First 10 Days with a New Flex-6400

Discussion in 'Amateur Radio News' started by N6OIX, Sep 10, 2019.

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  1. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Well no, that's not the whole story. With the preamp on the Flex 6400 (-136 dB) is within 2 dB of the Elecraft K3 (-138 dB) on CW MDS/Noise Floor, (first column). Adjust the controls to fit the operating goal.

    Note: Of course, on HF bands, the atmospheric Band noise is typically the limiting detection factor for most stations (not to mention man made ambient noise). Excess sensitivity becomes useless and nothing more than a bragging point.

    Flex 6400 Noise Floor.png
    Last edited: Sep 16, 2019
    KC7CS and N6OIX like this.
  2. VE3TCV

    VE3TCV XML Subscriber QRZ Page

    One thing to add is the preamp on the Flex 6600 is beyond anything I have used in the past, when there is a weak signal I simply crank it up to +32dB and the signal blasts through while the noise stays the same! Using receive specific antennas are a joy with a preamp of this class.
    N6OIX likes this.
  3. KR3DX

    KR3DX Ham Member QRZ Page

    Yours is not the whole story either. Turning on the preamp significantly degrades the dynamic range on an SDR, much more so than on a superhet. On Rob Sherwood's website, look at the dynamic range specs for the preamp on and the preamp off. Another limitation of a direct sampling SDR is that the FPGA has a maximum voltage limit that is affected by THE SUM VOLTAGE OF ALL OF THE SIGNALS WITHIN ITS PASSBAND, which add to its noise floor. The 6400 does not have band pass filters, so ALL of the signals on the ham band (think contest weekend) and ALL of the signals adjacent to the ham band (SW broadcast, etc.) are present on the input of the FPGA, severely limiting its ability to "hear" any individual signal. The ARRL and Rob Sherwood use a "two tone test" to determine dynamic range, which is a valid method for a superhet, but it falls far short of revealing the weakness of an SDR. With a superhet, you can have sensitivity AND dynamic range, with an SDR you must choose sensitivity OR dynamic range, which are both WORSE on the SDR. In the "real world", SDRs perform FAR worse than the "specs" seem to indicate. Look at the "100 kHz Blocking" figures on Sherwood's website. This is why the best receivers are superhets, and according to Kenwood, it's why they designed the TS890 as a superhet instead of an SDR.

    Yes, "band noise" is the limiting factor on the lower HF bands, but unless you NEVER operate above 20M, you will probably want a rig with decent sensitivity. 73
    Last edited: Sep 16, 2019
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  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    You can always add bandpass filters to the Flex radios. You can't add flex equivalent displays to any non-flex radios. :)

    Every radio has it's operating limitations and quirks. No radio does everything all the time in every mode.
    N6OIX likes this.
  5. KR3DX

    KR3DX Ham Member QRZ Page

    Adding band pass filters still does not negate the limitations of an SDR. Like the ham band filters on the Flex 6600 and 6700 series (which are MUCH more expensive than the 6400 series), they do NOT eliminate the in-band (ham) signals. Think contest, QSO party, special event, or any other scenario where the band is full of signals. It's a BIG disadvantage for the SDR vs. the superhet. Again, look at the "100 kHz blocking" specs on Sherwood's site, but even that doesn't tell the whole story. Regarding displays (eye candy), many other rigs have "pan-adapters" or external video display ports which have even more Flex-ability (pardon the pun) than the Flex. You could use an SDRplay RSP-2 receiver (< $200) for a wideband spectrum display by connecting it to a separate antenna, and connect the second input of the SDRplay to the IF output of your rig to display the rig's passband. That setup would also be more flexible than the Flex. I do agree with you that no rig is perfect.
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  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    BTW, The Marconi Italian Navy Coherer receiver has better EMP resistance than all modern radios. Therefore, all current production radios are terrible designs. :)

    The danger of the Sherwood numbers (as demonstrated in this thread) is that they can be cherry picked to highlight a particular radio and bash others claiming absolute superiority in a single number without context.

    The Flex 6400 radio is not a terrible radio. The Kenwood TS-890 is not the 'best" radio.

    The Flex 6400 isn't the best radio for CW contesting under battle conditions, or absolute weak signal CW work. So what. Pick a top of the line Yaesu and criticize the four deep menus or poor ergonomics or cheap knobs. Whatever. Comparing the Flex to the DISCONTINUED IC-706 is an exercise in pointlessness.

    Many excellent points have been brought up in the discussion. I think that contributors should back down on making absolute claims of superiority or inferiority. Lighten up bit. bill.
    Last edited: Sep 16, 2019
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    On the contrary. External bandpass filters (available off the shelf as plug and play e.g. from Array Solutions) DO eliminate the other 90% of the HF spectrum impinging on the Flex receiver, thereby improving the Dynamic Range performance on the desired band, which negates previous criticism.

    Point 2; Don't think contest battle conditions.
    Point 3: Non-graphic radios still can't compete with the primary graphic display and controls of the Flex's. Kluging low end RTL's, drilling and blasting and modifying expensive radios is not a hearts desire of most hams. Further most radios don't have IQ/IF outputs for plug and play. Additionally, you ares still left operating now two (2) radios in order to get the visual display that are the Flex forte.

    Thrust, parry, riposte! Touche'

    Bottom line: We have outstanding radios available to us today at all time low relative cost. Even the entry level radios today have excellent performance and features compared to a few decades ago! b.
  8. AJ2I

    AJ2I Ham Member QRZ Page

    Preamp adds noise. Most of the Non Flex radios made within the past 20 years have MDS numbers around -125+. Going +32 on a flex to equal a non-flex radio adds a TON of noise , almost to the point where you won't be able to hear the signal.

    I had a Ten Tec Eagle, and my 6400, side by side, A/B switch. Same antenna and everything. The Eagle heard the weak signal, the 6400 didn't. Hams need to A/B radios side by side to see the real world difference. The best way to decide for yourself.
    KA2FIR, AF6IF, K2NCC and 3 others like this.
  9. KR3DX

    KR3DX Ham Member QRZ Page

    I agree 100%
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  10. KR3DX

    KR3DX Ham Member QRZ Page

    I inserted my comments in bold after several of your statements in your reply above.
    Last edited: Sep 16, 2019
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