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difference between the FHM2 & FHM3 microphones

Is there a difference between the FHM2 & FHM3 microphones ? I received the 2 for my 6400, and the 3 for my Maestro and swapping the cables, they don't appear to be the same internally.


  • KA0B_Bill
    KA0B_Bill Member ✭✭
    edited March 2022
    HI - I have this question myself, but I don't see that there was ever an answer to it? Anybody? I have the FHM-3 that came with my Flex 6400, now see that I should have turned on the bias voltage to it. Although the documentation says that for the FHM-2, not specifically for the FHM-3 that I actually have. I don't have the Maestro, so my mic connects to the back of the 6400. What are the specs on FHM-3? Nothing on the Flex website, manual says FHM-2.
  • Dewey WØYWW
    Dewey WØYWW Member ✭✭

    Hi Bill,

    I’ve asked this question at 2-different hamfest Flex booths, and Flex response was that there is no difference between versions 2 & 3. The following data, from the Flex manual and prior community discussion, is obviously more than you requested:

    FHM-1:  The original Flex hand microphone: (+20dB gain, with no bias, menu setting).

              Element Type: Dynamic

               Impedance: ~200 ohm ± 30% @ 1 kHz (Tone setting in position 1)

               Sensitivity: -79 dB ± 3dB @ 1 kHz

               Frequency Response (Tone 1): Full range (preferred setting)

               Frequency Response (Tone 2): -14 dB ± 3dB @ 100 Hz

    The FHM-1 microphone has a tone control switch on the back of the microphone, that is used for adjustment of the microphone's frequency response.

    Setting Tone switch to "1" (left) position, enables a wider frequency response, resulting in higher fidelity audio.

    It’s recommended to set Tone switch to position-1 and use SmartSDR Transmit Equalization, to tailor tonal qualities of the microphone to your voice.

    Setting Tone switch to "2" (right) position, will roll off bass frequency response, resulting in more audio energy in your transmitted signal providing for optimum articulation for DX/communication quality audio. However, the same effect can be achieved by setting the Tone switch to position-1 and using the SmartSDR Transmit Equalization to reduce frequencies in the 50-400 Hz range.

    There has been several articles written about tips using the FHM series mics.

    FHM-2:  A high output condenser microphone that requires menu bias voltage setting to function properly.

              Element Type: Condenser

               Impedance: 2.2k ohm ± 5% @ 1 kHz

               Sensitivity: -38 dB ± 2dB @ 1 kHz

               Frequency Response: Full range (75-12k Hz @ -3 dB, flat)

              The FHM-2 mic had an issue, and it’s possible that the FMH-3 is either the manufacturer’s corrected            version, or Flex’s internal re-worked version (if their manufacturer had a parts availability issue).

               The issue was previously described as follows by Neil, N4FN:

                           FLEX does not "make" two different FHM-2 mics.  The issue is that FLEX received some mics

                           from the vendor that lack the capacitor and resistor so that it will pass BIAS. It is NOT a modular

                           cable problem. Gerald and I discussed this and they are working on a solution.  I discovered this

                           problem some time ago and did extensive testing with Neal (he spells his name wrong) and Tim

                           Ellison.  It was when I opened the mic and looked at the back of the circuit board that the

                           problem was discovered. Flex sent me a properly configured mic and the issue was solved.

                          When using MIC 2, with what I call the "pigtail" cable, there is no problem, because the Maestro

                          applies Bias on Mic 2 differently.  The issue is only on MIC 1 with the modular cable and a

                           FHM-2 mic head missing the components... As I understand it, in an email from Gerald, Lori                                   Hicks at Flex is working on this issue with the vendor.

    FHM-3:  A high output condenser microphone that requires menu bias voltage setting to function properly.

    Perhaps Flex might be willing to say what the FHM-3 mic nomenclature represents. Surely, they

    would not change version numbers without a reason to do so.

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