WHY antennas of "5/8" wavelength?
Joel Govostes
Here's an antenna question that I've never found an explanation for --
For mobile or fixed station use, a typical vertical antenna is 1/4 wave
and fed with low-impedance coaxial cable. The ground is provided by earth
ground, automobile body, or a set of "ground plane" elements. Okay.
This type of antenna matches 50-ohm coax and transmitter output circuits well.
So, who came up with the oddball figure of 5/8 wave for vertical antennas,
and why?
I know that the radiation pattern shape is somewhat "squashed" on the 5/8
wave, and that it provides some gain over the 1/4 wave. But 5/8
wavelength doesn't match 50 ohm coax feed, and so usually it is fed on a
loading-coil tap at the base of the vertical.
I'm wondering what is so special about the 5/8 wave antenna length; why
not just a 1/2 wave (4/8 wave)? Could 1/2 wave vertical be fed in a
similar way, and would it also provide significant gain over the 1/4
wave? Why not just go to 6/8-wave size, as that would match coax feed as
3/4 wave (odd multiple of 1/4 wave ~ approx. 50 ohms.) Thanks
Fractenna
A 5/8 wave OVER A VERY LARGE GROUND PLANE offers 3 dB gain over a 1/4
wave. As you gathered, however, it is NOT a resonant antenna.
With a counterpoise or small GP, very little gain is had (if any) over a
1/4 wave.( I'm not going to play games with one individual on this
matter--play with your own GP and report the results.)
73
Chip N1IR
altavoz
Joel Govostes wrote:
>
> Here's an antenna question that I've never found an explanation for --
>
> For mobile or fixed station use, a typical vertical antenna is 1/4 wave
> and fed with low-impedance coaxial cable. The ground is provided by earth
> ground, automobile body, or a set of "ground plane" elements. Okay.
>
> This type of antenna matches 50-ohm coax and transmitter output circuits well.
>
> So, who came up with the oddball figure of 5/8 wave for vertical antennas,
> and why?
ALTAVOZ: your 1/4w is actually odd ball also , its not 1/4w !
so lets call them 1/4w and 1/2w just for convenience , but knowing
that they have been shortened ( 1/4w) and lengthened ( 1/2w) to make
them capacitive ( so a coil will tune either, we dont use caps to tune).
The current peak on a 1/4w is at the feed point , so the main lobe
is pointing up at a high angle ( not good for horizon reception)
The current peak on a 1/2w is 1/4 w up the element and points
to the horizon and makes high gain.
>
> I know that the radiation pattern shape is somewhat "squashed" on the 5/8
> wave, and that it provides some gain over the 1/4 wave. But 5/8
> wavelength doesn't match 50 ohm coax feed, and so usually it is fed on a
> loading-coil tap at the base of the vertical.
altavoz: The coil needed for 5/8w is exactly the same as the coil needed
for the 1/4w .
> I'm wondering what is so special about the 5/8 wave antenna length; why
> not just a 1/2 wave (4/8 wave)? Could 1/2 wave vertical be fed in a
> similar way, and would it also provide significant gain over the 1/4
> wave? Why not just go to 6/8-wave size, as that would match coax feed as
> 3/4 wave (odd multiple of 1/4 wave ~ approx. 50 ohms.) Thanks
altavoz: You cant feed a 1/2w ( 2000+j00) . 3/4w doesnt work
( lobe is too high , worse than 1/4w )
Next we'll do an "L" network ( its just a single coil, but fed in
center makes it 2 coils) to match the 200-J100 antenna.
BTW the J pole doesnt work ( bad grnd plane )
______End of text from altavoz___________
Cecil Moore
Joel Govostes <jw...@cornell.edu> writes:
>I'm wondering what is so special about the 5/8 wave antenna length; why
has the maximum gain available from wire with no other
components. If I remember correctly, a 10/8 wavelength
dipole has 3dB gain over a 1/2 wavelength dipole because
the two main lobes are more concentrated. Above 10/8, a
cloverleaf pattern develops. It's interesting to model
a dipole with a program like EZNEC and gradually increase
the frequency while watching the radiation patterns.
73, Cecil, W6RCA, OOTC
altavoz
altavoz: 1/4w antennas are allways shorter than 1/4w to allow
an inexpensive coil to tune it to resonance. The 5/8w is exactly
the same as the <1/4w ( its capacitive) , in fact you use the same
coil . No good comes from 90 deg radials , the pattern is poor.
All 1/4w , 5/8w ant's must use 180 deg radials to get max
performance ( to get the lobe down on the horizon).
The comments above by CHIP N1IR on very large ground
plane is nonsense.
The 5/8w has more gain than the 1/4w and 2 colinear 5/8w
phased with a parallel res circuit, or hair pin ( RINGO
RANGER II ) has about as much gain as you can stand
for an omni directional ant , cause if it even tilts
slightly you may loose gain !
I suggest you dont make 1/4w and 5/8w antennas for
comparison, its better to compare store bought antennas for
their gain. You will see a 1/4w is far inferior to a 5/8w
no matter how many mfg's you compare !!
This DAMN religious antenna crap has to stop !
This is not religion, this is science !
THE 5/8 WAVE ANT' HAS MORE GAIN THAN A 1/4 WAVE !!!!!!
THE ARRL BOOK SAYS SO, JASIK SAYS SO, EVERYONE WHO IS ANYONE
SAYS SO !!!!
Fractenna
The coils are used to LOAD the antenna to resonance.
Again, a 5/8 has no benefit unless placed on a LARGE ground plane.
73
Chip N1IR
Cecil Moore
altavoz wrote:
> altavoz: 1/4w antennas are allways shorter than 1/4w to allow
> an inexpensive coil to tune it to resonance.
Hi Altavoz, Most prudent people avoid blanket statements using
the words, "always", "never", etc. because they are almost
always false. Both my 10m whip and 2m whip are 1/4 WL and
resonant without loading coils.
I would agree that most CB antennas are shorter than 1/4w...
73, Cecil, W6RCA, OOTC (not speaking for my employer)
altavoz
altavoz: I know what im talking about , so i made the absolute
statement , and i stand by it . Between .25w and .5w you'll need
a cap to tune and caps are expensive , so why not not just jump
to .6w and a coil does it and the 2nd lobe isnt significant.
What you're not looking at is the pattern (gain). .25w
pattern is trash.
Cecil Moore
altavoz <alt...@worldnet.att.net> writes:
>> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
>> > an inexpensive coil to tune it to resonance.
>statement , and i stand by it . Between .25w and .5w you'll need
not shorter than 1/4 WL then your statement is false. I
personally have two of them each centered at a certain
frequency. Below the center frequency, they are slightly
capacitive and above the center frequency, they are
slightly inductive. So what? No coil and no cap are
required so a 1/4 WL antenna is less expensive than
your short, coil-loaded less-than 1/4 WL antenna. I'm
not certain, but I think a 1/4 WL antenna has gain over
anything shorter than 1/4 WL and loading coils dissipate
power that would otherwise be radiated as RF.
73, Cecil, W6RCA
Tom Bruhns
altavoz (alt...@worldnet.att.net) wrote:
: ALTAVOZ: your 1/4w is actually odd ball also , its not 1/4w !
..
: altavoz: The coil needed for 5/8w is exactly the same as the coil needed
: for the 1/4w .
..
: altavoz: You cant feed a 1/2w ( 2000+j00) . 3/4w doesnt work
: ( lobe is too high , worse than 1/4w )
Gee, absolute statements like these are just about sure flame-bait in
this group.
I'll just note:
1. A radiator a bit longer than 1/4 wave fed against a ground plane
allows a simple series capacitor to match nicely to 50 ohms.
2. Therefore, clearly the "coil needed for 5/8w" is not exactly
the same as the coil needed for 1/4w, since a coil is not
necessarily needed in either case. Depends on what you are
doing.
3. You think I can't feed 2000+j0 ohms?? Hah.
--
Cheers,
Tom
to...@lsid.hp.com
altavoz
Tom Bruhns wrote:
> altavoz (alt...@worldnet.att.net) wrote:
> : ALTAVOZ: your 1/4w is actually odd ball also , its not 1/4w !
> : for the 1/4w .
> : ( lobe is too high , worse than 1/4w )
> Gee, absolute statements like these are just about sure flame-bait in
> this group.
altavoz: Thats cause they're idiots , they'd argue anything , and
learn nothing.
> 1. A radiator a bit longer than 1/4 wave fed against a ground plane
> allows a simple series capacitor to match nicely to 50 ohms.
altavoz: SIMPLE CAPACITOR $$$$ You're an idiot ! More important
whats the pattern like? I notice you bookworms never talk of pattern.
>
> 2. Therefore, clearly the "coil needed for 5/8w" is not exactly
> the same as the coil needed for 1/4w, since a coil is not
> necessarily needed in either case. Depends on what you are
> doing.altavoz: WRONG , you need a coil for both .
>
> 3. You think I can't feed 2000+j0 ohms?? Hah.
> Tom to...@lsid.hp.com
altavoz: I'll prove you wrong by JASIK,BROWN,LEE
You're going on my list " people who dont know and cant learn"
You must be a college grad !
altavoz
altavoz: WRONG. It needs it's own .6w gnd plane , not a large
gnd plain. And few antennas "benefit" unless on a gnd plain,
either 90 deg or 120 deg or 180 deg( best ).
The .6w vert' has the most bang/buck of any ant' .
--
W8JI Tom
In article <327573...@worldnet.att.net>, altavoz
<alt...@worldnet.att.net> writes:
>altavoz: I know what im talking about , so i made the absolute
>statement , and i stand by it . Between .25w and .5w you'll need
>a cap to tune and caps are expensive , so why not not just jump
>to .6w and a coil does it and the 2nd lobe isnt significant.
> What you're not looking at is the pattern (gain). .25w
>pattern is trash.
Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
arrives back on earth and interferes with the desired signal from the main
lobe, and gives rise to severe fading.
A 5/8 wl antenna ONLY acheives its' gain when over a very very large
groundplane, several wavelengths of near perfect ground. Without the large
perfectly reflecting ground, the 5/8 wl has about the same or slightly
LESS gain than a 1/2 wl with no reflecting ground.
Any slight matching advantage in matching is offset by these
disadvantages.
73 Tom
altavoz
Russ Renaud wrote:
>
> altavoz (alt...@worldnet.att.net) writes:
>
> >> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
> >> > an inexpensive coil to tune it to resonance.
> >>
> >> the words, "always", "never", etc. because they are almost
> >> always false. Both my 10m whip and 2m whip are 1/4 WL and
> >> resonant without loading coils.
> >>
> >> I would agree that most CB antennas are shorter than 1/4w...
> >>
> >> 73, Cecil, W6RCA, OOTC (not speaking for my employer)
> >
> > statement , and i stand by it . Between .25w and .5w you'll need
>
> nor capacitors. One is for the 2 metre amateur band, the other
> is UHF low band. Perhaps you're confusing shortened whips with
> those typically used on CB.
altavoz: It's there , you are too inexperienced to spot it.
Cecil Moore
altavoz wrote:
> altavoz: You are too theorectical, not practical, you need
> experience . You need to learn patterns and main lobes.
I need 2 aspirin and a double scotch.
73, Cecil, W6RCA, OOTC
Fractenna
Actually, I have found Cecil to be thoughtful, reasonable, and open
minded; I find his attitude refreshing.
73
Chip N1IR
Cecil Moore
altavoz wrote:
> altavoz: It's there , you are too inexperienced to spot it.
Does anybody else suspect a practical joker in our midst?
Maybe even one of the regulars willing to open a new account
for a free trial period?
altavoz
Fractenna wrote:
>
> Hey alatavoz, you are wrong.
>
> You need a sizeable GP to get the 3 dB gain.
altavoz: You need an exact GP not a sizeable one at .6w
> Also, I have a 1/4 wave vertical on 3 radials--and that works without a
> ground plane. Its called a 'counterpoise'.
altavoz: DUH , a counterpoise is a gnd plane .
> Speaking of attitudes, you do seem to have one.
>
> Chip N1IR
Russ Renaud
altavoz (alt...@worldnet.att.net) writes:
>> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
>> > an inexpensive coil to tune it to resonance.
>>
>> Hi Altavoz, Most prudent people avoid blanket statements using
>> the words, "always", "never", etc. because they are almost
>> always false. Both my 10m whip and 2m whip are 1/4 WL and
>> resonant without loading coils.
>>
>> I would agree that most CB antennas are shorter than 1/4w...
>>
>> 73, Cecil, W6RCA, OOTC (not speaking for my employer)
>
altavoz
W8JI Tom wrote:
>
> In article <327573...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes:
>
> >statement , and i stand by it . Between .25w and .5w you'll need
> >to .6w and a coil does it and the 2nd lobe isnt significant.
> > What you're not looking at is the pattern (gain). .25w
> >pattern is trash.
>
> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
> arrives back on earth and interferes with the desired signal from the main
> lobe, and gives rise to severe fading.
altavoz: FALSE .
