Shorted 1/4 wave coax (twin lead, strip line, ect) produces a HI -Z at
resonance
Shorted 1/4 wave coax (ect) produces a dead short at resonance
1/2 wave shorted coax (ect) produces dead short
1/2 wave open coax (ect produces HI-Z at resonance
This phonominom repeats every 1/4 wave (ad nausium)
If can find, look at July, 1965 edition of 73 magazine-- shows how to
calculate coaxial
striplines, ect for vhf/uhf circuits . if need (and these BIG files , 11
pgs) have in jpg, and some of it in word.

Jim NN7K

--
No trees were killed in the sending of this message. However, a large number
of electrons were terribly inconvenienced !

" People who never get carried away, should be! " --- Malcom Forbes

"Tom Bruhns" wrote in message
m...
If you just want to pass your signal, what's wrong with just
connecting the coax from the source to the load?

Or do you also want some filtering? If that's what you want, consider
two stubs. (Actually, a single stub is generally not a very good
filter...) These two will be attached to your feedline at the same
place. One will be shorted on the other end, and the other will be
open on the other end. Their total length will be 1/4 wave
(accounting for the line's propagation velocity). So you're feeding
your line through a 1/4-wave resonator, tuned to your signal
frequency. But the shorted part will reflect back a short at some
frequency, and knock that one out. And the open part will do
likewise. And you can so a similar thing, but with different notch
frequencies, if you use a half-wave resonator open on both ends, or
one shorted on both ends. The key is all these will pass the
frequency the resonator is tuned to. Beware of resonator losses if
you tap way down on it.

RFSim99 is a good tool for playing with this sort of thing. You can
readily see the inevitable harmonic responses that occur with stubs:
things tend to repeat at even and odd multiples of lowest resonance
frequencies. But you can get more accurate results by including the
line loss in your calcs. There are generally only a few "intersting"
frequencies to check, easy to do in a spreadsheet for example, using
accurate line equations.

There are lots of other configurations that can do interesting things,
too...you can make a harmonic filter out of series pieces which
alternate impedances above and below the main line's, for example.
It's not very easy to insert a stub in series with a piece of coax,
but I've seen examples of that with balanced line.

Cheers,
Tom




(PDRUNEN) wrote in message
...
Hi Group,

Many thanks to the folks that posted a message for my FM trap question.

I been studying the traps made out of coax for several years, they all
form a
parallel circuit.

Is there any way I could connect the inner conductor and braid such that
I form
a series circuit. I want to pass my signal not keep it in.

de KJ4UO