Posts by SV1BDS

    Hi,


    A HF signal monitoring system is build for research usage. This project idea can be used, if desired, to daily monitor QO100 NB & WB activity and usage. Statistics also can be calculated.


    An active antenna (LA8AK circuit) with a 1m whip can receive 10 KHz-30 MHz. A 4 way splitter provide the signal among others to a USRP1 SDR with a 0-30MHz Rx card. The USRP1 is connected to a i5 1.6 GHz low consumption PC with a 4TB HD and a 60 GB SSD for Ubuntu 18.04. The PC runs at about 50% CPU. A GNURadio generated Python script runs every 2 min for 100 seconds. It has 16 bit 6.4 MHz sampling rate, so the same RF bandwidth received. Three frequencies ranges are covered (1.6-20.8 MHz total covered frequency range). The frequency selection criteria was that this range is relative non infected from local interference. If it is installed in a better environment all the 30 MHz range can be easy covered. So every cycle it takes 6 minutes and then is repeated.


    Two 1024 FFT points run, one 100 per second and the other one once a minute. This gives 6.25 KHz resolution bandwidth per FFT point. The minimum signals is -150 dBm and the maximum is -150+128=-22 dBm (dynamic range 128 dB). A resolution of 0.5 dB is archived. Data are saved in two category files. The low resolution is saved in 3 daily produced files, one per frequency range. The high resolution is saved once per 100 seconds (3 files per 6 minutes). The high resolution produced files are 7.2 GB per day, giving hundred of days storage capability. The creation of files is automated with cronjob entries. Only delete is not automated as manual activity is desired.


    To visualise the recorded data three possible images files can be produced. All of them are spectrograms with X axis the frequency, Y axis the time and colour the received signal strength in dBm. A colour bar with dBm values exists also. The produced .PNG files are : 100 sec high resolution data files, the 6.4 MHz wide daily data files and the 3 frequency ranges combined daily file. The combined and the 3 daily image files are auto produced daily. Sample outputs are attached. Time is local UTC+2. It can easy noticed in the combined file, the usage at broadcasts bands.


    Ideas for new features and improvements are welcome, some of existing ones are:

    - video animation of daily image (combined) files

    - IQ data storage on trigger event

    It is examined that daily combined image files will be available via my site.

    Hi Matthias DD1US ,

    Thanks for your note, I measure S21 now and from 10 KHz to 500 MHz is flat 0 dB loss. No resonance exist. I use 0805 for both of them. The required response is 8KHz to 160MHz. This must be true for a non SMD one.

    Thanks again !!!

    Hi,

    A SI5351 lab generator is build using eBay ready PCB and a Arduino nano. Xtal is removed and clock is feeded from external GPSDO based 25 MHz reference. So 2 outputs can provided with GPSDO based accuracy and stability. A decoupling capacitor is required at output if feeded to 50 ohm load. Software is build from SV1EED and the pair of frequencies can saved if desired. A 7808 provides power independently from USB.

    Hi,

    A lot of phase noise seems to exist. You mention that you replace TCXO. Does the output soldered OK? Can you verify that at the decoupling capacitor exists normal signal? I have seen that with small clock signals Pluto works but with similar results...

    N.B. Tonight i have made a test:
    i have tried to TX with my Kenwood TS-2000X and RX with the Pluto and have noticed that if i TX in FM so the the

    modulation is clear and understandable perfectly while if i TX in USB, i get the problem above.
    If it can help to understand the problem.

    Thanks once more

    Hi,

    There is no sense to test with FM as you can not see the problem as you describe it. In order to find the source of the problem you must first identify better what the problem is, then try to isolate it and finally to solve it.

    For the first step my proposal is to send with a good source a steady carrier (CW) and see receiving it in Pluto in a zoom mode what you see in SSB Rx. You can post the image here to view it.

    For the second step try to isolate it. For example try to Tx a carrier and receive it . It has the same problem? Disconnect any possible power supplies , connections for possible ground loops. Can you hear the TCXO using a SSB receiver to see if the signal is clean? Do not use the Ethernet adapter if you do so. Replace the USB cable. In the isolation phase you have to find the root cause of the problem. If you can solve the problem anyway, is good starting point to isolate it.

    After isolating the problem you can see what solution you can provide to eliminate it.

    Hi,

    I test an RLC F-30-5000 suitable for 50W with a Nokia band7 modified SSPA. At 20W the second harmonic is about 30 dB lower. The 2nd is obvious that it is not covered by the LPF. I was not able to see the other harmonics. I will try with more dynamic range.Link