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6400 sensitivity discussion

A.J. AJ2IA.J. AJ2I Member
I've always felt the 6400 reciever was lacking when it came to RX sensitivity, particularly when it comes to pulling out weak signals. Tests I've done with signal generators and the recent Sherwood report confirms this. It's the worst on the list!Using a preamp at +16 on bands above 40m is a must if you're trying to hear a weak signal. The method listed in the article below is irrelevant when it comes to the 6400. https://helpdesk.flexradio.com/hc/en-...
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Comments

  • Paul LeachPaul Leach Member ✭✭
    edited May 2019
    This is disappointing news for 6400 owners. I am currently away from home ( cruise, celebrity edge - in case any fellow hams/flexors on board) I will check this out later today and read sherwood report.. 73’s Paul Gw4amz .
  • Stephen Hawkins NG0GStephen Hawkins NG0G Member ✭✭
    edited May 2019
    What "recent Sherwood report" are you referring to?  My 6400M seems to have no receive sensitivity problems.
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    6400 non m
  • Robert LonnRobert Lonn Member ✭✭
    edited May 2019
    My Flex 6600M is better in many comparisons to my ICOM IC-R8600... Something does not seem right. You should open a ticket with Flex... And that is with the PREAMP set to off or first setting...

    Robert
  • edited May 2019
    Just done a quick test GB3RAL 28.215 MHz is about 75 miles from me on ground wave I can just hear it above the noise - 6400 with preamps on CW mode 50Hz bandwidth with APF - compared to a KX3 set up the same way, same BW  CW etc.   if anything the Flex has just got the edge on the KX3.
    The beacon CW ident is almost "subliminal hearing" but it is certainly better on an A/B test than the KX3

    I have no complaints.

    Phil G4UDU

  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    This is regarding a 6400. Not a 6600,6700 or 6400m. A plain Jane 6400. The numbers are different for each radio. -112dBm on the noise floor. Every other radio on that list is around -124dBm with no preamp. My eagle with no preamp beats the 6400 on weak signal rx. An Icom 706 is -135! And that radio is 20 years old. Flex really dropped the ball on this.
  • edited May 9
    You can not compare radios by the manufactures description of pre amp on, off or whatever - they all have different gains and noise figures.  You also have to be very careful over what IF bandwidths you are using and again measure it for proof that what is stated for a filter is actually what you get on the receiver - they can all vary.

    THE ONLY way to check it is on a calibrated signal generator and measure the MDS and S/N ratio, then you can compare the readings, when I get a chance I will put my 6400 on the test set and measure it.

    For reference I have a K3 a KX3 and an Icom 7100 to compare it with.


    Phil G4UDU
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    I've used a signal generator and so has Sherwood. Conclusion to achieve equivalent RX of MDS vs my eagle is you need to go +16 on the 6400. Eagle does same with no preamp. -112 6400, -124 eagle. The numbers dont lie
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited May 2019
    The 6400 keeps up with the very best receivers made. I would start a help desk if you feel that the receiver is not performing well for you. Perhaps Mr Sherwood tested a brocken Flex, he has done that before then published the results.
  • KF4HRKF4HR Member ✭✭
    edited May 2019
    Some people rely way too heavily on Rob's receiver chart. 
  • edited May 2019
    My 6400 hears fine. Compared to my other radios. Tested with my Motorola communications test set. Hope you find your problem.
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    -112 is about what I got also. Bottom line is, you need +16 preamp to achieve the same RX compared to most other radios. That was the point of this post originally. To spread the word that you cant use the above method for determining if you need preamp. You need it period or you wont hear weak signals compared to other radios that can BECAUSE -112dBM is -112dBM is -112dBM. Which means deaf to.weak signals. Find a weak signal on 17 meters or 20 meters etc. Turn off preamp , then do same with a superhet radio and do A/B I bet the superhet will hear it and the flex wont
  • Joe N3HEEJoe N3HEE Member ✭✭
    edited May 2019
    AJ- Make sure the hardware updates were installed in your radio. There was an issue with heat sinks on ADC chips that caused sensitivity issues. I have 6600M with superb sensitivity on the high bands. I never need the preamp.
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    Thanks Joe. My flex shipped 5/2018. Which was supposedly after the updates were rolled out so it should be fine. I dont think there is anything wrong with the radio and its operating within spec, unfortunately just a poor spec. I think the 6400 is the black sheep of the 6000 series as it seems every other 6000 series is fine.
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited May 2019
    Again, never mind the specs. A direct sampling radio receiver will out perform any superhet receiver. The 6400 is not a black sheep in the Flex radio line up and have very good receivers.

