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What causes this bump in my panadapter?

KD0RC Member, Super Elmer Moderator

I have a Flex 6400 with a UT5JCW transverter for 2 meters. It works great, but I do see a large (nearly 10 dB) bump in the receiver response. Is this showing me the bandwidth of the transverter or am I seeing the bandwidth of the antenna? The antenna is a Ringo Ranger ARX2B.

I am asking this out of curiosity, not because I have any problems with this setup.


  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭

    Antenna resonance???

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Well, I think that I just answered my own question... I disconnected my antenna, and still see the same bump. I switched from my vert to an 11 element Yagi and get the same thing.

    I conclude that it is the bandwidth of the transverter that is showing on my panadapter. If anyone has other insights on this, I would be interested to hear them.

    These are the kinds of things that I never would have noticed without my 6400!

  • Duane  N9DG
    Duane N9DG Member ✭✭
    edited June 2023

    It probably is the response traits of the transverter.

    Curious though, how much more pronounced is the bump if you zoom the display out to the full 7 MHz?

    And what do you see if you run a second 7 MHz wide display either above or below 2M? Doing the two displays immediately adjacent gives you a frame of reference spanning 14 MHz.

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Duane, I did look at the 7 MHz wide chunk and it did not look any different. I agree, it is the transverter response that I am seeing.

    I would be interested to see what 144 - 148 looks like on a Q5 transverter. My guess is that it will be considerably flatter.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Hi Len

    If you where to take 100 readings with a signal generator across that entire spectrum and plotted it, that is what it would look like.


  • Lasse SM5GLC
    Lasse SM5GLC Member ✭✭✭

    You could try change the RX path from "28 common" to "RX only", open JP2... this would show a bandpass that is less steep on the high side due to the "top-loaded" bandpassfilters used on VHF... There is a LPF-filter in the common path that may cut the high side of what you see.

    All this is pure specutlations as I do not hve the transverter, only looking at the schematics :)

    BTW what is the corner frequency of the LPF in the flex (WB filter enabled I guess)?? Do you use 28-32 MHz IF?

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Lasse, once you tune higher than 146 MHz (30 MHz IF), the rig goes to "Wide". Also, if you have any panadapter showing more than 28 - 30 MHz IF it will go to Wide. Wide is a good thing...

    My transverter will tune 144 - 148 MHz, so that is an IF of 28 - 32 MHz.

    The Flex is quite flat, it is the transverter band pass that causes the non-flat response.

    I am not looking to "fix" anything, my original post was just curiosity as to what I was seeing.

    I would say that I have learned more about radio in general since I got this 6400. Being able to see things like this makes it obvious what is going on.

  • Lasse SM5GLC
    Lasse SM5GLC Member ✭✭✭
    edited June 2023


    that's why I wrote LPF... i.e. the wide is just a low-pass filter at the input of 6400, but depending on the cut-off frequency it could aid reducing the noise, but assume it has a lot higher cut frequency (it should remove the aliasing of ADC).

    And my comments were just beeing curious on why the noise looks as it does... I even d/l the schematics to see what was going on :)

    I have seen similar "****" but on lower frequency, but that is more likely due to a narrow resonant antenna.

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