1/4 vs 1/2 wavelength antenna

John Woodgate · Feb 26, 2005

I read in sci.electronics.design that gwhite <gwhite@deadend.com> wrote
(in <421FBB39.6BB0153C@deadend.com&gt

about '1/4 vs 1/2 wavelength
antenna', on Fri, 25 Feb 2005:

I'm sorry, but they are not. Nor are any power amps that I know of.
Efficiency (and thus necessarily output swing) is what matters for power
amps. To maximize swing requires load line matching, not impedance
matching.

What is a 'load line'? A straight line on an I/V graph? What does the
gradient of that line represent?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

John Woodgate · Feb 26, 2005

I read in sci.electronics.design that Larry Brasfield <donotspam_larry_b
rasfield@hotmail.com> wrote (in <5%TTd.87$MW3.2174@news.uswest.net&gt

about 'Say what you mean.', on Fri, 25 Feb 2005:

If I wanted to speak of an impedance inside of some circuit, I might
loosely speak of it as "internal", but in any useful discussion, it
would be spoken of as either an output impedance or an input impedance,

The problem is that people say 'output impedance' when they mean 'load
impedance'. To prevent misunderstanding I use the term 'output source
impedance'.

There are also some people who use 'input impedance' when they mean
'source impedance'. I don't talk to them. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Rich Grise · Feb 26, 2005

On Fri, 25 Feb 2005 21:42:37 -0800, Larry Brasfield wrote:

Uuugh. Mmmmph. Me drag woman to cave by hair.

Uh. Nuh. Drag _FROM_ hair.

Airy R.Bean · Feb 26, 2005

My "Bailey" amps (Wireless World c. 1970) have lots
of internal resistances, all soldered in neatly by hand.

In your comment below, I think that you have "output"
much "impudance".

"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote in message
news:cvovbf$6m2$1@sparta.btinternet.com...

The phrase "output impedance" in connection with amplifiers is ambiguous
and
likely to result in arguments.
The correct description is "internal impedance" or "internal resistance"
and
should always be used.

Cecil Moore · Feb 26, 2005

Rich Grise wrote:

On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.
--
73, Cecil http://www.qsl.net/w5dxp

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Allan Herriman · Feb 26, 2005

On Sat, 26 Feb 2005 04:53:03 +0000 (UTC), "Reg Edwards"
<g4fgq.regp@ZZZbtinternet.com> wrote:

The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

The correct description is "internal impedance" or "internal resistance" and
should always be used.

S22 is fairly well defined.

Allan

Rich Grise · Feb 26, 2005

On Sat, 26 Feb 2005 08:33:25 -0600, Cecil Moore wrote:

Rich Grise wrote:

On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.

No, just trying to make the point that it does, in fact, _have_ an
impedance. (even if it's running class E.) What that exact impedance is,
of course, is left as an exercise for the reader.

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

Thanks,
Rich

Cecil Moore · Feb 26, 2005

Allan Herriman wrote:

S22 is fairly well defined.

What's the S22 of an IC-756PRO?
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore · Feb 26, 2005

Allan Herriman wrote:

S22 is fairly well defined.

What's the S22 of an IC-756PRO? With that figure,
S22^2 is defined as:

Power reflected from the network output divided by
Power incident on the network output.

Better yet, we can then calculate the reflected power
dissipated by the IC-756PRO.
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore · Feb 26, 2005

Rich Grise wrote:

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

Therefore, the key to converting the non-linear source to
an equivalent linear source lies in a Fourier analysis?
Do the other-than-fundamental terms in the Fourier analysis
encounter a low impedance or a high impedance?
--
73, Cecil http://www.qsl.net/w5dxp

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Ken Smith · Feb 27, 2005

In article <421ffbaa_2@127.0.0.1>, Cecil Moore <w5dxp@hotmail.com> wrote:

Ken Smith wrote:
Now lets assume that you slightly decrease the resistance. Since we are
assuming that this is a well designed case, we can assume that the
designer took steps to ensure that the output devices would be protected
from excess currents.

Let's assume the designer is an amateur who didn't provide
any protection for his tube's output. The lower the resistive
load, the more current the output device draws until it fails.
What is the output impedance of the device?

At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

--
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Ken Smith · Feb 27, 2005

In article <422003f1_1@127.0.0.1>, Cecil Moore <w5dxp@hotmail.com> wrote:

Ken Smith wrote:
If you then
put in the output device protection they didn't include, you end up with
the matching as I explained elsewhere.

SWR foldback is part of impedance matching?

Yes for the purposes of the OP's case it is. He is trying to use an
existing transmitter design and a hunk of wire. This seems to be the part
of my argument that people are missing. I suggested he use a matching
network to match the wire to the transmitter's output.

--
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Cecil Moore · Feb 27, 2005

John Woodgate wrote:

Cecil Moore <w5dxp@hotmail.com> wrote:
Therefore, the key to converting the non-linear source to
an equivalent linear source lies in a Fourier analysis?
Do the other-than-fundamental terms in the Fourier analysis
encounter a low impedance or a high impedance?

