> Peter:
>    "Even a simple cover joint with wire-clad gasket has two or
>     three steps (depending on how you count).
>
> To what is this applicable? (Microwave oven or choke joint)?
>
> Jim

Both or none. I meant the cover joints normally used in RF proof equipment
boxes, with a channel and an o-ring clad with wire (and sometimes
flashing), as compared to oven doors. The simple box joints get it down by
40-55 dB in VHF/UHF in my experience, and they are more complex than the
oven door joint.

I believe what you say about the single-'step' continuously variable
attenuators you mention, they can be very good, it's just that as you
said, there are other factors (such as oscillator leakage) which prevent
them from working perfectly in real life. There is also the small issue of
the price tag of those parts and their 'wide' availability.

It is trivial to design a T-pad attenuator with resistors for say 80 dB in
one stage, but due to real life parasitics, radiative coupling, ground
conduction, etc, etc it will do 80 dB only at DC. This is what I meant wrt
'not possible to attenuate in 1 stage'. The 30 dB I gave is a rule of
thumb that comes from my experience with real life equipment and
attenuators, in the sense that a 30 dB T, L or PI assymetrical attenuator
calculated and implemented as designed will indeed attenuate 30 dB +/- 4
dB in the frequency band considered. Above that, the ifs become too many.

If I'm not wrong the ARRL handbook also gives (or gave ?) a DIY attenuator
schematic, and there too the first two stages are 26 dB, not a single 50
dB stage.

Peter

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