Magic guy wire lengths...
Peter J. Bertini
preferred length that handily avoids interactions with any of the Amateur
bands between 160 and 10 meters? Can the guys be checked for resonances
using a dipmeter? I will be using Strandvices on the insulators and I am
not sure of the effect they will have on the resonant frequencies.
What adverse effects - if any - would a resonant guys have on HF yagis or
LPYs? My main concern will be the inverted Ls running off of the tower for
160 and 80 meters, the higher frequencies are also a concern but they will
be covered by dipoles for 40/30 and a small KMA log antenna.
--
Peter, K1ZJH
W6RCecilA
> The reason is that when you cut up your guy wires you do not want to have them
> in the length of a quarter wave or multiple of a quarter wave .. In other words,
> Don't make them into an antenna.
Don't you mean 1/2 WL?
--
http://www.mindspring.com/~w6rca
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 80,000 Newsgroups - 16 Different Servers! =-----
Wes Stewart
>Nice idea,,, I think you will have a lot of trouble...
>The reason is that when you cut up your guy wires you do not want to have them
>in the length of a quarter wave or multiple of a quarter wave .. In other words,
>Don't make them into an antenna.
>Now with that said.. If you operated on only one frequency life would be simple.
>If you are that worried then use ropes for guy wires but find the correct type
>that will not break after the sun has been on them for a couple of years..
What's the matter with 1/4 wavelength???
N7WS
Richard Harrison
"I am going to break my new tower guy wires with insulators. Is there a
preferred length that handily avoids interactions with any of the
Insulated guy segments become resonant at 1/2-wavelengths. So, if you
break them at every 3 or 4 meters they can`t be 5 meters at 10-meters.
At lower frequencies you are well in the clear. That might require a lot
of insulators if your tower is tall.
Ed Laport says: "---seems that there is slight justification for the
expense of breakup insulators except where the guys are in very strong
fields, and this only because of the ease with which a guy can be
detuned by short-circuiting one or more of the insulators or placing
inductors across one or more of them."
Another after the fact way to detune a resonant guy wire or any resonant
re-radiator is to parallel it with another wire insulated from it at one
end and connected with it through a variable tuned circuit at the other
end. It makes a short-circuited stub that has opposing currents in its
two conductors. The fields will add to zero eliminating the problem with
proper circuit tuning.
You can use a dipmeter to find resonances. A 1/2-wave resonant segment
has maximum current in the center and maximum voltage at its insulated
ends.
You might just insulate the guys at the top of your tower and use a
couple of insulated sections at the lower end where you can reach them
so they may be shorted out for detuning the guy wire if necessary.
Best regards, Richard Harrison, KB5WZI
Richard Harrison
"What`s the matter with !/4 wavelength???"
It isn`t resonant as a guy section , so no problem, unless it is the
section connected to the grounded anchor. At a frequency where that
grounded segment is a small part of the entire guy, still no problem.
Tom W8JI
<comm...@home.com> wrote:
>I am going to break my new tower guy wires with insulators. Is there a
>preferred length that handily avoids interactions with any of the Amateur
>bands between 160 and 10 meters? Can the guys be checked for resonances
>using a dipmeter? I will be using Strandvices on the insulators and I am
>not sure of the effect they will have on the resonant frequencies.
The most important area for keeping the line sections short is right
up under the antenna. I break mine up about ten feet long near the
antennas, or use long fiberglass rods.
When out away from under or around the HF antennas a bit, I break them
up about every 20 feet. Near the ground I break them up every 40
feet.
73 Tom
Rudy Marcelletti
ham bands. The guys are broken by insulators on my tower at:
Bottom set: Guy is attached to tower and broken by insulator at
approximately 27 feet out. Balance of 1/4" EHS to anchor 80% of tower
height away from tower.
Middle set: 2 insulators, 1st at 27 feet from tower, 2nd 27 feet from 1st,
balance of 1/4" EHS to anchor.
Top set uses 3 insulators 27 feet apart, balance of 1/4" EHS to anchor.
Fewer insulators are needed the farther away from the antenna. If you are
going to load the tower, then insulate the guys at the tower also. You
could use the top guys and antennas as capacitance loading if you desire. I
don't know the math for this and don't care to learn it.
Peter J. Bertini wrote in message ...
Tom W8JI
<ru...@net-link.net> wrote:
>27 to 28 feet is in the middle of a "non-resonant" window length for all the
>ham bands. The guys are broken by insulators on my tower at:
Does this include the capacitance of the wire loops at the guy line
ends and the wire diameter, or ignore it??
>Bottom set: Guy is attached to tower and broken by insulator at
>approximately 27 feet out. Balance of 1/4" EHS to anchor 80% of tower
>height away from tower.
Contrary to popular myth, being "non-resonant" does NOT insure the guy
line will not change the antenna pattern. Resonance has something to
do with it, but not as much as we seem to assume.
The guy wire should always be much less than 1/2 wl long between
sections near the antenna or in areas where it can affect the pattern.
>Fewer insulators are needed the farther away from the antenna. If you are
>going to load the tower, then insulate the guys at the tower also.
We should ALWAYS insulate the guys at the tower, because the tower and
guy line will for an unpredictable combination. The guy line should
never be mopre than a few feet long from the tower before reaching an
insulator at HF.
73 Tom
Peter J. Bertini
"Tom W8JI" <2w...@akorn.net> wrote in message >
> Does this include the capacitance of the wire loops at the guy line
> ends and the wire diameter, or ignore it??
>
throught the insulators?
> Contrary to popular myth, being "non-resonant" does NOT insure the guy
> line will not change the antenna pattern. Resonance has something to
> do with it, but not as much as we seem to assume.
>
What is best for segment lengths vs. wavelength?
> The guy wire should always be much less than 1/2 wl long between
> sections near the antenna or in areas where it can affect the pattern.
>
>
Much less is very subjective... Would 1/4 wave for the highest frequency of
interest cover all bases?
> >Fewer insulators are needed the farther away from the antenna. If you
are
> >going to load the tower, then insulate the guys at the tower also.
If running an inverted L I assume the lower insulators and segment lengths
become equally important?
>
> We should ALWAYS insulate the guys at the tower, because the tower and
> guy line will for an unpredictable combination. The guy line should
> never be mopre than a few feet long from the tower before reaching an
> insulator at HF.
>
> 73 Tom
Regards
Pete
Tom W8JI
<comm...@home.com> wrote:
>Do I need to calculate or measure the capacitance of the Strandvise loops
>throught the insulators?
I'm not sure. I'd bet most guyline lengths are pulled out from near
someone's back pocket.
