation by nine standard
ITU propagation models, and counting the number of resulting decodes for
Propagation to the geostationary satellite QO-100 ahould closely
approximate the AWGN (additive white Gaussian noise) path, for which the
leftmost curve in the plot shows a 50% probability of decoding success
at SNR = -20.8 dB and a very small (less than 1%) probability at SNR =
-23 dB. The probability of decoding an FT8 signal with true SNR less
than -22 dB is extremely small.
Why is it, then, that the decoder sometimes reports SNRs as low -24 dB?
And why do we never see reported SNR -25 dB or lower?
All physical measurements have associated uncertainties. In principle
we could estimate and report an uncertainty along with each measured
value -- for example, something like SNR = -18 ± 2 dB. If WSJT-X were
intended as a measurement tool, we would do it this way; but for its
intended purpose such reports would be cumbersome, distracting, and
Reported SNRs lower than -22 dB are nearly always underestimates of the
true value. To avoid unwarranted focus of attention on very small
reported SNRs, we arbitrarily clamp reported FT8 SNRs at -24 dB.
Halo Edson and all others....
many thanks for your information about the station setup... that is very interesting ....
But i have no idea about the different decoding levels and the performance of WSJTX also on different days ....normaly the same signals on the transponder must reach the same SNR level if you have enough ground noise of the transponder.
Maybe there are some other influences in the signal path of the propagation and maybe also in the satellite hardware?
BTW: an very interesting test ....
73 for now
I am very puzzled about why some days are different than others. There are many variables involved and not having a way to instrument them, it may be hard to know for sure what could be the cause for the differences we have been observing.
73, Edson PY2SDR
some more have reached the -24dB .... but my receiver (85cm Dish, ADALM PLUTO) shows sometimes better signal levels of some stations ...
anyone have an idea about the difference in decoding levels... in WSJTX ???
Maybe it is interesting to hear some ideas about... and maybe it is helpful to get more about the monitoring station for this test...
which hardware is used?
Tnx and 73 de dg0opk
It is difficult to know for sure what could cause the differences in the SNR. Variantions in the uplink and downlink radio paths would probably the the main candidates.
The setup at the AMSAT-BR RX is the following:
As refletor I have a 1.2m offset dish. I use SDR Console to correct the LNBF frequency drift, demodulate and route the demodulated audio samples (16-bit @ 48 kHz) over the network to a Linux PC using UDP datagrams. At the Linux PC I receive the samples using netcat and route the samples via a shell pipe to a command-line process (ft8d) I have developed to write a WAV file in sync with the 15 seconds FT8 time windows. Once the WAV file is complete, the process calls the FT8 decoder (the original wsjt-x jt9 command-line process). The decoder returns the spots, if any, to ft8d which then filters the CQ spots and forwards them to the AMSAT-BR web site.
73, Edson PY2SDR
Until yesterday only one station was able to reach -23 dB (EbN0 = 3 dB), but today one station was able to reach -24 dB and several stations are being able to reach -23 and -22 dB. I am puzzled to what could cause this. No changes have been made to the RX hardware or software setup.
On a Twitter thread about the FT8 RB experiment, Phil Karn, KA9Q, and Daniel Esteves, EA4GPZ have suggested using EbN0 for measing the SNR instead of using the way the FT8 decoder displays SNR. EbN0 is a more standardized (and perhaps more meaningful) way to measure SNR in digital modes. I have added EbN0 to the RB page.
The Twitter post is:
Some background info about EbN0:
Hello guys, will try my luck as well ! This is where FTx makes sense.
Trying to slowly decrease pwr level step by step and see how far I can go.
I'm however not familiar with FT8, and wonder why despite my message is "RB F5MFO JN19", the Reverse Beacon reports "CQ F5MFO JN19" ... Any clue ?
The RB receive station does not change the received message. It only filters out non CQ messages. It seems that you station is transmitting CQ.
73, Edson PY2SDR
Maybe it would be better to look for FT-8 packets not with "CQ" but some other text, eg. "RB" or so.
There are OMs who answer to those CQ calls and are getting no answer..
The problem is that JT modes like FT8 can only support a very small set of structured messages (CQ in one of them) or up to 13 alphanumeric characters. Something like RB PY2SDR GG56 would not be possible.
I have been thinking about using only the callsign (6 characters max) and a six-character locator. For example PY2SDR GG56TV. A different frequency could be used so that the experiment would not interfere with FT8 QSOs. What do people think?