Lack of knowledge or problem with functionality -- CubicSDR

Discussion in 'Software Defined Radio (SDR)' started by K4VBB, Oct 19, 2019.

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  1. K4VBB

    K4VBB XML Subscriber QRZ Page

    Having a problem with CubicSDR in linux, and I'm not sure if the problem is with software functionality or with what is sitting between the keyboard and the back of the chair.

    Here's what I have:

    IC-7410 with IF tap to HupRF PAT70M installed.
    RTL-SDR2832U Panadapter

    Before getting too far, everything works as expected in Windows using HDSDR, so I know that there is no hardware problem.

    In Linux (both Fedora 30 and Ubuntu 18.04.03 Bionic Beaver), however, I am using CubicSDR. Since my goal was to reduce/eliminate my dependency on Windoze I'd like to continue using it if I can get things working.

    Here are my problems:

    First, LSB and USB appear to be backwards. If I want to listen to traffic using LSB, I have to tune to USB in CubicSDR in order to do so. For traffic using USB, I have to use LSB in the software. I 'could' live with that if I absolutely had to.

    However, the main problem is with rig control and tuning. In both Ubuntu and Fedora I can tune into an audio stream in the waterfall. If CubicSDR is controlling the rig, and when I click on a stream, the tuner on the rig changes to the frequency I clicked on and the whole band in CubicSDR shifts along with it, at which time the stream I clicked on moves as well.

    If Rig control is not enabled and I use the audio-out on the laptop, everything is fine.

    It appears that there is some kind of setting or offset that I need to configure, but I have not been able to figure it out.

    Is this a problem with the CubicSDR software, or is there something I am simply doing wrong?
  2. DK7OB

    DK7OB Ham Member QRZ Page

    The USB/LSB reversal may indicate swapped I/Q signals. On gqrx, which I use on Linux, there is a button for this, I don't know if CubicSDR has a similar setting.

    If the I/Q signals are swapped, the received spectrum is mirrored at the "DC spike" (the SDR hardware frequency, don't know how that is called on CubicSDR), so if your DC spike is at 14200 kHz and there is an USB signal on 14170 kHz USB, that signal appears on 14230 kHz LSB on the spectrum.

    <Additional note>
    I just noticed you are using an IF tap. Depending on the RX, the sideband reversal may happen in the RX already and has to be compensated by swapping I/Q in the software.

    Also for tuning, you have to the the IF offset into account.
    Last edited: Oct 19, 2019
    PY2RAF likes this.
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    It is assumed that the IF tap is at the first IF at 64.455 MHz in the IC-7410.

    The mixing scheme of the IC-7410 is such that USB at the signal frequency comes out as LSB at the first IF, which common for all up-conversion HF receivers.

    (IF = LO-RF, so if USB at RF is represented as
    RF+delta, the IF becomes LO-[RF+delta]
    = IF-delta or LSB.

    The other issue is most probably software configuration dependent.

  4. K4VBB

    K4VBB XML Subscriber QRZ Page

    Ok, thanks to your help I think I've come to understand a little bit more about the software configuration.

    Under "Settings" there is an option for I/Q swap. I'll give it a shot and see if that reverses the LSB/USB.

    Under "Rig Control" I have a setting called "SDR-IF". In order to receive properly I set this to the IF frequency of the LO on the rig, which is 64.455MHz. If I understand things correctly, I'll need to offset the RF frequency by the IF frequency.

    Under "Settings" I have the option for "Frequency Offset" and "Device PPM". I'm not sure I understand the difference between the two, but I'm going to assume that I'll set this offset in the "Frequency Offset" setting.

    If I have this right, I'll offset the frequency that I'm trying to tune, say 7.120MHz, by -64.455MHz.

    I'd have tested this already, but I'm in the process of running my feedlines through conduit that I just buried in the back yard. I don't currently have an antenna hooked up, but I should be finished by tomorrow. I'll post back after I get access to my antenna again.
  5. K4VBB

    K4VBB XML Subscriber QRZ Page


    thank you for your assistance. I now have a working (almost) install of CubicSDR. The I/Q swap worked for the USB/LSB problem, and the frequency offset of the LO frequency seems to have done the trick for the tuning anomaly.

    I did, however, have to remove Fedora 30 from my laptop, as I found CubicSDR to be quite buggy compared to Ubuntu 18.04. There are still a couple of little bugs. Not getting audio from CubicSDR most of the time, but I don't care because I use audio from the rig.

    The bug I don't like dealing with is that in order to get rig control I have to launch CubicSDR from the command line using 'sudo'. Is there a fix/workaround for this? Seems like it's just a permissions issue.
  6. K4VBB

    K4VBB XML Subscriber QRZ Page

    OK folks, I've figured this one out too, and I'll leave the answer here for posterity, as I'm sure someone else will need this at some point in the future. I hope they find it to be useful.

    Having worked so long with the DoD, I've been a RedHat guy for years. I've only ever dabbled with a Debian based linux OS such as OpenSuse and Ubuntu, so I don't know my way around as well as I do on RedHat based systems like CentOS and Fedora. Definitely a learning curve there. I HATE netplan, for the record.

    Back to the topic at hand:

    The issue I had with fldigi, Hamlib, WSJT-X, CubicSDR, and probably a whole host of other software that interfaces with the rig in Ubuntu is permissions related if you're running the software as a regular user. Workarounds may include running the software from the command line using 'sudo' which can work, but there are more elegant solutions.

    One solution that I did not try, and won't address here is to make a rule in udev. From a security standpoint this is probably the better solution, as the rule can be tailored to give access to ONLY the USB/Serial port that will be in use by the software, and the application will only have access to the specified device while the application is running.

    However, since I'm lazy and I'm the only one that will ever use this computer, I simply added my user account to the "dialout" group. If one doesn't already know, to do this type the following at the command line:

    sudo adduser <username> dialout

    where <username> is the loginID for the user. So if you log in as "fred", then you'll type (without quotes) "sudo adduser fred dialout"

    I accept the extremely small risk that someone 'could' 1: target my specific laptop remotely, 2: spend significant time finding their way through my firewall (Juniper SRX), 3: find their way through the UFW rules on the laptop, 4: find a way to exploit my userID, and finally 5: control the devices attached to the laptop via USB and Serial ports. At present that would include my IC-7410 and my FT-450D. I'm sure that there may be some super-hacker that could bypass steps 2-3 by flying to my QTH, breaking into my home, deal with the dog--or the Remington 1100 should I be home, and hack my laptop locally.

    With the exception of logging software (which I have yet to select--any suggestions?), I am now completely NON-dependent on Winblows for HAM Radio operation.

    For those who have contributed to my knowledge base, I offer my gratitude. Thank you, Gentlemen.
    N0NB, G8XQB and KA2CZU like this.
  7. N0NB

    N0NB Subscriber QRZ Page

    For logging software look into CQRlog for general logging and perhaps Tlf for contest logging.

    Thanks for the tips here. I'll give them a look with my K3/P3 IF OUT.

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