Are thes values from your own RX or Goonhilly? Remember the topic! (I think you mean Goonhilly, not Green ..)
The NB beacon is transmitted from Bochum and is also subject of fluctuatios un the uplink side ...
It says JO21fx, and this is not in the UK
The QO100 beacon strength might be correlated to relative humidity. All of these measurements take more than two minutes and are done in periods when there is nobody on the NB transponder. The satellite transponder also has an AGC, so if there are strong transmitters it will reduce its gain, keeping my fingers crossed that the transponder beacons are always at the same strength. You can measure the beacon SNR with matlab script readsnr.m which needs signal history files from SDRconsole, see also https://github.com/ejo60/hamradio
I caught this one last night 2-7-2021 (time information is in the screenshot), it pushed down the SNR of a NB signal and I was listening. My best guess is that the AGC of the transponder kicked in.
Ernst, click on [CW] at the CW-beacons
Which gives me the 25+ dB I was looking for 
One possible clue is to look at the signal to noise ratio, the SNR, and not the signal in dBm because that could very well be affected by SDR software parameter settings. SNR is much less affected, in SDR console you can get it from the signal history and save it in a CSV file. What I do notice is that the SNRs are GoonHilly are less compared to what I receive at home, no idea why this is the case.
The size of the dish will not do that, why?
The excel sheet calculates the expected signal to noise ratio (SNR) in dB of your transmission that is received by the satellite, all parameters in yellow affect that SNR since a bigger dish means that you have a higher gain so more signal (but not noise) arrives at the satellite. The analogy is: a better pointer makes a brighter spot.
Yes, I know, but will not double the SNR if the TP noise was received before....
The size of the dish will not do that, why?
I do not understand the calculation results of the excel table.
At the moment when you receive the transponder noise, should the SNR change only insignificantly with larger antenna diameters?
A twice as large antenna area (so a 1.414 times larger diameter) yields 3 dB which is a factor two. See also https://www.electronics-notes.…enna-gain-directivity.php
Maybe try this calculator in excel or matlab. In excel specify your set-up in the yellow fields, don't change the green fields and in the end it returns in orange the SNR in dB which is probably the best you can achieve on the waterfall. Filled in is already my setup.
Display MoreI found your signal even more useful than expected, while testing link margin during a thunderstorm. I know I lost at least 15dB at its worst, and that happened while the streets were still dry. I could "see" the thunderclouds drifting towards the sat path. When the rain started, signals went up
Using WebSDR, I saw that my own signals were not attended as much which is strange (2.4 is the max water absorption frequency ?!?)
Having longer signals at a level would be useful. "zero" is short to measure.
Is 0dB the beacon level? I don't think it is, but propagation is strange right now.
I any case, this is useful, but perhaps t needs to be there structurally. Good stuff!
If you lose so much signal then it is probably water on the feed or whatever, if you have a canopy on the feed then you won't don't see such attenuation levels during rain. Contrary to impossible to erase believe, 2.4 GHz is NOT a water absorption frequency. The earliest water vapor resonance frequency is 22 GHz.
I think it is QRM
Results of the ZRO beacon test, I submitted 18 but want to remark that not all pulses are sent at a predictable strength, for a next test maybe try a 1000 tone and ask people how many tones they heard?
2600 Hz SSB filter in SDR console over end beacon remains steady at 28 dB, just export the values to an excel sheet and calculate the dBm difference within excel. It doesn't matter really how you do this. For instance take a mean dB value through the values at the lowest and the highest level and subtract them. I take the noise measurement a few kHz away from the beacon, and the signal measurement over the beacon. I find no convincing difference with the earlier described CW-U 50 Hz method.
Updated a link budget calculation to my blog, https://pa1ejo.wordpress.com/2021/06/08/link-budget-qo100/
DL5CN This is why I specify the procedure, 50 Hz BW, CW-U filter, the rest of the parameters in SDR console to not affect the results too much unless you really do strange things.
Hallo Ernst,
interesting idea. Would you please give a short description of your equipment and method to make the results comparable.
Thanks
73
Andreas
You only need SDRconsole and a SDR, go to view -> signal history and you can get an the situation as shown, best guess the peak dBm values in both 50Hz CW decoders and subtract them, this morning I got approximately 29 dB, meaning also that there is nothing attenuating the satellite signal (like rain water on the canopy of the antenna feed). Signal history in sdrconsole even has the possibility to download the dBm values in a csv file that you can import in a spreadsheet. I focus on peak values of what I see in SDR console.
You will see that the SNR that you find is mostly unaffected by settings of the SDR, even the bandwidth of the demodulator should not matter too much in my opinion. Important is that you get the maximal signal of the CW beacon for the moment that it is continuous and the real noise floor somewhat but not too far away from the beacon.
Martin DM4IM did this test also I learned during a QSO, he got 34 dB but his antenna is taller than my TDS88 from Triax which I rate at 90cm diameter, his is 150cm, the difference in the antenna gain is like 4 dB (see the 31-May article on my blog), the rest of the differences are due to downconverter or LNB differences or simply the antenna efficiency. I think these are interesting tests to compare. It says in my opinion everything about receiver sensitivity.
I know that SDRplay's rspduo results in realistic dBm values, used a HP stepper attenuation device, a HP power meter and a signal source to calibrate the dBm scale in SDRconsole, it is fine in my opinion.
What you are discussing is related to the link budget, there is a RX and a TX part, the RX part concerns your receive sensitivity at 10 GHz and the TX is the other way around.
Let's do something everyone can do, and that is to look at a unique signal of the satellite from both end beacons where it is assumed that they always operate on the same power level.
What you do is to test your signal to noise ratio at the begin or end beacon of the NB transponder, so you measure with a 50 Hz wide CW filter the dBm's of a continuous wave transmitted by the CW beacon, and one repeats that measurement 5 kHz below the beacon in a region where you only see the noise floor.
In the end you get two dBm values and you subtract them, in my case I find 28 dB and this is a value corresponding to my receive sensitivity. The former receiver performance where I had a semi-rigid problem between the feed and the downconverter and a smaller dish it was 20 dB which is in my opinion poor receive sensitivity, that problem is gone so I can hear others better.
Assume the value of 28 dB as an artibrary reference, assume a factor 2 (or 3dB) in the sensitivity test and complete the following poll, this is a QRM free test everyone can do.
If afraid that is not something I can easily test since the antenna is 10m away outside point to QO100 over a garage roof, normally I don't see any signal outside the NB transponder band.
SQ6QV: thanks for this explanation.
This is what I saw on 23-6 at 11:29 CET, in my opinion a pretty powerful signal including splatter for 25 seconds at 433.830 MHz on the SDR
