transmission line varia
>> sqrt(L/C) is a SIMPLIFIED VERSION. some references do not point
>> this out. The full form (from memory) is more like SQRT ((L+R)/(C+g)).
>> R is the series reistance (per unit length in tx line work).
>> g is a 'conductance' related to resistive leakage thru the insulation.
>> For the USUAL range of RF intrest (say 500KHz to 500GHz) the R is so
>> small relative to the Xl and the g is so 'small' realtive to XC that
>> the simplified form works out. (Yeah. I switched for L to XL. Bear
>> with me...). AS THE FREQS GO DOWN, THE SIMPLIFIED FORM BECOMES
>> PROGRESSIVELY LESS ACCURATE. (I had cause some years ago, to
>> xperimentally verify this. got paid for it. NOT new knowledge,
>> tho. First recognized at the turn of the century....)
(References, for one, Transmission Lines, Antennas & Wave Guides,
King, Mimno & Wing, p 13, eq 14.2, etc.
[Std disclaimer, i am working from an RF perspective. Many of the
std rf approximations don;t apply, but many do.... imo...
>I realize there are simplifications in the L/C thing. Interestingly,
>Schelkunoff doesn't take the distributed parameters into account
I don't know Schelkunoff wel enuf to debate, but my recollection
is that he was ca 1930s, short wave antennas 'classical rf' where the
approximations work. (nb: this is NOT an adhiminem on S., simply
my perception that HIS approximations worked where HE was using
them. Take the extreme case of an 18" 1/4 wave on my scanner and
compare the 'r' in that to the 'r' of a 1/4 wave at 200 Khz... The
r in one case is negligible, in the other maybe not...
>It simply derives a value from the geometry of the system.
>In general, the answers are comparable in a lot of cases but I do
>wonder about using formulae that are right in only some situations.
>It'd be nice if one or other was applicable to the lot.
For Tx line work (and, i think, antenna work, which can be handled,
muchly, as a specialized form of tx line work). The 'complete'
form should work all the time, but for the cases where the simplified
form WORKS, its mucho easier to handle.
Transmission lines, as such, are more or less inapplicable to to Tesla coil
work, as near as i can tell. For 'regular radio' with a 'transmitter' (power
amp/osc) "over there' and an antenna 'over the other way' they are critical.
The usual coiling config puts the 'load' (i am trying NOT to say
antenna....8)>>) 'in' the Power Oscillator. When used as Tx lines, yeah,
keeping things matched, unlsees designed not to is RF practice.
Howsomever, fo rth special case of the antenna-handled-as-transmission line,
the portion wich IS the anteann is not 'matched' in the usual sense and is
'designed' (most cases) to have a high VSWR ON ITSELF. (handwaving,
not rigor, follows....). The open end is an open circuit, so MUST have a
voltage peak. The base (sticking to quarter waves) will have current flowing
in so must have some, relatively low, impedance. If worked 'grounded'
(as usual in coiling) a variety of 'inlooking' impedances are availble, mostly
Or i could be wrong...