    Any difference in specs you read can not be heard with the human ear, they are only lab test.

    Most comments I have read is that people are very happy with the receiver. Some here have just said they find the 6400 to be just fine to them.

    I will repeat. you should start a help desk. something is not right.
  • A.J. AJ2IA.J. AJ2I Member
    edited June 23
    I'm not spending $150 in shipping costs to have flex tell me there is nothing wrong with my radio and its operating within spec. I will make a video with a signal generator, proving the flex hears within the published spec. I will then make a video showing the eagle hears signals the flex cannot unless you turn on the preamp to +16 which correlates to the published spec.
  • HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭
    edited June 2019

    The particular preamp setting that results in the best receiver noise floor is immaterial.  The available settings are a design decision (such as compensating for bandpass filter loss), and varies by radio.  It’s a trade-off.

    BTW, high sensitivity affects dynamic range.  By your reasoning the Collins 75-S3B (on the Sherwood chart) beats them all.  Great rig in its time I’m sure, but looks at its dynamic range!  You need to look at the stats in context. 

    But as was mentioned, if you actually suspect low sensitivity, by all means submit a trouble ticket.

    Howard


  • A.J. AJ2IA.J. AJ2I Member
    edited June 2019
    Exactly howard. The best way to get dynamic range is to make a deaf reciever. Different tools for the job. The reason I have more then 1 radio in the shack. Some are better at things then others. But the people that say a flex 6400 will hear as good as a ftdx5000 etc are just plain wrong. The proof is in the testing and the numbers.
  • edited May 2019
    Dynamic Range is great with the IC-7851 but you have to pay more for it than a SDR Rig 73 Mike
  • HCampbell  WB4IVFHCampbell WB4IVF Member ✭✭
    edited May 2019
    Deaf receiver?? 141 (ftdx5000) vs. 136 dBm?  That’s down in the noise.  Sorry, couldn’t resist!  (-: 

    Howard

  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited May 2019
    You have to use the preamp.  There is insertion loss from the preselectors and the RF preamp is needed to overcome the insertion loss.
  • David Okay PattonDavid Okay Patton Member ✭✭
    edited May 2019
    With the preamps engaged, the radio has good sensitivity; if the band noise is so high that the front end gain causes problems, then the full 16dB gain isn't needed. For a location with very low ambient noise, and under ideal band conditions, the 6400, even with +16dB of preamp, may not have sufficient RF gain.  But for most of us, under most conditions, the receiver sensitivity isn't the limiting factor on what we can dig out of the noise.  

    A.J.'s initial comment is spot on: if you own a 6400, you likely want to operate the radio with the preamp at +16dB, and only drop the preamp gain under very noisy or large signal conditions.  Otherwise, that really quiet band may have some weak signals you'll never know are there.  

    I'm on the fence whether to call this a design flaw, but it is important that 6400 owners know that the optimum preamp settings are different for the 6400 than for most rigs.   With the right preamp settings, this radio is a delight!
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    Thanks for the confirmation David that I'm not insane .
  • Robert LonnRobert Lonn Member ✭✭
    edited May 2019
    Make sure your signal generator has an updated CAL sticker on it.. :-) 
  • David Okay PattonDavid Okay Patton Member ✭✭
    edited May 2019
    Which Tim from Flex confirmed earlier in this thread: "You have to use the preamp.  There is insertion loss from the preselectors and the RF preamp is needed to overcome the insertion loss."

    BTW, I'm not saying your not insane, just that you're not wrong!  :^)
  • Michael WheatleyMichael Wheatley Member ✭✭
    edited May 2019
    Why and how is the 6400 different from the 6400M? I hought they were the same radios except for the front panel on the M.
  • Art CArt C Member
    edited May 2019
    Well now that we’re on the subject of Test Lab Numbers.. Yesterday the results were posted and the King Flex 6700 was finally beat by the New kid on the block. The Yaesu FT-101D. Flex 6800 ??
  • Rich McCabeRich McCabe Member ✭✭
    edited May 2019
    Yea I was about to ask the same. The front panel (M) should just be a client to the rest of radio.
  • A.J. AJ2IA.J. AJ2I Member
    edited May 2019
    Then the M is just as deaf without a preamp
  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited May 2019
    Amazing considering the 6700 is around 8 years old.

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