[Antennaware] When is a stub not just a stub
Wolfgang K. Meister
meister at via.at
Tue Jun 3 19:01:00 EDT 2003
Hello Mauri, you wrote:
i4jmy> If I understand your question, definitely it can be a practical approach
i4jmy> although with some peculiar impedances a single stub could be not enough
i4jmy> to cancel reactances and match to 50 Ohm.
i4jmy> I used this technique to utilize a quarter wave 40m GP on 20m, in practice
i4jmy> placing a shorted stub of proper lenght along the line, at the right distance
i4jmy> from the radiator.
i4jmy> VSWR is high in the stub (can heat if the line used has losses and the power
i4jmy> is high) and in the above case the voltage rised very much at the antenna
i4jmy> end, so the line type has to withstand it.
I used it once with good results and raised my question now:
Coax T-stub -
'is this a good solution to match *any* or most of our short wave antennas?'
'do I really have to layout the coax in T shape 90 deg?'
Zl = antenna
Zo = 50ohm feedpoint
L3 = any length coax
L1 and L2 are calculated with MMANA. There are two solutions all the
time and L2 can be either 'open' or 'short' with different length. All
values for L1 and L2, depending on the coax used, are given by MMANA after
calculating an antenna. 'Options' 'Options and Setup' and tab 'Line Match2'
OK, sometimes a balun is required to go from balanced to unbalanced at
the Zl side, where the antenna is connected.
Have a look at http://www.qsl.net/oe1mww/station.html and at the
bottom of the page look for my portable antenna. Literature says the T
must be 90 deg. I have mine in parallel, L2 bent to L1, it works quite
good. Two years ago I used this antenna with 5 Watt on a parking lot near
Vienna. Worked all over Europe and a W3 station at 11:00 in the morning.
reply to: meister at via.at
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