I was asking a question Pete because I'd wager no consideration at all
was given to the end-capacitance in the insulator connections. That
can be appreciable in large cables.
>> Contrary to popular myth, being "non-resonant" does NOT insure the guy
>> line will not change the antenna pattern. Resonance has something to
>> do with it, but not as much as we seem to assume.
>
>What is best for segment lengths vs. wavelength?
As below Pete.
>> The guy wire should always be much less than 1/2 wl long between
>> sections near the antenna or in areas where it can affect the pattern.
>>
>Much less is very subjective... Would 1/4 wave for the highest frequency of
>interest cover all bases?
Much less would be say 70% or smaller of a half wave. It would depend
on how close to the antenna it is, and how the antenna behaves nearby.
But I'd guess that .35 wl would be safe.
>> >Fewer insulators are needed the farther away from the antenna. If you
>are
>> >going to load the tower, then insulate the guys at the tower also.
>
>If running an inverted L I assume the lower insulators and segment lengths
>become equally important?
Yes, but the frequency is lower with the low band antennas so the
lengths can be longer.
I would think this could all be modelled, with loads used for the
insulators to represent the wire loops at the insulators.
I wonder if anyone has done that?
73 Tom
Frank Donovan
You should always use an insulator within a few feet of a guyed tower.
It should be just far enough away so that a climber's head can't hit it
(an insulator makes a much bigger "target" for the climber's head
than the guy wire alone).
Since you did not place an insulator near the tower, your minimum
wire length is actually 28 feet times two (56 ft), plus the width of the
tower
face, plus an additional lengthing factor because you have three wires
instead
of two, plus the capacitive end loading factor of the insulators and loops
at
end of each wire...
My judgement is that your guy configuration is highly likely to degrade any
40 meter antenna on or near your tower. A little effort modelling your
tower and 40 meter antenna could quickly move this out of the conjecture
domain. I'd suggest adding another insulator to each of your guys.
The 27 to 28 foot length you specified was popular prior to the introduction
of the "WARC" bands. Unfortunately, that length makes a darn good
reflector for the 18 MHz ham band! I wouldn't want it within a wavelength
of an 18 MHz antenna that you expect to perform properly.
Steel guys for a tower that will (or potentially will) support antennas for
all
HF bands should be designed as follows:
- An insulator at the tower, just out of "headache" range.
- The remaining lengths of wire should be less than 0.35 wavelengths at the
highest frequency antenna that will be within one wavelength of that
wire.
(Don't forget to think about all antennas below the guy as well).
If you are not using directive antennas that you have invested lots of
blood,
sweat and money in, you could consider relaxing one wavelength distance
to one-half wavelength.
For these reasons, many designers of high performance amateur arrays have
opted for non-conductive guys; however, this comes at the price of
a more mechanically fragile system. You never want to drop anything on
a non-conductive guy (especially fiberglas!). If you do (and the tower
doesn't fail), your first order of business is a very thorough inspection
of the guy(s) for damage!
73
Frank
W3LPL
dono...@erols.com
Frank Donovan
You should always use an insulator within a few feet of a guyed tower.
It should be just far enough away so that a climber's head can't hit it
(an insulator makes a much bigger "target" for the climber's head
than the guy wire alone).
Since you did not place an insulator near the tower, your minimum
wire length is actually 28 feet times two (56 ft), plus the width of the
tower
face, plus an additional lengthing factor because you have three wires
instead of two, plus the capacitive end loading factor of the insulators
and loops at the end of each wire...
My judgement is that your guy configuration is highly likely to degrade any
40 meter antenna on or near your tower. A little effort modelling your
tower and 40 meter antenna could quickly move this out of the conjecture
domain. I'd suggest adding another insulator to each of your guys.
The 27 to 28 foot length you specified was popular prior to the introduction
of the "WARC" bands. Unfortunately, that length makes a darn good
reflector for the 18 MHz ham band! I wouldn't want it within a wavelength
of an 18 MHz antenna that you expect to perform properly.
Steel guys for a tower that will (or potentially will) support antennas for
all HF bands should be designed as follows:
- An insulator at the tower, just out of "headache" range.
- The remaining lengths of wire should be less than 0.35 wavelengths at
the
highest frequency antenna that will be within one wavelength of that
wire.
(Don't forget to think about all antennas below the guy as well).
If you are not using directive antennas that you have invested lots of
blood, sweat and money in, you could consider relaxing one wavelength
distance to one-half wavelength.
For these reasons, many designers of high performance amateur arrays have
opted for non-conductive guys; however, this comes at the price of
a more mechanically fragile system. You never want to drop anything on
a non-conductive guy (especially a fiberglas guy!). If you do (and the
tower
doesn't fail), your first order of business becomes a very thorough
Jim Warner
discertations would be if we were using pencils?
Frank Donovan <dono...@erols.com> wrote in article
<9adtsp$7r4$1...@bob.news.rcn.net>...
Rudy Marcelletti
Jim Warner wrote in message <01c0bd71$d6bae2e0$1dde1b3f@jpwarner>...
Richard Harrison
transmitting stations all over the globe. Ed says:
"---seems that there is slight justification for the expense of breakup
insulators except where the guys are in very strong fields, and this
only because of the ease with which a guy can be detuned by
or more of them."
Ed is saying guy breakup insulators are not particularly advantageous.
Any conductor hanging out there in the r-f field only deforms the field
to the extent it is excited. It must be near some multiple of 1/2
wavelength if it is ungrounded and insulated at both ends. So, if you
hit resomance in a guy wire what happens?
If there were enough loss resistance in the guy to equal its radiation
resistance, the worst condition possible exists. The guy would waste 1/2
the power accepted from the field and re-radiate the other half,
distorting the antenna`s radiation pattern. Off-resonance or off-match,
the guy`s influence would be less deleterious.
I`ve put up countless support towers for HF and VHF communication
antennas with never a guy breakup insulator. They worked just fine.
All the medium wave broadcast transmitters I`ve worked with used breakup
insulators in their tower guys because the tower was an antenna array
element. The breakup insulators insured the pattern was not deformed.
Non-directional antennas use them too.
I`ve put up many rhombics for shortwave broadcasting. Many of these were
accepting 100 KW. None with guy breakup insulators and no problems.
If a problem occurs, you can detune the troublesome guys by detuning
them with parallel wires as I described in a previous posting.
Best regards, Richard Harrison, KB5WZi
Tom W8JI
(Richard Harrison) wrote:
>Ed is saying guy breakup insulators are not particularly advantageous.
