3/4 wgp vs. 1/2 wgp TOA ??

[BOOTY MONSTER]

are 1/4 WGP's more naturally resonate ?
are multiples if it more naturally resonate also ? for example 1/2 waves or 3/4 waves .
is the loss of TOA and shape of the lobes on a 3/4 WL antenna any better or worse compared to a 1/2 WL antenna .

could a 1/2 WGP or even a 3/4 WGP with no matching device (tuned purely by length like a dipole) be used effectively on 27MHz. ?

since a 1/2 wave verticle can work well without or doesnt need ground elements would the 3/4 behave in a similar way ? if it needed a coil to tune could it work well without ground elements like a over grown ringo ?

 

[Henry HPSD]

are 1/4 WGP's more naturally resonate ?
are multiples if it more naturally resonate also ? for example 1/2 waves or 3/4 waves .
is the loss of TOA and shape of the lobes on a 3/4 WL antenna any better or worse compared to a 1/2 WL antenna .

could a 1/2 WGP or even a 3/4 WGP with no matching device (tuned purely by length like a dipole) be used effectively on 27MHz. ?

since a 1/2 wave verticle can work well without or doesnt need ground elements would the 3/4 behave in a similar way ? if it needed a coil to tune could it work well without ground elements like a over grown ringo ?

Hi BM!

TOA also highly dependes on heigth/ground conductivity.
On my homesite there is quite some information wich migth be of intrest for you
pse see heigth/take of angle and verticals section. at 11 meter Dx antenna systemx
You can see that a halve wave at 2 feet heigth can outperform (on Dx) a halve wave at 18 feet!

No, not any length can be used without a matching device.
Although the antenna can be in "resonance" it can have a impedance for example of 100 ohms
so that will show a 1:2 on the SWR meter.
In such a case you'll still need to match the impedance.
Resonance is if there is no inducitve or capacitive value...but Ohms are not a issue.

The word is when you look at a antenna and there is a current bow...
As is the case with a 1/4 wave and 3/4 wave youll need radials..
When there isnt one you'll need them less.
There where the current is high (at the bow) impedance is always low..
As in the middel of a dipole or end of a groundplane.
THere where the current is low..(end fed halve wave) the impedance is high.
So by simply changing the feed point of a end fed halve wave you change impedance.
When placed in the middel we end up with a center fed halve wave aka dipole..


kind regards,

Henry

 

[jazzsinger]

Hi BM!

TOA also highly dependes on heigth/ground conductivity.
On my homesite there is quite some information wich migth be of intrest for you
pse see heigth/take of angle and verticals section. at 11 meter Dx antenna systemx
You can see that a halve wave at 2 feet heigth can outperform (on Dx) a halve wave at 18 feet!

No, not any length can be used without a matching device.
Although the antenna can be in "resonance" it can have a impedance for example of 100 ohms
so that will show a 1:2 on the SWR meter.
In such a case you'll still need to match the impedance.
Resonance is if there is no inducitve or capacitive value...but Ohms are not a issue.

The word is when you look at a antenna and there is a current bow...
As is the case with a 1/4 wave and 3/4 wave youll need radials..
When there isnt one you'll need them less.
There where the current is high (at the bow) impedance is always low..
As in the middel of a dipole or end of a groundplane.
THere where the current is low..(end fed halve wave) the impedance is high.
So by simply changing the feed point of a end fed halve wave you change impedance.
When placed in the middel we end up with a center fed halve wave aka dipole..


kind regards,

Henry

WHAT CAN INFLUENCE THE TAKE-OFF ANGLE?
To this question there are only three answers:
- The polarity of antenna we use
- The height of the antenna
- The ground conditions.


Hi Henry,
i've taken this from your site,but i notice one omission.I'm assuming by ground conditions you mean conductivity and not height asl.

There is also one other condition that affects take off angle Henry,that would be the height of the ground above sea level,obviously the lower the ground is in relation to sea level,the further it will be till the signal strikes the ionosphere at any given mounting height or at any given take off angle.Although the takeoff angle is effectively the same the distance the antenna mounted on lower ground strikes the ionosphere is clearly different.

in your country that obviously isn't a major issue as most of the Netherlands lies at or below sea level (reclaimed land) ,but in many other countries it would be very critical,here in scotland which has much high ground i find the closer to sea level you are the further the dx you can work.

for instance if you use the same antenna,on the same mast,one at sea level and one at 100m asl,it stands to reason the one at sea level will strike the ionosphere further away everything else being equal.which is also another reason m/m stations do so well dx wise.its simple trigonometry.



there is one major difference between 1/4 wave and 3/4 wave antennas,the 1/4 wave only has one imax (current bow) at the feedpoint,whereas the 3/4 wave will have two,one at the feedpoint and one 1/4 wave below the tip of the antenna.