Yes. Not facetious; the impedance matching network can be configured to
minimise individual or a few harmonic emissions by adjusting its
impedances at harmonic frequencies. Either high or low (or perhaps both)
can minimise the emission, depending on the configuration.

Whether the harmonic impedance is high or low would affect
the efficiency, no?
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore · Feb 27, 2005

Ken Smith wrote:

At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?
--
73, Cecil http://www.qsl.net/w5dxp

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John Woodgate · Feb 27, 2005

I read in sci.electronics.design that Cecil Moore <w5dxp@hotmail.com>
wrote (in <42214c3d$1_1@127.0.0.1&gt

about '1/4 vs 1/2 wavelength
antenna', on Sat, 26 Feb 2005:

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

If the FM is what passes for music these days, it's MUCH better IMHO.
(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Tom Ring · Feb 26, 2005

Jerry Martes wrote:

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote in message
news:e62dnZNJCPRTMILfRVn-ig@comcast.com...

"gwhite" <gwhite@deadend.com> wrote in message
news:421E98CC.6E3BDC78@deadend.com...

Richard Clark wrote:

On Wed, 23 Feb 2005 19:08:20 GMT, gwhite <gwhite@deadend.com> wrote:

RF transmitters are not ....

Sorry OM,

This was all nonsense.

Nice articulation. I don't know who OM is, but RF transmitter power amps
are
not "impedance matched." Neither are audio power amps for that matter.

My stereo amp has a spec on output impedance. As I recall, it was around
0.16 Ohms. Intended load is 4 - 16 Ohms.

Tam

Tam

An audio amplifier can have an improved capability of minimizing a
speaker's deviation from its desired displacement if it has a low output
impedance. That is, the speaker's cone tends to swing past its desired
displacement when its terminals are loaded to a high impedance.

Jerry

Correct - in the case of an audio amplifier damping factor is critical
to accurate reproduction of transients. In an RF amp, it is normally
not required or desired.

tom
K0TAR

Ken Smith · Feb 27, 2005

In article <42214c3d$1_1@127.0.0.1>, Cecil Moore <w5dxp@hotmail.com> wrote:

Ken Smith wrote:
At the point where it fails, the output goes to zero, I assume. If so,
wouldn't that be the impedance as I've been defining it.

Is an amp that fails at one minute with 100w FM
better matched than an amp that fails at two minutes
with 100w CW?

No, you've got the concept backwards. Obviously the worst matched is the
1 o=minute case, next would be the 2 minute case and so on up to one which
runs for about its MTBF at the connected load. This last case would
likely be the one the designer was targeting.

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Ken Smith · Feb 27, 2005

In article <CVcFzUAFBXICFwjZ@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
[...]

If the FM is what passes for music these days, it's MUCH better IMHO.

There is very little that is sent in the form of radio waves that is worth
the electrical power to send it. The really sad thing is that much of
what is send via FM is really "voice grade" material. When FM was new,
the material for FM was specially produced to take advantage of the wide
bandwidth and large dynamic range.

--
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Ken Smith · Feb 27, 2005

In article <kuv321dou23k2p02788nrmfup2h0m5aejr@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[....]

But I vaguely recall a 5/8 wavelength antenna that had a good
low-angle pattern.

Unfortunately, the OP (is he still here?) was stuck with a box to short to
even fit a 1/4 wave whip. I also think that this box could not be assumed
to be resting on the ground

If you squint at the ASCII art below, you will see more or less the
radiation pattern of a 5/8 whip over a large ground plain.
.................................
.................!...............
...........******!*****..........
..........*......!......*........
..........*......!......*........
...........****..!..****...A.....
........*******..!..*******......
.....***.........!.........***...
...*.............!.............*B
********************************

If you don't have a large enough ground plain, the notch in the side
labeled "A" starts to go away and the peak at "B" reduces.

--
--
kensmith@rahul.net forging knowledge

Jim Thompson · Feb 27, 2005

On Sun, 27 Feb 2005 17:52:52 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <kuv321dou23k2p02788nrmfup2h0m5aejr@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[....]

But I vaguely recall a 5/8 wavelength antenna that had a good
low-angle pattern.

Unfortunately, the OP (is he still here?) was stuck with a box to short to
even fit a 1/4 wave whip. I also think that this box could not be assumed
to be resting on the ground

If you squint at the ASCII art below, you will see more or less the
radiation pattern of a 5/8 whip over a large ground plain.
................................
................!...............
..........******!*****..........
.........*......!......*........
.........*......!......*........
..........****..!..****...A.....
.......*******..!..*******......
....***.........!.........***...
..*.............!.............*B
********************************

If you don't have a large enough ground plain, the notch in the side
labeled "A" starts to go away and the peak at "B" reduces.

--

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1/4 vs 1/2 wavelength antenna

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