>Any conductor hanging out there in the r-f field only deforms the field
>to the extent it is excited. It must be near some multiple of 1/2
>wavelength if it is ungrounded and insulated at both ends. So, if you
>hit resomance in a guy wire what happens?
>If there were enough loss resistance in the guy to equal its radiation
>resistance, the worst condition possible exists. The guy would waste 1/2
>the power accepted from the field and re-radiate the other half,
>distorting the antenna`s radiation pattern. Off-resonance or off-match,
>the guy`s influence would be less deleterious.
That is not correct. The worse case condition is if the guy wire is
LOSSLESS, and resonant or near resonance. Under these conditions the
guy wire will re-radiate ALL of the energy that excites it. That
re-radiation is the real problem we face, not the I^2R loss you and
your friend Ed worry about.
>I`ve put up countless support towers for HF and VHF communication
>antennas with never a guy breakup insulator. They worked just fine.
How do you know that? Why do you think that means something in other
applications?
>All the medium wave broadcast transmitters I`ve worked with used breakup
>insulators in their tower guys because the tower was an antenna array
>element. The breakup insulators insured the pattern was not deformed.
>Non-directional antennas use them too.
That's right, and that is the real reason. So the patterns are not
changed.
The guy line does NOT have to be resonant to affect the pattern, it
simply has to have noticable current. That easily occurs in long guy
lines that are NOT resonant because their impedance is moderated by
the long length.
We should never use guy wires anywhere near...or longer that...1/2 wl
in a strong field area of a radiator unless we are absolutely sure the
re-radiated field does not harm the pattern of the overall system in a
deleterious manner. Not being resonant, by itself, is not enough
unless the guy line section is short compared to a 1/2 wave.
>I`ve put up many rhombics for shortwave broadcasting. Many of these were
>accepting 100 KW. None with guy breakup insulators and no problems.
How do you know?
>If a problem occurs, you can detune the troublesome guys by detuning
>them with parallel wires as I described in a previous posting.
So you are saying we can take a guy wire near a 160-10 meter
transmitting station, and with a simple parallel wire detune the guy
wire on all bands?
Seriously, we all should know better than that!
73 Tom
Wes Stewart
>Rudy,
>
> You should always use an insulator within a few feet of a guyed tower.
>It should be just far enough away so that a climber's head can't hit it
>(an insulator makes a much bigger "target" for the climber's head
>than the guy wire alone).
I have to ask... why?
Wes Stewart N7WS
>
[snip]
W6RCecilA
> We should never use guy wires anywhere near...or longer that...1/2 wl
> in a strong field area of a radiator unless we are absolutely sure the
> re-radiated field does not harm the pattern of the overall system in a
> deleterious manner.
Egads, what effect are my new 40m vertical's elevated radials going to
have on my 20m-10m rotatable dipole? Does the coax braid attached to the
radials detune them in a passive configuration?
Tom W8JI
wrote:
>Egads, what effect are my new 40m vertical's elevated radials going to
>have on my 20m-10m rotatable dipole? Does the coax braid attached to the
>radials detune them in a passive configuration?
>--
>http://www.mindspring.com/~w6rca
Even if (magically) four elevated radials near earth make a good
ground system, they certainly cause other problems.
I avoid having as many unneeded wires hanging in the air as I can.
73 Tom
W6RCecilA
> Even if (magically) four elevated radials near earth make a good
> ground system, they certainly cause other problems.
Fortunately or unfortunately, they are not near earth. They are at
the same height as my 20m-10m rotatable dipole.
Allodoxaphobia
where is the URL where he sells "wire lengths"?
HIHI
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | OS/2
| Gunnison, Colorado | @ | Jonesy | linux __
| 7,703' -- 2,345m | frontier.net | DM68mn SK
Reg Edwards
be modelled as a secondary tuned circuit coupled to an RF generator
via a primary tuned circuit. The primary and secondary circuits
will each have a value of Q and there will be a coefficient of
coupling due to mutual inductance and capacitance.
The coefficient of coupling between the tuned circuits will be
small unless the secondary is intended to be, say, a reflecting
element. And even then the coupling coefficient need not be greater
than the 'critical' value at which the primary and secondary
currents are approximately equal when both circuits are resonant.
Nobody worries about the power lost in a reflecting element. Or
even in the radiating element. So no-one need worry about the power
lost in a guy wire even if it is resonant.
The principal effect of a guy wire (or any nearby phone lines) is
to distort the radiation pattern. In most amateur HF installations
(multi-band dipole, inverted-L, etc) the radiation pattern can only
be described as randomly multi-directional in both vertical and
horizontal planes. The effects of a guy wire leave the pattern
description unchanged.
So don't allow a guy wire of any length to pass through your 10m
multi-element beam. On the other hand there's nothing you can do
about your neighbour's house, complete with power lines, phone
lines and copper plumbing system being in the way of a desirable DX
direction.
If one of your antenna guys is of almost resonant length running
crudely in parallel with antenna elements, and you have a worrying
disposition, you will obtain relief by inserting an insulator about
half way along it. If the input impedance of the system remains
unchanged by the insertion then you will at least have learned
something.
----
***********************************
Regards, Reg, G4FGQ
Free radio design & modelling software
http://www.btinternet.com/~g4fgq.regp
***********************************
Truelove39
My sailboat's mast has twin backstays; one of them is insulated as a SSB
antenna. The other (grounded) backstay is within a foot or so of the antenna
backstay at the top and about 6' at the bottom. The length of the insulated
portion is about 45'. I don't "get out" too well, and it's been suggested that
I should insulate the grounded stay in one or possibly two places to improve
transmission.
What would you recommend?
Regards,
John
Reg Edwards
effect on radiating efficiency. It will have a minor effect on the
radiating pattern. It will have a small effect on tuner settings.
More info needed please -
How do you know you don't "get out" too well ?
A good check on "getting out" is to ask how well does it "drag 'em
in" ?
Against what have you compared performance ?
A 45-feet vertical above water should be OK unless it is parked
under a bridge.
Is it salt water or fresh water ?
What is an SSB antenna ? Do you mean it is used on the 160m to 10m
bands ?
Of what materials are the guys, mast and hull made ?
Presumably it is tuned against ground. What is your ground
electrode ? How do you make contact with water ?
---
Regards, Reg, G4FGQ
================================
Truelove39 wrote
Truelove39
Thank you for the reply.
Friends on boats in the same anchorage as I (Eastern Caribbean) can talk to
their friends in the States with no problem whereas I am barely heard and
vice-versa.
The antenna is at about a 45 drgree angle. The water is salt.