 

[Henry HPSD]

Hi There,

Thanks for your thoughts!

Would heigth above see influence TOA or would it(marginal) influence the distance where it hits the layers ?. those are two individual things..would you agree?

Ofcourse i can be wrong...but was looking more at in this ways:

Real "dx"took place through the F2 layer wich is roughly 300..400km above the earth....
Now think of a signal wich is send under a angle of 5 degrees away....at 0 meters heigth.
Now think of that same signal at 5 degrees send at 100 meter asl heigth (your example).
Would the difference where it "hits" the ionosphere be of that big influence?
No...it is the angle under wich it is send that makes the difference.

It is not that heigth above sea level would be the most important issue.
As in that case all "world service" broadcasting stations would place there location at the lowest point in a country..
The important issue is the ability of the ground to reflect waves. In mountain terrain the conductivity is not as good as salt water.
That is why /MM stations (at salt sea) are always loud..not because they are low placed.
That is also why stations at moist ground...are outperforming stations in industrial or city enviroment.


Yes i mean ground conductivity...but also a bit more..
It is always difficult to analyse the "ground" for sure in mountain terrain.
A lot of things are variable.
Some people think the waves reflect at the earth atmosphere where they penetrate the earth. It varies on how deep and how "effective" they are reflected

A Good mountain dx location would be with slooping ground from my mind i believe about 10..30 degrees and you needed to sit just below the "top"

About the current bow, thanks for your info!,you are rigth. I would have been better to refered to the currents at the feedpoint.

Kind regards,

Henry

 

[jazzsinger]

Would heigth above see influence TOA or would it(marginal) influence the distance where it hits the layers ?. those are two individual things..would you agree?

Ofcourse i can be wrong...but was looking more at in this ways:

Hi Henry.

I agree they are two different things,although height above or below sea angle won't change the actual take off angle what i was trying to get across was it will give an effective change to it.if it didn't then no matter what height above sea level you mounted your antenna at the distance it strikes the ionosphere would be the same as would the distance gained.

the way i view it is both antennas are theoretically geographically located at point A,the higher mounted one strikes the ionosphere at point B,the lower one at point c,both have exactly the same take off angle,but the effective take off angle has been slightly changed,not the physical one.

even although as you point out it is marginal,it is a fact nontheless that effectively your range would be increased,which i believe was the purpose of your article,maximising distance.which is what dx'ing is all about.

as for the current maxima on a 3/4 wave,i believe its the upper one thats more critical to performance,which is what i beleve makes the sigma 4 style antennas unique,i believe that the lower i max is somehow reflected up to the higher one via the basket arrangement in phase adding to the signal in a similar way a reflector on a beam antenna works,

i may of course be wrong but that is the reason we are both here,to learn and increase our understanding of how antennas work and how radio waves actually propagate,a subject few venture into but just accept.i believe that even in a vacuum there is tiny unknown particles that are the carriers of rf energy.it may be quantum physics just hasn't discovered them,it may be it just doesn't fully understand how they interact,it may be i'm totally wrong,hopefully one day we'll find out for certain.

what is accepted as fact today more often than not is proven to be fiction tomorrow,that has always been the way of science and our world.

 

[Captain Kilowatt]

WHAT CAN INFLUENCE THE TAKE-OFF ANGLE?


There is also one other condition that affects take off angle Henry,that would be the height of the ground above sea level,obviously the lower the ground is in relation to sea level,the further it will be till the signal strikes the ionosphere at any given mounting height or at any given take off angle.Although the takeoff angle is effectively the same the distance the antenna mounted on lower ground strikes the ionosphere is clearly different.

in your country that obviously isn't a major issue as most of the Netherlands lies at or below sea level (reclaimed land) ,but in many other countries it would be very critical,here in scotland which has much high ground i find the closer to sea level you are the further the dx you can work.

for instance if you use the same antenna,on the same mast,one at sea level and one at 100m asl,it stands to reason the one at sea level will strike the ionosphere further away everything else being equal.which is also another reason m/m stations do so well dx wise.its simple trigonometry.

