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6600 Bandpass filters

I have read on previous postings some basic information about the Bandpass filters in the 6600, yes I understand they are seventh order filters and I also have read that the bandwidth changes relative to the spectral display so that if you are within the filter bandwidth you have full functionality - but the filter is dynamically widened to match the spectrum being monitored, i’m not sure this is absolutely correct but I think I’m on the right idea.

What I would really like is access to a full service manual so that I as a “professional radio tech” could better understand what is going on inside !

If that is not possible can someone within flex give me a more technical description explaining what are the actual characteristics of the seventh order filters. 

A group of us were discussing last week how the various transceivers from different manufacturers cope in a high RF environment such as a multi multi contest, and this question came up.

This is to understand how to have the radio set up to achieve the maximum possible preselection from the bandpass filters

Many thanks

Phil G4UDU



Answers

  • Bill -VA3WTB
    Bill -VA3WTB Member ✭✭✭
    edited February 2020
    Interesting question, It would be nice to read a good paper on the filtering in  the 6600. But till then their is this good read to start with.
    https://community.flexradio.com/flexradio/topics/why-does-the-flex-6600-need-band-preselectors

  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited April 2020
    @Phil, there is no service manual available, but I'll be happy to address your question.

    The preselectors are not dynamically widened, they are fixed width filters that encompass the bandwidth of individual ham bands. 

    Whether or not the filter is enabled is dependent on the SCU(s) and the bandwidth of the panadapter.  The SCU module is where the preselectors, RF preamp and the wideband ADC are grouped together in a functional unit.

    Only one RX antenna (the analog signal input) can be connected to an SCU at a time for RF to be digitized by the ADC.  This signal is fed to the FPGA.  The FPGA is what generates the spectrum data for the panadapters.

    When viewing a panadapter, the SmartSDR software knows how much spectrum you are viewing and if what is being displayed is less than the preselectors filter bandwidth, then the preselector is automatically engaged.  If the pandapter is too wide or you have another panadapter that is using the same RX antenna (and consequently using the same SCU) but it is on a different band then the preselectors are disabled.

    So if you see the word WIDE displayed in the top right-hand corner of a panadapter, then the preselectors are not enabled.
  • KF4HR
    KF4HR Member ✭✭
    edited February 2020
    Tim - reference the 6700; since this transceiver does not have the 7th Order Filters, what toggles the WIDE indication?  I notice on my 6700 the WIDE indication shows up sometimes and other times it doesn't. 
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited February 2020
    The filters drop out and WIDE shows up when you have a receiver on that SCU exceeding the bandwidth of the HF band.  If you are focused on 20M but then also go to 40M on the same SCU, then you will see wide.  

    If you post a screen shot of SmartSDR when you see this, we can help explain it.

    Mike

  • WW1SS - Steve
    WW1SS - Steve Member ✭✭
    edited February 2020
    The wide indication is toggled when you have 2 pans open on 2 different bands

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