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Hi, I have an IC-746PRO whose ALC and output jump. I tested it in FM mode on 2 meters (which is what I primarily use) and find the ALC jumps and the output jumps but I can still get full power output at times. If I have the RF power control fully turned up the ALC on the meter jumps around, it can go from 0 to full and then back and the output jumps from say 70 to 100 watts and around. I get good reports always but it's annoying, is there a somewhat easy fix to keep it stable? Please reply to my e-mail if possible. Thanks for any help!
Adam Farber W4AJF
Cooper City, FL
adamf@eeco.com

Hello Adam,

In my 35 years of Land Mobile Radio equipment and systems, I've never seen anything related to ALC and the FM mode of operation. Perhaps you have an antenna problem with VSWR mismatch. Get a reliable RF VHF Wattmeter, Bird, Coaxial Dymanics or even Mirage MP-2 and minimum 100 - 250 Watt 50 Ohm Coaxial Dummy Load. A length of 2~3 Feet of either RG-213/U or 8214 50 Ohm Jumper cable with the appropriate RF connectors and adaptors.

Disconnect your external antenna from the radio. Connect the coaxial jumper cable to the IC746 and the Input of the RF wattmeter and take the 50 Ohm Dummy Load and connect it to the Output of the RF wattmeter using the appropriate adaptors. If you are using a Bird RF Wattmeter, insert a 250 Watt 100 - 250 MHz sensing slug into the wattmeter with the ARROW pointing towards the Dummy Load.

Key the transmitter, set the the Power Output for 100 watts on the wattmeter and observe the RF Power Output meter for 1~2 minutes. Is the RF Output jumping around? Verify your connections are tight, If they are, the problem points to the internal ICOM Transceiver. If the RF Power Output doesn't jump around, the problem points to your antenna system.

With your transceiver Unkeyed, disconnect the 50 Ohm Dummy Load and connect the coaxial connector from your antenna's feedline. Key the transmitter for 1~2 minutes and observe the RF Output wattmeter and now flip the sensing element around so the ARROW points at the ICOM transceiver. If the meter indicates Higher Forward Power Output and 5 to 25 watts Reflected Power, You have an antenna / coaxial cable VSWR problem. And if the RF Power is jumping around with these readings, something is loose on the antenna and/or coaxial feedline.

Do not use RG-58 type coaxial cable on VHF because the RF Losses are too great!

Hi, thanks for the note. I used 2 different dummy loads with the appropriate cables and that was not it. However, at the suggestion of Paul Whatton G4DCV who told me a friend of his had a similar problem and tightened all the screws in the RF board area, I did that and now the radio is staedy at 100 watts! Thanks again, Adam Farber

It is the dreaded ic 151 failure....perhaps?