Re: attenuators, power dissipation

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Greg Broburg
Posts: 156
Joined: Sat Apr 28, 2018 6:48 pm

Re: attenuators, power dissipation

Post by Greg Broburg » Wed Sep 16, 2009 1:21 pm

I think that the first idea for an attenuator would be 10 dB steps and

watch out for the maximum power dissipation on the one that is used for

the input. Since the analyzer has huge dynamic range, the idea is to

complement that dynamic range with useful attenuation. For instance if

the analyzer overloads at +5 then to be useful, a 40 dB attenuator needs

to withstand +45 dBm to see its full benefit. That means that the

components in the attenuator need to have this power dissipation concept

in mind. Inside the HP programmable attenuators there are laser trimmed

glass pads and ceramic pads. The glass pads are the norm and the ceramic

pads are used to dissipate more power. I assume that the glass pads are

more accurate. I have 1 dB steps on all of my analyzers but do not

consider this to be essential. Thanks to Scotty and the excellent, huge,

dynamic range plus computing capability and this makes the attenuators

much less necessary.

If you are analyzing in the wild (from an antenna) the attenuator allows

you to see if the front end is overloading. To do this you kick in -10

dB and look at the forest. If the forest falls by more than -10 then you

are in overload. I use the -10 level just to protect the mixer from

things like esd when connecting hoses. Especially with huge dynamic

range there really is no penalty. The only time I remove the -10 is when

I am sniffing and looking for little signals. Granted using -3 or so

will help a great deal with this problem I consider -10 to be a great

help for normal use. It would be best for the attenuators to remember

their last setting. That way if you turn the unit off you still have

protection for esd when disconnecting cables. Otherwise you need to be

in the habit of not touching the input until the power is on and the

attenuator is active.



Since I already have two rotary stepping 0-30 db in 1 db steps

attenuators, would it be recommended or wise to use both of them in the

MSA, one for the input and the second one for the output of the tracking

generator ?




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