Posts by DL3JOP

Ah, so while taking pictures I might have found a solution to the "problem":

GQRX and SDRConsole seem to use different styles of displaying the spectrum:


GQRX has very small steep lines also when zoomed out and also updates very quickly which leads to belive that the SNR lower. I had to trigger the screenshot exactly right to get this SNR, which comes far closer to the one in SDRConsole.

SDRConsole has a smoother and slower change on the spectrum display which makes seeing the peaks easier. There is also some kind of "smoothing" which decreases when zooming which leads to assuming that the Noise floor is lower. When zooming in this "smoothing" disappears.


So all in all it is a matter of zoom level and the difference in displaying style.
Sorry for bothering but maybe someone will have this "issue" to in the future.

Regards,
DL3JOP

Hi,

yeah, the SNR calculations are different but I did not use them. I just looked on the height of the signals in the spectrum display and did not read any calculations. I'll upload two pictures which describe the phenomenon in a few minutes

Hi, after some troubleshooting I have a very strange conclusion about the SNR displayed on the spectrum on GQRX and SDR Console:
All SNR are read by looking on the grid background and the index on the side, so there is a certain tolerance.

On gqrx I get around 16-20 dB on the CW beacon when it is on it's peak. Without changing the dish position, bias-tee voltage or sdr, I switch from Linux to Windows an start SDR Console. In there I can read a SNR of around 25dB to 32db which keeps me wondering why the SNR is different in two other applications without changing the hardware.
Did anyone of you experience the same issue?

Regards

Quote from dj0abr

The 30W option was originally developed for small camping dishes, like the dish we are using for our portable club station. If you are using a normal >=80cm dish, then the 10W amp is a good choice. It gives real 8W which is enough the trigger Leila.

Hi, thank you , that's very good to know. With my current drive level and the gain you measured I should get around 4-5 Watts. I'll work on from there. Thank you for sharing your design. I'll answer here when I have everything assembled and measured!

Quote from OE3GBB

but you should consider to use a BLF7G27LS-90.

Thank you for your input, I put it on the backburner for now and see how far I come with the 10 Watt Version.

Regards,
Joshua

Hi Matthias,
thank you for the qso and your signal report too! I started working on my ocxo pcb to mitigate the drift!

I already studied the BOM and decide to order everything for the 10W and 30W version because the 30W Version uses mostly similar parts. I read your test on the 10W amp and had the fear that the power would not be enough or similar to the power of the wifi amp. But I'll try the version and look how far I will come!

Regards,
Joshua

Hi,
I want to upgrade from my "8" Watt WiFi Amp to a better pa. I want to built DJ0ABRs 10W and 30W amplifier but the LDMOS (BLF2425M9) for the 30W Version is out of stock everywhere. I've looked for drop-in replacements but I couldn't find ones with the same footprint. Do you know of any similar ICs which might work or a supplier which doesn't prices them for around 120€ ? Otherwise, I'll just use the 10 Watt version for the time being if it is an improvement instead of the wifi amp?

Regards,
Joshua,
DL3JOP

Hi,
thank you all for your answers. The last days I worked on a gnu radio flowgraph which is capable of generating LSB/USB, now I'm experimenting how I could lock my loop onto the signal. Using an sub-audible tone is hard (at least for me) due to the small bandwidth.
Otherwise I will go with the TCXO/OCXO approach.

Regards and 73,
Joshua,
DL3JOP

Hi, I try to rephrase my question:

I lock my recieving software of one of the beacons of QO-100 which eleminates signal drift effectively becuase the received signal will be as stable as the beacon itself.

Now comes the transmitting part.
The LimeSdr Mini as 4ppm drift when running for a longer time which results in a maximal drift of 9.6kHz at 2400Mhz which is way to high.
The usual way would be to stabilize the LO using an GPSDO or other frequency standard.
My approach instead would be:
Since the received signal of the transponder is drift-corrected as mentioned above you can see your actual transmitting frequency when transmitting. So as a consequence you can precisly see how your transmitted signal drifts around on the downlink due to the 4ppm drift of the LO. As a next step you start tracking your own signal on the downlink and its drift and correct the drift by actively changing the transmitting frequency.

Because the whole system is locked on the Beacons frequency, there is no cat-bites-tail problem.

Hi,
I want to built portable a station with as less components as possible. Second I wanted to know if someone already had the same idea?

Regards,
Joshua

Hi,
I am currently building an groundstation for QO-100 and thought about replacing the GPSDO with a piece of software:

There are gnuradio flowgraphs like this on github which lock the received signal to the nb transponders beacons using a costas loop and pipe the stabilized downlink spectrum to gqrx or similar.
My idea is as follows: The same flowgraph will be expanded to transmit the uplink signal. The receiving part then also tracks my uplink signal received from the satellite and corrects the transmit frequency if the signal is drifting. Is this practical and or even possible? It's harder to track a changing ssb signal than a constant carrier I presume.

Regards,
Joshua,
DL3JOP