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6600M TX distortion

I bought 6600M before a week and I've been trying for a few days to figure out what's going on and the radio's TX sound is compressed and slightly cramped. I understand that most people just put a microphone to communicate but I bought this radio just for ESSB looking for a crystal clear audio. After many tests I realised that the sound is really incredible and crystal clear only when the "potentiometer" of the power is about 10 - 20W and the volume of the microphone does not exceed -10. At this point the sound is really unformed and crystal clear without any kind of distortion. As I turn the power to 100 the sound starts to mess up and distort slightly as if it loses its linearity. Is there anything I can do about it. Looking on the web i found some people with the same problem so i think its not my transceiver's problem but design problem. Any solution?


  • FotisGR
    FotisGR Member ✭✭

    I forgot to say that i don't use COMP, EXP or radio's EQ and the mode is SSB for 50Hz - 4000HZ or even 6Khz and i am using high quality very expensive audio external processing. I bought this radio because i was thinking it would clear and free of distortion for my ESSB hobby. I am very disappointed. Is there any solution even by software even by hardware to leave it without any kind of distortion?

  • John KB4DU
    John KB4DU Member ✭✭✭

    To help, need some more info. How is the tx audio being checked?

  • FotisGR
    FotisGR Member ✭✭

    thank you john. By ears. I means i didnt use any bench i just listen my TX audio to FDX or to my IC-775 and my IC-7851 always transmitting to a dummy load. Suddenly searching on google i found more hams with the same problem. I think the problem is general not mine but most people just plug a mic to contact so dont care about it. Power supply ir rock solid stable and analog.

  • W7NGA_2
    W7NGA_2 Member
    Good morning from Oregon, USA. Sure sounds to me like a very common problem. RF is getting into your transceiver. No issues at low power, but it doesn't take much RF ingress to distort the signal chain. Lots of mitigating possibilities outlined here on the forum as this is an issue with SDR architectures that can be difficult to overcome. Ferrites, grounding, placement, SWR, microphone type ... you'll find it if this is the problem.

    Best of luck ... 73's

    Daniel W7NGA
    Seaside, Oregon
  • FotisGR
    FotisGR Member ✭✭

    Thank you Daniel, its not RFI at all. I forgot to say that this happens even with dummy load and all of the tests are to dummy load. Its not so tragic distortion but for someone who likes to play with high quality essb audio TX this is a fault. Does anyone knows how the Power's output "potentiometer" working? I say this because this happens when the potentiometer is going more than 20. It looks like something change after 20-50 and 50-100. From 0-20 its like AB1 Class and going forward to 100 its like Class C. In dummy load from 1-20 (power ****) its like a cd TX sound . 20-50 It starts to compress a little TX audio but for many people will not critical and going to 100 its compressed enough! Is there a schematic or a knowledge how this radio adjust the power or or how it manages bias?

    is there anyone here from flex or only we talk to each other?

    Fotis Visilias - SV3EAO

  • FotisGR
    FotisGR Member ✭✭

    Thank you Daniel and all the friends trying to help me.

    After some tests those days i finally found that the distortion problem increases respectively with the power potentiometer.

    That is, it has nothing to do with the actual power output of the 6600Μ but with how open or closed is the power potentiometer. If for example the power potentiometer is at "10" the sound it is crystal clear like AB class. No distortion at all with a fantastic high quality TX audio. But if the potentiometer is at "100" there is a squeeze and a compression in the sound like is going to Class C.

    Its not RFI. I tried everything with no success. The radio is connected only with the dummy load and balanced microphone. Nothing else! I tried different PSU (i have 2 Damond GSV3000 @ 14V/30A) but they are extremely stable without ripple.

    Is someone has the knowledge to make a description what happens exactly when we move the power potentiometer from 100 to 10?

    I know that many ham radio operators needs just to contact with other hams with a simple microphone and don't care about distortion and i respect it, but i bought this radio only for essb crystal clear TX/RX audio otherwise for DX i am using my 7851 with my Orban 9105A external processor.

    Even my 7851 with 200W output don't have so much distortion changes form 5-200W .

    Yesterday i did a IMD TX test and i didnt found something wrong with 6600m. The 3rd odds was about -33db from 10-100W. I was asking my self if the 6600M has something like adaptive predistrortion because IMD results are strangely stable from 1-100W. I was thinking if the distortion i hear its because some artefacts from a predistortion or something similar. I hear something like an AGC compressor when i increase the potentiometer to 100 even if my real power is 20-40 W.

    Any idea? Any help?

  • FotisGR
    FotisGR Member ✭✭

    I forgot to say that COMP, EXP, BIAS, DAX are all OFF

    73 - SV3EAO

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Contact the EU Flex dealer for support. This forum is primarily peer to peer support.

    I use a Flex 6600m with external audio gear into the mic jack. I do not see the issue you are describing. I use the Processor on and in Normal position. Make sure the level peak indicator (the single block to the right of the bar graph meter) does not go above -5.

    Dave wo2x

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