IC-7300 Average SSB power modification
If you Google the title of this post, I’m sure you’ll come across some results which detail a very simple modification you can make to your IC-7300 which some believe increases the RF output power. This is vague and misleading.
The PEP (Peak Envelope Power) of the IC-7300 is rated at 100 watts. This would be denoted by “+Vmax” and “Positive Peak” on the image on the right. The RMS of a peak waveform is 0.707 times the peak, and the average of a pure sine wave can be determined by 0.637 times the peak value. However, a voice waveform is far from a pure sine wave, so the average must be calculated differently. One way you can calculate the average of a non-sinusoidal waveform is by dividing the waveform into sections over time, adding the amplitudes of each section together, and dividing it by the number of sections. The more sections you divide the waveform into, the more accurate the result. See the image to the right for an example.
See page 24 of this fantastic technical document on the IC-7300 by AB4OJ for a visual indication of the IC-7300 PEP, and much much more: http://www.ab4oj.com/icom/ic7300/7300notes.pdf
Back to the modification – This is a hardware modification to increase the average SSB power. Even though it is mentioned in the modification notes that adjusting the audio settings will not bring up the average SSB power, I disagree. Average SSB power can certainly be increased by having your audio setup optimized. There is no need to void your warranty or risk damage to your equipment by modifying it. If you want to do it, go ahead, but in my humble opinion there is certainly no need to do it.
Don’t expect the IC-7300 (or any radio) settings to be optimized right out of the box. Use the microphone gain, compressor, and EQ to set up your audio correctly, and tailor it to your voice. You can eliminate the need for such a modification if this is done correctly. Compression is particularly important, as it increases the apparent volume of your speech and also increases the average power. For example, a 3:1 compression ratio will result in a 1 dB change in output level from a 3 dB change in input level. Since SSB power is directly related to the audio input (ALC aside, somewhat) then the audio dynamics translate directly to RF output power dynamics. Sort your audio out.
Certainly this hardware modification will increase the average SSB power, and achieves this by slowing down the ALC response, but is this a good thing? Is it worth doing?
It is important not lose sight of the real decibel impact of such a modification. The RF world is logarithmic, not linear. Even if this modification Increases the average SSB power from 40 watts to 70 watts – what does that get you? It gets you 2.4 dB of increase. That’s less than half of an S-unit. Another thing to consider is how much extra stress is being placed upon the output stage of the RF PA by holding the average power artificially high?
The point of this post is not to oppose the hardware modification. It is your radio, you can do what you want, and experimentation is at the core of amateur radio. However, I think it is important to understand the difference between average and peak levels, and to understand the direct relationship between the audio waveform driving the transmitter and RF output waveform.