>
> A 5/8 wl antenna ONLY acheives its' gain when over a very very large
> groundplane, several wavelengths of near perfect ground. Without the large
> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> LESS gain than a 1/2 wl with no reflecting ground.
altavoz: FALSE , a .6w ant needs exactly .6 radials(current pk at .35w)
, a .25w requires anything over .1w radials as it's current peak is
at the feedpoint(you only need radials at the current loop)
> Any slight matching advantage in matching is offset by these
> disadvantages.
>
> 73 Tom
altavoz: GO BACK TO SCHOOL !
altavoz
W8JI Tom wrote:
>
> In article <327573...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes:
>
> >altavoz: I know what im talking about , so i made the absolute
> >statement , and i stand by it . Between .25w and .5w you'll need
> >a cap to tune and caps are expensive , so why not not just jump
> >to .6w and a coil does it and the 2nd lobe isnt significant.
> > What you're not looking at is the pattern (gain). .25w
> >pattern is trash.
>
> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
> arrives back on earth and interferes with the desired signal from the main
> lobe, and gives rise to severe fading.
>
> groundplane, several wavelengths of near perfect ground. Without the large
> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> LESS gain than a 1/2 wl with no reflecting ground.
>
> disadvantages.
>
> 73 Tom
altavoz: Read Paul H. Lee page 84 "Am' Rad' Vert' Ant' HB"
As he proves you must have a counterpoise for a 1/2w ant.
A J POLE DOESNT WORK ! IT HAS POOR LOW ANGLE RADIATION .
He says " Actualy the 5/8w vert is better than the 1/2
vert from the standpoints of low angle radiation and feedpoint
impedance.."
altavoz
Cecil Moore wrote:
>
> altavoz <alt...@worldnet.att.net> writes:
>
> >> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
> >> > an inexpensive coil to tune it to resonance.
>
>
> >statement , and i stand by it . Between .25w and .5w you'll need
>
> not shorter than 1/4 WL then your statement is false. I
> personally have two of them each centered at a certain
> frequency. Below the center frequency, they are slightly
> capacitive and above the center frequency, they are
> slightly inductive. So what? No coil and no cap are
> required so a 1/4 WL antenna is less expensive than
> your short, coil-loaded less-than 1/4 WL antenna. I'm
> not certain, but I think a 1/4 WL antenna has gain over
> anything shorter than 1/4 WL and loading coils dissipate
> power that would otherwise be radiated as RF.
>
> 73, Cecil, W6RCA
altavoz: You are too theorectical, not practical, you need
experience . You need to learn patterns and main lobes.
The .25w ant is poor gain . The .6w ant has much higher gain.
You got to be very desparate to pull CONJUGATE from theoretical
amthematics over to antennas/xmission lines just to win an
argument !! BUT YOU HAVE A STINKING ATTITUDE TOWARDS LEARNING.
Fractenna
Hey alatavoz, you are wrong.
You need a sizeable GP to get the 3 dB gain.
Also, I have a 1/4 wave vertical on 3 radials--and that works without a
ground plane. Its called a 'counterpoise'.
Speaking of attitudes, you do seem to have one.
Chip N1IR
MR A MULDER
In article <5550of$e...@freenet-news.carleton.ca> ae...@FreeNet.Carleton.CA (Russ Renaud) writes:
>From: ae...@FreeNet.Carleton.CA (Russ Renaud)
>Subject: Re: WHY antennas of "5/8" wavelength?
>Date: 29 Oct 1996 13:27:43 GMT
>altavoz (alt...@worldnet.att.net) writes:
>>> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
>>> > an inexpensive coil to tune it to resonance.
>>>
>>> Hi Altavoz, Most prudent people avoid blanket statements using
>>> the words, "always", "never", etc. because they are almost
>>> always false. Both my 10m whip and 2m whip are 1/4 WL and
>>> resonant without loading coils.
>>>
>>> I would agree that most CB antennas are shorter than 1/4w...
>>>
If that was the case then they would not work....They are usually 1/4w
electrically but not often 1/4w in actual measured length..
>>> 73, Cecil,
>>>W6RCA, OOTC (not speaking for my employer
)>>
>> altavoz: I know what im talking about , so i made the absolute
>> statement , and i stand by it . Between .25w and .5w you'll need
>I have two commercial mobile 1/4 wave antennas, and neither have coils
>nor capacitors. One is for the 2 metre amateur band, the other
>is UHF low band. Perhaps you're confusing shortened whips with
>those typically used on CB.
I think this is the case, he is getting confused.
mike....@ziplog.com
In <3276D1...@worldnet.att.net>, altavoz <alt...@worldnet.att.net> writes:
>W8JI Tom wrote:
>>
>> In article <327573...@worldnet.att.net>, altavoz
>> <alt...@worldnet.att.net> writes:
>>
>> >statement , and i stand by it . Between .25w and .5w you'll need
>> >to .6w and a coil does it and the 2nd lobe isnt significant.
>> > What you're not looking at is the pattern (gain). .25w
>> >pattern is trash.
>>
>> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
>> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
>> arrives back on earth and interferes with the desired signal from the main
>> lobe, and gives rise to severe fading.
>
Dead wrong. In practice, it DOES work out Tom's way! Go ask why WOAI
in San Antonio, for a number of reasons, moved their tower installation from
down-town San Antonio out into a much better tower site. If you monitored
it and looked at the average signal strength from that 50 KW station with an
Estherline Angus recorder, as it was suggested that I try by old W5VO, now
deceased Chief Engineer for the old plant, you found out that the fading problem
was INTENSE as Tom describes it, even AFTER that move.
I think I know the base fed tower at the new site was voltage fed and the
height was up in the > .25 range because of the story that the Mexican
crew that cut the grass lost a member on a dare to a stray weed slinger,
as I was told. He reached up and touched the base, with his weed slinger,
on a bet, after which they couldn't ANY of them even NEAR the thing to cut
the weeds.
Deep fade momentarily I suppose.
Old Square Root Jackson, W5VO, so nick named since only the square root of
his math classes at A&M ever passed when he got on staff here, said that it
was FAR worse with the metro location up on the building top and with
the effect exacerbated by the elevated feed point!
At night WOAI has terrible fade problems and phase distortion here, 175
miles from San Antonio...
>> A 5/8 wl antenna ONLY acheives its' gain when over a very very large
>> groundplane, several wavelengths of near perfect ground. Without the large
>> perfectly reflecting ground, the 5/8 wl has about the same or slightly
>> LESS gain than a 1/2 wl with no reflecting ground.
>
>altavoz: FALSE , a .6w ant needs exactly .6 radials(current pk at .35w)
> , a .25w requires anything over .1w radials as it's current peak is
>at the feedpoint(you only need radials at the current loop)
>
>> Any slight matching advantage in matching is offset by these
>> disadvantages.
>>
>> 73 Tom
>
>altavoz: GO BACK TO SCHOOL !
I am beginning to feel that the only solution to a misplaced antenna
profile is a frontal lobotomy that can be achieved by shorting the antenna
input terminals together... and the only other solution is a bottle in front
of me for an insulator!
:)
//-----------------------------
Mike - W5WQN
Mike....@ziplog.com
MIke....@f3000.n117.z1.fidonet.org
Fractenna
Hey!
Tom and I agree!
No gain with a 5/8 WITHOUT a large GP.
Go try it or model it and you'll see.
73
Chip N1IR
Tom Bruhns
Cecil Moore (Cecil_...@ccm.ch.intel.com) wrote:
: Does anybody else suspect a practical joker in our midst?
: Maybe even one of the regulars willing to open a new account
: for a free trial period?
Yes, that occured to me. Practical joker or just plain a**h***.
I have a short list of possiblities. Don't make no nevermind
nohow, it won't be long till nobody pays attention to the soprano.
Just hope it doesn't drive away those who actually contribute
to understanding on the group.
--
Cheers,
Tom
to...@lsid.hp.com
altavoz
Mandy Wright wrote:
>
> In article <3276D1...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes
> >W8JI Tom wrote:
> >>
> >> In article <327573...@worldnet.att.net>, altavoz
> >> <alt...@worldnet.att.net> writes:
> >>
> >> >altavoz: I know what im talking about , so i made the absolute
> >> >statement , and i stand by it . Between .25w and .5w you'll need
> >> >a cap to tune and caps are expensive , so why not not just jump
> >> >to .6w and a coil does it and the 2nd lobe isnt significant.
> >> > What you're not looking at is the pattern (gain). .25w
> >> >pattern is trash.
> >>
> >> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
> >> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
> >> arrives back on earth and interferes with the desired signal from the main
> >> lobe, and gives rise to severe fading.
> >>
> >> groundplane, several wavelengths of near perfect ground. Without the large
> >> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> >> LESS gain than a 1/2 wl with no reflecting ground.
> >>
> >> disadvantages.
> >>
> >> 73 Tom
> >
> >As he proves you must have a counterpoise for a 1/2w ant.
> >A J POLE DOESNT WORK ! IT HAS POOR LOW ANGLE RADIATION .
> >He says " Actualy the 5/8w vert is better than the 1/2
> >vert from the standpoints of low angle radiation and feedpoint
> >impedance.."
>
> Antenna Standards Working Group" in the UK, to devise a method for
> accurate comparison tests for antennas used for Land Mobile Radio in the
> VHF and UHF bands. We required a predictable ground plane for use with
> over a broad band. After reading the experiments carried out by Myers
> and Sumner (see Kraus Antennas) with both a square and a circular ground
> plane, they reasoned partial cancellation will occur as the diagonal is
> square root 2. These results were still unpredictable.
>
> Our reasoning, where the diagonal is twice the shorter side and at least
> 1/4 a wavelength to the nearest edge( ie 1/2 wavelength to the furthes
> edge), cancellation should occur. Use was made of a rectangle with the
> ratio 1:root3. This gave smoother results but still showed some
> variations in the response. The final test bed consisted of an elipse
> ratio 2:1, the intention being to avoid any resonances. The effect of
> this would be the same as the root 3 rectangle but without any sudden
> changes in direction, and would give a flatter response. This test-bed
> is now in use by several British companies.
altavoz: Does anyone back you up on this ?
And 2ndly and more important is how does this effect what i
asid about a .5wl ant needing a .5wl radial system ?
>
> Dimensions of 1.25 x 2.5 metres with a 1/4 wave antenna mounted at the
> centre, were tested at 30 mc/s to 1 g/s. Impedance measurements carried
> out and when compared to calculated figures gave errors of less than 10%
> at 30mc/s , 5% at 50mc/s, 2% above 80mc/s. From 300 mc/s upwards there
> were no significant errors, tests showed a 1/4 wave radiator has a
> radiation resistance of approx 37 ohms and the reactance is zero at
> 84/85 degrees in length.
>
> Note: if a ground plane is 1/4 wavelength in radius it becomes a
> counterpoise, and is part of a resonant system in the same way as a 1/4
> wave with radials. See Jasik - Antenna Engineering Handbook Chapter 22-
> 4. If the ground plane, as in our case, is non-resonant it is intended
> to work in the same way as an infinite ground plane, and provide an
> image of the radiating element.
>
> To obtain a perfect match to a 50 ohm source a capacitor may be added in
> series, at the feed point, to cancel the inductive component when the
> length has been extended to approx. 130 degees, to increase the
> radiation resistance.
altavoz: Why 130 degree antennas ? When 190's have better pattern,
higher gain ?
altavoz BULL SHIT ! Antenna Makes are the real test . They wont
touch it unless it's produceable and has high gain , your stuff
is theoretical BS.
altavoz
Fractenna wrote:
>
> A 5/8 wave OVER A VERY LARGE GROUND PLANE offers 3 dB gain over a 1/4
> wave. As you gathered, however, it is NOT a resonant antenna.
>
> With a counterpoise or small GP, very little gain is had (if any) over a
> 1/4 wave.( I'm not going to play games with one individual on this
> matter--play with your own GP and report the results.)
>
> 73
>
> Chip N1IR
altavoz: We dropped the use of the word RESONANT years ago.
It's meaningless. We use Q . Q is rate of change of reactance
over frequency . A .5wl ant has many times greater Q than a
.25 wl ant' . It takes very little stretching to turn
a 2000+j00 .5wl ant into a 200-J100 antenna .
It takes 10 times that freq change to change the R in
a .25wl ant'
altavoz
altavoz wrote:
>
> Fractenna wrote:
> >
> > Hey alatavoz, you are wrong.
> >
> > You need a sizeable GP to get the 3 dB gain.
>
>
> > ground plane. Its called a 'counterpoise'.
>
>
> > Speaking of attitudes, you do seem to have one.
> >
> > Chip N1IR
altavoz: The one who wins an argument always has an attitude.
Madjid
Cecil Moore wrote:
>
> altavoz wrote:
> > altavoz: It's there , you are too inexperienced to spot it.
>
> Maybe even one of the regulars willing to open a new account
> for a free trial period?
>
Noooo, we are too inexperienced to spot it :)
Madjid VE2GMI @ mbo...@cam.org
altavoz
Cecil Moore wrote:
>
> altavoz wrote:
> > altavoz: It's there , you are too inexperienced to spot it.
>
> 73, Cecil, W6RCA, OOTC (not speaking for my employer)
altavoz: Are you tearing apart your antennas yet ?
You will find the coils/caps . ha ha ha ha ha
Cecil Moore
Tom> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
Tom> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
Tom> arrives back on earth and interferes with the desired signal from the main
Tom> lobe, and gives rise to severe fading.