Simple trigonometry hey? Perhaps you should apply that simple trig and see what kind of difference it makes. Here's some algebra to help: 2 X sq.rt (FA) where FA stands for F@*^ All. 100m over a distance of 100-300 Km? That's not even taking into account refraction and bending along the path. Salt water lowers the take off angle and tat is why /MM stations do so very well. Their antennas are mounted over nearly perfect "ground". The same thing happens to broadcast stations in the medium and LF bands,the signal is "pulled down" by greater ground conductivity of the salt water and that is why the groundwave signals are greatly improved over those areas even without any ionospheric influence.

 

[jazzsinger]

Simple trigonometry hey? Perhaps you should apply that simple trig and see what kind of difference it makes. Here's some algebra to help: 2 X sq.rt (FA) where FA stands for F@*^ All. 100m over a distance of 100-300 Km? That's not even taking into account refraction and bending along the path. Salt water lowers the take off angle and tat is why /MM stations do so very well. Their antennas are mounted over nearly perfect "ground". The same thing happens to broadcast stations in the medium and LF bands,the signal is "pulled down" by greater ground conductivity of the salt water and that is why the groundwave signals are greatly improved over those areas even without any ionospheric influence.

i did say it was ANOTHER reason maritime mobiles do so well,not the only reason.i think perfect ground is like a perfect vacuum,neither exist.

 

[W5LZ]

Height above sea level is meaningless for antenna purposes. Height above ground level is very meaningful for antenna purposes. Height above sea level, or ASL, is meaningful for determining relative three dimensional positioning.
The important thing about how high an antenna is above ground is how it will affect it's input impedance (along with where the thing is 'fed'). That's because of how the proximity of an antenna to ground affects it's reactance (how the thing reacts). And since reactance plays a huge importance in resonance, height above ground level can determine the length of antenna required for resonance. (Isn't that a nasty idea? Resonance length can change! )
Does height above sea level mean anything as far as 'DX', or how far your signal goes? No, it doesn't. But antenna height above ground level can determine how far, and how, and how much of your signal get's to where it's going. Is that height above gound level always the exact same for any particular frequency? Nope, it changes because of several other aspects. As in conductivity of dirt, what's around that antenna (higher / lower dirt?), the frequency of use, and if the @#$ antenna is painted pink or not!

Don't get 'fixated' on just one aspect of it, such as height, the whole mess is what determines how an antenna behaves. It's all relative...
- 'Doc

 

[jazzsinger]

Height above sea level is meaningless for antenna purposes. Height above ground level is very meaningful for antenna purposes. Height above sea level, or ASL, is meaningful for determining relative three dimensional positioning.

As usual totally misguided innacuracies.both antenna height above or below sea level and ground level both affect how far your signal travels amongst a myriad of other things that affects it too.

i suppose when you drive your new red pick up truck up a hill and despite your antenna being the same height above the ground but increased height in relation to sea level your signals don't improve because everything else you say defies the laws of physics so theres no reason to suppose your antennas don't too.

i ain't even getting into reactance with you.

i certainly ain't fixated about height,as i have a far better understanding off RF theory than worrying about only one small aspect of it.

 

[GnG8d]

i suppose when you drive your new red pick up truck up a hill and despite your antenna being the same height above the ground but increased height in relation to sea level your signals don't improve because everything else you say defies the laws of physics so theres no reason to suppose your antennas don't too.

That has everything to do with height above surrounding landscape and nothing to do with sea level.

 

[Captain Kilowatt]

That has everything to do with height above surrounding landscape and nothing to do with sea level.

Agreed. Professional communications people use the term HAAT which stands for Height Above Average Terrain, or in some cases EHAAT for when the height is simply Estimated. They also use AMSL for Above Mean Sea Level too but only when talking about the base of the antenna structure usually. Increased range due to increased height is due to the increase in HAAT and has nothing to do with AMSL unless you use the arguement that increaseing one is the same as increasing the other. Either way if you can't "see" beyond the average terrain it doesn't matter if you raised the antenna another 100 feet above sea level.

 

[Henry HPSD]

Hi Jazzsinger!

Although i certainly do not want to "upset" you i am in agreement with w5lz.
Please see it as "positive" critisme (my English lacks so you migth misunderstand).

I have to disagree with you.
Although signals are stronger "local" as the antenna can see futher (line of sigth communication).
For DXing it all depends on take of angle.
As mentioned there are many many variables but overall you could say..

