Beginner antenna question
 

While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ

Beginner antenna question
 

On 03 May 2007 20:43:19 GMT, Spam Collector
wrote:

While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Hi Frank,

Your question encompasses a lot of territory (beyond the literal 300 x
500 feet).

You could get every question answered and still not be informed. An
other approach would be to download EZNEC and (even with the
limitation of 20 segments) model this and just see what happens.
Within its limitations this modeler will reveal many insights AND
allow you to vary things to suit those outcomes.

73's
Richard Clark, KB7QHC

Beginner antenna question
 

On 3 May, 13:43, Spam Collector wrote:
While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ

Frank, all of your antennas will work for receiving in one way or
another, the real problem is matching your radio to the antenna
whether it is for receive or transmitting the latter being the most
important. Cofiguration of the antenna determines the matching ability
as well as the directivety. The bottom line is where do you wish to
communicate to and then design accordingly which means determining
first the frequency, then the direction and then attaining a suitable
match between the radio and the antenna. If you are only concerned
with receiving then most of those requirements fall by the wayside in
terms of operational importance. The main excitement that antennas
bring is when you introduce skywave type of deflections of radio
paths, even the simplest of antenna arrangements provides unexpected
surprises that tittilates your imagination such you become more
adventurous about your desires and where you are aware that your
transmitter could easily fail if you did not take protective measures
which requires good matching between the antenna and your radio.
Regards
Art

Beginner antenna question
 

On 3 May, 13:43, Spam Collector wrote:
While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ

Frank, I did not adress your comment with respect to antennas of
narrow bandwidth. For receiving you have relatively unlimited
bandwidth because the antenna match is for extremely small power
transfer, the signal may become weaker but no damage is going to
occur. For transmitting it is a whole new ball game since the matching
syystem will have to transfer power in the order of a few watts or
even a kilowatt which is O.K. for a light bulb which is enclosed but
you really don't want the wires inside your transmitter to glow!
This is where matching the connection becomes important because tho
you can match the radio connection easily the antenna makes it harder
as you stray from the initial matching frequency such that wire
connections could easily glow and fail. Unfortunately it is very
difficult to design a antenna that will remain a close match to your
radio, this is just a fact of life. Usually you have to design an
antenna for a narrow band of frequencies which means more than one. In
your case where you have long wires it is possible to insert a black
box
that will provide a useable match across a large band of frequencies
but the other side of the coin is that antenna directivety is lost
since directivity is directly related to frequency.
As with all things there is no free lunch but it will sure provide a
lot of fun when playing with antennas and talking to the World.
Art
Art

Beginner antenna question
 

You will get many, many lobes in various directions. If one happens to
be pointing in a direction you want to communicate to, you'll find that
the antenna "works". If it doesn't, you'll find that it "doesn't work".

Roy Lewallen, W7EL

Spam Collector wrote:
While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ

Beginner antenna question
 

On 03 May 2007 20:43:19 GMT, Spam Collector
wrote:

While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

I use a ~550 foot horizontal loop fed with 450 ohm window line. A
balanced double L tuner is used as a matching device on HF. Homebrew
balanced tuners permit the loop to be used on 6 and 2M. On 6M the loop
performs well for an omnidirectional antenna. My primary 6M antennas
are Sterba curtains. The loop works FB on 2M FM but it is not suitable
for weak signal work.

73 de n4jvp
Fritz

Beginner antenna question
 

"Spam Collector" wrote in message
...
While reading about antennas, I've been unable to find
answers to what I thought would be basic questions.
Most of what I've read seems to concentrate on narrow-
bandwith antennas, and even at that seems to concentrate
on what happens when lengths become shorter and ignores
the effects of longer lengths (for definitions of 'longer'
meaning 'much longer, as in many wavelengths longer).
The question is how various low-band antenna types
will perform at higher bands. For example, if I were
to run a wire around my property (about 300 x 500 feet),
giving me about 1600' of antenna length, I could run it
as a folded random wire (fed from one end), a loop (fed
from a corner or the middle of one side), or as a dipole
(if fed like the loop but cut on the oposite side).
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Thanks for any insight,
Frank
KE5MJZ



When I was a kid I did pretty much what you are suggesting with a receiving
antenna hooked up to a hallicrafter s40 b. At first I thought this was a
really great antenna becuase it picked up a lot of staions I had never heard
before. Unfortunately it didnt pick up the stations I wanted to hear so I
went back to using a 15ft piece of wire thumb tacked to my bedroom wall.