> altavoz: FALSE .
Hey Guys, I just modeled a 5/8 vertical on 40m over MNec ground.
EZNEC sez a minor lobe at 60 deg TOA about 5 dB (one 'S' unit?)
down from the major lobe at 16 deg TOA. Anybody using a 5/8 WL
vertical on HF?
altavoz
altavoz wrote:
>
> Mandy Wright wrote:
> >
> > In article <3276D1...@worldnet.att.net>, altavoz
> > <alt...@worldnet.att.net> writes
> > >W8JI Tom wrote:
> > >>
> > >> In article <327573...@worldnet.att.net>, altavoz
> > >> <alt...@worldnet.att.net> writes:
> > >>
> > >> >altavoz: I know what im talking about , so i made the absolute
> > >> >statement , and i stand by it . Between .25w and .5w you'll need
> > >> >a cap to tune and caps are expensive , so why not not just jump
> > >> >to .6w and a coil does it and the 2nd lobe isnt significant.
> > >> > What you're not looking at is the pattern (gain). .25w
> > >> >pattern is trash.
> > >>
> > >>
altavoz: "......Antenna Makers ....." NOT "....Antenna Make..."
You are getting real desparate trying to use HF skip to disprove
the .6wl antenna . On VHF it's the best omni antenna you can get,
and Paul H. Lee proves it works on HF . In fact he has the same
problem with idiots saying verticals dont work on HF !
Your REDNEC antenna modeling software is in error .
Fractenna
Moxon Rules!
altavoz
Cecil Moore wrote:
>
> Joel Govostes <jw...@cornell.edu> writes:
>
> >I'm wondering what is so special about the 5/8 wave antenna length; why
>
> Hi Joel, a 5/8 vertical with a good ground or a 2x5/8 dipole
> has the maximum gain available from wire with no other
> components.
altavoz: You're wrong . A .6 wl needs a .6 wl RADIAL SYSTEM.
Read my post on Paul H. Lee page 84 on radials on a half wave.
Joel , the pattern of a .6wl antenna is much greater on the horizon
than a .25wl antenna ( and a .5wl ant'), in spite of the minor lobe.
> 73, Cecil, W6RCA, OOTC
--
Marc Illsley Clarke
>>>>> "Tom" == Tom Bruhns <to...@lsid.hp.com> writes:
In article <55861u$b...@hpcvsnz.cv.hp.com> to...@lsid.hp.com (Tom Bruhns) writes:
Tom> Cecil Moore (Cecil_...@ccm.ch.intel.com) wrote: : Does
Tom> anybody else suspect a practical joker in our midst? : Maybe
Tom> even one of the regulars willing to open a new account : for
Tom> a free trial period?
Tom> Yes, that occured to me. Practical joker or just plain
Tom> a**h***. I have a short list of possiblities. Don't make no
Tom> nevermind nohow, it won't be long till nobody pays attention
Tom> to the soprano. Just hope it doesn't drive away those who
Tom> actually contribute to understanding on the group.
Tom> -- Cheers, Tom to...@lsid.hp.com
altavoz or whatever his login was made it into my author's kill file
several days ago. Lots of noise, lots of sparks, no discernable
signal.
--
Marc Illsley Clarke, m...@frii.com, KB0YDL, KB0YDL@N0MPI.#NECO.CO.USA.NOAM
4857 North Sheridan Avenue, Loveland, Colorado 80538-1767 USA
(Representing solely myself, I am emphatically NOT a representative of
any employer, club, group, church, league, organization, or government!)
altavoz
altavoz: AAHHHH lovers
Mandy Wright
Hi Altavoz, I like your style. Do you want a big wooden spoon for
Christmas?! (Hope this translates OK) A little controversy and a lively
exchange of views usually leads to enlightenment all round.
I once heard it said by the Chief Rabbi in the UK "If you win an
argument you've gained nothing, only if you lose an argument can you
learn something" ;)
During 1990/91 myself and a colleague were carrying out tests for "The
Antenna Standards Working Group" in the UK, to devise a method for
accurate comparison tests for antennas used for Land Mobile Radio in the
VHF and UHF bands. We required a predictable ground plane for use with
over a broad band. After reading the experiments carried out by Myers
and Sumner (see Kraus Antennas) with both a square and a circular ground
plane, they reasoned partial cancellation will occur as the diagonal is
square root 2. These results were still unpredictable.
Our reasoning, where the diagonal is twice the shorter side and at least
1/4 a wavelength to the nearest edge( ie 1/2 wavelength to the furthes
edge), cancellation should occur. Use was made of a rectangle with the
ratio 1:root3. This gave smoother results but still showed some
variations in the response. The final test bed consisted of an elipse
ratio 2:1, the intention being to avoid any resonances. The effect of
this would be the same as the root 3 rectangle but without any sudden
changes in direction, and would give a flatter response. This test-bed
is now in use by several British companies.
Dimensions of 1.25 x 2.5 metres with a 1/4 wave antenna mounted at the
centre, were tested at 30 mc/s to 1 g/s. Impedance measurements carried
out and when compared to calculated figures gave errors of less than 10%
at 30mc/s , 5% at 50mc/s, 2% above 80mc/s. From 300 mc/s upwards there
were no significant errors, tests showed a 1/4 wave radiator has a
radiation resistance of approx 37 ohms and the reactance is zero at
84/85 degrees in length.
Note: if a ground plane is 1/4 wavelength in radius it becomes a
counterpoise, and is part of a resonant system in the same way as a 1/4
wave with radials. See Jasik - Antenna Engineering Handbook Chapter 22-
4. If the ground plane, as in our case, is non-resonant it is intended
to work in the same way as an infinite ground plane, and provide an
image of the radiating element.
To obtain a perfect match to a 50 ohm source a capacitor may be added in
series, at the feed point, to cancel the inductive component when the
length has been extended to approx. 130 degees, to increase the
radiation resistance.
Has anybody got spare copies of the following that they would like to
lend to Altavoz, I need mine for my business!
Reference Data for Radio Engineers ITT
Antenna Engineering Handbook Jasik
Antenna Engineering Handbook 2 Johnson and Jasik
Antennas Kraus
Antenna Theory and Design Volumes 1 and 2 H Paul Williams ( my mentor!)
Radio Engineering BBC Manual E K Sandeman
HF Antennas Leslie Moxon (my other mentor!)
VHF Radio Keller
Mandy
(Replying on behalf of my husband who hates computers
despite being a practising RF Engineer!)
Sussex
UK *Please note the NEW ADDRESS!*
BCol...@aol.com
My thoughts here are that everything in antennas is a compromise. A 1/4 wave
vertical can be hooked directly to 50 ohm coax, with radials bent down 45
degrees, without a matching device. A 5/8 wave will give you more gain than
a 1/4 wave (due to the *squashed* radiation pattern), but requires a matching
device. A 1/2 wave vertical needs a more complex matching device, but does
not require radials, which makes it a good choice for HT operations.
Bob
KD8WU
A N Thompson
[My instincts tell me that I shouldn't get involved in this
discussion, but I can't resist]
I agree with Chip, Tom, et al, regarding the theoretical
advantage of the 5/8-wavelength antenna vs. the results
obtainable in practice over a less than ideal ground
plane; i.e., it's not as effective in the real world as it is on
paper. When over lossy ground, the very low angle
radiation from the 5/8-wavelength antenna is absorbed
in the ground rather than being reflected. Under those
circumstances the high-angle lobe becomes a major
portion of the far field radiation from the antenna.
The taller (1/2- and 5/8-wave) verticals require more
extensive grounds than does the 1/4-wave vertical. The
1/4-wave antenna will outperform a 1/2-wave antenna unless
an (excellent) ground plane extends out to about 1.5 wave-
lengths. The 5/8-wave antenna requires and even more
extensive ground.
73,
Arliss
W8JI Tom
In article <19961030.2026...@juno.com>, w7...@juno.COM (A N
Thompson) writes:
>The taller (1/2- and 5/8-wave) verticals require more
>extensive grounds than does the 1/4-wave vertical. The
>1/4-wave antenna will outperform a 1/2-wave antenna unless
>an (excellent) ground plane extends out to about 1.5 wave-
>lengths. The 5/8-wave antenna requires and even more
>extensive ground.
>
>73,
>
>Arliss
As a bit of practical experience, I did broadcast consulting work in the
70's. I had occasion to "sneak" various towers on 160 late at night.
The 280-300 ft towers were always great performers within a few hundred
miles, but stank for 100 mile and longer work. At one site, a 60 ft tall
inverted L beat the 300 ft tower over and over again outside of a few
hundred miles.
At a location in a swampy area, a dipole at 350 ft absolutely killed a 280
ft vertical, yet a 140 ft vertical at my house a few miles came close to
the high dipole.
These are less than ideal comparisons, and I would never claim them to be
conclusive, but they certainly indicate something.
I walked away with the same gut feeling Arliss expressed. The low wave
angle, coupled with lossy soil (even though it was almost 30 mS/m at the
one site), actually hurts the lower angle skywave signals.
73 Tom
Mandy Wright
(Replying on behalf of my husband, Tim (G1BCR / G9BZW), who hates computers
despite (or maybe because of) being a practising RF Engineer.)
Sussex UK
mike....@ziplog.com
In <32784E...@worldnet.att.net>, altavoz <alt...@worldnet.att.net> writes:
>Marc Illsley Clarke wrote:
>Capacitors are not used to tune most antennas cause they
>cost much more $, cant be trimmed, and where they're used
>there is less gain ( .25 to .5 wl), Break easier, dont
>stand up to wx.....
Absolutely false. I've used small chunks of coax cable as gamma match
capacitors in arrays for YEARS at a time and they cost next to nothing, are
so simple to trim it is a no-brainer, have virtually no effect on gain, NEVER
break and hang out in total exposure to the weather for YEARS unattended!
Haven't you ever used a small chunk of coax for a capacitor??????
It's stupidly simple, works wonderfully, even out in the weather for YEARS
and costs only pennies to use! Just tie the center to one end and the shield
to another and push the shield around on the outside in the near-values to
trim it. You final the trim with a pair of dikes and tape it.
Presto.. Instant success, but not unless you have played with stuff like
this for real and need to accomplish things cheaply....
Try it; you'll like it!
JAMES MCEWEN
***********************************************************
The Wiz of altaOZ wrote:
altavoz: We dropped the use of the word RESONANT years ago.
It's meaningless. We use Q . Q is rate of change of reactance
over frequency .
Wiz, I just don't understand what you said here.
For instance: In a series RLC circuit
XsubL = 2Pi_f_L so by your statement
Q = dt(2Pi_f_L)/f
since 2Pi & L are constant
they can come outside the function
Q = 2PiL dt(f)/f = 2PiL (1) = a constant
Are you saying that Q = 2PiL ?
I think by the definition of Q, it is a meaningful number only
at the resonant frequency. In a series RLC circuit Q is defined
as:
Q = (2Pi_f-sub-r_L)/R where f-sub-r is the resonant
frequency and R is the series resistance of the circuit.
So going back to your original statement quoted at the top of
this posting, what were you trying to explain?
Jim KA6TPR
Roy Lewallen
In article <jwg6-27109...@cu-dialup-1828.cit.cornell.edu>,
jw...@cornell.edu (Joel Govostes) wrote:
>Here's an antenna question that I've never found an explanation for --
>
>For mobile or fixed station use, a typical vertical antenna is 1/4 wave
>and fed with low-impedance coaxial cable. The ground is provided by earth
>ground, automobile body, or a set of "ground plane" elements. Okay.
>
>This type of antenna matches 50-ohm coax and transmitter output circuits
well.
>
>So, who came up with the oddball figure of 5/8 wave for vertical antennas,
>and why?
>
>I know that the radiation pattern shape is somewhat "squashed" on the 5/8
>wave, and that it provides some gain over the 1/4 wave. But 5/8
>wavelength doesn't match 50 ohm coax feed, and so usually it is fed on a
>loading-coil tap at the base of the vertical.
>
>I'm wondering what is so special about the 5/8 wave antenna length; why
>similar way, and would it also provide significant gain over the 1/4
>wave? Why not just go to 6/8-wave size, as that would match coax feed as
>3/4 wave (odd multiple of 1/4 wave ~ approx. 50 ohms.) Thanks
Imagine putting a vertical on a perfect ground plane, flat and infinite in
extent. Start with a very short vertical, just a small fraction of a
wavelength high, and look at the radiation pattern. From an infinitesimal
height to a height of 1/4 wavelength, the pattern and gain change very
little. (There's less than 0.5 dB change in gain, and a correspondingly
small change in pattern shape. Remember we're neglecting losses here.) The
pattern is just 1/2 that of a dipole of twice the length in free space, the
familiar donut pattern. As the height of the vertical increases from 1/4 to
1/2 wavelength, the donut flattens, increasing the gain at the horizon as
it decreases at higher angles. The gain of a 1/2 wavelength vertical over
a perfect ground is about 2 dB greater than a 1/4 wave vertical. As the
antenna increases in height above 1/2 wavelength, a lobe appears at 60
degrees above the horizon. Just above 1/2 wavelength, it's still small and
doesn't represent much of the antenna's total energy output, but grows as
the height increases. The horizon lobe continues to get narrower and
stronger as the antenna lengthens above 1/2 wavelength, until it reaches
about 5/8 wavelength. At this point, the gain at the horizon is about 3 dB
greater than a 1/4 wavelength vertical. The 60-degree lobe is significant
at this point, which is why the 5/8 wave antenna isn't used by
broadcasters. The signal from the upper lobe can arrive at a listening
station via skywave, cancelling the desired groundwave signal if the two
arrive out of phase.
