MFJ-1788 Loop Antenna and ICOM 7300 - Tuning the Antenna

Discussion in 'General Technical Questions and Answers' started by KG5LWD, Jul 18, 2021.

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  1. KG5LWD

    KG5LWD Ham Member QRZ Page

    This question is posed to those who have experience with an ICOM 7300 and MFJ-1788 loop antenna. I am trying to figure out a way to better tune my MFJ-1788 loop antenna with my Icom 7300. The antenna instructions for the antenna say to put an unmodulated tone through the antenna to any desired frequency between 10.1 and 29.7 MHz (between 1 and 50 watts). I tried configuring my radio mic to use the down button to act as a straight keying device for CW. But the antenna's separate tuner does not seem to work to adjust the SWR in CW mode. However if I use the RTTY mode, I can get things to work. Is this the correct way to tune the antenna on the 7300 or would the CW be better and how do you accomplish tuning this way? It seems to me using the RTTY to tune while on FT8 mode I will be causing a lot of QRM since it takes up a lot of the bandwidth and interfere with other signals.
     
  2. W6MK

    W6MK Ham Member QRZ Page

    Read the instructions on how to send CW with your rig. You don't want to use the mic controls to send a carrier without a modulated tone. Using a mic means sending a voice (sideband)
    signal which will only occur with an audible input into the mic. Such a modulated signal won't be appropriate for the antenna tuning device to work.

    This usually means to choose the CW mode, configure the key input properly (straight or manual key), wire a key appropriately (to tip and sleeve of plug that inserts into key jack), and plug that key in.

    Easy peasy. Push key to send CW or your carrier without a modulated tone.

    You will also want to disable the rig's ATU.
     
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The antenna is smart, the rig is ridiculously stupid.:)

    RTTY should work fine, but turn power down to a watt or two, not 50W. The 1788 tunes with just "received noise" pretty well, and can be "touched up" with a very low-powered carrier signal.

    I don't have an IC-7300 but do have an MFJ-1788 (for about 25 years now, it's not new) and usually tune it just by received noise, which gets it very close to the correct tuning point.

    Be sure to disable (turn OFF) the IC-7300 internal antenna tuner. It won't help.
     
    WB5YUZ likes this.
  5. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    So this.
     
  6. K0INN

    K0INN Ham Member QRZ Page

    I have an IC7300 and MFJ1788. I've constructed a "tuner activator switch" which is described in this YouTube video

    .

    The device plugs into the external antenna tuner connector on the rear of the rig. When you press the tuner button on the rig, you get a 10w CW carrier for about 10 seconds. During that time I tune the antenna.

    If you don't want to construct the device, you can find them for sale on that popular auction site for 10 to 15 bucks.
     
  7. K0INN

    K0INN Ham Member QRZ Page

    Oops....wrong video. The correct one is below. This one makes the "tuner" switch on the rig front panel give you a CW tuning carrier.



    The video I cited before is if you want to flip your own switch to trigger the tuning carrier.
     
  8. KO4LRJ

    KO4LRJ Ham Member QRZ Page

    I have talked to tech support at MFJ and Icom and they both tell me to tune up using
    RTTY at 5 W. So I locate a station I want to transmit on and tune the radio to that
    frequency and go from there.
     

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