Jimmie

Beginner antenna question
 

On 03 May 2007 20:43:19 GMT, Spam Collector
wrote:

While reading about antennas, I've been unable to find
Random antennas yield random results.
John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Beginner antenna question
 

Spam Collector wrote in
:

....
What are the performance differences between the
three configurations, and is there a upper frequency
limit for practical use of them? For example, would it
work on say 2m or 70cm, where the antenna would be
hundreds of wavelengths long?

Frank, as you will have noted from others' responses, the answer to this
is not simple.

Longer or larger antennas are not necessarily better. You would benefit
from examining the changes in pattern and feedpoint impedance of a loop
as it grows from 1/10 of a wavelength to 10 wavelengths per side, and
compare a very large loop with a rhombic.

You can only evaluate different antennas in your own context if you list
the relevant factors and rank their importance, factors like size,
height, frequency agility, transmission lines, matching arrangements,
automated operation etc.

Efficient and effective multi-band antennas don't happen by accident,
they are a significant challenge, and an efficient and effective 160m to
70cm is an extreme challenge. On the other hand, you will see proof that
"loading up the fencewire works", but it goes to the meaning of 'works',
which is less specific than 'effective and efficient'.

Owen

Beginner antenna question
 

On 2007-05-04, Owen Duffy wrote:

Efficient and effective multi-band antennas don't happen by accident,
they are a significant challenge, and an efficient and effective 160m to
70cm is an extreme challenge. On the other hand, you will see proof that
"loading up the fencewire works", but it goes to the meaning of 'works',
which is less specific than 'effective and efficient'.

Thanks to all for the insightful replies. Evidently the reason
I couldn't find much information on 'oversized' antennas is that
they aren't very effective. Then again, if you never experiment
with unconventional ideas you'll never discover anything new, so
I may just try it and see what happens. If all else fails I can
always make several smaller narrowband antennas out of the wire.

Thanks again,
Frank
KE5MJZ

Beginner antenna question
 

Spam Collector wrote:
Evidently the reason
I couldn't find much information on 'oversized' antennas is that
they aren't very effective.

My 130 ft. dipole is 'oversized' on 10m and has a
gain of 10.6 dBi at a take off angle of 12 degrees.
--
73, Cecil http://www.w5dxp.com

Beginner antenna question
 

Beginner antenna question
 

On 08 May 2007 17:47:27 GMT, Spam Collector
wrote:

On 2007-05-04, Owen Duffy wrote:

Efficient and effective multi-band antennas don't happen by accident,
they are a significant challenge, and an efficient and effective 160m to
70cm is an extreme challenge. On the other hand, you will see proof that
"loading up the fencewire works", but it goes to the meaning of 'works',
which is less specific than 'effective and efficient'.

Thanks to all for the insightful replies. Evidently the reason
I couldn't find much information on 'oversized' antennas is that
they aren't very effective. Then again, if you never experiment
with unconventional ideas you'll never discover anything new, so
I may just try it and see what happens. If all else fails I can
always make several smaller narrowband antennas out of the wire.

Thanks again,
Frank
KE5MJZ
I put about 2000 feet of wire in the grass this winter for radials.
There is always another use for extra wire...
John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Beginner antenna question
 

Beginner antenna question
 

Roy Lewallen wrote:
So in what way does the full wave dipole "perform better" than a half
wave dipole?

My 20m rotatable dipole gives ~2dB gain on 10m according
to EZNEC.
--
73, Cecil http://www.w5dxp.com

Beginner antenna question
 

Roy Lewallen wrote in
:

wrote:

Wrong, it just means you didn't read the whole posting. The issue
with a doublet of two full half waves is feed impedence is very high
and a very poor match for coax. Feed it properly (voltage feed) and
it will perform better than a 40m dipole. . .

A full wave dipole has less than 2 dB more gain than a half wave dipole
at its best angle. It has gain equal to or more than that of a half
wave
dipole over only 88 of the 360 degrees of coverage -- at all other
angles the full wave dipole has less gain. In fact, over 140 of the
total 360 degrees, the gain of a full wave dipole is more than 10 dB
less than that of a half wave dipole.

So in what way does the full wave dipole "perform better" than a half
wave dipole?

Roy,

We have had discussions about characterising baluns, and I understand the
complexity... however, let me try a rough analysis.

