Yes, World Radio is in the process of publishing a 2nd edition of his
book. He's been working on it for a couple of years now, and I'm looking
forward to it. It was supposed to hit the newsstands this month, but
they have not announced it yet.
73, Duane AC5AA
On Thu, 25 Jan 2001 13:52:35 -0800 "Simmons, Reid W"
<reid.w.simmons@intel.com> writes:
>
> FYI
>
> Walt Maxwell's series of articles, "Another Look At Reflections",
> started
> with the April 1973 issue of QST.
>
> Did someone mention that his book on this subject is going back
> into
> publication? I would like to get a copy and ARRL no longer
> publishes this
> one.
>
> Reid, K7YX
>
> -----Original Message-----
> From: Sherrill WATKINS [mailto:SEWATKINS@dgs.state.va.us]
> Sent: Thursday, January 25, 2001 9:27 AM
> To: tentec@contesting.com
> Subject: [TenTec] "A low vswr will kill you"
>
>
>
> While I must agree with Dr. Johnson's statement that the
> mathematical
> definition of a resonate antenna pertains to the phase angle of the
> voltages
> and currents; I find this mathematical definition too abstract to
> understand
> for my limited education (feeble mind). Since most hams, including
> me, have
> never understood higher math, I prefer to visualize what is
> happening by
> more simple concepts as graphical current and voltage waves. Since
> most
> ham's do not have discs or similar items at the end of their
> antennas , the
> graphical concept of current node at the ends and current loop at
> the center
> is quite valid and helpful to understand what is happening on a
> resonate
> antenna system. As I stated in my previous post, in a resonant
> condition, a
> center fed wire antenna (with out discs, etc. the ends) is
> accompanied by a
> current loop or maximum at the center and zero current or a node at
> the
> ends. (The voltage wave is just the opposite with voltage at a loop
> or
> maximum at the ends !
> and zero at the center; i.e. the voltage wave is 90 degrees from the
> current
> wave.) When the antenna is operated in the non-resonant condition,
> the
> current loop moves or shifts to other positions on the antenna,
> along with
> changes in the position of the voltage wave. This may or may not be
> good or
> bad. As an example, should a 160 or 80 meter center fed zep be
> operated on
> say, 15 or 10 meters, then because of the multiple current loops on
> each leg
> of the antenna, the antenna will begin to act like two end fed,
> back to
> back long wires and will exhibit directivity and gain off the end of
> each
> wire. ( At this point, their may be a high vswr on the transmission
> line.)
> This shift in the radiation pattern can be put to good use if one
> desires to
> work certain parts of the world where the radiation pattern is
> directed.
> However, less I digress, other than possibly changing the angle of
> radiation
> of the antenna when it is operated in a non-resonant or harmonic
> condition,
> ALL TH!
> E RF POWER DELIVERED TO THE ANTENNA TERMINALS IS RADIATED WHEN THE
> ANT
> resonance does NOT have to be accomplished at the actual antenna
> itself but
> can be easily accomplished with a suitable tuner at the operating
> postion.
> For an in-depth and thorough technical explanation of this fact,
> please read
> the articles that appeared in QST by Mr. Walter Maxwell, W2DU, from
> about
> 1974 to 1977, entitled " Another Look at Reflections" or the book by
> the
> same name. Now for another important point: If one is using a well
> designed
> antenna tuner, the fact that one may have a very high vswr on the
> transmission line is only important if one is using a high loss
> type
> transmission line, i.e. coax. If very low loss line is used, such
> as open
> wire type, then a very high vswr (i.e. 20:1) is not significant,
> provided
> the tuner and transmission line are designed to handle it. This is
> because
> the tuner, when tuned to resonance, will take all of the reflected
> power
> coming back down the transmission line toward the tuner, and reverse
> its
> direction and add it, IN PHAS!
> E, to the incident power going back up the transmission line to the
> antenna.
> When it reaches the antenna, it flows out and along the antenna and
> is all
> radiated. It is a basic fact that when the SYSTEM is resonant,
> regardless
> if the actual antenna is resonate or not , ALL the r.f. power is
> radiated by
> the antenna. (I am talking theory here and not anomalies such as
> loose or
> corroded connections, etc. that may absorb power and give a false
> low vswr
> reading.) This can be confirmed by the use of forward and reverse
> reading
> watt meters inserted in the transmisson line between the tuner and
> the
> antenna. - 73's - Corn -k4own
>
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/tentec
> Submissions: tentec@contesting.com
> Administrative requests: tentec-REQUEST@contesting.com
> Problems: owner-tentec@contesting.com
>
>
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/tentec
> Submissions: tentec@contesting.com
> Administrative requests: tentec-REQUEST@contesting.com
> Problems: owner-tentec@contesting.com
>
>
Duane A. Calvin, AC5AA
Austin, Texas
ac5aa@juno.com -or- ac5aa@earthlink.net
Day: dacalvin@us.ibm.com
--
FAQ on WWW: http://www.contesting.com/FAQ/tentec
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
|