Hi Dick,
Sure, you're welcome to forward stuff like this.
As to stuff on my website -- I do NOT permit it to be copied to other
websites, but I DO encourage links to it.
73, Jim K9YC
On Wed,2/1/2017 8:16 AM, Richard Fjeld wrote:
Jim,
If you don't object, I'd like to save this and forward to people as
arguments develop on these subjects.
I wish you had touched on '4:1 baluns'. Except for this group, so
many people I talk to think a balun should be 4:1, even in their
tuners. I think it is DX Engineering that addresses this well.
Dick, n0ce
On 1/31/2017 12:50 PM, Jim Brown wrote:
All of this discussion becomes badly confusing by failing to describe
these circuit elements by their real name. The word "balun" is a
bastard -- it is widely used to describe nearly a dozen things that
are VERY different from each other.
W4TV got it right by adding the correct description, and this post
starts to get at it, but adds another bastard word, unun.
Two-windings that are coupled by a magnetic field are a TRANSFORMER.
If the two windings have a terminal in common, they are an
AUTO-TRANSFORMER. A coil of coax is a common mode choke (and not a
good one). A section of transmission line wound around a ferrite core
is a COMMON MODE CHOKE, and if well designed (choice of ferrite
material, number of turns) can be a very good one.
Transformers and auto-transformers transform impedance by virtue of
their turns ratio. Arrays of common mode chokes can also be used to
match circuits of different impedances.
Last I looked, there was no description of the Elecraft "balun"
telling us what it is. Perhaps Eric or Wayne could add that to the
catalog listing for it.
Another point. SWR is NOT an indicator of how well an antenna works.
High SWR DOES increase loss in a feedline, but that matters only with
long feedlines and small diameter coax. That does NOT matter for
typical portable (or even mobile) operation, where feedlines are much
too short for loss to matter.
A high value of SWR as seen by a transmitter DOES limit that power
that the transmitter can put into the antenna. That's where the
antenna tuner comes in -- it transforms the impedance at the
transmitter end of the feedline (or the end of a wire plugged into the
coax connector combined with the counterpoise connected to the
chassis) to the 50 ohm resistive impedance that the transmitter wants
to drive.
If we make RF current flow in a wire, it will radiate. How well it
radiates depends, of course, on its orientation. A wire laying on the
ground doesn't radiate very well. :) A wire without a counterpoise
will use whatever it sees as a signal return. If that return happens
to be the earth, the earth, which is essentially a big resistor, will
burn much of the transmitter power. The "good" lengths of wire Wayne
and those spreadsheets list are simply lengths that are likely to
present an impedance within range of most antenna tuners for the bands
that the operator is likely to use.
73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
