Tom Rauch wrote:
>Rich Measures wrote:
>> ? For c. five years, the ARRL Handbook had the wrong Pi-L tank values -
>> - despite being repeatedly told about the problem. .
>
>Is it easy to explain what is wrong about the values?
>
If we're talking about the same formulae, they were approximations that
assumed a high loaded Q. They were probably good enough for designing
output tank circuits, but gave major errors in Q values for cathode
circuits with deliberately low loaded Qs.
Accurate design formulae have been given in the Amplifiers chapter since
1995. If you analyse a network designed using the post-1995 formulae, the
actual loaded Q is exactly correct. The reference is not given (a long-
term failing in the ARRL Handbook's editorial policy, IMO) but I believe
it was to a QST article in the early 1990s.
>> since 1995, the Handbook has had an inaccurate method of calculating RF
>> current in a DC blocking cap. My guess is that it will remain there until
>> sometime around 2040. .
>
>What is the correct method?
The formula given is described as a "conservative and very rough rule of
thumb" - the implication being that it's an over-estimate, which should be
adequate for the purposes of choosing a suitable capacitor. If there's any
evidence that the formula can ever under-estimate the current, I'm sure
we'd all like to know.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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