[Antennas] Hardline Questions

2003年10月28日 14:30:09 -0600

An electrical 1/4-wavelength section of 62 ohm coax would match the 75 ohm
line to 50 ohms if you are worried about the 1.5 minimum SWR. Remember,
also, that the SWR meter you are likely to use is calibrated for use in a 50
ohm line so it will read incorrectly when used in the 75 ohm line.''73/72,
George
Amateur Radio W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"Starting the 58th year and it just keeps getting better!"
[email protected]
----- Original Message ----- 
From: "Donald E. "Buck" Stiles" <[email protected]>
To: <[email protected]>; "Robert Lay" <[email protected]>
Sent: Tuesday, October 28, 2003 1:14 PM
Subject: Re: [Antennas] Hardline Questions
> Bob,
>> Regardless of all others factors, the transmitter is looking for a 50 ohm
> load but the transmission line is 75 ohm. It is impossible to achieve
below
> a 1.5:1 swr. It may be higher, but never lower...
>> The may be insignificant at HF, but quite the opposite at VHF/UHF if you
are
> counting watts.
>> ----- Original Message ----- 
> From: "Robert Lay" <[email protected]>
> To: "Donald E. "Buck" Stiles" <[email protected]>
> Sent: Tuesday, October 28, 2003 12:16 PM
> Subject: Re: [Antennas] Hardline Questions
>>> > Don't forget, Tim and Don, that the 1.5:1 mismatch may or may not occur.
> > First of all, do you know what the antenna impedance is - maybe it's
> closer
> > to 75 ohms than it is to 50 ohms, in which case the VSWR would be
closer
> to
> > 1:1.
> >
> > Furthermore, in a typical installation, there is at least 1.5:1 VSWR on
> the
> > transmission line - generally much higher. The fact that we put a tuner
at
> > the transmitter end to transform the impedance seen by the rig to 50
ohms
> > (thus giving us the "perfect match" to the transmitter), does NOT change
> the
> > fact that the VSWR on the line has NOT changed at all. It is STILL
> > determined by the line impedance and the antenna impedance.
> >
> > Bob Lay (W9DMK) in Dahlgren, VA
> > http://www.qsl.net/w9dmk
> >
> >
> >
>>> - - -
>> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
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