A antenna placed higher will be better for DX
(there is no usable mystery heigth 11 meter wave length heigth etc for everyone).
The better your ground conductivity the better "ground gain" you will have.
It will also lower your take off angle!

(take in mind sproadic E propagation is another thing!!)

The "radio world service" i was refering to...they also transmit on 25mhz...so if they dont "take adventage" of it....(indeed on MW there are...other things).

I fully understand you have excaptable knowledge,as i highly appriciate your opinion.
But we all have knowledge,
For example mine comes froms guys who work for "world broadcast services"..
If they want a 500kw tranmitter location at 2000 meters cause that will be better for "short range" communication it will be done!...
(you could also bennifit of the downside you mention!).

Instead they suggest: alter TOA
Besides that, I used to be a antenna/hf/propagation instructor within the recon..
(ps also stood a year on the first staffordshire inf. reg. )
It turned out that i was in charge on the "normal" army there antenna systems aswell as it didnt function oke..
In Afghanistan we needed to have "short range" communication as the outer mountains of the Himalya block the satelliet and VHF..so we took advantege of NVIS
(near vertical incidence skywave)

Now that background is probarbly more than most "CB"users but it doesnt tell me i am rigth...if there is one thing i learned it would be to be carefull with "statements" as everything depends on each other. I could be very wrong..

What i am missing so far to my opinion is your story is based on your personal experience.
It isnt what is truly has been under investigation it neither (so far) failed to see facts.

The story we are providing however can be "backed up".

It is not for nothing in the old days people always buildt new villages near rivers/sea as the ground is good..wet...rock isnt..
It is impossible to create a "prefect" ground...but salt water comes real..real close..!

And there is a big difference in "ground gain" when one would use industrial or rock instead of salt water.

Try to keep a open mind in it and think about it for a nigth...

Ofcourse more than willing to share thoughts as mentioned higlhly appriciate the information!

As you mentioned, were here to learn and it is always difficult to interp how things are written..

Kind regards,

Henry

 

[jazzsinger]

Agreed. Professional communications people use the term HAAT which stands for Height Above Average Terrain, or in some cases EHAAT for when the height is simply Estimated. They also use AMSL for Above Mean Sea Level too but only when talking about the base of the antenna structure usually. Increased range due to increased height is due to the increase in HAAT and has nothing to do with AMSL unless you use the arguement that increaseing one is the same as increasing the other. Either way if you can't "see" beyond the average terrain it doesn't matter if you raised the antenna another 100 feet above sea level.

sadly radio waves don't stop when they hit average terrain,in many cases they pass over it,leaving only a blind spot on the other side of the higher ground due to refraction.if that was the case then from the valley i live in i wouldn't be able to work into northern ireland every single night,but i can easily,so that rules out skywave propagation modes and leaves only line of sight,refraction from the obstacle plus whatever the signal travels beyond that due to refraction again over the curvature of the earth.

as all height on this planet is measured against the mean sea level i fail to see how increasing height of the antenna in relation to sea level will not increase the line of sight distance achievable.although as you point out garth the increase is also an increase in relation to the average terrain too.

when it comes to dx via skywave that is an altogether different animal,and whether height or in fact lack of it is better is more down to the angle that the ionosphere will reflect at any given time,but the fact remains with all things equal,mast height,antenna,ground conditions and take off angle then the antenna mounted on lower ground will strike the ionospher further away barring any obstacles in its path,which in turn means the signal coing from the ionospher will leave a dx footprint further away.

try drawing it on a piece of paper and you will see what i mean.the angle of reflection is equal to the angle of incidence barring there being any refraction.

to use world service style transmission to say height is better for dx can't be compared to dx at high frequencys as they generally use much lower frequencies where groundwave is predominant or rely on skywave for extended coverage, ithink you'll find they use the height to increase their groundwave signal and accept that if they use a low take off angle they will also have significant skip distance as well.

i accept an antenna placed higher in relation to ground will lower the take off angle and increase both dx and line of sight,but thats not what i'm getting at here.i am getting at two antennas with the same height relation to ground and the same ground conditions/take off angle but their actual elevation relative to sea level or mean terrain,whichever you prefer.

 

[Captain Kilowatt]

I say that the vertical beamwidth of an antenna's major lobe is broad enough to negate any minute difference that one may possibly, but not likely, see from having an antenna "further from the ionosphere" by placing it at a lower elevation in reference to sea level. The difference in the angle of incidence is just plain too minute to make a difference. I fully understand what you are sy=aying but I disagree with the results that you expect to find.