RHF wrote:

...
JS,

Good Antenna Building Concept :
You Can't Talk To Them -unless-
You Can First Hear Them. ~ RHF
.

Well, I'd like an antenna like this one (see URL, below.) He comes into
my location in the low valley of CA like a door buster, from his secret
location in NV. Jumping the high Sierra Mountains in a single leap! grin

http://www.smeter.net/w6obb/antenna-farm.php

Regards,
JS

Dave wrote:

...
Your analogies don't hold up. You cannot transmit with a Beveridge and
you cannot transmit with a ferrite loop.


You CAN transmit with both.

And, only emphasizes the importance of what I have been saying, most
would pick the most efficient possible antenna--both examples, of yours,
are less than most efficient ... even for receiving, the ferrite
loop-stick on an a AM/MW radio is far from first choice ... it is
convenient, cheap and highly-portable, however.

Regards,
JS

RHF wrote:

[...]

Anyway you cut it ... a matchbox never will improve the performance of a
poor antenna, increase the capture area of a poor antenna, etc.

It will MASK that antennas' short-comings ... same as sweeping dirt
under a rug (notice, another mechanical analogy to the above.)

Regards,
JS

Dave wrote:

...
5/8 wavelength antennas do not require a ground plane, do they?

Yeah, in my experience, a vertical 5/8 will require the same as would be
necessary for a 1/4 vertical ... the 1/2 is nice in that advantage, only
requiring a minimal counterpoise.

A few I have seen articles and pictures from, swear the 5/8 beats out
the 1/2--I simply have not found that in actually comparisons. However,
in such situations, I suspect it may be something I am doing wrong, but
for the life of me, I can't find what it could be ... and, it SHOULD
produce a superior radiation pattern for my uses.

And, in a homebrew omni antenna for my 2.4Ghz router, I went 5/8,
mounted ~20ft. in the air, it works well.

Regards,
JS

In message
,
Telamon writes
In article ,
Ian Jackson wrote:

In message
,
Telamon writes
In article
,
RHF wrote:

On Dec 28, 8:36*pm, Telamon
wrote:



You are confusing the characteristic impedance of the coax with its
ability to be an effective transmission line. The coax only behaves as
an effective transmission line when both ends of it are terminated at
its characteristic impedance.

Are you really sure about this sweeping statement?

Yes. It is basic transmission line theory. RF energy entering or leaving
a coax line has to be at the same impedance or energy is reflected. That
is a basic rule.

For starters, please define 'effective'.

The word effective was used in the context of the coax meeting its
specifications within reason.

If the source and load impedances are NOT the same as the characteristic
impedance of the coax, any 'ineffectiveness' as a transmission line will
not as a result of the coax not meeting its specifications. You simply
haven't used coax with the RIGHT specifications.

And are you sure that transmitter output impedances are 50 ohms (or
whatever)?

If it is specified to be 50 ohms and it is not then it should find its
way back to the manufacturer for repair or redesign.

Indeed, the specs for transmitters do sometimes say that the output
impedance is 50 ohms. This is almost certainly wrong. What it really
means is that the transmitter is designed to work into a 50 ohm load.
The two are rarely the same. Transmitters are designed for best
efficiency and/or linearity. The actual output impedance is not really
relevant. [Signal generators are different. They SHOULD be 50 ohms. This
subject has been discussed ad nauseam in several NGs.]
--
Ian

Here's why antenna efficiency is important for transmitting but not for
HF receiving.

First, the definition of efficiency: For a transmitting antenna, it's
the fraction of the power applied which is radiated. The remainder is
turned into heat. For receiving, it's the ratio of the power which is
delivered to the receiver to the power which could be delivered to the
receiver if the antenna had no loss. The efficiency of a given antenna
is the same when transmitting and receiving. Sometimes people use
"efficiency" to mean other things -- this is the meaning of the term in
all antenna literature and texts.

Consider this communications system:

transmitter - antenna - propagation path - antenna - receiver - listener

A receiver unavoidably adds noise to the received signal. So if no noise
is injected in the propagation path, the signal/noise ratio is the ratio
of the signal entering the receiver to the noise created by the
receiver's input circuitry. This is generally the case at VHF and above.

When receiver noise dominates, as above, increasing the receive
antenna's efficiency increases the signal arriving at the receiver, so
the signal/noise ratio improves. This allows you to hear the signal
better. But it only works for VHF and above.

HF is a different story. At HF, there's a lot of atmospheric noise
(injected in the "propagation path" part of the system), and unless the
receive antenna and receiver are exceptionally bad, the atmospheric
noise is much greater than the noise created by the receiver. I
mentioned a simple test in my last posting, to see whether this is the
case -- just disconnect the antenna. If the noise level drops,
atmospheric noise dominates. It's not hard to make a receiver that
atmospheric noise will dominate with a 3 foot whip antenna at HF. So at
HF where atmospheric noise dominates, the signal/noise ratio is the
ratio of the signal entering the receiver to the atmospheric noise
entering the receiver. Compare this to the situation described above for
higher frequencies.

Now let's see what happens when we improve the efficiency of an HF
receiving antenna. Because both the signal and the dominant noise come
from locations in front of (that is, on the transmit side of) the
antenna, improving the efficiency of the antenna makes both the signal
and noise greater in the same proportion when they arrive at the
receiver. There's no improvement at all in the signal/noise ratio. The
effect is the same as turning up the receiver volume control. The only
way you can improve the signal/noise ratio is to somehow favor one over
the other, such as by making the antenna directional. And an
inefficient, directional antenna like a Beverage or small loop will
nearly always enable you to hear better in some directions than an
efficient, nondirectional antenna because directionality helps and
inefficiency doesn't hurt.

How about transmit antenna efficiency?

