On Aug 7, 2006, at 8:53 AM, Ian White GM3SEK wrote:
> R L Measures wrote:
>>> But that resonance belongs to the whole circuit, involving the
>>> anode and
>>> cathode and all their associated components. There are too many
>>> unknowns
>>> in that loop to understand what the frequency of the observed dip
>>> might
>>> be telling us about reverse feed-through from the anode back to the
>>> cathode.
>>
>> It tells me that the grounded grid is no longer acting as a
>> perfectly wondrous shield between the anode and the cathode.
>
> Sorry, wondrousness is not a valid SI unit. I thought the intention
> of a measurement was to quantify something.
Good point, Ian. The sentence should have read: The grid is no
longer acting as a perfect shield between the output and the input of
the amplifying device.
>
>>>> I must admit that I've never had a lot of use for GDO
>>>
>>> Me neither, because it's so difficult to understand what a dip
>>> actually
>>> means, except in the very simplest cases.
>>
>> The dip means that the entire circuit has a resonance at that
>> frequency.
>>>
>>> The GDO is deceptively simple instrument. The trick is to tell
>>> when it
>>> stops being simple, and starts being deceptive.
>>
>> Can a dipmeter indicate resonance when there is none?
>
> Probably not - but the instrument never tells you what that dip MEANS,
Correct, but it does tell the operator where the DUT's resonances are.
> and with a dipmeter the interpretation is always open to question.
So if there's a dip at say 10MHz that isn't there when the dipmeter
is not coupled to the circuit under test, it's debateable?
>
>
>
> --
> 73 from Ian GM3SEK
>
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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