Power spike / Overshoot on transmit for Yaesu FT-736 & FT-790 and Kenwood TR-9000

In order to solve some problems with solid state amplifiers, my friend Jack PE1KXH measured the power spike of some transceivers. The first exercise was to see if something could be measured at all.

Jack tested his own transceivers in FM mode at various power levels. Measurements were carried out using a 32dB attenuator and a 50 Ohm termination in the oscilloscope. The oscilloscope used is a Tektronix TDS744A


Kenwood TR-9000 This radio had a homebrew power setting and appears to be fairly clean.





Yaesu FT-790

This radio is used to drive transverters at PE1KXH QTH. Measurements again in FM. This transceiver is not so clean. This is with 3W power out.



The following picture is in low power.



Yaesu FT-736 on 144MHz

Full power

Medium power


Yaesu FT-736 on 432MHz

Full power

Medium power


Yaesu FT-736 on 1296MHz

On 1296MHz measurements are only relative. The oscilloscope is a 500MHz type so, not very trustworthy levels.

Medium power

Nice to see that the first CW pulse is growing slowly in amplitude and  second is very “square”.