v1.623 [also, RF attenuator control discussion]

From the CHANGE_LOG file:

v1.623 September 4, 2023

  Added "RF" tab to user control panel. KiwiSDR 2 RF attenuator control is here.

    In the future other functions will move here like the antenna switch.

  Admin control tab: "daily restart" now a menu allowing restart or reboot (thanks Glenn, N6GN).

  Other changes to support KiwiSDR 2.


  • Are you saying that the attenuator will be controlled by the user?!!

  • jksjks
    edited September 4

    Yes, but TBD are options to limit this for the case of public Kiwis. We could have different modes that match different expected situations:

    You could imagine adjustment being purely manual or set to a schedule. Like adding 15 dB of attenuation in the evening for a Kiwi in the EU where the SWBC signal levels are very high during that time.

    For public Kiwis there could be options for no user control, control only for password-protected channels, or open where users could fight over it (the antenna switch allows for these kind of access options). In the latter case all connections would get a notification when the attenuation changed (as is done with the antenna switch now) so they understand why the signal levels are varying.

    All kinds of possibilities here..

  • jks, thank you for your work! Adding a controlled attenuator gives a lot of interesting things! Schedule management is brilliant! And of course the admin has to decide whether the user can control the attenuator.

  • The v1.623 release was mostly for the change requested by Glenn. But I added the "RF" tab and RF attn slider to get some feedback.

    I'm working on putting the antenna switch in there too, so you can use it while other extensions are open. But this requires a bunch of changes not ready yet.

  • Hi John,

    Just some random thoughts for further discussion.

    My opinion is still that in many cases, it is strong local medium wave broadcast stations that cause the majority of problems, especially when the antenna is a broadband active loop, and that this can usually be fixed by means of a simple external passive amplitude / slope equaliser.

    However, getting back to the main topic. To be honest I hadn't really envisaged the attenuator being under 'public' control, as I think it could lead to a lot of problems.

    My thoughts were that it would be pretty much automatic, in that if ADC overloads occurred, the attenuation would be slowly (perhaps a minute per 1dB) increased step by step until the ADC overloads stopped. Then gradually the operation would be reversed until the ADC overloads appeared again and the attenuation would once again be increased.

    This is a bit like 'riding' the master gain on an audio mixing desk. It is quite subtle and just helps to maintain sufficient headroom and preserve the overall dynamic range during louder sections of the recording.

    Some broadcast transmission limiters use a similar technique of having two time constants, one fast time constant limits short duration peaks (like AGC) and the other, much longer time constant (like the attenuator), maintains the average modulation level.

    Maybe a further test would be to see if the noise floor at a quiet HF frequency around 30MHz was greater than 6dB above the KiWi noise floor. In which case attenuation could safely be added.

    The scheduling is a good idea, and maybe a manual, or perhaps even automated hit list of problematic frequencies and levels could be generated, so that it could be used to predict the times at which attenuation may need to be added.

    As attenuation is added, could the dB value of attenuation be shown on the GUI, and also the S Meter, Waterfall and spectrum display be corrected to compensate for any additional attenuation that is applied.

    As I said just my thoughts, and I'm sure I'd be happy with whatever is finally implemented.



  • edited September 5

    >I'm working on putting the antenna switch in there too,

    Oh, this will be really good! Thank you. Is there a particular hardware switch I should be putting on order?

  • @G8JNJ Automatic control is an interesting idea. No reason why we couldn't experiment with an idea like that. Also, good idea about compensating the WF/spec for gain changes. Like we compensate now for zoom level changes.

    @k5mo The Github page for the antenna switch extension has a list of currently supported switches. There is also a backend to drive the Beagle GPIO pins on the P8 connector. Although you have to be extremely careful doing so.

  • I just ordered a SV1AFN 4 port switch which looks handy for a SDR antenna switch (and quite affordable). This might be an interesting antenna switch hardware option since it's receive-only and tiny (and quite affordable :-) )

    Thanks for all you do.

    John K5MO

  • Re: SV1AFN switch. It says 3.3V compatible. Just make sure it's configured that way and has no chance of back-feeding 5V into the Beagle/Kiwi P8 header pins. That would take out both the Beagle and the Kiwi.

  • This old thread my be of interest if you are planning to use the GPIO port for antenna switching.


    If you wish to better protect your KiWi and also reduce radiated noise, then adding some series resistors and decoupling capacitors is a worthwhile precaution.



  • Thank you both for the inputs. I will be very careful (and keep an eye on the Kiwi2 availability just in case. :-).

    Might be a good idea to optically isolate the two.

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