IM3 testing of some 27MHz amplifiers at 28MHz.
IM3 output spectrum of the Elecraft K3 at 10Watts. Using the built-in dual tone option. The output power setting in dual tone is 5Watts for 10Watts output. If delivering 100Watts (50Watts setting) the spectrum is about the same. This means the IM3 is about -28dB @ 28MHz. This is quite normal for transistors used at 13.8V. This signal is used as an input for the amplifiers below. The IM3 is better if lower power is used. (for the KLV550 test below the K3 output is 2Watts) |
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The amplifier KL40 (27mc) is used with a home made harmonic filter to keep this amplifier within the regulations. (see small blue box in the picture) The amplifier is not 40Watts as given but 25Watts at 13.8V. And The IM3 performance is about -12dB which is far to low. This amplifier is using a low cost switching FET, Another issue is that the input is not 50 Ohms. (SWR at input = 2.8) |
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The dual tone spectrum of the KL40 amplifier: |
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KLV550 amplifier. Modified by me to be used for 18-28MHz ham bands. It is equipped with harmonic filters and even the rebuild of quiescent current circuitry was necessary. The maximum output is about 350Watts. Although they claim 550Watts. This test is done at 200Watts output. For more power it needs an external power supply. Transistors are 28V types. The internal transformer is far too small for continues signal (FM) and even for SSB. The claimed 14-28MHz is not possible due to the ferrite cores used into the transformers. Also the 550Watts is not possible. At 100Watts output the voltage drops to 24V already. |
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The Elecraft K3 can be over-driven if the dual tone option is used. Adjusted to 100Watts wil give this spectrum on the output: (it can of course not deliver 200Watts) The ALC reduces the output power. The 50Watts setting is ok for IM3 delivering 100Watts in total. |
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