If the vertical height is increased beyond about 5/8 wavelength, the
horizon lobe decreases as the 60 degree lobe increases, so the gain at the
horizon is maximum at a height of about 5/8 wavelength -- about 3 dB
greater than a 1/4 wavelength vertical. This is why the "magic" length.
This analysis was done with a perfect ground which real ground never is. At
HF, you'll probably see less than 3 dB gain (relative to a 1/4 wave
vertical) from a 5/8 wave radiatior. This is because the ground absorbs
low-angle reflections from vertically polarized antennas. Since a larger
fraction of the radiation from the 5/8 wave vertical is at very low angles,
a larger fraction of it is absorbed. The actual gain difference is a
function of the ground conductivity, dielectric constant, and frequency.
A 1/4 wave vertical will actually have more gain at some low angles than a
5/8 wave for some ranges of ground characteristics and frequency.
You can see this for yourself with any of the modeling programs, including
the ELNEC demo available from ftp.teleport.com/pub/vendors/w7el as
ELNECDEM.EXE. ("Running" it expands it into several files, including a
READ.ME file.) I believe it's also available via WWW.
I haven't had a chance to model 5/8 wave antennas over abbreviated ground
planes (such as a car top), but think there's reason to believe that the 3
dB gain advantage may not be realized when the antennas are mounted on an
abbreviated ground plane. There was an interesting paper on this topic
titled "The 5/8-Wavelength Antenna Mystique", by Donald K. Reynolds, K7DBA,
in the ARRL Antenna Compendium, Vol. 1.
Roy Lewallen, W7EL
W8JI Tom
In article <327852...@worldnet.att.net>, altavoz
<alt...@worldnet.att.net> writes:
>You are getting real desparate trying to use HF skip to disprove
>the .6wl antenna . On VHF it's the best omni antenna you can get,
>and Paul H. Lee proves it works on HF . In fact he has the same
>problem with idiots saying verticals dont work on HF !
> Your REDNEC antenna modeling software is in error .
Altavoz,
Please quit taking mushrooms and take some thorazine. If you keep chasing
rabbits you'll keep falling through holes and even Paul H. Lee won't be
able to save you from the men on the chess board.
I suggest you put on some stereo headphones, and listen to Jefferson
Airplane CD's, or perhaps Cream or the White Album. Stay away from the
computer until you crash.
A "Big Hug" from your dear friend across town...
Tom
W8JI Tom
In article <32784E...@worldnet.att.net>, altavoz
<alt...@worldnet.att.net> writes:
>altavoz: I am contributing , but assholes like you , lose arguments
>and throw a tantrum .
There is no need for this, unless you are two years old. Atavoz, please
talk nicer.
All that does is make you look dumb.
73 Tom
altavoz
altavoz DUH , RATE OF CHANGE OF REACTANCE OVER FREQ ( this is a
repeat for those who cant read)
altavoz
Mandy Wright wrote:
>
> In article <3276D1...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes
> >W8JI Tom wrote:
> >>
> >> <alt...@worldnet.att.net> writes:
> >>
> >> >altavoz: I know what im talking about , so i made the absolute
> >> >statement , and i stand by it . Between .25w and .5w you'll need
> >> >a cap to tune and caps are expensive , so why not not just jump
> >> >to .6w and a coil does it and the 2nd lobe isnt significant.
> >> > What you're not looking at is the pattern (gain). .25w
> >> >pattern is trash.
> >>
> >> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
> >> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
> >> arrives back on earth and interferes with the desired signal from the main
> >> lobe, and gives rise to severe fading.
altavoz : It does not ( minor lobe). They were required by FCC to
"gaurd " , and they had to have antennas that were very complex.
> >> A 5/8 wl antenna ONLY acheives its' gain when over a very very large
> >> groundplane, several wavelengths of near perfect ground. Without the large
> >> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> >> LESS gain than a 1/2 wl with no reflecting ground.
> >>
> >> Any slight matching advantage in matching is offset by these
> >> disadvantages.
> >>
> >> 73 Tom
> >altavoz: Read Paul H. Lee page 84 "Am' Rad' Vert' Ant' HB"
As he proves you must have a counterpoise for a 1/2w ant.
A J POLE DOESNT WORK ! IT HAS POOR LOW ANGLE RADIATION .
He says " Actualy the 5/8w vert is better than the 1/2
vert from the standpoints of low angle radiation and feedpoint
impedance.." , he's talking about HF 5/8 wl .
altavoz
Roy Lewallen wrote:
>
> In article <jwg6-27109...@cu-dialup-1828.cit.cornell.edu>,
> jw...@cornell.edu (Joel Govostes) wrote:
> >Here's an antenna question that I've never found an explanation for --
> >
> >For mobile or fixed station use, a typical vertical antenna is 1/4 wave
> >and fed with low-impedance coaxial cable. The ground is provided by earth
> >ground, automobile body, or a set of "ground plane" elements. Okay.
> >
> >This type of antenna matches 50-ohm coax and transmitter output circuits
> well.
> >
> >So, who came up with the oddball figure of 5/8 wave for vertical antennas,
> >and why?
> >
> >I know that the radiation pattern shape is somewhat "squashed" on the 5/8
> >wave, and that it provides some gain over the 1/4 wave. But 5/8
> >wavelength doesn't match 50 ohm coax feed, and so usually it is fed on a
> >loading-coil tap at the base of the vertical.
altavoz: WHY SO INTIMIDATED ON ANT' MATCHING ? A SINGLE COIL !!
> >I'm wondering what is so special about the 5/8 wave antenna length; why
> >not just a 1/2 wave (4/8 wave)? Could 1/2 wave vertical be fed in a
> >similar way, and would it also provide significant gain over the 1/4
> >wave? Why not just go to 6/8-wave size, as that would match coax feed as
> >3/4 wave (odd multiple of 1/4 wave ~ approx. 50 ohms.) Thanks
altavoz: main lobe points up, poor gain ! ( 6/8 wl )
Cant feed a 1/2 wl .
> Imagine putting a vertical on a perfect ground plane, flat and infinite in
> extent. Start with a very short vertical, just a small fraction of a
> wavelength high, and look at the radiation pattern. From an infinitesimal
> height to a height of 1/4 wavelength, the pattern and gain change very
> little. (There's less than 0.5 dB change in gain, and a correspondingly
> small change in pattern shape. Remember we're neglecting losses here.) The
> pattern is just 1/2 that of a dipole of twice the length in free space, the
> familiar donut pattern. As the height of the vertical increases from 1/4 to
> 1/2 wavelength, the donut flattens, increasing the gain at the horizon as
> it decreases at higher angles. The gain of a 1/2 wavelength vertical over
> a perfect ground is about 2 dB greater than a 1/4 wave vertical. As the
> antenna increases in height above 1/2 wavelength, a lobe appears at 60
> degrees above the horizon. Just above 1/2 wavelength, it's still small and
> doesn't represent much of the antenna's total energy output, but grows as
> the height increases.
alatvoz:Why would you want a > 5/8 wl ? And why are you so affraid of
radials ? ( perfectly conducting ground )
> The horizon lobe continues to get narrower and
> stronger as the antenna lengthens above 1/2 wavelength, until it reaches
> about 5/8 wavelength. At this point, the gain at the horizon is about 3 dB
> greater than a 1/4 wavelength vertical. The 60-degree lobe is significant
> at this point, which is why the 5/8 wave antenna isn't used by
> broadcasters. The signal from the upper lobe can arrive at a listening
> station via skywave, cancelling the desired groundwave signal if the two
> arrive out of phase.
altavoz: No , they dont use 5/8 wl because its illegal. They're required
by FCC to not transmit outside of a limited area. Those SWL stations
that are allowed do use 5/8 wl . And i would use 3 , 5/8 wl phased .
There is no higher gain for skip than a 5/8 wl ant , a 1/2 wl above
ground .
> If the vertical height is increased beyond about 5/8 wavelength, the
> horizon lobe decreases as the 60 degree lobe increases, so the gain at the
> horizon is maximum at a height of about 5/8 wavelength -- about 3 dB
> greater than a 1/4 wavelength vertical. This is why the "magic" length.
>
> This analysis was done with a perfect ground which real ground never is. At
> HF, you'll probably see less than 3 dB gain (relative to a 1/4 wave
> vertical) from a 5/8 wave radiatior. This is because the ground absorbs
> low-angle reflections from vertically polarized antennas. Since a larger
> fraction of the radiation from the 5/8 wave vertical is at very low angles,
> a larger fraction of it is absorbed.
altavoz: So we should not try for low angle , we should try for high
angle so it doesn't skip !!!! NOT ! YOU NEED 3 to 10 DEGREES TO SKIP
AT THE 2000 mile 1st hop.
> The actual gain difference is a
> function of the ground conductivity, dielectric constant, and frequency.
> A 1/4 wave vertical will actually have more gain at some low angles than a
> 5/8 wave for some ranges of ground characteristics and frequency.
altavoz: WRONG .When you use radials and proper ht, you're arguement dies.
> You can see this for yourself with any of the modeling programs, including
> the ELNEC demo available from ftp.teleport.com/pub/vendors/w7el as
> ELNECDEM.EXE. ("Running" it expands it into several files, including a
> READ.ME file.) I believe it's also available via WWW.
altavoz Modeling progs dont work for HF.
> I haven't had a chance to model 5/8 wave antennas over abbreviated ground
> planes (such as a car top), but think there's reason to believe that the 3
> dB gain advantage may not be realized when the antennas are mounted on an
> abbreviated ground plane. There was an interesting paper on this topic
> titled "The 5/8-Wavelength Antenna Mystique", by Donald K. Reynolds, K7DBA,
> in the ARRL Antenna Compendium, Vol. 1.
>
> Roy Lewallen, W7EL
altavoz: 5/8 wl ant's need a full 5/8 wl radial system . at 90 deg'
the main lobe is pushed up too high . Thats why for the last 20 years
the commercial makers have made them with 180 deg' radials.
altavoz
altavoz: Sure thats why all commercial makers use stubs . NOT !!
An open stub ( Xc) is not nearly as high Q as a shorted stub ( XL)
And i dont need to you why.
altavoz
W8JI Tom wrote:
>
> In article <32784E...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes:
>
> >altavoz: I am contributing , but assholes like you , lose arguments
> >and throw a tantrum .
>
> There is no need for this, unless you are two years old. Atavoz, please
> talk nicer.
>
> All that does is make you look dumb.
>
> 73 Tom
altavoz: Then act nicer .
altavoz
altavoz: You're wrong , 1/2 wl ant's require 1/2 wl radials,
but at 2000 ohms , it makes no sense and 5/8 wl has more gain
anyway. The 5/8 wl vert compared to 1/4 wl is not squashed, it's
concentrated on the horizon , and the 1/4 wl is mostly up at
45 degrees ( great for talking to airplanes) . I can bent the
coil for a 5/8 wl in 10 seconds of no. 12 cu wire .
If all the books agreed , we'd have no problem , but some
of the best books have it wrong , and that means for lazy people
who beleive the most expensive book is right, this is the truth.
We've known for a long time that the ARRL words things so poorly
especially antennas, that it causes a lot of fighting .
Read it's explanation on traps ! ha ha ha .....
They dont even touch on what happens if the element above the
trap is 1/2 wl !!! A trap is an electrical short circuit to a 1/2
wl element above it !!
Paul H. Lee "Amatuer Rad' vert' antenna HB" page 84 .
"...if he is content to throw away 40 to 80% of his radiated
power in earth losses.." (1/2 wl w/o radials)
Harbin Osteen
>
> I see many posts "sizeable, substancial....GP for a .5wl antenna.
>
> You are wrong . it needs a .5 wl radial system, not a substancial...
> You dont know what you're talking about on half waves.
>
> ______End of text from altavoz___________
I am going to get a 5/8 MaCo antenna for my C.B. (11 meters?).
I got in on the thread late, but are you saying that ground
raidials have to only be equal to 1/2 wave in length to get
a dB gain? The MaCo does not come with raidials, so will it
work with raidals without messing up the SWR? I think a ground
plane will help any vertical antenna, but I'm not shure.
SeeYaa:) Harbin
W8JI Tom
hello albatros,<alt...@worldnet.att.net> writes:
I wote
>> Actually the minor lobe of a 5/8 wl is not insignificant, that's why
most
>> broadcast stations abandoned them by the 30's. On sky wave, the minor
lobe
>> arrives back on earth and interferes with the desired signal from the
main
>> lobe, and gives rise to severe fading.
>> A 5/8 wl antenna ONLY acheives its' gain when over a very very large
>> groundplane, several wavelengths of near perfect ground. Without the
large
>> perfectly reflecting ground, the 5/8 wl has about the same or slightly
>> LESS gain than a 1/2 wl with no reflecting ground.
