[AMPS] one more point

[John Lyles]

Soeren, OZ1FTU, made this observation:

>I tuned up on 20m, and was I surprised. The AL1500 produced signals up to
>350MHz!!! No wonder the neighbor had complained about TVI. Parasitics or
>not, I don't know. The broad band spectrum only exists when the amp. is
>excited. Keying the bias on/off can't produce any unwanted behavior.
>And yes, I checked the TS-680 for harmonic suppression, and the signals
>was definitely not coming from the driver, though it wasn't the best I've
>seen.

I forgot to add the point that the probe used (a wire) definitely has a
frequency response, probably capacitive, so it has a rising sensitivity
with frequency. Even directional couplers do. Like 6 dB/octave.
So the apparent parasitics will show up high level compared to even the
fundamental on a spectrum analyzer, and also they can easily overload the
S/A mixer -- even high harmonics can.

So bear in mind that these are all pitfalls that can cause a lot of VHF
readings on a spectrum analyzer, that are not necessarily really those
levels in circuit. Maybe, in your case, the amplifier is truly dirty... but
check that none of these conditions are present (in this and the first
email I sent on the subject).
73
John
K5PRO



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