ICOM IC-7000 too much Audio Fix(Road Noise)

Discussion in 'Mobile Radio' started by VK4GAP, Sep 16, 2020.

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  1. VK4GAP

    VK4GAP Ham Member QRZ Page

    Putting this up here now as i'll forget the details later on , sitting in the Vehicle right next to the river at 3AM calling CQ on 80M 50klm south from home , Using the laptop on 3G .

    When i get home around 11AM i'll post up the method pictures which worked , that above was the pre-face .

    So , i found over the last few weeks whilst mobile sitting on 100kph (60mph) and calling CQ on 80M with no audio from me there was a half or more scale on the power meter output of road noise being transmitted , on trying different settings with the mic gain and compressor the only time i could actually stop it from happening was when the mic gain was at 0 (zero) , even at 1% there was 20 to 30w being emitted and since i want the compressor on i looked into a why?

    The ICOM HM-151 mic has the electret always hot with no adjustment so even with 1% mic gain there is still to much drive from the electret element (schematic will be up later) , so that output needed to be adjusted , i did it the most easier way for me with the limited resources i have .

    Now after testing along the way here for a half hour drive down the highway i had compressor on at the default 5 setting , mic gain set at 20% driving along at highway speeds holding PTT down and no speech from me the power meter just flicks the 1st green led on the bar-graph yet then when calling CQ the radio drives to full output still with plenty of room to increase the gain if need be .

    Stock mic no mods (until now) , radio recently acquired , mic sounds real good at base as i have listened on the websdr's so nothing wrong with it , even listened here mobile parked this morning on the websdr's and all good .
    Later ---------------- Paul
  2. KB7WG

    KB7WG Ham Member QRZ Page

    What kind of vehicle? Windows open? Grainy road? Hard tires?

    Throat mic.
  3. VK4GAP

    VK4GAP Ham Member QRZ Page

    Are you aware you have left out a question mark after Throat Mic? so i have just remedied that for you out of Irony .
    ND6M likes this.
  4. KB7WG

    KB7WG Ham Member QRZ Page

    Perhaps something like the radio shack "audionic" FM walkie talkie of old might help. The microphone is in your earbud, and picks up your voice thru your eardrum. No outside noise.
  5. VK4GAP

    VK4GAP Ham Member QRZ Page

    Back to the HM-151 , pics included

    As one can see its a simple affair , just limit the audio output with the VR , atm it's too low i have found out as the setting atm does not allow enough compression BUT atm it does not pick up any external noises like before , i can point the mic facing away at 2ft and talk in a normal voice with ptt down and there is no rf output with comp setting 5 and mic 50% but there is only a bar or 2 showing on the comp meter when speaking into/across the mic even though there is full output from the radio .

    So from that quick experiment the thing to do is adjust the VR and find the "Balance" of picking up external noises like cabin drumming AND a decent amount of compression showing on the meter , that is it and i'll stick at it as i gather i'll find that balance .
    And yes that is the only size gigantic VR i had , the pads are already there so i took the easy way .



    KF7KIN likes this.
  6. N2PQW

    N2PQW Ham Member QRZ Page

    Hello Paul,
    It's worth noting that the ICOM SM-50 Desk microphone, an option for the IC-7000, has a dynamic element (not that you'd use this in your mobile install); certainly a dynamic mic could be adapted to your IC-7000, which should have much less gain, and dampen the cabin & road noise.

    According to Heil Sound, here's the pinout for that radio [don't take insult, I'm sure you already know this, but I like to include these things for other readers and users :) ]
    " 8-pin Modular (IC-703/706/2000/7000)
    Pin 4: PTT
    Pin 5: Microphone Ground
    Pin 6: Microphone In*
    Pin 7: Ground

    *Pin 6 also carries voltage for the electret elements used in Icom mics. This voltage must be blocked for use of Heil Sound dynamic elements. "

    I can't personally confirm this scheme, but I trust the source of the info, so I'd tend to believe it.

    David / N2PQW
  7. VK4GAP

    VK4GAP Ham Member QRZ Page

    Pin1 is the 8v to supply the mic (leds, the IC and mic element) look at he schematic again David , that is a screen grab of the icom HM-151 service manual .
  8. N2PQW

    N2PQW Ham Member QRZ Page

    Paul, please accept my apology for breaking my own rule, "Only accept information from the Source of Origin". In this case, I certainly should have looked to Icom directly, and not the third-party, Heil Sound.
    Here's a tabular breakout of the diagram you posted, taken directly from page 10 of the IC-7000 Instruction Manual, directly from an ICOM website:
    IC-7000 Microphone PinOut.jpg

    I stand corrected, but I still would like to see your opinion about substituting a Dynamic mic element for the Electret unit. I believe it would be easily done using pin 6 (Mic Input) and pin 5 (Mic Ground), and bypassing the circuitry of the electret system.

    David / N2PQW
  9. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Nothing wrong with electret mics. They are used in aircraft; a far noisier environment. Perhaps what you need is a 'noise cancelling" mic element. I suggest looking at David Clark and Bose aviation headset designs for clues. Aviation noise cancelling mic elements typically have openings on both the front and backside of the electret element.
  10. VK4GAP

    VK4GAP Ham Member QRZ Page

    Pin 6 is the Mic Output , cant you read schematics? , look again at the post #5 schematic , also in where the modular break-out is also there .

    No opinion from me btw , concurrently the OP is all about the HM-151 and stays that way from me .

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