First AM contact

Discussion in 'Amplitude Modulation' started by AA4OO, Jan 31, 2021.

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  1. AA4OO

    AA4OO XML Subscriber QRZ Page

    I made my first AM contact today with local ham on 40m, while testing out a newly acquired GRC-9. I have been successful with CW contacts since receiving the old radio but wanted to try out the old Shure Army T-17 carbon mic that shipped with it with on a voice contact.

    The unit is rated at a mighty 7 watts out on PHONE-HI but according to my QRP watt meter it was belting out 10 watts as I talked. Likely not going to be setting any AM records with it. The other station was running 10 watts on a Yaesu 450D. We are both CW ops so finding his microphone took longer than the contact.

    The other station told me my modulation was good and it sounded like me. He also reported good frequency stability.

    One thing that I need to track down... It seems that something responsible for AM modulation isn't powered until key down; so before speaking for the first time, or after a long pause between transmissions, I have to wait 3-5 seconds for something to wake up before speaking. I see no power output on key-down for a few seconds. I suppose it could be the carbon mic. I'm not familiar with their operation, but as there's no output I'm assuming it's a tube filament that isn't powered prior to transmit. Hopefully more knowledgeable individuals can chime in.

    All-in-all it was fun to "talk" using this antique, with my mouth rather than my fingers (CW) for the first time.


    I may try checking in on a military AM net but with my limited power it seems unlikely unless there is fantastic propagation.
    WQ4G, KA1SHU and W1BR like this.
  2. W1BR

    W1BR Ham Member QRZ Page

    Final is 2E22 battery tube, directly heated cathode so it takes a few seconds on key down to warm up..
  3. AA4OO

    AA4OO XML Subscriber QRZ Page

    I'm pretty sure that when I had it apart I observed the 2E22 heater glowing whenever the transmitter was set to SEND mode. Maybe I didn't switch it to PHONE when I had it apart tracking down a voltage problem from the Vibrator power supply.

    When I'm in CW mode output is fully available from the initial key-down (as a bonus the GRC-9 CW is full break-in).

    Come to think of it, when I'm in modulated CW mode (MCW) I get full output on the initial key-down and that mode employs amplitude modulation, so it's something related to the PHONE mode.

    As I think through this I'm leaning toward the old WW2 carbon microphone as the culprit. I've tried getting the carbon capsule out to wack it but the bakelite mouthpiece cover is firmly attached, and isn't unscrewing. Anyway, it works, I just have to let the other operator in an AM conversation know that it takes me a while to answer :)
    1 person likes this.
  4. W7TFO

    W7TFO Premium Subscriber QRZ Page

    The carbon mic element won't delay the RF output.

    However, if the internal switch is wonky, that might be the problem..

    Again, some of the filaments don't fire until you PTT.

    If I remember correctly, the GRC-9 is wired that way.

    BTW, the T-17 mic mouthpiece is held to the handle by several little screws, usually sealed with black paint.

    Check your TM for functions.

  5. N1BCG

    N1BCG Ham Member QRZ Page

    This is an AWESOME story! Welcome to AM, the original voice mode! While I'm not familiar with your transmitter, I do want to applaud your interest. Plus, your timing is great given that the AM Rally operating event is next weekend. I hope you join in and take advantage of the activity on the various bands, and you'll get a lot of mileage with modest power on 40 and 20 meters, which I expect will be very active.

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