I have a good ground and the SWR is 1.3:1 at worst on 4mHz and usually 1:1 on
other freqs. The rig is an SEA 235R with the 1610 coupler. The coupler and
xmtr are grounded with 3" copper foil run separately to a point on the engine
block. The backstay is 3/8" 316 stainless wire, end-fed with GTO.
The hull is fiberglass.
The frequencies allocated for marine use are in the 2,4,6,8,12,16 and 22 mHz
regions; all USB. We use 4,6,& 8 the most. Usually talk to the states just
after sundown on 6.209, 6.212 or 6.215.
Regards,
John
Peter J. Bertini
Pete
"Truelove39" <truel...@aol.com> wrote in message
news:20010421185301...@ng-fo1.aol.com...
Bill Nelson
: I have a good ground and the SWR is 1.3:1 at worst on 4mHz and usually 1:1 on
: other freqs. The rig is an SEA 235R with the 1610 coupler. The coupler and
: xmtr are grounded with 3" copper foil run separately to a point on the engine
: block. The backstay is 3/8" 316 stainless wire, end-fed with GTO.
: The hull is fiberglass.
How is your grounding to the ocean itself? Does the boat have a counterpoise
ground?
The antenna and tuner should not be grounded to the motor. They should both
be grounded to a common point which is where your ocean ground occurs. The
motor should also be grounded to this common point - as should many other
items on the boat.
Obtaining proper rf ground on a fiberglass or wood boat is not trivial.
There are books available that cover the subject in detail. I would suggest
that you purchase one or two of them.
Whatever you do, don't mess with the integrity of the other backstay. It
is not the cause of your problems.
--
Bill Nelson (bi...@peak.org)
Truelove39
SEA came up with the counterpoise grounding to the engine based on their tests.
Previously, I had tried running 3" foil all around (especually under the feed
point) on the inside of the hull and connecting it to all the thru-hulls, etc.
The way it is now is much better. The problem is that my boat's hull is so
thick that the foil doesn't couple to the sea as it does in most boats. (Think
I read this in Gordon West's book). So the ground is by virtue of the propeller
shaft and prop.
The only other ground on the boat is the Dynaplate which is a dedicated
lightning ground for the mast. Conventional wisdom precludes connecting
anything else to it.
I have in fact read just about everything available on counterpoises for boats
and have tried most of the suggestions. The current scheme is not worse than
any I have tried, so I am looking elsewhere. The SWR suggests that the power is
getting to the antenna and that the counterpoise is adequate, no?
It's difficult for me to believe that a grounded wire parallel to and within a
few feet of the antenna won't be absorbing some portion of the signal.
John
Peter J. Bertini
Magazine several years back. My memory is dim, but I think the gentleman
who wrote the article mentioned something about using the keel as a ground,
even though it was encapsulated.
pete
"Truelove39" <truel...@aol.com> wrote in message
news:20010422143255...@ng-ch1.aol.com...
Bill Nelson
: SEA came up with the counterpoise grounding to the engine based on their tests.
: Previously, I had tried running 3" foil all around (especually under the feed
: point) on the inside of the hull and connecting it to all the thru-hulls, etc.
: The way it is now is much better. The problem is that my boat's hull is so
: thick that the foil doesn't couple to the sea as it does in most boats. (Think
: I read this in Gordon West's book). So the ground is by virtue of the propeller
: shaft and prop.
A counterpoise does not need coupling to a ground.
: The only other ground on the boat is the Dynaplate which is a dedicated
: lightning ground for the mast. Conventional wisdom precludes connecting
: anything else to it.
Hm. It would seem to me that the Dynaplate should be your common ground
point for all rf. Not having it connected to the ground for the rest of
your system is asking for problems. You need the propeller etc at the
same ground potential as the Dynaplate.
: I have in fact read just about everything available on counterpoises for boats
: and have tried most of the suggestions. The current scheme is not worse than
: any I have tried, so I am looking elsewhere. The SWR suggests that the power is
: getting to the antenna and that the counterpoise is adequate, no?
It partly depends on where you are making the SWR measurement. If it is before
the tuner, then it simply means that your tuner is providing a 50 ohm load to
the transmitter. It says nothing about out efficient a radiator you have on
the other side of the tuner. For example, you could remove the tuner and
antenna and replace them with a 50 ohm dummy load. You would get a 1:1 SWR
indication, but the signal transmitted would be minute.
It is possible that the tuner is absorbing most of your power and radiating it
as heat.
: It's difficult for me to believe that a grounded wire parallel to and within a
: few feet of the antenna won't be absorbing some portion of the signal.
Sure, it will absorb a small amount of the signal. But not anywhere near the
amount needed to produce the poor transmission/reception that you report.
I would suspect there is a problem with your antenna - such as the top end of
it being shorted to the mast, or where the antenna is fed through the deck to
the backstay, or to the bottom portion of the backstay.
You should be able to disconnect the antenna from the tuner - then check for
a DC short to various items.
--
Bill Nelson (bi...@peak.org)
Tom W8JI
>: I have in fact read just about everything available on counterpoises for boats
>: and have tried most of the suggestions. The current scheme is not worse than
>: any I have tried, so I am looking elsewhere. The SWR suggests that the power is
>: getting to the antenna and that the counterpoise is adequate, no?
>
>It partly depends on where you are making the SWR measurement. If it is before
>the tuner, then it simply means that your tuner is providing a 50 ohm load to
>the transmitter. It says nothing about out efficient a radiator you have on
>the other side of the tuner. For example, you could remove the tuner and
>antenna and replace them with a 50 ohm dummy load. You would get a 1:1 SWR
>indication, but the signal transmitted would be minute.
SWR does not indicate system efficiency.
>It is possible that the tuner is absorbing most of your power and radiating it
>as heat.
But unlikely. In most cases the tuner would fail if power were being
"ate up" in the tuner. Unless you run very low power or have a very
big tuner.
>: It's difficult for me to believe that a grounded wire parallel to and within a
>: few feet of the antenna won't be absorbing some portion of the signal.
>
>Sure, it will absorb a small amount of the signal. But not anywhere near the
>amount needed to produce the poor transmission/reception that you report.
It certainly can be causing big problems. It greatly affects the
pattern of the antenna, and can make the radiation resistance very
low....leaving him with mainly loss-related resistances to load into.
73 Tom
Bill Nelson
:>
:>It partly depends on where you are making the SWR measurement. If it is before
:>the tuner, then it simply means that your tuner is providing a 50 ohm load to
:>the transmitter. It says nothing about out efficient a radiator you have on
:>the other side of the tuner. For example, you could remove the tuner and
:>antenna and replace them with a 50 ohm dummy load. You would get a 1:1 SWR
:>indication, but the signal transmitted would be minute.
