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*Subject*: RE: [amsat-bb] Question on 1/4 wavelength matching section*From*: "Howard Long" <howard@xxxxxxxxxxxxxx>*Date*: Tue, 25 Sep 2001 22:35:05 +0100*In-Reply-To*: <00d201c145f7$a9bf26c0$76a0f7a5@desktop>

Hello Floyd: > won't odd multiples of 1/4 > wavelength perform the same transformation as 1/4 wave?). Yes but with reduced bandwidth. Off center frequency, the cumulative (1/4 waves +/- a bit) make it less and less accurate. > I don't > understand why matching section is 72 ohm line. Each 72 ohm 1/4 wavelength line transforms the individual 50 ohm antenna feed points to about 100 ohms or so. Two of these antennas plus 1/4 wl transformers, of 100 ohms each, in parallel brings you back to 50 ohms combined at the tee piece. > I want to use system (A) in that > diagram .... I'm puzzled by why the 1/4 wave delay line is 95 ohms. OK, referring to (A) on fig 10.11 the two antennas have native 50 ohm feed points. each is transformed to ~100 ohms by separate 75 ohm 1/4 w/l transformers to the tee pieces at the coax relay. Therefore each T piece has two lots of ~100 ohms coming into it, making ~50 ohms at each of the two relay positions. In the up position, antenna A radiates 1/4 w/l ahead of antenna B and in the down position vice versa. The 95 ohm is not there for impedance transformation - that's the delay section. It's just close enough to the desired 100 ohms and 95 ohm coax is fairly easily available. On your original problem, you have a 1" offset. To apply (A) of fig 10.11, you'll need to add (velocity factor * 1") of 50 ohms delay to the feedpoint of the foremost set of elements to make them seem 'back in line' (not very easy: you might like to make it VF * [1/2 w/l + 1"] long to make it physically easier and switch the sense of RHCP/LHCP). Sometimes it's easier to consider the power splitter and the CP phasing entirely separately: example (A) combines both function and so can lead to confusion, although it is quite an elegant solution IMHO. 73 Howard G6LVB ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**Re: Question on 1/4 wavelength matching section***From:*Floyd Sense

**References**:**Question on 1/4 wavelength matching section***From:*Floyd Sense

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