AM Thread on Flex Radio Forum

Discussion in 'Chat' started by WD5JKO, May 13, 2016.

  1. WD5JKO

    WD5JKO Member

  2. W5HRO

    W5HRO Administrator

    A much better question, why would anyone want a Flex?

    Except for maybe smug type appliance operators, AM'ers included. Like the ones on :lol:
  3. WD5JKO

    WD5JKO Member

    Groucho Marx once said, "Once you use an SDR receiver you don't go back!" 8)

    The receive experience is fantastic. You can tell a signal that has high IMD at a glance. Also the receiver can be used as a spectrum analyzer to analyze a vacuum tube AM transmitter. I attach a spectrum analysis of my Central Electronics 20A running 10W AM @ 100% modulation when the audio is driven with two tones of 700 hz and 1900 hz. Tests such as this are not SMUG, but more SMART since a quality spectrum analyzer is a very useful piece of test equipment in the ham shack.

    I use a Flex 3000 running PowerSDR 2.7.2 with enhancements made by Darrin KE9NS at Revision T6.

    It is interesting that the older SDR hardware out there (Flex 5000, 3000, 1500) has the most advanced Gui features, many of which make them excellent for a quality AM exciter capable of low distortion modulation up to 10 Khz.


  4. W5HRO

    W5HRO Administrator

    Not with this puppy... They just don't go well with vintage equipment. Maybe if you have a separate setup or room consisting of all modern gear, but they don't look good or work well sitting next to old boatanchors.

    Anyway, for that price I’d rather buy a 75A-4 and a vintage station monitor and make it work.
  5. WD5JKO

    WD5JKO Member

    Actually, mixing the two stations allows me to characterize the boat anchor stuff.

    The attached image shows my CE 20a with a 1 Khz tone into the Mic jack, and rig set for LSB. In the image I see many things, which include:

    Carrier is -44 db below LSB tone
    The unwanted USB is 50 db down from the desired SB
    The 2nd harmonic of the LSB is -40 db or 1% distortion
    The third harmonic is -42 db down
    The 4th harmonic is -40 db down
    The 5th harmonic is -70 db down
    The carrier, LSB, and LSB 2nd harmonic show some FM, perhaps 20 hz wide at LSB (40 hz at 2nd harmonic)

    I have done similar work with my Gonset G-76. It's very interesting to see what happens when the negative peak limiter kicks in.

    Actually a Flex 1500 is much more affordable, especially a used one, and does not have to issue with the now obsolete Firewire ports that have disappeared from modern computers. Also some of the features on the 1500 that were turned off by Flex as a marketing ploy have been renabled by the KE9NS with his downloadable software. Two examples are 10 Khz audio on transmit (20 Khz wide on AM), and 15 khz audio on receive (30 khz BW).


    2nd_Day_1Khz_40 watts_LSB.jpg
  6. W5HRO

    W5HRO Administrator

    If you are worried about that kinda stuff just get one of the below or build one.

  7. WD5JKO

    WD5JKO Member

    That is like going from a 2012 BMW to a 1975 Chevy Impala. No spectrum analysis with that Halliscratcher box. Still, I could use a Simpson 260, but I prefer my Beckman and Fluke DVM's. All a matter of preference, desire, and choice.
  8. W5HRO

    W5HRO Administrator

    DVM's have their place like for trying to read or set DC supply levels that are stable and don't move, but they completely suck when trying to read AC/DC analog inputs or outputs that do move around.

    I'll use a Simpson analog meter over a DVM every time to do a lot of things. One example is when tuning a receiver for its peak audio output level when a tone is injected.

    Anyway, both types of meters have their place. It just depends on what you are trying to do.