>> Any slight matching advantage in matching is offset by these
>> disadvantages.
And you replied
>altavoz: Read Paul H. Lee page 84 "Am' Rad' Vert' Ant' HB"
>As he proves you must have a counterpoise for a 1/2w ant.
Of course you do, if the antenna is end fed especially. Without one the
antenna can NOT even be fed at the end. That is the main mistake of the J
pole, it uses a matching stub as both counterpoise and matching section,
and current moves the wrong way.
So when you say:
>A J POLE DOESNT WORK ! IT HAS POOR LOW ANGLE RADIATION .
We agree.
When you say
>He says " Actualy the 5/8w vert is better than the 1/2
>vert from the standpoints of low angle radiation and feedpoint
>impedance..
We also agree, but NOT for broadcast band use where skywave is present and
not unless the groundplane extends out many wavelengths. As a matter of
fact, in the NAB Engineering Handbook this very reason is explianed, and
shorter verticals are called NON-FADING verticals for this reason.
Another thing the 5/8 wl antenna does is force or compress radiation at a
low wave angle where the earth losses absorb signal. That is OK for ground
wave (because you have to have the signal there anyway) but is bad for
skywave. As the vertical for HF skywave is made taller than 1/4 wl
efficiency GOES down unless the antenna is over a large body of saltwater.
You can find that by modeling the antenna on computor, trying the antenna
in life, or by reading a good book that has sections about earth effects
like Antennas and Transmission Lines by Dr. Kuecken. I had a 1/2 wl
vertical on 80 meters and it stunk compared to a 1/4 wl vertical, and I
tried the same thing on 40 and 160 and they stank. For groundwave, I could
work many miles, but for skywave even into DX they were the poorest
antennas I ever used even though they were over large radials.
By the way, there was a guy on the American Motors/ Rambler list using the
name the "mad mispeller" that used to make people mad. Did you ever own a
Rambler car?
73 Tom
PS. Captain Kangeroo is better about radials than Captain Lee. He needs
to go back to radial school.
Alan Fowler
mike....@ziplog.com wrote:
>I think I know the base fed tower at the new site was voltage fed and the
>height was up in the > .25 range because of the story that the Mexican
>crew that cut the grass lost a member on a dare to a stray weed slinger,
>as I was told. He reached up and touched the base, with his weed slinger,
>on a bet, after which they couldn't ANY of them even NEAR the thing to cut
>the weeds.
Mike,
I have climbed onto a live mast fed with two 10 kW MF transmitters
quite a few times without ill effects. I haven't ever been burnt
while getting on or off although I know quite a fet who have.
We had a team of painters smartening up the mast at one time, working
in bosuns chairs slung from the mast. The problem was at the end of a
brush stroke. If the brush wasn't pulled away smartly, it drew an arc
- making a VERY loud speaker.
I have been burnt by putting the palm of my hand down on the grass
near a 50 kW mast. My hand ended up covered with dozens of burns from
the arcs as I lifted my hand away. Only little ones tough, not
serious.
regards, Alan.
,-._|\ Alan Fowler.
/ Oz \ Mail Address: PO Box 272, Balwyn 3103 Vic, AUSTRALIA.
\_,--.x/ Phone: +613-9857-7128 Member, Melbourne PC User Group.
v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Mandy Wright
In article <557kbu$7...@newsbf02.news.aol.com>, Fractenna
<frac...@aol.com> writes
>Hey!
>
>Tom and I agree!
>
>No gain with a 5/8 WITHOUT a large GP.
Absolutely! ^^^^^
Read Jasik or Terman or Laporte (refering to MF and HF broadcasting
antennae and ground conductivity
>
>Go try it or model it and you'll see.
>
>73
>Chip N1IR
All the best!
Mandy
Mandy Wright
In article <19961030.2026...@juno.com>, A N Thompson
<w7...@juno.COM> writes
>[My instincts tell me that I shouldn't get involved in this
>discussion, but I can't resist]
>
>I agree with Chip, Tom, et al, regarding the theoretical
>advantage of the 5/8-wavelength antenna vs. the results
>obtainable in practice over a less than ideal ground
>plane; i.e., it's not as effective in the real world as it is on
>paper. When over lossy ground, the very low angle
>radiation from the 5/8-wavelength antenna is absorbed
>in the ground rather than being reflected. Under those
>circumstances the high-angle lobe becomes a major
>portion of the far field radiation from the antenna.
>
>extensive grounds than does the 1/4-wave vertical. The
>1/4-wave antenna will outperform a 1/2-wave antenna unless
>an (excellent) ground plane extends out to about 1.5 wave-
>lengths. The 5/8-wave antenna requires and even more
>extensive ground.
>
>73,
>
>Arliss
a notable exception in this group. ;)
mike....@ziplog.com
In <55ckhc$o...@wombat.melbpc.org.au>, amfo...@melbpc.org.au (Alan Fowler) writes:
>mike....@ziplog.com wrote:
>
>>I think I know the base fed tower at the new site was voltage fed and the
>>height was up in the > .25 range because of the story that the Mexican
>>crew that cut the grass lost a member on a dare to a stray weed slinger,
>>as I was told. He reached up and touched the base, with his weed slinger,
>>on a bet, after which they couldn't ANY of them even NEAR the thing to cut
>>the weeds.
>
>Mike,
> I have climbed onto a live mast fed with two 10 kW MF transmitters
>quite a few times without ill effects. I haven't ever been burnt
>while getting on or off although I know quite a fet who have.
Source for this remark is Dr. George Huebner, W5GDK. Don't
know the specifics on exactly how the weed slinger was made.
Would make a difference....
> We had a team of painters smartening up the mast at one time, working
>in bosuns chairs slung from the mast. The problem was at the end of a
>brush stroke. If the brush wasn't pulled away smartly, it drew an arc
>- making a VERY loud speaker.
:) Isn't English a WONDERFUL language? :)
> I have been burnt by putting the palm of my hand down on the grass
>near a 50 kW mast. My hand ended up covered with dozens of burns from
>the arcs as I lifted my hand away. Only little ones tough, not
>serious.
Leading me to the conclusion, though I've never been faced with
actually doing it, that one has to play kangaroo to become a
mast monkey at a more base level in the feeding chain?
:)
> regards, Alan.
Right?
mike....@ziplog.com
In <4+6TuKA1...@the-symposium.demon.co.uk>, Mandy Wright <Ma...@the-symposium.demon.co.uk> writes:
>In article <557kbu$7...@newsbf02.news.aol.com>, Fractenna
><frac...@aol.com> writes
>>Hey!
>>
>>Tom and I agree!
>>
>>No gain with a 5/8 WITHOUT a large GP.
>Absolutely! ^^^^^
>Read Jasik or Terman or Laporte (refering to MF and HF broadcasting
>antennae and ground conductivity
>>
>>Go try it or model it and you'll see.
>All the best!
>Mandy
>(Replying on behalf of my husband who hates computers
>despite being a practising RF Engineer!)
>Sussex
>UK
Where MF and HF and greater than 1/4 wave vertical elements are concerned,
as a layman, I've always understood that far field ain't far fetched over lousy
ground and carefully taught by my pocketbook that I can't overlay all the
surounding country with copper...
:)
I used to have the most fascinating tape recording of VK3IM driving down
into the salt water with his 40 meter mobile CW signal, driving back up the
road to the cliff overlooking the Pacific path to Texas and then driving away
from the cliff on level ground back to his home a few miles away.
Most practical demonstration I've ever seen about far field ground effects..
20-30DB difference upward while in the effect of a real salt water ground
vs. the regular land terrain just a few miles from the aperature....
He will be S5-6 for real in the salt water with his wheels in it. He will
be S9 or better, sometimes going up the ramp. He will be S4-6 at the
top of the cliff overlooking the ocean. As he drives away from the cliff
edge going home, he will drop off. Parked in his driveway, he will be in the
noise or S1-2 at the most.
We've repeated the deal a number of times for kicks...
So much for argument over the real effects at HF and MF over a few feet of
radials in support of any practical help for skywave lobe effectiveness as
far as my observation is concerned. Control of the far field per my
observation is even more important here, given even a half way realistic
attempt to build a practical ground system for verticals, one that will let
the impedance matching stabilize season to season, where most ham radio
vertical HF installations are concerned.
THAT is why buying property in relation to the anticipated paths
is the single most important decision most hams could make about
their amatuer radio carreer, and, in practice, the one that most of
them can do very little about, ... in retrospect...
:)
Mandy Wright
In article <96103020464...@emout20.mail.aol.com>,
BCol...@aol.COM writes
>My thoughts here are that everything in antennas is a compromise. A 1/4 wave
>vertical can be hooked directly to 50 ohm coax, with radials bent down 45
>degrees, without a matching device. A 5/8 wave will give you more gain than
>a 1/4 wave (due to the *squashed* radiation pattern), but requires a matching
>device. A 1/2 wave vertical needs a more complex matching device, but does
>not require radials, which makes it a good choice for HT operations.
>
>
>Bob
>KD8WU
a notable exception in this group. ;)
W8JI Tom
Hi Alan,
In article <55cju8$o...@wombat.melbpc.org.au>, amfo...@melbpc.org.au (Alan
Fowler) writes:
> The mast was a triangular lattice steel guyed construction, 704
feet
>high and about 9 feet per side. Tke bottom 10 feet ot so tapered to
>about one foot diameter and sat on a single tubular porcelain
>insulator. The feed point was about 8 feet from the ground.
That's another thing they got away from here, triangular structures. It
causes a loss in vertical directivity and a decrease in BW. The preferred
radiator is uniform cross section or thicker (by top loading) at the open
end.
Unfortunately my books and references on AM BCB installations went with
the sale of my business years ago, but I'm sure someone on here has a copy
of the NAB Broadcast Engineering Handbook. The idea was to shorten the
radiator slightly from 5/8 wl to decrease the high angle lobe. Even though
a little ground wave signal was given up, fading was greatly reduced.
The problem with the 5/8 antenna was the high angle lobe arrives back in
the area of fringe ground wave signal, giving rise to severe fading.
Wish I could quote the page, but I'm reasonably sure that's the book. And
I'm positive that was the practice here after the 30's when antenna
systems settled in to cookbook recipies.
73 Tom
Jim Weir
w8j...@aol.com (W8JI Tom) shared these priceless pearls of wisdom:
->We agree.
->We also agree
You got a mouse in your pocket or sumpin'??? Or maybe Prince Charlie in
disguise?
Jim
Jim Weir VP Engineering | You bet your sweet patootie I speak for the
RST Engineering | company. If I don't, ain't nobody gonna.
Grass Valley CA 95945 |
http://www.rst-engr.com | AR Adv WB6BHI--FCC 1st phone---Cessna 182A N73CQ
j...@rst-engr.com | Commercial/CFI-Airplane/Glider-A&P-FAA Counselor
Scott Ellington
ON4UN also has an interesting discussion about the effect of
ground losses on the performance of low-band verticals over a quarter
wavelength long in his book, "Low Band DXing".
--
73,
Scott K9MA
sdel...@facstaff.wisc.edu
Mandy Wright
In article <32796D...@worldnet.att.net>, altavoz
<alt...@worldnet.att.net> writes
Alan Fowler
w8j...@aol.com (W8JI Tom) wrote:
>Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
>broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
>arrives back on earth and interferes with the desired signal from the main
>lobe, and gives rise to severe fading.
>A 5/8 wl antenna ONLY acheives its' gain when over a very very large
>groundplane, several wavelengths of near perfect ground. Without the large
>perfectly reflecting ground, the 5/8 wl has about the same or slightly
>LESS gain than a 1/2 wl with no reflecting ground.
>Any slight matching advantage in matching is offset by these
>disadvantages.
Tom,
I'm intrigued by your comment that most broadcasting stations
abandomed them in the 30's. To the best of my knowledge the National
Broadcasting Stations (Australian Broadcasting Commission) is still
using them. I think that the Commercial stations are still using them
too. Perhaps we are lucky in having a very tightly controlled
allocation of station locations, and far fewer stations than
elsewhere.
I was closely involved with them 1957-1964, particularly with the
3AR - 3LO pair working at 620 kHz and 770 kHz. The aerial was a
compromise 5/8 aerial, and there was a very big difference in the feed
point impedance at the two frequencies. I have the values on file if
anyone is interested.
The mast was a triangular lattice steel guyed construction, 704 feet
high and about 9 feet per side. Tke bottom 10 feet ot so tapered to
about one foot diameter and sat on a single tubular porcelain
insulator. The feed point was about 8 feet from the ground.
Ground mat was 144 radials a bit longer than hald wave, terminating on
a copper cable, open circuit ring, about 15 feet diameter with a
single lead into the coupling unit.
We replaced that with a continuous copper sheet about 15 foot square
with all radials bonded directly to it. That did two things (a)
stabilised the base impedance with changes in soil conductivity over
the seasons, and (b) substantial reduced the near field ground losses.
We define our service area as the distance from the aerial to the
start of the fading zone, and use transmitters on other frequencies to
cover the remainder of Victoria.
