Icom IC-746 TX power calibration
In some cases you might need to give a little bit more in your transmit power from your Icom IC-746. You might want to do this so you can have near or just 100w while you speak on SSB modulation which is more common or you just want to see your transceivers capabilities(for testing purposes)! The procedure is quite simple and does not require any specialty on electronics, you just need to be careful!
You will need a bench, 2 screwdrivers one very small and another one to open your transceiver. Also you will need a descent power meter, preferably a Bird Power Meter, and a dummy load for HF frequencies. In my case i had a Diamond SX-600 SWR/Power Meter and a dummy load.
The procedure:
1) Turn upside down your transceiver
2) Start by unscrewing the screws at the bottom and the side of the transceiver
3) Remove carefully the bottom cover
4) Find the 4 turning pads which are located over the plug of the voice module.
As you can see from the picture above ,the area that we care about to make the changes is located in the red box. From left to right there are 4 screw pads.(they are tiny!)
1) R989 = HF TX POWER
2) R991 = 50MHz TX POWER
3) R993 = 144MHz TX POWER
4) this one is the AM Carrier TX POWER
Now the measurement will be made on the 20m band and specifically at 14.100.00MHz. You have to turn your transceiver to RTTY mode, and set the TX Power to minimum. Connect the dummy load, press the transmit button and check your external power meter while you are setting the transmit power from the 746 to maximum. My opinion and setting is to set the TX Power to approx. 120W continuous carrier. This way you will achieve close to 100W SSB without over-stressing your transceiver. Once you finish your calibration close the transceiver, and you are done!!! If you measure the power output in all the HF bands you should see minimum variations from 120W max to 115W min.
Proceed at your own risk!!!!
73's
PS: The measurment you see in the first picture was made after i finished the calibration with the dummy load ,and the transceiver is loaded on my antenna, that is why you see SWR to 1.2 and the TX Power is slightly less(due to SWR).