: SWR does not indicate system efficiency.
Which is what I stated above.
:>It is possible that the tuner is absorbing most of your power and radiating it
:>as heat.
: But unlikely. In most cases the tuner would fail if power were being
: "ate up" in the tuner. Unless you run very low power or have a very
: big tuner.
Most marine radios are low power - usually 25 watts or less.
:>: It's difficult for me to believe that a grounded wire parallel to and within a
:>: few feet of the antenna won't be absorbing some portion of the signal.
:>
:>Sure, it will absorb a small amount of the signal. But not anywhere near the
:>amount needed to produce the poor transmission/reception that you report.
: It certainly can be causing big problems. It greatly affects the
: pattern of the antenna, and can make the radiation resistance very
: low....leaving him with mainly loss-related resistances to load into.
It can affect the radiation pattern, but not much. Remember that the
antenna is almost vertical - so is the other backstay. It is basically
a base loaded Marconi, and probably with a rather imperfect ground.
The radiation resistance will be lowered, which reduces efficiency, but
remember that this is a separate non-connected wire. It would act like
a parasitic element that is too close to the radiating element.
One thing that does need to be checked is that unused backstay is not
a resonant length at the operating frequencies - In this case, the
combination of stay and mast need to be checked. If the rig performs
poorly over all the marine frequencies, then this is unlikely to be
the problem.
This type of antenna has been used for many years, with decent results.
So something has to be wrong with the installation itself. Aside from
potential antenna problems, it could be a defective marine radio, or
a defective tuner. There is a small chance that it could be defective
coax - although that might be obvious. It could be a combination of
all of these.
I am still waiting to hear where the SWR was checked. I would also like
to know if the output power has been checked.
--
Bill Nelson (bi...@peak.org)
Tom W8JI
>It can affect the radiation pattern, but not much. Remember that the
>antenna is almost vertical - so is the other backstay. It is basically
>a base loaded Marconi, and probably with a rather imperfect ground.
The induced current in a close-spaced wire is generally opposite that
in the exciting wire. Connected or not, grounded or not, it can make a
large change in pattern and efficiency.
>One thing that does need to be checked is that unused backstay is not
>a resonant length at the operating frequencies - In this case, the
>combination of stay and mast need to be checked. If the rig performs
>poorly over all the marine frequencies, then this is unlikely to be
>the problem.
It all needs to be looked at. A conductor does not need to be resonant
to have a large effect on the pattern.
>This type of antenna has been used for many years, with decent results.
>So something has to be wrong with the installation itself. Aside from
>potential antenna problems, it could be a defective marine radio, or
>a defective tuner. There is a small chance that it could be defective
>coax - although that might be obvious. It could be a combination of
>all of these.
Could be. The problem could be anything. There simply isn't enough
information. The only thing that we do know is SWR doesn't mean
anything.
73 Tom
Richard Harrison
"A conductor does not need to be resonant to have a large effect on the
pattern."
If a conductor is not near resonance it accepts little energy from a
radio wave and therefore has little effect. Resonant structures near
broadcast antennas only require detuning to disappear as factors in the
broadcast pattern.
Best regards, Richard Harrison, KB5WZI
Gray Frierson Haertig
Richard,
Take your 90 degree AM tower and put a floating 225 degree tower 90
degrees away from it. Are you telling me that the effect on the
omnidirectional pattern is minimal?
Any guess as to the F/B ratio?
The only re-radiators that have minimum effect are short ones, ones that
are very far away and ones that are orthogonal.
Gray
--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
g...@haertig.com
Bill Nelson
: On 24 Apr 2001 04:10:41 GMT, Bill Nelson <bi...@spock.peak.org> wrote:
:>It can affect the radiation pattern, but not much. Remember that the
:>antenna is almost vertical - so is the other backstay. It is basically
:>a base loaded Marconi, and probably with a rather imperfect ground.
: The induced current in a close-spaced wire is generally opposite that
: in the exciting wire. Connected or not, grounded or not, it can make a
: large change in pattern and efficiency.
Sure, but it is only close-spaced at one end.
:>One thing that does need to be checked is that unused backstay is not
:>a resonant length at the operating frequencies - In this case, the
:>combination of stay and mast need to be checked. If the rig performs
:>poorly over all the marine frequencies, then this is unlikely to be
:>the problem.
: It all needs to be looked at. A conductor does not need to be resonant
: to have a large effect on the pattern.
:>This type of antenna has been used for many years, with decent results.
:>So something has to be wrong with the installation itself. Aside from
:>potential antenna problems, it could be a defective marine radio, or
:>a defective tuner. There is a small chance that it could be defective
:>coax - although that might be obvious. It could be a combination of
:>all of these.
: Could be. The problem could be anything. There simply isn't enough
: information. The only thing that we do know is SWR doesn't mean
: anything.
Agreed. That is why I was asking more questions - especially in regards
to power measurements.
--
Bill Nelson (bi...@peak.org)
Bill Nelson
: On 24 Apr 2001 04:10:41 GMT, Bill Nelson <bi...@spock.peak.org> wrote:
:>It can affect the radiation pattern, but not much. Remember that the
:>antenna is almost vertical - so is the other backstay. It is basically
:>a base loaded Marconi, and probably with a rather imperfect ground.
: The induced current in a close-spaced wire is generally opposite that
: in the exciting wire. Connected or not, grounded or not, it can make a
: large change in pattern and efficiency.
:>One thing that does need to be checked is that unused backstay is not
:>a resonant length at the operating frequencies - In this case, the
:>combination of stay and mast need to be checked. If the rig performs
:>poorly over all the marine frequencies, then this is unlikely to be
:>the problem.
: It all needs to be looked at. A conductor does not need to be resonant
: to have a large effect on the pattern.
Oops, I forgot this in my previous response.
If the nearby conductor is not close to resonant, then it will not
affect the radiation pattern significantly. It will not absorb or
reradiate enough energy to matter.
--
Bill Nelson (bi...@peak.org)
Gray Frierson Haertig
Non-resonant reradiators can have pretty big affect on antenna patterns.
The only reradiators that have minimal impact are those that are far
away, very short, or are orthogonal. A few simple eznec models will
prove this to your satisfaction.
Whether the reradiator is floating or grounded can make a pretty big
difference as well.
Though on a boat I suppose they're all floating. (c:
Gray
Bill Nelson wrote:
> If the nearby conductor is not close to resonant, then it will not
> affect the radiation pattern significantly. It will not absorb or
> reradiate enough energy to matter.
