Tom: Nice try. You should use better examples the E-mails I got also point
out. Originally I gave a "very short and general answer" also suggesting
some modifications to get some or more RF to Flow in the MFJ as the" meter
doesn't lie"--as many others have done. It was not a Doctor's Thesis to
cover all variations and tricks needed to get some action to cover all your
usual forth coming objections why nothing ever works as claimed--because you
can't get it to work.
By the way adding a 1/8 WL coil to a 5/8's wave doesn't make it act like a
3/4 wave WL antenna as you suggest. It still has the 5/8's wave pattern but
ELECTRICALLY IT ACTS LIKE A 3/4 WL, PRESENTS LOWEST RESISTIVE LOAD THAT
ENHANCES CURRENT FLOW FROM THE FEEDLINE TO THE ANTENNA--MUCH LIKE THE
ARTIFICIAL GROUND DOES ITS THING. Puts some thought to that Tom. Try again
and use better examples. No on second thought--no more nonsense.
The Artificial Ground may not duplicate the very low R of a 1/4 wave radial
every time, I never said it did and it's capable of sucking RF off of a hot
chassis by those who know how to make it work making it a useful feature. I
and others are sick and tired of literally being called a liar or didn't know
what we were doing when we describe something that worked for us. You must
have been a Funeral Director in a previous life as you insist on literally
killing the usefulness and sales of every piece of equipment you can't make
work, embalming it with your technical illusions, limitations and burying
it--when is the funeral? You must have a big equipment grave yard behind
your shack. The Artificial Ground still has some life, I've developed a
special "W8JI Vaccine" for it, please leave it alone and we will all struggle
as needed to make it do it's thing without all your special brand of
"Negative Theory" known only to you that you generate all the time. I'd sure
like to see your library--if you even have one.
When I've asked you for the sources of this nonsense in the past, you told me
"you couldn't find it now." Would you please just once "find something good"
about an antenna or equipment for a change? You have wasted too much time of
us who defend what works for us an others. You have trashed everything you
can't make work. Leave it alone or learn how to use it. End of story. How
about showing us what antennas you use. Who installed them and made them
work for you? You even need help on using a Boy Scout Compass. K7GCO
In a message dated 11/17/01 5:05:30 AM Pacific Standard Time, w8ji@akorn.net
writes:<<
Hi Al,
Let's leave all the personal attacks for bar fights, and keep it
technical here. My point is simple.
One of the big common myths in antennas is that a simple
inductor in series with a line, or a combination of series
components, can change "length" or make an antenna (or in this
case ground lead) "longer", or a different "electrical length".
That myth isn't true. Transforming impedance requires both shunt
and series reactive components, and there is no way to get a shunt
component when working with two terminal devices like this.
When we add a loading coil to a mobile antenna, we are not
making the antenna "longer". The coil simply cancels reactance, or
corrects power factor. That is why, if we have an antenna that is 1
ohm -500j and we add a series inductor of 3 ohms +500j, the feed
impedance becomes 4 ohms j0. This is true for loaded Yagi's, for
5/8th wl antennas, and even for ground leads.
This is why linear loading is not as good as touted, because the
linear loading adds series reactance just like an inductor does. It
just uses more wire length to add the same reactance as a
conventional inductor at the same *effective* location would add,
and having more wire linear loading usually has more loss for a
given thickness of wire! It does NOT make the element longer.
Same with a 5/8th wave mobile antenna. We often hear people say
"I added 1/8th wl of wire in the coil, and now it is (or acts like) a
3/4wl antenna". That isn't true. What they did is add a certain
series inductance that cancels the reactance. Resistance remains
unchanged, except for whatever increase finite coil Q adds.
If we pack 50 feet of wire in a two foot antenna, we still have a two
foot antenna! We just have 50 foot of "copper loss" and the added
reactance. Same for ground leads.
So you see, this stuff all ties together in a clear concise way.
Learning how an artificial ground works will help dispel other myths,
like an inductor somehow adds "length" to the antenna.
A simple series L/C circuit can only change the reactive part of the
impedance of the system, it can not change the impedance nor
can it make a lead "longer" or "shorter".
The MFJ artificial ground is a simple series L/C circuit. Being such
a two-terminal device, it can not modify resistance except perhaps
add a slight increase from the finite Q of components. We may not
all like that, but that is **exactly** how it works. If we keep in mind
what it is, we can find a way to use it (or something similar) in
100% of the cases. It will no longer be blind dumb luck if we get it
working!!
If you have a long ground ground lead with a shack-end impedance
of 350 -200j ohms, you can use a series circuit (like the one being
discussed) to "remove" the 200 ohms reactive part.... but it will not
change the 350 ohms R. If the ground lead presents 10 ohms R
and 500 ohms X, it will make a great improvement because the X
will "vanish".
What that means is if you have ground leads that present a low
resistance but a high reactance, a device like this can make
a large difference in termination impedance. If the length,
termination, and routing of the ground lead is such that resistance
is high, you are stuck with a problem unless you alter the ground
lead length, termination, or routing. If you have a problematic
ground lead length, you will need to alter the physical configuration
of grounding.
The MFJ Artificial ground is most useful when tuning insulated
counterpoise wires that just over 1/4 long or quite a bit shorter than
1/4 wl long, since it can cancel reactance of the lead and provide
minimum impedance. It would be useless in the example of a
ground lead near 1/4 wl long that is grounded at the far end, or 1/2
wl long and open at the far end.
What it does do is eliminate the requirement a long ground lead or
counterpoise be exactly resonant. It will not change the electrical
length of the ground lead and magically make a 1/4 wl lead
grounded at the far end good, it only cancels reactance. So you
might, despite some incorrect claims made, still have to change
the ground system. End of topic.
Some of us may not like it, but that is how it works. Tom
(right here is left out a bunch of my points you couldn't answer.)
> The MFJ Artificial Ground like the Match Box works just fine when
> "properly
> used"--please leave them alone or learn how to properly use them. I
> wish the Artificial Ground was still made. Tom, you have this "Total
> Misconception and Delusion" that every thing or new idea has to be
> approved by you to be useful, worth trying or you get on your "TT RF
> Negative Soap Box." It's not a W8JI Ham Radio Police State as yet but
> it's getting there. The rest of us still reserve the right to use
> what we want although appreciate legitimate info on equipment
> deficiencies. Lets support equipment that works and new ideas even if
> you didn't think of them. If you need some help on how something
> works, I'll be glad to help you.
>
> Dave, I thank for your support. You get the "K7GCO Good Samaritan
> Award" for "Defending What Works." I'm all alone sometimes supporting
> equipment and proven ideas that work. MFJ appreciates it also. Wait
> until Martin F Jue hears of this. K7GCO
>>
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|