ICOM 746pro 2m FM problems

Discussion in 'General Technical Questions and Answers' started by N8DEL, Nov 20, 2021.

ad: L-HROutlet
ad: l-rl
ad: Left-3
ad: Left-2
ad: L-Geochron
ad: abrind-2
ad: L-MFJ
  1. N8DEL

    N8DEL Ham Member QRZ Page

    My Icom 746 pro, with a new Diamond 2m and 70 c.m, antenna, when sending out on the 2M to the East Coast Reflector (ECR) 147.150, Duplex 147.750, tone 123.00, my SWR goes full max., I hit the ECR but cannot be heard, all distorted or static. When I use the 70C.M., for 440 band my SWR is a very good 1.1 .

    My other antenna port is a brand new Comet antenna for 3.5 to 57MHz. SWR is all good there too, only problem is on FM, 147.150, full max on SWR.

    Any suggestions, help, greatly appreciated.



    Attached Files:

  2. WA9SVD

    WA9SVD Ham Member QRZ Page

    Is the problem only on 2 Meter FM, or other modes as well on 2 Meters? Have you checked the SWR on 2 Meters CW using an FM simplex frequency (with voice ID via FM afterwards to be LEGAL:cool:) to see if the problem is with the radio, or a defective antenna? (A dual band antenna MAY well work reasonably on 70 cm, but have problems on 2 Meters.)

    One other thing: have you tried using the radio on 2 Meter FM into a dummy load to see if the SWR is (at least, close to) 1:1; if it isn't, then the problem may well be with the radio.
    Last edited: Nov 20, 2021
  3. N7VGO

    N7VGO Ham Member QRZ Page

    I have to ask, is the 2 meter antenna plugged into the 2 meter jack?
  4. N8DEL

    N8DEL Ham Member QRZ Page

  5. N8DEL

    N8DEL Ham Member QRZ Page

    Good Sunday morning and thanks for the replies. My Icom 746pro, with 3 antenna ports, the 2m port is fitted with the new Diamond 2. and 70c.m., dual band antenna.
    The other two ports a dual band base antenna 2M / 440 for VHF / 2 m / UHF 70cm. port # 2 and the new comet antenna model # CHA-250B multi band from 3.5 to 57MHz. into port # 1 . No transmitting when using the diamond antenna into the 144 MHZ port / 2 m.,
    After two days of trying different adjustments, I then took the Comet Antenna which is for 3.5 to 57MHz and plugged it into the 2 M port / 144 MHz. // My SWR went down and transmission became possible, my SWR is at 3.1 . Is there something wrong with my transceiver/ antenna problems, the comet 2 m / 70cm?
    Thanks again for advice,

  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    From what you describe, it sounds like the antenna you WERE trying to use for 2 Meters (dual-band Diamond?) is malfunctioning. The HF/ antenna could well have a (unintended) resonance near the 2 Meter band, and that is why it "works" after a sort, but with an SWR of 3.1:1
  7. N8DEL

    N8DEL Ham Member QRZ Page

    Thanks for the reply. The Diamond 2m and 70c.m, appears to be not working. I plug in the Comet Antenna a 3.5 57 MHz into the 144 MHZ and my 2 m side works, but with "white" noise in the background. Can I be using my 746pro wrong, as in not having the correct settings?
  8. VE4CY

    VE4CY Ham Member QRZ Page

    Of the three ports on the 746 Pro, only one will accept a VHF antenna.. That's the one in the middle. The other two ports up on the corner are for HF/6 meters only. You can't use a VHF antenna plugged in to either of these. So you can only connect one of your VHF antennas to your 746. (The image below is from the 746 Pro manual).

    If you have your Diamond antenna plugged into the VHF connection and it still gives you high SWR, then it probably is an antenna fault. You'll need to buy/beg/borrow or steal an SWR meter to accurately check it out.

    Attached Files:

Share This Page