>
> --
> Bill Nelson (bi...@peak.org)
--
Richard Harrison
"Whether the radiator is floating or grounded can make a pretty big
difference as well."
Sure, if grounded, the first resonant length is 1/4-wave. If it is not
grounded, the first resonant length is 1/2-wavelength.
A table or graph for parasitic array design will indicate the amount of
induced current and its effect on antenna pattern. If the parasitic
element is at right angles, or far away, it has little effect.
Truelove39
Bill Nelson bi...@spock.peak.org wrote:
The SWR is measured and displayed at the remote head following the coupler's
tuning solution. I don't know where the measurement is made. This is a
software auto-tuner; not an RF-powered tuner like the SGC 230.
The only coax is from the transciever to the tuner. The coupler's output is via
GTO.
The PEP is 150w, switchable to 25W
The length of the "unused" backstay is approx. 60' It is "grounded" at the
masthead where it is attached to the mast.
The "bottom" is insulated by virtue of the attachment point (chainplate) being
bolted to the fiberglas hull.
This makes it about a half-wavelength on 8mHz. I can say that the tuner has
great difficulty obtaining a solution (and sometimes cannot) on 4mHz, and so
perhaps this is due to the "unused" backstay.
I'm a bit hampered in supplying more info, as the boat is in Trinidad, and I'm
in Vermont.
Regards,
John
Tom W8JI
Not true at all Richard, and I would expect you to know that.
Any long or large conductor can have a large effect on pattern. The
only conductors that have minimal effect are very short conductors
comperaed to the size of the nearby antenna and the wavelength.
One example you should be aware of is power lines. Even if the poles
(incombination with ground wires and static wires at the top) are NOT
resonant, the severly distort the pattern of AM BC stations. The
vertical conductor has to be sectionalized by tuning an area of it to
parallel resonance, which has the effect of breaking it as if an
insulator was inserted.
There are counteless example of non-resonant conductors that radiate
or extract appreciable energy, including things like terminated
Rhombics. They are non-resonant, as is the reflector on a dish
antenna.
My 5/8th wl insulated tower causes a 6 dB null in the pattern of a
vertical that is 500 feet away, and it is "not resonant".
Let's not confuse people trying to learn, by making misstatements just
because we might be sore at someone else.
73 Tom
Tom W8JI
>Tom W8JI <2w...@akorn.net> wrote:
>: On 24 Apr 2001 04:10:41 GMT, Bill Nelson <bi...@spock.peak.org> wrote:
>
>
>:>It can affect the radiation pattern, but not much. Remember that the
>:>antenna is almost vertical - so is the other backstay. It is basically
>:>a base loaded Marconi, and probably with a rather imperfect ground.
>
>: The induced current in a close-spaced wire is generally opposite that
>: in the exciting wire. Connected or not, grounded or not, it can make a
>: large change in pattern and efficiency.
>
>Sure, but it is only close-spaced at one end.
No, that isn't true. It only requires the conductor to be large and in
the way. My 318 foot tower is non-resonant, yet it put a measureable
null (about 6 dB) in the pattern of a vertical 500 feet away.
This fellow is talking about other conductors that are only a small
fraction of a wavelength away!!!
>: It all needs to be looked at. A conductor does not need to be resonant
>: to have a large effect on the pattern.
I stand by that statement.
73 Tom
Tom W8JI
So the reflector in my dish antenna is resonant?
How about the screen behind my UHF TV antenna? Is it resonant?
What about power poles near BC stations?
What about the guy lines?
What about a Rhombic? Does it absorb energy and re-radiate energy even
though it is non-resonant?
Why does my signal refuse to go past metal roofs that aren't resonant?
Sorry, a conductor does NOT need to be resonant to have a large effect
on the system. This is especially true when it is closeby, although it
can have an effect at a large distance also.
73 Tom
Gray Frierson Haertig
grounded or not. How much distortion of the pattern of a 90 degree
vertical, 90 degrees away, do you think it might cause - whether
grounded or not?
Gray
--
Richard Harrison
"How muh distortion of the pattern of a 90 degree vertical, 90 derees
away, do you think it might cause - whether grounded on not?"
If a parasitically excited element is placed at 90 degrees from a
radiator, some of the radiated wave travels the 90-degree distance to
the parasitic element and excites re-radiated energy which by Lenz`s law
is 180-degrees out-of-phase with the excitation. Some of this
re-radiated energy returns through the 90-degree distance to the
originial radiator where it is now in phase with the newly emerging
energy. This produces forward gain. The pattern can be affected. My
guess is that the best case must be less than a double of effective
field, and I would expect less.
I suspect that the radiator would be a grounded vertical. If it is
1/4-wave, it must be grounded to be effective as a radiator. If the
parasitic element is also 1/4-wave and is ungrounded, it will have
little effect. It will have almost no current.
In a 2-tower directional AM BC-band array of 1/4-wave radiators, if one
of the towers is simply floated above ground, the self-impedance of of
the other tower can usually be accurately measured. The floating tower
is out of the picture.
In a 2-tower array of 1/2-wave radiators, all that is necessary to make
a self-impedance measurement of only one tower is simply
to short the second tower to ground. Whip out the bridge and measure
away. Gray already knows all of this. Maybe I didn`t understand his
question.
In the boat, the mast stay has one end returned to a fiberglas deck. If
significant current is appearing in this cable, a wire can be attached
to detune the structure, or another wire can be added in parallel with
the backstay. This is a very simple problem.
Roy Lewallen
>
> Gray Frierson Haertig wrote:
> "How muh distortion of the pattern of a 90 degree vertical, 90 derees
> away, do you think it might cause - whether grounded on not?"
>
> If a parasitically excited element is placed at 90 degrees from a
> radiator, some of the radiated wave travels the 90-degree distance to
> the parasitic element and excites re-radiated energy which by Lenz`s law
> is 180-degrees out-of-phase with the excitation. Some of this
> re-radiated energy returns through the 90-degree distance to the
> originial radiator where it is now in phase with the newly emerging
> energy. This produces forward gain. The pattern can be affected. My
> guess is that the best case must be less than a double of effective
> field, and I would expect less.
But we can change a reflector to a director simply by changing its
length, without changing the spacing at all (which is typically much
less than 90 degrees for a Yagi). How do you explain this with Lenz's
law?
Roy Lewallen, W7EL
Richard Harrison
"How do you explain this with Lenz`s law."
If a parasitic element is parallel to the electric field of the
radiation, it tends to short the electric field and current flows in the
element. This current sets up its own electromagnetic field.
