Weak RF output? "Real PEP" is NOT a meter!

P.E.P. ?

"Why is my radio only putting out 80 watts or less? I'm using a Peak-reading meter."

I've heard this many, many times in the past. Here is what is going on.

Most "peak-reading" meters, are not able to read the true PEP of most SSB transmitters. I would say at least 99% are not able to read "true" PEP SSB output. This is due to a "sampling rate" that is not fast enough. There is only one RF meter I know of that has a high enough sample rate to do it, the Bird 4391A, it costs $1400, not including slugs. Not going to get one in my shack! I'd rather have a good oscilloscope, which IS the single best piece of gear for reading P.E.P. and many other tests.

I have done the following test many times, always with the same results, no matter what radios I tested.

This time, I wanted to test my IC-756PROII & 746PRO.

I set up my Tektronics 2335, 100MHz O-scope & both of my good quality "peak-reading" meters (Yaesu YS-60 & RF apps VFD). These meters use Op-amps to sample the signal and drive the meter display to the appropriate level. These meters have a rate of about 20KHz. The YS-60 has a measured error of +/- 10% at full scaled reading. The VFD has a measured error of about +/- 5%. This means that a reading on the YS-60 @ 2kW (full scale) the reading could be off of (actual) RF output by up to 200 watts +/- of the reading on the meter. This is due to the non-linearity of the analog meter. The VFD error is linear across the entire range of reading.

My friend Adam VA7OJ/AB4OJ, has a web page similar to mine, that includes the test set-up. A companion page can be found here.

First, I placed the radio in CW mode, RF power output set full, and connected to the 50-ohm dummy load. I keyed the radio, and read both meters at about 104 watts CW, I then calibrated the O-scope screen cal lines to align with the screen RF display. Next, I placed the radio in SSB mode, full RF power output and spoke normally without compression on, and normal ALC readings(2/3-3/4 scale on ICOM HF radios), I noted that both meters read about 80-85 watts out in PEP mode. At the same time, the O-scope peak displays were the same as the CW maximum amplitude readings. This test has once again proved that the meters can't read the true PEP like the O-scope can, and I'm convinced that even when my meters read 80-85 watts on SSB, the "actual" RF peak output is actually about 100-104 watts.

Below, you can see simulated O-scope screen displays of the test I did. I could not get actual pictures of the screen display, due to difficulties in getting the photos. The simulated pictures, however, are accurate.

It is a well-known fact that a solid-state radio, can NOT exceed the Maximum CW output, in SSB mode. It is a simple law of engineering and physics.

Don't worry yourself too much, if your RF power meter "seems" to read lower than it should, it's likely that it can't read the truth.

All RF power meters are "relative" anyway. Just like S-meters...

I hope this has helped to clear up some of the confusion.