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## R: R: [antennaware] Feeding cable lenght

 To: R: R: [antennaware] Feeding cable lenght Maurizio Panicara"
 ``` Already you got the answer by Serge, if into the line there is an High SWR (like in the well known 1:4 coaxial balun) and if the line is long this can be a considerable amount of extra losses added. I can also add that much less than 1:12 SWR is enough to rise coaxial lines losses while open wires are much less subject to this effect. 73, Mauri I4JMY > If you use 600 ohm line, and load impedence is 50 ohms to > 50 ohms, the only loss will be the normal attenuation of a line > of that length. SWR is and will indicate 1:1 But SWR in any point of this line will be 600/50=12:1. And attenuation in line will be bigger then when SWR 1:1. SWR never depends of line length. (It will be only better on trx side because of losses in line). 73 de Serge UT2IO. -----Messaggio Originale----- Da: K4SB A: Maurizio Panicara Cc: Stefan Samu ; Data invio: martedì 3 agosto 1999 23.25 Oggetto: Re: R: [antennaware] Feeding cable lenght > > Maurizio Panicara wrote: ( I think ) > > > Hi to all, > > > > > > I have spent a lot of time to calculate the feeding coaxial cable to my > > > 40m inv "V" antenna. I know if I get waveleght/2 or its multiplies the > > > antenna impedance comes down to the radio and I eliminate the loss. > > > > ....everything in your statements works until last four words. > > And Stefan Samu replied > > > > The only loss you can eliminate is eventually that one between > > cable and RTX at transmitter edge, value that comes out when > > antenna and/or line are different, and/or different than RTX > > impedance. > > You can use what so ever cable impedance to feed a 50 Ohm > > antenna into a 50 Ohm transmitter, but inherent cable losses > > will occurr. > > > > To minimize coax losses match antenna to RTX and line > > impedance. > > > > 73, > > Mauri I4JMY > > This may be a case of my not understanding Mauri's reply, but to > clarify a little... > > 1. An electrical 1/2 wave, or multiples thereof, of any type and > impedence will ALWAYS repeat the load impedence at the opposite > end. This occurs regardless of the charateristic impedence of the > line. For instance, if you have a 50 ohm load and a 50 ohm Tx > output, AND the coaxial line is an electircal multiple of 1/2 > wave, it matters NOT what the impedence of the coax ( or whatever > else you use ) is. You can use any impedence line, and the losses > incurred will ONLY be that which is ordinary from the coax > itself. If you use 600 ohm line, and load impedence is 50 ohms to > 50 ohms, the only loss will be the normal attenuation of a line > of that length. SWR is and will indicate 1:1 > > As others have pointed out, a 70 to 50 ohm ( or 30 to 50 ) > mismatch does not introduce enough loss to even worry about. > > And as a matter of determination, when cutting that line, ( > assumming you > have a device such as a MFJ or similar or even just a SWR bridge > ) if you will cut the line at a even multiple of the frequency > you want, the accuracy of the cut is much closer. For example, > suppose you want a 1/2 > wave electrical line for 7.0 Mhz. If you set your device to 140 > Mhz ( a multiple of 20 ) you will find a much narrower range of > dip. You can be > off 200 kHz at 140, which will translate into only 20 kHz at 7.0 > > 73 > Ed > > -- > FAQ on WWW: http://www.contesting.com/antennaware-faq.html > Submissions: antennaware@contesting.com > Administrative requests: antennaware-REQUEST@contesting.com > Problems: owner-antennaware@contesting.com > -- FAQ on WWW: http://www.contesting.com/antennaware-faq.html Submissions: antennaware@contesting.com Administrative requests: antennaware-REQUEST@contesting.com Problems: owner-antennaware@contesting.com ```
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