The incident and induced fields combine vectorially and so depend on the
magnitude and phase of current in the parasitic element. An element that
is not exactly resonant has reactance. The sign and magnitude of the
reactance depend on the length and position of the parasitic element and
whether the element is too short or too long to be resonant. Reactance
flips sign at resonance. The director or reflector bit results from
vector combinations.
If I thought Roy was sincere in a quest for knowledge, I might expand
the explanation, but alas I think he is just trying to irritate, so I`m
through.
Lenz`s law is applicable to every induction.
Richard Clark
(Richard Harrison) wrote:
>
>If I thought Roy was sincere in a quest for knowledge, I might expand
>the explanation, but alas I think he is just trying to irritate, so I`m
>through.
Hi Richard,
A very unfair characterization. Roy shows far more tolerance than the
lot of us combined.
73's
Richard Clark, KB7QHC
Roy Lewallen
explanation of how a parasitic element works, with its radiated field
always being 180 degrees from the incident field, with the fact that a
Yagi pattern can be dramatically altered by modifying the element
length. The explanation you just gave is closer to what I know happens.
But it seems to contradict your initial explanation.
Roy Lewallen, W7EL
Richard Harrison
"How about the screen behind my UHF TV antenna?"
conductor.
"What about power poles near BC stations?"
These are no where near resonance so neither they nor the stations had
to be moved.
"What about the guy lines?"
That question started this discussion long ago. Nearly all medium-wave
broadcast stations breakup guys in non-resonant lengths that cause no
problems.
"What about a Rhombic? Does it absorb energy and re-radiate energy even
though it is non-resonant?"
Certainly. It is multiple wavelengths long and the wires are aligned for
coincidence of the radiation lobes in its long wires. This is not simple
parasitic excitation. It is cumulative response to a traveling wave.
"Why does my signal refuse to go past metal roofs that aren`t resonant?"
We just went through a knock-down, drag-out over shielding. Surely Tom
remembers how induced currents in the shield`s surface counteract the
incident signal. But, skinny cable does not make a shield.
"Sorry, a conductor does NOT need to be resonant to have a large effect
on the system".
Of course, that is true in some particular cases, the ones that Tom will
swear that he was thinking of all the time, but it is false in the case
of lesser conductors, far from resonance, and having little mutual
impedance with the radiator which might be affected by re-radiation.
Tom W8JI
(Richard Harrison) wrote:
>is 180-degrees out-of-phase with the excitation. Some of this
>re-radiated energy returns through the 90-degree distance to the
>originial radiator where it is now in phase with the newly emerging
>energy. This produces forward gain. The pattern can be affected. My
>guess is that the best case must be less than a double of effective
>field, and I would expect less.
Richard, that is not how an antenna generally developes gain. The
phase of the fields at any point does not have to add....it simply
must cancel less than the field in other directions.
The effect is much more complicated than simply adding the two fields
together. As a matter of fact, the highest gain in a two element
antenna occurs when the fields at the most in-phase point are almost
in phase quadrature.
>I suspect that the radiator would be a grounded vertical. If it is
>1/4-wave, it must be grounded to be effective as a radiator. If the
>parasitic element is also 1/4-wave and is ungrounded, it will have
>little effect. It will have almost no current.
That's because it is electrically much shorter than a 1/2 wl, and not
grounded.
>In a 2-tower directional AM BC-band array of 1/4-wave radiators, if one
>of the towers is simply floated above ground, the self-impedance of of
>the other tower can usually be accurately measured. The floating tower
>is out of the picture.
Yes, but that does not apply to what any of us were talking about.
>In a 2-tower array of 1/2-wave radiators, all that is necessary to make
>a self-impedance measurement of only one tower is simply
>to short the second tower to ground. Whip out the bridge and measure
>away. Gray already knows all of this. Maybe I didn`t understand his
>question.
1/2 wl and grounded is a point of minimum interaction. But if the
length is not 1/2 wavelength, if it is longer or not significantly
shorter and floating, it can greatly affect the pattern. An element
does not have to be resonant to affect the pattern . It simply has to
be electrically long, and near the other elements.
>In the boat, the mast stay has one end returned to a fiberglas deck. If
>significant current is appearing in this cable, a wire can be attached
>to detune the structure, or another wire can be added in parallel with
>the backstay. This is a very simple problem.
Maybe, maybe not. We don't know enough about the problem to answer it.
73 Tom
Richard Harrison
"I just couldn`t reconcile your explanation of how a parasitic element
OK. I see the rub. Gray specified the problem I was trying to solve.
Gray specified a 90-degree parasitic element spaced at 90-degrees from
the radiator. A 90-degree grounded parasitic element is resonant and
contributes no aditional phase shift one way or the other, as I
remembered the problem. Now, I am remembering 225 degrees. Don`t know
which memory is faulty. If it was 225 degrees, the parasitic element
wasn`t resonant. It would be capacitive and take a lot less current from
the radiation.
My description would be accurate for the way I remembered the problem I
was trying to explain. I am sorry if it proves to be the wrong problem.
But, the question is really: What can be done if the
backstay/mast/other-rigging foul the performance of a sailboat antenna.
Chances are it can be fixed by detuning just as guy-wires can be
detuned. Ed Laport says just short a guy insulator if a cable happens to
hit resonance. Others suggest attaching a parallel wire at one end of a
resonant section and adjusting it as a now-folded section for detuning.
If it is far from resonance, its current and effect are insignificant,
else guys on towers used as radiators might be a disaster. We have ample
experience that they are not. You should look at the rigging for a
curtain array used in international broadcasting. I`ve constructed quite
a few myself. Many supporting cables are close and parallel to the
radiators carrying 100KW or more. They run cool and the patterns measure
almost exactly as predicted. The trick is simply breaking them into
pieces with insulators which are far from resonance. That`s all there is
to it.
Gray Frierson Haertig
Richard Harrison wrote:
>
> "What about the guy lines?"
> That question started this discussion long ago. Nearly all medium-wave
> broadcast stations breakup guys in non-resonant lengths that cause no
> problems.
>
Actually, they break up guy lines into electrically short pieces not
non-resonant pieces. Electrically short pieces will be non-resonant,
but much longer pieces, say 225 degrees, will also be non-resonant and
can have a profound effect on the pattern.
Gray
Tom W8JI
(Richard Harrison) wrote:
>Tom, W8JI wrote:
>"How about the screen behind my UHF TV antenna?"
>It is non-resonant, but extensive, nothing like a simple non-resonant
>conductor.
OK, so if it is a large conductor it has an effect even if
non-resonant.
>"What about power poles near BC stations?"