I have no idea how this applies to HF. But I thought someone may be
interested.
Alan.
>73 Tom
altavoz
altavoz ( the magnificent,all powerful, all knowing, and all that other
bullshit....)
You're getting close to the idea with your "Q = fo/f1-f2"
Quit fighting it ,and you'll see the value in it.
People are so busy fighting others ideas , that they aren't picking
up the concept. For example , an 20 meter horiz 1/2 wl dipole
has a feed point of 80 ohms , right ? HELL no you say ! it's 72 !
Wait a minute , what if its .625 wl above gnd ? ( 58 ohms)...
or .35 wl above gnd ? (97 ohms). We're arguing so much , we're not
learning from each other.
altavoz
A N Thompson wrote:
>
> [My instincts tell me that I shouldn't get involved in this
> discussion, but I can't resist]
>
> I agree with Chip, Tom, et al, regarding the theoretical
> advantage of the 5/8-wavelength antenna vs. the results
> obtainable in practice over a less than ideal ground
> plane; i.e., it's not as effective in the real world as it is on
> paper. When over lossy ground, the very low angle
> radiation from the 5/8-wavelength antenna is absorbed
> in the ground rather than being reflected.
altavoz: Does SEA WATER absorb the signal too !
ha ha ha .....Thats why hams near ocean cant do
DX ?!!1 ha ha ha ha
Thats why boats cant transmit HF ?! ha ha ha ha.
IM WAITING FOR YOUR ANSWER !!!
> circumstances the high-angle lobe becomes a major
> portion of the far field radiation from the antenna.
altavoz: Untrue.
> The taller (1/2- and 5/8-wave) verticals require more
> extensive grounds than does the 1/4-wave vertical. The
> 1/4-wave antenna will outperform a 1/2-wave antenna unless
> an (excellent) ground plane extends out to about 1.5 wave-
> lengths. The 5/8-wave antenna requires and even more
> extensive ground.altavoz: WHAT IS THIS "EXCELLENT" ground plane ? It needs
only a 5/8wl radial sys' for a 5/8 wl antenna .
>
> 73,
>
> Arliss
altavoz
W8JI Tom wrote:
>
> In article <19961030.2026...@juno.com>, w7...@juno.COM (A N
> Thompson) writes:
>
> >The taller (1/2- and 5/8-wave) verticals require more
> >extensive grounds than does the 1/4-wave vertical. The
> >1/4-wave antenna will outperform a 1/2-wave antenna unless
> >an (excellent) ground plane extends out to about 1.5 wave-
> >lengths. The 5/8-wave antenna requires and even more
> >extensive ground.
> >
> >
> >Arliss
>
> As a bit of practical experience, I did broadcast consulting work in the
> 70's. I had occasion to "sneak" various towers on 160 late at night.
>
> The 280-300 ft towers were always great performers within a few hundred
> miles, but stank for 100 mile and longer work. At one site, a 60 ft tall
> inverted L beat the 300 ft tower over and over again outside of a few
> hundred miles.
altavoz: How would you know ? OOhhh thats right , you got signal reports,
right ? ha ha ha very scientific !
> At a location in a swampy area, a dipole at 350 ft absolutely killed a 280
> ft vertical, yet a 140 ft vertical at my house a few miles came close to
> the high dipole.
>
> These are less than ideal comparisons, and I would never claim them to be
> conclusive, but they certainly indicate something.
altavoz: They are indicative of your lack of scientific ability.
> I walked away with the same gut feeling Arliss expressed. The low wave
> angle, coupled with lossy soil (even though it was almost 30 mS/m at the
> one site), actually hurts the lower angle skywave signals.
>
> 73 Tom
altavoz: And that proves, therefore that this low angle radiation
OVER SEA WATER must be totally absorbed . NOT !
altavoz
>73 Tom
Alan Fowler.
/ Oz \ Mail Address: PO Box 272, Balwyn 3103 Vic, AUSTRALIA.
\_,--.x/ Phone: +613-9857-7128 Member, Melbourne PC User Group.
v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
altavoz: 5/8 wl antennas work at MF,HF,VHF,UHF .
BUT THEY DONT WORK OVER LOSSY GROUND ( NOT )
altavoz
altavoz: I know what im talking about , so i made the absolute
statement , and i stand by it . Between .25w and .5w you'll need
a cap to tune and caps are expensive , so why not not just jump
to .6w and a coil does it and the 2nd lobe isnt significant.
What you're not looking at is the pattern (gain). .25w
pattern is trash.
Tom says:
> >> Actually the minor lobe of a 5/8 wl is not insignificant, that's why most
> >> broadcast stations abandoned them by the 30's. On sky wave, the minor lobe
> >> arrives back on earth and interferes with the desired signal from the main
> >> lobe, and gives rise to severe fading.
> >
altavoz: FALSE . Read
Mike says:
> Dead wrong. In practice, it DOES work out Tom's way! Go ask why WOAI
> in San Antonio, for a number of reasons,.....snipped Mikes blitter
> ........because of the story that the Mexican
> crew that cut the grass lost a member on a dare to a stray weed slinger,
> as I was told. He reached up and touched the base, with his weed slinger,
> on a bet, after which they couldn't ANY of them even NEAR the thing to cut
> the weeds.
> Deep fade momentarily I suppose.
> Old Square Root Jackson, W5VO, so nick named since only the square root of
> his math classes at A&M ever passed when he got on staff here, said that it
> was FAR worse with the metro location up on the building top and with
> the effect exacerbated by the elevated feed point!
> At night WOAI has terrible fade problems and phase distortion here, 175
> miles from San Antonio...
Tom says:
> >> A 5/8 wl antenna ONLY acheives its' gain when over a very very large
> >> groundplane, several wavelengths of near perfect ground. Without the large
> >> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> >> LESS gain than a 1/2 wl with no reflecting ground.
altavoz: FALSE , a .6w ant needs exactly .6 radials(current pk at .35w)
, a .25w requires anything over .1w radials as it's current peak is
at the feedpoint(you only need radials at the current loop)
Tom says:
> >> Any slight matching advantage in matching is offset by these
> >> disadvantages.
> >>
> >> 73 Tom
altavoz: GO BACK TO SCHOOL !
Mike says ( but who cares, he adds nothing tech )
> I am beginning to feel that the only solution to a misplaced antenna
> profile is a frontal lobotomy that can be achieved by shorting the antenna
> input terminals together... and the only other solution is a bottle in front
> of me for an insulator!
> Mike - W5WQN
Alan Fowler says
>73 Tom
,-._|\ Alan Fowler.
/ Oz \ Mail Address: PO Box 272, Balwyn 3103 Vic, AUSTRALIA.
\_,--.x/ Phone: +613-9857-7128 Member, Melbourne PC User Group.
v +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
altavoz: Tom , you could get diseases with that unwashed foot
in your mouth.
altavoz
Harbin Osteen wrote:
>
> >
> > I see many posts "sizeable, substancial....GP for a .5wl antenna.
> >
> > You are wrong . it needs a .5 wl radial system, not a substancial...
> > You dont know what you're talking about on half waves.
> >
> I am going to get a 5/8 MaCo antenna for my C.B. (11 meters?).
> I got in on the thread late, but are you saying that ground
> raidials have to only be equal to 1/2 wave in length to get
> a dB gain? The MaCo does not come with raidials, so will it
> work with raidals without messing up the SWR? I think a ground
> plane will help any vertical antenna, but I'm not shure.
> SeeYaa:) Harbin
altavoz: 1/2wl antennas need 1/2wl radials and 5/8wl ant's need 5/8wl
radials . The radials must be 180 degrees to put the max gain
on the horison . And dont use it over lossy ground cause it will
be totally absorbed ( NOT !! its a little inside joke).
altavoz
Mandy Wright wrote:
> To obtain a perfect match to a 50 ohm source a capacitor may be added in
> series, at the feed point, to cancel the inductive component when the
> length has been extended to approx. 130 degees, to increase the
> radiation resistance.
> Has anybody got spare copies of the following that they would like to
> lend to Altavoz, I need mine for my business!
> Reference Data for Radio Engineers ITT
> Antenna Engineering Handbook Jasik
> Antenna Engineering Handbook 2 Johnson and Jasik
> Antennas Kraus
> Antenna Theory and Design Volumes 1 and 2 H Paul Williams ( my mentor!)
> Radio Engineering BBC Manual E K Sandeman
> HF Antennas Leslie Moxon (my other mentor!)
> VHF Radio Keller
> Mandy
altavoz: Can you make a coherent connection between the 130 degree
antenna and the text references ? Are you saying that JASIK wants
us to use 130 degree antennas ? I hear laughter in the background.
Now i hear laughter all 'round ha ha ha ha ........
altavoz
W8JI Tom wrote:
>
> hello albatros,
> In article <3276D1...@worldnet.att.net>, altavoz
> <alt...@worldnet.att.net> writes:
>
> I wote
> most
> >> broadcast stations abandoned them by the 30's. On sky wave, the minor
> lobe
> >> arrives back on earth and interferes with the desired signal from the
> main
> >> lobe, and gives rise to severe fading.
> >> groundplane, several wavelengths of near perfect ground. Without the
> large
> >> perfectly reflecting ground, the 5/8 wl has about the same or slightly
> >> LESS gain than a 1/2 wl with no reflecting ground.
> >> disadvantages.
>
>
> >altavoz: Read Paul H. Lee page 84 "Am' Rad' Vert' Ant' HB"
> >As he proves you must have a counterpoise for a 1/2w ant.
>
> Of course you do, if the antenna is end fed especially. Without one the
> antenna can NOT even be fed at the end. That is the main mistake of the J
> pole, it uses a matching stub as both counterpoise and matching section,
> and current moves the wrong way.
> So when you say:
> >A J POLE DOESNT WORK ! IT HAS POOR LOW ANGLE RADIATION .
> We agree.
>
> When you say
> >He says " Actualy the 5/8w vert is better than the 1/2
> >vert from the standpoints of low angle radiation and feedpoint
> >impedance..
> We also agree, but NOT for broadcast band use where skywave is present and
> not unless the groundplane extends out many wavelengths. As a matter of
> fact, in the NAB Engineering Handbook this very reason is explianed, and
> shorter verticals are called NON-FADING verticals for this reason.
altavoz: And the NAB Engineering HB couldnt be in error ?
I mean, there's never been a case where an Eng book has been in error,
absolutely positively .....NEVER ! NOT ONCE !
Minor lobe at 60 degrees ? hhhhmmmmmm . You're saying that 60 degrees
is a good angle to "SKIP" on the ionosphere ? What do you think the
ARRL would say about 60 degree skip ? On the 3rd hop that would put us
at 300 miles ? ha ha ha ha .......
> Another thing the 5/8 wl antenna does is force or compress radiation at a
> low wave angle where the earth losses absorb signal. That is OK for ground
> wave (because you have to have the signal there anyway) but is bad for
> skywave. As the vertical for HF skywave is made taller than 1/4 wl
> efficiency GOES down unless the antenna is over a large body of saltwater.
alkaselzer says: "....over a largebody of seawater" Tom , you cant have
it both ways , you said prev' that absorbtion over lossy gnd.....and now
you say "...where earth losses absorb signal" what do you think sea
water is ? IT IS LOSSY . IT IS MORE LOSSY THAN DIRT .
Those transmitting on 2182khz ( marine radio ) had better stop ,
cause all your signal is being absorbed.
> You can find that by modeling the antenna on computor, trying the antenna
> in life, or by reading a good book that has sections about earth effects
> like Antennas and Transmission Lines by Dr. Kuecken. I had a 1/2 wl
> vertical on 80 meters and it stunk compared to a 1/4 wl vertical, and I
> tried the same thing on 40 and 160 and they stank. For groundwave, I could
> work many miles, but for skywave even into DX they were the poorest
> antennas I ever used even though they were over large radials.
altavoz: That proves that you cant make it work and others can ,too bad.
It takes great courage to admit such a failure. Im proud of you.
>
> 73 Tom
>
> PS. Captain Kangeroo is better about radials than Captain Lee. He needs
> to go back to radial school.
altosax: Stay tuned , it over til it's over .
William E. Sabin
altavoz wrote:
>
> Q is rate of change of reactance.
Consider a series LCR circuit connected to a voltage generator:
1) At F0 the impedance is R
2) At FHI the current is down 3 dB and XHI = R (XHI Inductive)
3) At FLO the current is down 3 dB and -XLO = R (XLO Capacitive)
4) dX/dF = (XHI - XLO) / (FHI - FLO) = 2 * R / (FHI - FLO)
5) Q = F0 / (FHI - FLO)
Combine 4 and 5 to get
6) Q = (F0 / 2 * R) * (dX/dF)
So if we know R and F0, Q can be found from dX/dF. This assumes that X
varies linearly, which is only approximate but OK for high Q.
altavoz had the right idea but was a bit sloppy, math-wise.
Bill W0IYH
William E. Sabin
Correction: 6) should be:
6) Q = (F0 / (2 * R)) * (dX/dF)
CHARLES J. MICHAELS
There seems to be some confusion of language in this string.