Following the discussion with one of the chaps I mentioned in the earlier
posting, he was using a full wave dipole, a RAK BL-50A balun and 25m of
foam RG58 (cellular) feedline, I have had a rough attempt at
characterising the balun (I have one) at 7MHz. It is a 1:1 voltage balun,
and o/c it appears to look like 3000 ohms resistance in shunt with 10uH
of inductance with very low applied voltage (at 7MHz).

This balun is rated at 1kW CW in 50 ohms, so the rated primary voltage
would be 223V RMS. If the apparent shunt resistance remained constant
(and it doesn't if flux is high... but flux should be kept low to avoid
excessive core loss / temperature), the core loss would be 16W. The
package could probably dissipate 40W of core and copper loss, so 16W+ for
core loss seems consistent with package size, so maybe 3000 ohms is about
right, possibly as low as half of that at full operating flux.

So, in the case of a full wave dipole low over ground, the modelled
feedpoint impedance is around 4200+j0 ohms. If this is shunted by
something in the range 1500 to 3000 ohms of core loss resistance,
efficiency ranges from 35% to 58%, and the antenna can absorb a max of
223^2/4200 or 12W before overheating the balun (perhaps a little more
since there is almost zero copper loss).

Then the feedline will have an efficiency from 20% to 10% due to the high
VSWR.

So this "more metal" antenna system, looks like it has some small
increase in directivity (1.6 from your posting), an efficiency of 7% to
6%, quite low gain (directivity * efficiency = -10dB compared to a
lossless half wave dipole+feed), a maximum input RF power rating of 50W
to 100W for a radiated power of around 12W. The EIRP is much lower
(almost 10dB lower) than a 100W transmitter feeding the same antenna of
half the length.

Gee, that all looks pretty complicated, no wonder people find "rules"
like "bigger is better" so appealing, it saves all that thinking and
understanding... but wait a minute, isn't that was ham radio was about?

73
Owen

PS: I am thinking about trying to characterise the balun at 223V applied,
I will see how time goes today.

Beginner antenna question
 

On Wed, 09 May 2007 13:11:01 -0700, Roy Lewallen
wrote:

wrote:

Wrong, it just means you didn't read the whole posting. The issue
with a doublet of two full half waves is feed impedence is very high
and a very poor match for coax. Feed it properly (voltage feed) and
it will perform better than a 40m dipole. . .

A full wave dipole has less than 2 dB more gain than a half wave dipole
at its best angle. It has gain equal to or more than that of a half wave
dipole over only 88 of the 360 degrees of coverage -- at all other
angles the full wave dipole has less gain. In fact, over 140 of the
total 360 degrees, the gain of a full wave dipole is more than 10 dB
less than that of a half wave dipole.

So in what way does the full wave dipole "perform better" than a half
wave dipole?

Roy Lewallen, W7EL
In the direction the lobe points. In general for an omnidirectional
antenna, it isn't as good.
--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

Beginner antenna question
 

what does the squiggly line mean?
On May 9, 1:21 pm, Cecil Moore wrote:
Roy Lewallen wrote:
So in what way does the full wave dipole "perform better" than a half
wave dipole?

My 20m rotatable dipole gives ~2dB gain on 10m according
to EZNEC.
--
73, Cecil http://www.w5dxp.com

Beginner antenna question
 

Beginner antenna question
 

Beginner antenna question
 

wrote:
what does the squiggly line mean?

Approximately....


On May 9, 1:21 pm, Cecil Moore wrote:
Roy Lewallen wrote:
So in what way does the full wave dipole "perform better" than a half
wave dipole?
My 20m rotatable dipole gives ~2dB gain on 10m according
to EZNEC.
--
73, Cecil http://www.w5dxp.com

Beginner antenna question
 

ok not much to worry about then. I had the imprssion it was.
On May 10, 1:00 pm, Cecil Moore wrote:
wrote:
what does the squiggly line mean?

Approximately
--
73, Cecil, w5dxp.com

Beginner antenna question
 

Cecil Moore wrote:
Roy Lewallen wrote:
So in what way does the full wave dipole "perform better" than a half
wave dipole?

My 20m rotatable dipole gives ~2dB gain on 10m according
to EZNEC.


All you need to do is rotate it! That does work for your instance. But
it is a long way between your 20 meter rotatable on 10 meters and 10
meters on a 160 meter dipole. But the statement from someone that more
metal in the air rules - or something to that effect - isn't correct.

My nice antenna pattern on 80 meters is starting to look a little funny
on 40, and it gets downright weirdly lobey looking on 10 meters. Some
places it works great, and some it doesn't. No free lunch. If you add at
one place, you subtract from another.

- 73 de Mike KB3EIA -