Digimode interface affecting mic sensitivity on IC-718?

Discussion in 'Microphones, Speakers & Audio Processing' started by KB1UJS, May 1, 2012.

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  1. KB1UJS

    KB1UJS Ham Member QRZ Page

    Hi all. I have an XGGCOMMS audio and CI-V interface cable (IC-Cable-8 at http://www.xggcomms.com/userimages/procart2.htm) connected to the accessory port on my IC-718. It does its interface job well, but I noticed a drop in output on SSB when using the handheld mic with the interface connected to the accessory port. I can easily get the ALC meter to register by speaking too loudly into the mic with the mic gain at 50 and the interface disconnected. There is no ALC action at all with the interface connected and all other conditions the same. When watching the power meter on the radio, I'm seeing less power out of the radio with the interface attached than when it's not attached. I'm thinking the interface is loading the mic line or in some other way affecting the mic's signal output. Any ideas on what is going on here would be greatly appreciated.

  2. KA1MDA

    KA1MDA Ham Member QRZ Page

    If the output impedance of the interface is too low, it could be loading down the AF amplifier stage associated with the ACC port. Does the interface have a selectable output impedance? If ity does, try setting it higher, like 5K or 10 Kohms.

    Tom, KA1MDA
  3. KB1UJS

    KB1UJS Ham Member QRZ Page

    The interface has no adjustments of any type. It's a pretty simple cable with the correct pinout to match audio in and out and ptt to the correct pins in the ACC connector. There is a PTT keying circuit and a pad on the audio input line to prevent overloading the receiver, but not much else for circuitry. I think you're right about the too low impedance being the issue.

    Would a 1:1 audio transformer help in this case?

  4. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Some radios don't play well with microphone and data devices plugged in at the same time. You may need to unplug the device that is not in use at the time.
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