Why does a classic envelope detector produce a negative voltage for some periods, when high frequencies are put in?
v1 1 0 sin(0 2 150MEG)
...
tran 5us 50ms

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What's wrong with this picture?

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The sampling time is violating Shannon's Law.  Measurement error.

What is the diode spec?


Rectification efficiency \$V_{HF} = 2 V, f = 100 MHz ~~~ η_r = 45 \text{%}\$


It won't work well because recovery time is 4ns with 100 Ohm load and yours is only 500k.

Although Cj=2pF is ok. ( even though max in the datasheet is 4pF )

As @Sparky256 said try a UHF diode. 

These have faster recovery time than 8ns on a signal with a 6.7ns cycle time.
 This is why efficiency is poor at 100MHz and worse at 150MHz.

Try a Falstad simulator.  Limited parameters no custom parts. You make the passive part models and LOGIC, OA's have 0 Ohms out. Same with Voltage sources.

Press Reset anytime.