First we must differentiate between a quarter wave antenna
that is a full quarter wave length long, and one which is shortened to
produce a purely resistive feed-point impedance. An infinitely thin
quarter-wave length antenna has a feedpoint impedance of about
36.6 + j 22.5. Finite thickness antennas have somewhat lower
values. They are customarily made somewhat shorter than a quarter
wave length to make the input impedance purely resistive. This
might then be called more properly a "resonant quarterwave". At
greater lengths the feedpoint has an inductive reactance and at
shorter lengths a capacitive reactance.
A resonant quarter wave vertical over a good ground or
ground plane system usually has feedpoint impedance lower than
the commonly used 50 ohm coax.
One way to transform the feedpoint impedance up to 50
ohms is to use an Lnet between it and the coax. One such L net
might consist of a series inductor between the antenna feedpoint and
the coax and a shunt capacitor across the coax. Another might
consist of a series capacitor between the antenna feedpoint and the
coax and a shunt inductor across the coax.
The series element in these L nets is usually a very small
reactance. The antenna may be adjusted in length to make its
feedpoint equal to the series reactance required by the L net.
Thus, only the shunt reactance remains and the system is
resonant.
Sometimes a series element (which may be a capacitor or
and inductor) is used to permit adjustment of the antenna resonant
frequency as the reactive component of most antennas changes
much more with frequency than the resistive component.
The shunt element is NOT a loading device, it is an
impedance transforming device. Putting it across the coax does
indeed change the resonant frequency somewhat, however this is
simply the antenna acting to produce the missing series element. I
call this element of the matching L net, a "virtual component"
acquired in bringing the antenna to resonance.
With a substantial lengthening of a "quarter wave" antenna
the R component can be brought to 50 ohms and the inductive
reactance acquired can be canceled by a series capacitive reactance.
In this case, the series element is primarily for purpose of adjusting
resonant frequency of the system.
A "matching" element is primarily dependent on the
impedance of the feed line selected. A "resonating" element is
primarily dependent on the antenna selected.
Charlie, W7XC
--
Cecil Moore
CM> Hi Joel, a 5/8 vertical with a good ground or a 2x5/8 dipole
CM> has the maximum gain available from wire with no other
CM> components.
> altavoz: You're wrong . A .6 wl needs a .6 wl RADIAL SYSTEM.
> Read my post on Paul H. Lee page 84 on radials on a half wave.
Isn't a ".6 wl RADIAL SYSTEM" a good ground? It either is or it
isn't. If it is, guess who was correct. If it isn't, guess who
is incorrect.
Most compact cars don't have .6 wl of body on 2m. Does that mean
that a .6 wl is not a good 2m mobile antenna for compacts?
73, Cecil, W6RCA, OOTC (not speaking for my employer)
Cecil Moore
CHARLES J. MICHAELS wrote:
> First we must differentiate between a quarter wave antenna
> that is a full quarter wave length long, and one which is
> shortened to produce a purely resistive feed-point impedance.
Hi Charlie, I have always assumed that since the actual speed
of light is never achieved in an antenna conductor, that when
anyone says "quarter-wavelength", they are talking in context
about a "90 degree electrical quarter-wavelength" rather than
a "physical quarter-wavelength". Is that the convention or
have I assumed too much?
Roy Lewallen
In article <55irj7$f...@news.asu.edu>,
ha...@aztec.asu.edu (CHARLES J. MICHAELS) wrote:
>
> There seems to be some confusion of language in this string.
>that is a full quarter wave length long, and one which is shortened to
>quarter-wave length antenna has a feedpoint impedance of about
>36.6 + j 22.5. Finite thickness antennas have somewhat lower
>values. They are customarily made somewhat shorter than a quarter
>wave length to make the input impedance purely resistive. This
>might then be called more properly a "resonant quarterwave". At
>greater lengths the feedpoint has an inductive reactance and at
>shorter lengths a capacitive reactance.
> A resonant quarter wave vertical over a good ground or
>ground plane system usually has feedpoint impedance lower than
>the commonly used 50 ohm coax.
> One way to transform the feedpoint impedance up to 50
With a perfect ground system, a resonant vertical of typical diameter will
have a feedpoint resistance of around 36 ohms. (A very fat one will be a
little lower.) This would cause an SWR of 1.4:1 on a feeding 50 ohm line.
Ground loss will raise the feedpoint resistance, lowering the SWR. (Unless
the ground system is very poor. With one "radial" -- the feedline itself --
the resistance is unlikely to be much above 80 ohms, or 1.6:1 SWR for 50
ohm feedline.) So why bother with a matching network?
Roy Lewallen, W7EL
altavoz
Cecil Moore wrote:
>
> CM> Hi Joel, a 5/8 vertical with a good ground or a 2x5/8 dipole
> CM> has the maximum gain available from wire with no other
> CM> components.
>
> > altavoz: You're wrong . A .6 wl needs a .6 wl RADIAL SYSTEM.
> > Read my post on Paul H. Lee page 84 on radials on a half wave.
>
> Isn't a ".6 wl RADIAL SYSTEM" a good ground? It either is or it
> isn't. If it is, guess who was correct. If it isn't, guess who
> is incorrect.
altavoz: Mr Wizzard , mind telling us whats on your alledged mind ?
Cause we're not mind readers .
> Most compact cars don't have .6 wl of body on 2m. Does that mean
> that a .6 wl is not a good 2m mobile antenna for compacts?
altavoz: Beats a 1/4wl but needs 180 radials to really dance well.
But you should have known that .
>
> 73, Cecil, W6RCA, OOTC (not speaking for my employer)
--
altavoz
William E. Sabin wrote:
>
> altavoz wrote:
> >
> > Q is rate of change of reactance.
>
> Consider a series LCR circuit connected to a voltage generator:
>
altavoz: Series LCR (1/4 wl) , parallel LCR ( 1/2 wl antenna.)
> 1) At F0 the impedance is R
>
> 2) At FHI the current is down 3 dB and XHI = R (XHI Inductive)
>
> 3) At FLO the current is down 3 dB and -XLO = R (XLO Capacitive)
>
> 4) dX/dF = (XHI - XLO) / (FHI - FLO) = 2 * R / (FHI - FLO)
>
> 5) Q = F0 / (FHI - FLO)
>
> Combine 4 and 5 to get
>
> 6) Q = (F0 / 2 * R) * (dX/dF)
>
> So if we know R and F0, Q can be found from dX/dF. This assumes that X
> varies linearly, which is only approximate but OK for high Q.
>
> altavoz had the right idea but was a bit sloppy, math-wise.
>
> Bill W0IYH
Forget the math, concept is that the function of Z with respect to
freq ( how Z changes when freq is changed) ,is highly non lin' and needs
a picture . And the picture takes 2nd seat to the pattern ( most important).
In spite of the fact 5/8 wl has a 2nd lobe greater than 1/2 wl , the 5/8
has more gain on the horizon . Its accidental that its also easier to load.
All ant's 180 degree radials.
Cecil Moore
altavoz wrote:
>
> Cecil Moore wrote:
> > Isn't a ".6 wl RADIAL SYSTEM" a good ground? It either is or it
> > isn't. If it is, guess who was correct. If it isn't, guess who
> > is incorrect.
>
> altavoz: Mr Wizzard , mind telling us whats on your alledged mind ?
> Cause we're not mind readers .
The following is cut-and-pasted for clarity:
Well, you said:
>alatvoz:...
>why are you so afraid of radials ? ( perfectly conducting ground )
So you must consider radials to be a good ground. I said:
>>... a 5/8 vertical with a good ground ... has the maximum gain
>>available from wire with no other components.
You replied:
> > altavoz: You're wrong . A .6 wl needs a .6 wl RADIAL SYSTEM.
> > Read my post on Paul H. Lee page 84 on radials on a half wave.
And I replied with the first quote, above.
So: You said radials are a perfectly conducting ground i.e. a good
ground and turned around and said my statement about "a 5/8 vertical
with a good ground" was wrong. We are left with the following
possibilities:
I was wrong and therefore you were wrong because you said the same
thing I did, or I was right and you were wrong for saying I was wrong.
The only thing that I was guilty of was using the generic word "ground"
when technically I should have said "ground system" but you did exactly
the same thing. In trying to have it both ways, you have it neither.
altavoz
Hmmm ?! Are you sure you have an adequate supply of MIDOL ?
CHARLES J. MICHAELS
Cecil said -
Hi Charlie, I have always assumed that since the actual speed
of light is never achieved in an antenna conductor, that when
anyone says "quarter-wavelength", they are talking in context
about a "90 degree electrical quarter-wavelength" rather than
a "physical quarter-wavelength". Is that the convention or
have I assumed too much?
Cecil,
That is the trouble, in much of the literature it is
unclear as to just what is meant.
Charlie, W7XC
--
Christopher W. Boone
altavoz wrote:
>
> Harbin Osteen wrote:
> >
> > >
> > > I see many posts "sizeable, substancial....GP for a .5wl antenna.
> > >
> > > You are wrong . it needs a .5 wl radial system, not a substancial...
> > > You dont know what you're talking about on half waves.
> > >
> > I am going to get a 5/8 MaCo antenna for my C.B. (11 meters?).
> > I got in on the thread late, but are you saying that ground
> > raidials have to only be equal to 1/2 wave in length to get
> > a dB gain? The MaCo does not come with raidials, so will it
> > work with raidals without messing up the SWR? I think a ground
> > plane will help any vertical antenna, but I'm not shure.
> > SeeYaa:) Harbin
>
> altavoz: 1/2wl antennas need 1/2wl radials and 5/8wl ant's need 5/8wl
> radials . The radials must be 180 degrees to put the max gain
> on the horison . And dont use it over lossy ground cause it will
> be totally absorbed ( NOT !! its a little inside joke).
This is RUBBISH!!! ANY ground plane antenna needs only a 1/4wave radial
system NOT a radial of the same length...the radials only need to emulate
ground......the VERTICAL section is of the proper length to provide for
radiation at the horizon correctly....but a 5/8wave antenna with 1/4wave
radials will work JUST FINE...
We do it all the time in Broadcasting...and in two way too!
Chris
WB5ITT
telecom tech since 1975
Broadcast Engineer since 1976
Currently ABC Radio Network Engineer-Dallas
Christopher W. Boone
altavoz wrote:
>
> Russ Renaud wrote:
> >
> > altavoz (alt...@worldnet.att.net) writes:
> >
> > >> > altavoz: 1/4w antennas are allways shorter than 1/4w to allow
> > >> > an inexpensive coil to tune it to resonance.
> > >>
> > >> Hi Altavoz, Most prudent people avoid blanket statements using
> > >> the words, "always", "never", etc. because they are almost
> > >> always false. Both my 10m whip and 2m whip are 1/4 WL and
> > >> resonant without loading coils.
> > >>
> > >> I would agree that most CB antennas are shorter than 1/4w...
> > >>
> > >> 73, Cecil, W6RCA, OOTC (not speaking for my employer)
> > >
> > > statement , and i stand by it . Between .25w and .5w you'll need
> >
> > nor capacitors. One is for the 2 metre amateur band, the other
> > is UHF low band. Perhaps you're confusing shortened whips with
> > those typically used on CB.
>
> altavoz: It's there , you are too inexperienced to spot it.
> --
In the case of TRUE 1/4wave antennas, NO cap is needed....my Motorola, or
MAXON or Larsen 1/4waves on 2 or 220 or 440 have NO caps, etc....even my
DB201 1/4wave groundplane on lowband (6mtrs) has no cap, etc!!!
Now for a 5/8wave, you need a SERIES coil to electrically lengthen the
antenna to 3/4wave so it will be a good match for 50 ohms...the 5/8wave
PHYSICAL length is best for gain at the horizon....but the impedance is
not a good 50 ohm match (has capacitive reactance) so a series coil is
needed to match it.....a TRUE 3/3wave antenna needs no coil (I have used
a 48 Mhz lowband whip on 145 Mhz with 1:1 SWR but poorer performance than
a 5/8wave cut to 2mtrs)
73
Chris
WB5ITT
ABC Radio Engineering - Dallas
frac...@aol.com
RE: Chris's Comments
Chris is absolutely right; the reactance takes the 5/8 to the resonance of
a 3/4. Let's think about this: over a large GP this resembles a virtual
(that is 'mirrored') 1 1/2 wave antenna. Check the gain on that and
you'll find 3+ dB. The problem is that you need a LARGE GP to get this
mirror effect. A counterpoise will not provide such gain at low angles.
Now here's an interesting question: does a 5/8 WITHOUT a large GP
outperform a 1/4 in, say, a mobile environment? Not as dumb as it sounds!
Consider cellular (33cm wavelength). In urban environments most of the
cells are closely spaced (or should I say closer) and usually high up.
MUCH of the time the cells are NOT at the horizon but from 10-60 degrees
launch angle. So very low launch angles not as important. In a real
situation, which antenna beats which?
73
Chip N1IR
frac...@aol.com
RE: Tom's comments
Ton, absolutely extraordinary. I don't know where to begin without writing
a tome in response.
I stick by my assessment of your comments.
73
Chip N1IR
frac...@aol.com
On the other hand, there was a typo you exploited, so I went back to EZNEC
to check the numbers.
