Add a PIN limiter diode across the input terminals. Why a PIN diode and not an ordinary small signal diode like 1N4148? The former's longer carrier lifetime prevents the diode from "following" the RF signal; i.e. being turned on and off and producing intermodulation products. A good reference is this: . Referring to fig. 1 in the referenced article, the shunt inductor can be omitted as the loop plays the same function.
73, Leong, 9M2LCL, ex-9W2LC
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