I have an Icom IC-756 with lower output on 28nhz and it increases as you go down in frequency, here is what I mean, this is output:
28mhz= 40 watts
24.5mhz=50 watts
21mhz= 70 watts
18mhz= 80 watts
14mhz= 90 watts
10mhz= 100 watts
7mhz= 105 watts
3.5mhz= 115 watts
1.8mhz= 98 watts
Tested in to a dummy load without the antenna tuner on.
Any help greatly appreciated it!
Thanks,
Adam Farber W4AJF
Cooper City, FL
Help with output on Icom IC-756 please?
I don't own a IC756 but there are several things I would compare on this transceiver using good test equipment and observation.
What is the A+ reference set at on the DC Power Supply: +12.0V DC or +13.8V DC?
Does the DC Power Supply regulation drop in voltage more than .2V DC on transmit?
What is the DC Current draw (in Amperes) at 14MHz versus 28 MHz?
Have you gone to the ICOM Webpage and looked at their published electrical specifications for higher frequencies and does ICOM degrade the RF Power Output at 28 MHz?
What happens if you switch in the "Automatic Antenna Tuner" into the circuit ... does the RF Power Output Increase or Decrease?
What type RF Dummy Load are you using: Bird, Coaxial Dynamics, MFJ, a Heath Kit Cantenna or something Homebrew?
What type of a RF Wattmeter are you using to indicate Foward & Reverse Power: Bird, Coaxial Dynamics, H-P/Agilent, Motorola, Mirage, Heath Kit or Diamond?
In testing this transceivers RF Power Output, which mode of operation are you using: CW, AM, USB or FM?
Does the RF Transistors Heatsink get extremely Hot to the touch on the 28 MHz band compared to 14 MHz?
Do you have a Service Manual and Schematics for this transceiver?
What is the A+ reference set at on the DC Power Supply: +12.0V DC or +13.8V DC?
Does the DC Power Supply regulation drop in voltage more than .2V DC on transmit?
What is the DC Current draw (in Amperes) at 14MHz versus 28 MHz?
Have you gone to the ICOM Webpage and looked at their published electrical specifications for higher frequencies and does ICOM degrade the RF Power Output at 28 MHz?
What happens if you switch in the "Automatic Antenna Tuner" into the circuit ... does the RF Power Output Increase or Decrease?
What type RF Dummy Load are you using: Bird, Coaxial Dynamics, MFJ, a Heath Kit Cantenna or something Homebrew?
What type of a RF Wattmeter are you using to indicate Foward & Reverse Power: Bird, Coaxial Dynamics, H-P/Agilent, Motorola, Mirage, Heath Kit or Diamond?
In testing this transceivers RF Power Output, which mode of operation are you using: CW, AM, USB or FM?
Does the RF Transistors Heatsink get extremely Hot to the touch on the 28 MHz band compared to 14 MHz?
Do you have a Service Manual and Schematics for this transceiver?
Maybe not...
If the finals are producing 115 watts on 75 meters the problem probably is NOT the final power transistors. Before going any further, run the test again using a completely different coax cable at least 23 feet long and a completely different dummy load. Good luck...
Al
Al
P.S.
Some years ago the Icom 735 had similar problems. Turned out to be excessive reactance in the power supply being used. When the rig was powered with a battery (pure DC) the problem went away. This is written up on the Icom support site. Leads to another suggestion, hook the rig up to a battery and see if the problem continues.
AL
AL