A 5/8 LOADS to approximate a 3/4 wave; its GAIN is that of the 5/8. A 5/8
x 2 DIPOLE LOADS like a 1 1/2 wave but has the gain of a 1 1/4 wave.
The 5/8 x 2 dipole has 3 dB gain over a 1/2 wave dipole but needs to be
LOADED to resonance.
The 3/4 x 2 dipole has a clover pattern about 2/3 dB down from the 5/8 x
2.
Finally, as for the cell comment--unbelievable. Lets just say that lotsa
people would pay BIG $$$ for the opportunity to place cells on the
observer's horizon in most cities. It don't happen. Why? Cuz when you put
them on low places (like supermarkets or hotels or billboards) you place
yourself in a box surrounded by higher buildings, ergo your cell coverage
is pathetic; multipath is a nightmare. Ergo you have to stick them higher
up instead, and the launch angle becomes deliciously larger than zero. Or
you have to put up more cells, which zoning boards love, and creates HUGE
expenses. Occasionally you find an ideal low-location with good horizon,
such as in sprawled min-malled cities or near airports.
Also, in most urban environments the cells are often 1/2 a mile or less
from each other to accomodate the volume of calls.
Now some angles. Lets approximate. A cell up 200 feet (moderately high)
from 1000 feet is about 1/5 of a radian. That puts its launch angle at
about 12 degrees. Marginal on the 'ideal horiozn' case. Now drive downtown
next to that cell and the launch angle is substantially higher. An ideal
case would be to put the cell say, at 40 feet and be 6000 feet away--in
which case there's your beautific horizon. Want some examples? I was in
Kansas City 2 weeks ago and saw cell sight nightmares with building of 200
feet or more scattered around. Cell heaven? Fort Lauderdale Florida, where
save for the coastal condos and a small but high business district, cell
are placed on banks and mini-mall abodes.
So, Thomas, instead of ANSWERING the reasonable question, you attempted to
reduce it as moot. Its hardly that. IF you have the answer, I for one
would be interested in knowing it: WHICH WORKS BETTER IN URBAN (CELLULAR)
ENVIRONMENTS: 5/8 or 1/4?
73
Chip N1IR
w8j...@aol.com
In article <19961110144...@ladder01.news.aol.com>,
frac...@aol.com writes:
>
>Chris is absolutely right; the reactance takes the 5/8 to the resonance
of
>a 3/4.
No, not at all. The reactance simply cancels the capacitive reactance of
the element. It is a circuit problem, NOT a problem of adding missing
length.
If it made the element "look" 3/4 wl long, the pattern and feedpoint
resistance would change. As it is, only the feedpoint reactance is
cancelled, the other parameters remain unchanged, coil or no coil.
>Let's think about this: over a large GP this resembles a virtual
>(that is 'mirrored') 1 1/2 wave antenna. Check the gain on that and
>you'll find 3+ dB.
No. It resembles the gain of a 10/8 wl antenna, which is 1-1/4 wl. Not a
1-1/2 wl antenna.
>The problem is that you need a LARGE GP to get this
>mirror effect. A counterpoise will not provide such gain at low angles.
The mirror image is a ficticious tool created to explain patterns. Using
it as a literal example creates mental image problems.
A small groundplane allows radiation fields to spread into an area beow
zero degress wave angle. This lowers power in the half sphere of radiation
from zero degrees up.
>Now here's an interesting question: does a 5/8 WITHOUT a large GP
>outperform a 1/4 in, say, a mobile environment?
No.
>Consider cellular (33cm wavelength). In urban environments most of the
>cells are closely spaced (or should I say closer) and usually high up.
>MUCH of the time the cells are NOT at the horizon but from 10-60 degrees
>launch angle.
Is it really necessary to point a lobe at a 200 ft high antenna when you
are a few hundred feet away? In most cell systems I've seen, the antennas
are intentionally mounted at low heights. This is done so one cellphone
doesn't occupy several cells.
Even ten degrees is a bit high . At one mile, the optimum wave angle is
typically only a few degrees above the horizon.
When the user is right under the antenna, the distance is very short.
Field intensity is so strong, antenna gain or ERP is of no concern.
> So very low launch angles not as important. In a real
>situation, which antenna beats which?
The desired pattern would be low angle (a<20 deg), in flat terrain it
would be lower than in hilly terrain. In almost any case, high angle
energy is wasted energy.
73 Tom
w8j...@aol.com
Hi Chip,
In article <19961110184...@ladder01.news.aol.com>,
frac...@aol.com writes:
>
>A 5/8 LOADS to approximate a 3/4 wave; its GAIN is that of the 5/8. A 5/8
>x 2 DIPOLE LOADS like a 1 1/2 wave but has the gain of a 1 1/4 wave.
No, that is an totally incorrect description. A 5/8 wl does not "load to
be a 3/4 wl". A 10/ 8 wave dipole is a "10/8 wave dipole", and in most
cases inductance isn't even added. If it were added, it would ONLY vary
the feedpoint impedance.
The series inductive reactance merely cancels capacitive reactance
appearing at the feedpoint, all parameters in the antenna remain exactly
the same with or without the coil in either case. It is for matching, not
changing the antenna's effective length.
>The 5/8 x 2 dipole has 3 dB gain over a 1/2 wave dipole but needs to be
>LOADED to resonance.
No, it has that gain with or without any coil. The coil is for the benefit
of the transmission line and transmitter, not the antenna.
>Finally, as for the cell comment--unbelievable. Lets just say that lotsa
>people would pay BIG $$$ for the opportunity to place cells on the
>observer's horizon in most cities. It don't happen. Why? Cuz when you put
>them on low places (like supermarkets or hotels or billboards) you place
>yourself in a box surrounded by higher buildings, ergo your cell coverage
>is pathetic; multipath is a nightmare.
I indicated 200 feet for antenna height. We have very few 200 foot tall
hotels, supermarkets, and billboards in Atlanta and most of the cities
I've been in. Do you have lot's of 20 story tall billboards and
supermarkets in your town?
> Ergo you have to stick them higher
>up instead, and the launch angle becomes deliciously larger than zero. Or
>you have to put up more cells, which zoning boards love, and creates HUGE
>expenses. Occasionally you find an ideal low-location with good horizon,
>such as in sprawled min-malled cities or near airports.
Chip, please calculate the antenna height required to require a 60 degree
wave angle at a base distance of one mile. Perhaps you are using fractal
geometry by mistake?
>Also, in most urban environments the cells are often 1/2 a mile or less
>from each other to accomodate the volume of calls.
So you are saying cell companies enjoy huge expenses, and try to keep
cells a 1/2 mile or less apart. But while they dothat, they also place the
antennas way up in the air? That sounds like you are disputing yourself
Chip.
Anyway, they sure don't do that here in Atlanta, and not in Toledo and
Detroit (where my old company installed Cellular antennas).
>Now some angles. Lets approximate. A cell up 200 feet (moderately high)
>from 1000 feet is about 1/5 of a radian. That puts its launch angle at
>about 12 degrees.
I'd be disappointed if my cell phone was designed to cover 1/2 mile, since
the cell centers here are sometimes fifteen miles or more apart.
>So, Thomas, instead of ANSWERING the reasonable question, you attempted
to
>reduce it as moot. Its hardly that. IF you have the answer, I for one
>would be interested in knowing it: WHICH WORKS BETTER IN URBAN (CELLULAR)
>ENVIRONMENTS: 5/8 or 1/4?
In your example, the 1/4 wl would be better. But I don't think your
description is correct. I wonder if anyone else knows how far apart the
cells are in most systems, and the average antenna height? The one's I've
seen are lower in the city, and higher in the rural areas, but average
about 200 feet.
73 Tom
Cecil A. Moore
altavoz wrote:
> > > altavoz: Mr Wizzard , mind telling us whats on your alledged mind ?
> Hmmm ?! Are you sure you have an adequate supply of MIDOL ?
Hi Altavoz, if you don't want an answer, don't ask for one. :-)
73, Cecil, W6RCA, OOTC
k1...@aol.com
Chip--
In his reply, Tom wrote:
The series inductive reactance merely cancels capacitive reactance
appearing at the feedpoint, all parameters in the antenna remain exactly
the same with or without the coil in either case. It is for matching, not
changing the antenna's effective length.
Snip
I believe Tom is correct on this point. I've done lot of work with 2 x
5/8 dipoles, first for Cushcraft and later for MFJ (Joe Reisert explained
it to me in just that way several years ago when I was working on a
sidemount). In the 2 x 5/8 that I use here, the coils are shielded inside
the support structure--I don't even consider them part of the antenna.
-- Rick
frac...@aol.com
RE: Rick's comments
Hi Rick--
You (perhaps) didn't see the follow up: the typo should read 1 1/4, not 1
1/2.
Therefore, we ALL agree. Also, I don't recall saying that the LOADING
produces the gain; why would you put those words in that aren't there? The
LOADING produces the RESONANCE. OK? The only way to get the 'loading' to
produce a gain change is to shape it, such as in echelon.
73
Chip N1IR
k1...@aol.com
Chip--
I just reread my post three times--and I don't see the word "loading" in
there. Perhaps we're not talking about the same post.
--Rick
w8j...@aol.com
In article <19961110230...@ladder01.news.aol.com>,
frac...@aol.com writes:
> Also, I don't recall saying that the LOADING
>produces the gain; why would you put those words in that aren't there?
Because you said:
In article <19961110184...@ladder01.news.aol.com>,
frac...@aol.com writes:
>A 5/8 LOADS to approximate a 3/4 wave; its GAIN is that of the 5/8. A 5/8
>x 2 DIPOLE LOADS like a 1 1/2 wave but has the gain of a 1 1/4 wave.
The coil does not make the "5/8 wl load to approximate a 3/4 wl", nor the
10/8 wl "dipole load like a 1-1/2 wl antenna". That's simply the wrong way
to say it.
All the inductor does is cancel the reactance. The resistive part of the
feedpoint impedance remains the same (with the reactance added in series)
so nothing in the system, neither impedance or pattern, looks like a 3/4
wl or 1-1/2 wl.
>The 5/8 x 2 dipole has 3 dB gain over a 1/2 wave dipole but needs to be
>LOADED to resonance.
No, it does not. It will have the very same gain whether resonant or not.
The coil simply modifies feedpoint impedance..
>The
>LOADING produces the RESONANCE. OK?
That's OK.
>The only way to get the 'loading' to
>produce a gain change is to shape it, such as in echelon.
No. Loading can change gain and pattern simply by moving it up in the
radiator. There is no reason to "step it" or "shape it", all we need do is
move it to a location that changes the radiator's current distribution.
Are cell antennas in Boston really way over 200 feet in the air and only a
mile apart?
73 Tom
altavoz
frac...@aol.com wrote:
>
> On the other hand, there was a typo you exploited, so I went back to EZNEC
> Also, in most urban environments the cells are often 1/2 a mile or less
> from each other to accomodate the volume of calls.
altavoz: No , close, to get a clear signal.
You could put them 1' apart and they couldnt handle any more
calls , thats limited by the number of channels . When they're
very far apart ( far enuf so each tower could transmit on the same
ch) then the number of "calls" would increase . When towers are very
close and ur moving , you r handed off ,but to a different ch, if
the towers are far enuf apart , you can be handed to the same freq
( but arent for other reasons ).
> IF you have the answer, I for one
> would be interested in knowing it: WHICH WORKS BETTER IN URBAN (CELLULAR)
> ENVIRONMENTS: 5/8 or 1/4?
>
> 73
> Chip N1IR
altavoz: IS THIS ALT.CELL.ANTENNAS ?
5/8 wl antennas at HAM FREQUENCIES work great .
altavoz
w8j...@aol.com wrote:
>
> Hi Chip,
>
> In article <19961110184...@ladder01.news.aol.com>,
> frac...@aol.com writes:
> >
> >A 5/8 LOADS to approximate a 3/4 wave; its GAIN is that of the 5/8. A 5/8
> >x 2 DIPOLE LOADS like a 1 1/2 wave but has the gain of a 1 1/4 wave.
>
> be a 3/4 wl". A 10/ 8 wave dipole is a "10/8 wave dipole", and in most
> cases inductance isn't even added. If it were added, it would ONLY vary
> the feedpoint impedance.
altavoz: Well said , TOM . One small point , we do parallel some
induct' to raise the antennas XC to 200-J115 and then series a 00+j86 so
that the "L" network can match to 50+j00.
Chip thinks that adding XL to an antenna will lengthen it. ( wrong)
An 1/8 wl antenna matched with a feedpoint XL does not radiate the
same pattern as a 1/4 wl and this proves the XL does not lengthen the
antenna . If the XL is placed in the center of the radiator , it will
lengthen the antenna .
> that decrease
> The series inductive reactance merely cancels capacitive reactance
> appearing at the feedpoint, all parameters in the antenna remain exactly
> the same with or without the coil in either case. It is for matching, not
> changing the antenna's effective length.
>
> >The 5/8 x 2 dipole has 3 dB gain over a 1/2 wave dipole but needs to be
> >LOADED to resonance.
>
> No, it has that gain with or without any coil. The coil is for the benefit
> of the transmission line and transmitter, not the antenna.
altavoz: Your right Tom , Chip does not inhale , he just holds the
joint for a friend.
> 73 Tom
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