>These are no where near resonance so neither they nor the stations had
>to be moved.
Not true. Power poles near directional arrays often have to be
sectionalized with tuning networks that parallel tune a section of the
vertical conductors to prevent interaction. The pole does not have to
be resonant to cause a problem, it simply has to be in the pattern and
a tall pole.
>"What about the guy lines?"
>That question started this discussion long ago. Nearly all medium-wave
>broadcast stations breakup guys in non-resonant lengths that cause no
>problems.
But they use very short sections. They could easily save money by only
making the guy wire non-resonant....but instead they break the lines
up into very short sections.
>"What about a Rhombic? Does it absorb energy and re-radiate energy even
>though it is non-resonant?"
>Certainly. It is multiple wavelengths long and the wires are aligned for
>coincidence of the radiation lobes in its long wires. This is not simple
>parasitic excitation. It is cumulative response to a traveling wave.
It is non-resonant.
>"Why does my signal refuse to go past metal roofs that aren`t resonant?"
>We just went through a knock-down, drag-out over shielding. Surely Tom
>remembers how induced currents in the shield`s surface counteract the
>incident signal. But, skinny cable does not make a shield.
At what point does this "resonance" effect suddenly appear?
>"Sorry, a conductor does NOT need to be resonant to have a large effect
>on the system".
>Of course, that is true in some particular cases, the ones that Tom will
>swear that he was thinking of all the time, but it is false in the case
>of lesser conductors, far from resonance, and having little mutual
>impedance with the radiator which might be affected by re-radiation.
What is a "lesser conductor"?
It is not necessary for a conductor to be resonant to have a profound
effect on the pattern.
73 Tom
Tom W8JI
(Richard Harrison) wrote:
>almost exactly as predicted. The trick is simply breaking them into
>pieces with insulators which are far from resonance. That`s all there is
>to it.
Although you've modified the statement to make the conductor "far"
from resonance, that is not entirely true. The conductor has to be
small compared to the wavelength and small compared to the distance to
the radiator to have minimal effect.
Non-resonant conductors can have a profound effect when close to an
element. Especially when the conductor is over 1/2 wl long and only
1/8 wl from the antenna. You have to be very careful what you are
doing, and it will be virtually impossible to find a magic length that
does not affect the pattern when the radio is used on multiple
frequencies or bands.
If it was this easy, I wouldn't have dozens of insulators in my guy
lines. Neither would BC stations. It is more than just resonance at
work.
73 Tom
Richard Harrison
"Actually they break up the guy lines into electrically short pieces not
non-resonant pieces."
True. Ed Laport reports the work of Abbot and Fisher in "Radio Antenna
Engineering". It shows that parasitic radiation grows with the length of
the re-radiator.
Here is a summary of what Ed says of guy wires. I gave his exact words
at the start of this thread ages ago.
Guy current is proportional to the induced electromotive force.
Try to put guys where the fields are weak.
If a guy is resonant, detune it.
The chance of resonance is about the same whether the guy is broken with
insulators or not. So, there is little justification for guy insulators
except in very strong fields and this is only to make detuning easy by
shorting out one or more insulators. (This is what Gray seems to
disagree with, but this is what I`ve done and the practice has caused me
no trouble in many installations.)
Explore the guys for parasitic currents as you would measure current in
individual wires of a transmission line. If troublesome current is
found, detune the guy wire.
Ed Laport has a chart of the far-field strength ratio of radiation from
a parasitic element over that from the driven element. The driven
element is a 1/4-wave unipole and the parasitic element has various
lengths and spacings. Ed took the data from the work of Abbot and
Fisher. It is found on page 299 of "Radio Antenna Engineering"
Here are the ratio values for 1/4-wave spacing and different parasitic
lengths:
0.1wl 0.1
0.15wl 0.2
0.9wl 0.28
0.375wl 0.3
0.22wl 0.3
0.2wl 0.4
0.25wl 0.55
In general, the radiation from the parasite increases with its length.
Closer spacing excites the parasite more. Shorter parasites radiate
less.
Best regards, Richard Harroison, KB5WZI
Richard Harrison
"If it was that easy, I wouldn`t have dozens of insulators in my guy
lines."
That`s pogress. "Dozens" is almost a number.
Today, I discovered coverage of guy wires in the new 19th edition of the
ARRL Antenna Book. It starts about page 22-14. It says that if your guy
wires resonate near your operating frequency they may become
re-radiatrors and alter your radiation pattern, as if they were
parasitic antenna elements. The extent of guy wire disruption depends on
two things, it is said, resonant frequency and the degree of coupling.
The magic guy wire lengths are presented for the eight HF amateur bands
on page 22-17.
There is a wealth of information in the new Antenna Book. I`m glad I got
one.
Peter J. Bertini
"Richard Harrison" <richard...@webtv.net> wrote in message
news:1476-3A...@storefull-117.iap.bryant.webtv.net...
> > The magic guy wire lengths are presented for the eight HF amateur bands
> on page 22-17.
>
> There is a wealth of information in the new Antenna Book. I`m glad I got
> one.
>
Don't keep me in suspense... what are the magic numbers??
Richard Harrison
"Don`t keep me in suspense...what are the magic numbers?"
Well, a wire insulated at both ends should avoid multiples of 1/2-wave,
or near half-wave multiples. ARRL copyrights control distribution but a
small sample should be considered only a teaser or ad for the larger
collection. So, here are the values for the 10-meter band as perceived
with my dim eyes:
14 to 18 feet
29 to 38 feet
44 to 57 feet
Anything longer than 59 feet.
I really recommend the book. I thought it was overpriced, but it is
worth the price in today`s market if you are interested in antennas.
Richard Harrison
"So here are the values for the 10-meter band..."
I realize that it may not be clear that the listed values are to be
avoided as they define a spectrum around multiples of 1/2-wavelength.
Any guy length not included in the list (the spaces between the
listings) should be OK.
Tom W8JI
(Richard Harrison) wrote:
>I realize that it may not be clear that the listed values are to be
>avoided as they define a spectrum around multiples of 1/2-wavelength.
>Any guy length not included in the list (the spaces between the
>listings) should be OK.
OK, I modeled a two vertical wires, with one fed and the other 58
feet long insulated from ground. The change in pattern when the second
wire is added is:
160m nil
80m nil
40m 4.22 dB
30m 6.5dB
20m 3dB
17m 8 dB
15m 2.5db
12m 3.2 dB
10m 1.5dB
It looks like to make sure the second conductor does not influence
pattern, you need to make sure the segments are shorter than 1/4 wl or
so.
73 Tom