The signal strength from the transmit antenna is proportional to the
antenna's efficiency. (It also depends on other things, but I'm just
talking about efficiency here.) So if the efficiency of the transmit
antenna increases from, say, 33% to 66%, the power levels of the signals
at the receive antenna and the receiver double, and there's no change to
the received noise, on either HF or VHF and above. So improving the
transmit antenna efficiency always improves the signal/noise ratio at
the receiver, in this case by 3 dB.

That's why you can hear bunches of HF stations with a very inefficient
antenna, but they won't hear you if you try to transmit using that same
antenna -- it's because the noise is injected into the system between
you. And it's likely that you'll be able to hear stations just as well
with the very inefficient antenna as with a much larger, efficient one.

Roy Lewallen, W7EL

In article ,
Ian Jackson wrote:

In message
,
Telamon writes
In article ,
Ian Jackson wrote:

In message
,
Telamon writes
In article
,
RHF wrote:

On Dec 28, 8:36*pm, Telamon
wrote:



You are confusing the characteristic impedance of the coax with its
ability to be an effective transmission line. The coax only behaves as
an effective transmission line when both ends of it are terminated at
its characteristic impedance.

Are you really sure about this sweeping statement?

Yes. It is basic transmission line theory. RF energy entering or leaving
a coax line has to be at the same impedance or energy is reflected. That
is a basic rule.

For starters, please define 'effective'.

The word effective was used in the context of the coax meeting its
specifications within reason.

If the source and load impedances are NOT the same as the characteristic
impedance of the coax, any 'ineffectiveness' as a transmission line will
not as a result of the coax not meeting its specifications. You simply
haven't used coax with the RIGHT specifications.

OK. I don't understand your point though. My original reply is that coax
has a characteristic impedance based on its design not what it has for
terminations on either end.

And are you sure that transmitter output impedances are 50 ohms (or
whatever)?

If it is specified to be 50 ohms and it is not then it should find its
way back to the manufacturer for repair or redesign.

Indeed, the specs for transmitters do sometimes say that the output
impedance is 50 ohms. This is almost certainly wrong. What it really
means is that the transmitter is designed to work into a 50 ohm load.

I have to disagree with you here. I work with a lot of test equipment
and if this was true good luck getting anything to work. Signal
generators and amplifiers have to have output impedances that match the
coax impedance or you would not be able to predict how test setups would
work.

The two are rarely the same. Transmitters are designed for best
efficiency and/or linearity. The actual output impedance is not really
relevant. [Signal generators are different. They SHOULD be 50 ohms. This
subject has been discussed ad nauseam in several NGs.]

I don't want to get nauseated then. The arguments to the contrary make
no sense. Signal generators, amplifiers, or transmitters all have to
have the same system impedance or the RF just gets reflected back at the
source, which has to dissipate that additional energy as heat usually.
So you would have to beef up the output devices in the source and you
would be wasting a portion of the RF generated.

--
Telamon
Ventura, California

Ian Jackson wrote:

...
There is not a lot of difference between the radiation of a 1/2 wave and
a 5/8 wave vertical antenna.

A 1/2 wave needs something like (typically) an L-match (low-to-high
impedance) at the feedpoint. As the antenna is voltage-fed, you can get
away without much of a ground (plane) system (but it does no harm if you
have one). Also, being voltage-fed, the insulation needs to be good
(especially in wet weather).

A 5/8 wave can be 'loaded' to a 3/4 wave by adding a series inductor.
The match to 50 ohms is pretty good. You do need a good ground (plane).
In the horizontal direction, it has a bit more radiation in the 1/2
wave, but not a lot. Mechanically, a VHF/UHF antenna 5/8 wave is robust,
and can resemble a simple base-loaded whip.

Essentially, you pays your money, you takes your choice.

Yes, my actual "hands-on" bears out your, above, text ...

However, after much experiments with differing form of matching schemes,
I have found a gamma match on 1/2 or 5/8 produces the most efficient
matching scheme I have attempted, others mileage may vary.

The gamma does distort the radiation pattern a bit, and can be seen if
modeled in EZNEC/MMANA-GAL, and it is actually seen in hands-on use, if
you rotate the gamma towards, then away from the station you are
receiving a very slight variation in signal can be seen, usually about a
meter-needles-width ... I consider it a very minor anomaly ... again,
others mileage may vary.

Even in a 160m, 50ft "flagpole" DLM, I constructed, this distortion, by
the gamma, is apparent ... however, it consistently shows up as 1
s-unit in hands-on use. I don't have open enough area around the
antenna to even begin taking measurements with a calibrated FSM, and end
up with anything near meaningful measurements ... indeed, surrounding
structures, homes, vehicles, etc., most-likely, distort the signal(s) to
a greater degree.

Regards,
JS

Roy Lewallen wrote:

...
Roy Lewallen, W7EL


YEAH, what he said! LOL

And, I must defer to him, his experience allows nothing less ...

Regards,
JS

RHF wrote:

Dave here is a Picture of a . . .
5/8 WL Ground Plane Antenna

No it isn't.

http://users.belgacom.net/hamradio/s...calantenna.htm

"The "ringostar" based coil:
Is made out of 26 cm of 2,5mm installation wire. Remove the isolation of
the wire and tin with a soldering iron the entire wire. The coil is 1,2
turns and has a diameter of 5 cm. One side is connected to the antenna
and the other side to the boom."
.
Note "Installation Instructions" of 5/8 wave vs 1/4 wave antennas. 1/4
wave verticals require a proper ground plane (radials or sheet metal)
to approximate the other half of a center fed dipole. The 5/8 wave is
already over a half-wave long; no plane required. The coax shield
needs a ground, the antenna doesn't.

http://www.diamondantenna.net/m285.html

http://www.diamondantenna.net/hf6fx.html