4 - ELEMENT QUAD HELP NEEDED

[unit_399]

I lost my 2-element quad in a severe storm about 6 months ago, and am building a 4-element quad replacement. In a few days, I'll be ready to string the wire on the elements. I'm using #10 enameled motor winding wire on the driver element, and want to use #16 enameled wire on the 3 parasitics. I'm no antenna guru, and was wondering if using a different wire gauge on the parasitic elements vs the driver will affect performance ?? Common sense tells me that it won't make any difference, but I want to be certain before I build it and put it up. I was hoping that Henry, or Marconi, or HomerBB, or any of the other antenna experts on this forum have an opinion. Thanks and 73s

- 399

 

[Captain Kilowatt]

It won't make any difference except for strength and durability . The may be a very slight narrowing of bandwidth but it likely it will be imperceptible.

 

[Robb]

Gonna take any pics?

 

[Henry HPSD]

Hello,

No guru either....but very enthousiastic

Take a look at your antenna like this:

Example:
Your radiator has a "resonant" frequency of 27.0 Mhz
now, the directors are shorter...so the individual resonant frequency will be sligthly higher. If we would take the directors away from the quad and measure them seperatly you could come up with (for example)
27.2 ..27.4..27.6 MHz.

Now, those resonant frequencies equals length of the loop.
If your really into "beams" you tend to start thinking in "resonant frequency" rather then lengths.
There are a quite a couple things that influence that resonant frequency.
Two of them are : diameter and secondly if its bare ware or insulted.
It is very plausible the resonant frequency will shift several 100 Khz's by changing diameter etc.

Say you or someone else has done there homework and designed a beautifull 10+ dBI 4el cubical quad.
The length of the element is based on the resonant frequency.
If this is designed with #10 bare and your going to use # 16 it is logical the resonant frequency will shift, providing slightly off optimum respons.

Wheter or not the effect is there, can be confirmed in moddeling software.
And if it can be "spotted" using software...it still is the question wheter or not anyone can hear the difference in "real life".
We all do our best to "gain" 0,1 dB extra...but in reallity no one can notice of course.
However, you have asked the question, so wheter or not anyone can "hear" the difference the question probarbly lies a bit more in the direction of: Would you be happy with the thougth that it migth not perform to its potential ? I guess not, so:

Wise would be to get confirmation if it is still "within the limites".
My best guess would be you have a "plan" for a 50 ohms direct fed 4el quad.
If that is the case, it would be more reason to get confirmation as diameter will effect ALL parameters, including impedance.

But heck, im often too precise...and its not nuclaire sciences were talking about hihi

Hope it helped !

Kind regards,

H.

 

[Captain Kilowatt]

Since most of the RF current is in the driver element changing it would have the most effect. The parasitic elements, while affected, would not make a bjg difference as far as performance goes. Yes the freq may be shifted a bit but you compensate with length. Using different size wire for the different elements won't really burt anything. I really cannot see it changing a couple hundred KHz going from 10 ga. to 16 ga. on tbe parasitic elements.

 

[Henry HPSD]

Not wanting to irritate you, but as you you mention ...you cant "see" this happening.
Well, we have a >50 percent change that is correct...totally agree.
But do we know for a fact ?

It all depends on the design he is using.
I have seen and measured it many times.
As stated above wheter or not in this case the effect will be noticable will depend on the design of the antenna. If its a "forgiving" design...(which it probarbly is)...no problem what so ever.
If it is not...the effect will be there.

Wheter or not the most amount of current is in the radiator lies again in the design.
Most people dont realize:
You can not state without futher investigation that it is in the radiator.
There are quite some beam antenna designs, where this is not the case.

Wise for him would be to get confirmation...

Hope it helped,

Kind regards,

Henry

 

[Captain Kilowatt]

Any antenna I have seen has the most RF current in the driver element and first director with negligible current in the reflector and further directors. I would like to see some directional parasitic antennas where most of the RF current is somewhere other than the driver or first director. Any examples?

 

[vkrules]

If the original design calls for# 10 and you use #16 you will have to make the #16 loops 8 cm shorter. bandwidth and gain will be slightly less.(not enough to worry about)

 

[vkrules]

Insulated wire will be 3 to 5% shorter.

 

[wavrider]

399 some great info here from forum members,
So to break it down a PURIST will analyze every element of the quad and make sure it is resonant on the frequency it needs to be to get the maximum performance out of the antenna.

In reality us antenna experimenters and cheap ass ham guys will build an antenna out of whatever we have laying around.

Use what wire you have, build it to the best dimensions you can find to suit your needs get the antenna in the air and make some contacts before the solar cycle is gone.

Most of all, HAVE FUN

 

[Captain Kilowatt]

Agreed. Most of us don't really completely design an antenna anyway and simply follow a tried and true example making slight changes along the way to suit the materials on hand etc. Worrying about an extra tenth of a dB at the expense of a perfect match is a bit much. Any antenna I have built, and there have been lots, surely could have been tweaked a bit better however I was on the air with a really good antenna long before I ever could have tweaked the death out of it.

 

[2RT307]

Agreed. Most of us don't really completely design an antenna anyway and simply follow a tried and true example making slight changes along the way to suit the materials on hand etc. Worrying about an extra tenth of a dB at the expense of a perfect match is a bit much. Any antenna I have built, and there have been lots, surely could have been tweaked a bit better however I was on the air with a really good antenna long before I ever could have tweaked the death out of it.

I'll give you two big thumbs up on that! I know too many guys that spent hours and hours trying to get their SWR perfect. All time that could have been spent on the air with a 1.3:1 ratio instead!

I'm anxious to see how 399's antenna turns out. The 4 element quad I built years ago was pretty clumsy, but it worked well. Sounds like he's got a sleeker design going up to beat the weather!

73,
Brett

 

[vkrules]

Take some pics A 4el quad is a beautiful thing .My wife and family don't agree though.

 

[Henry HPSD]

Since most of the RF current is in the driver element changing it would have the most effect. The parasitic elements, while affected, would not make a bjg difference as far as performance goes.

Wheter or not the most amount of current is in the radiator lies again in the design.
Most people dont realize:
You can not state without futher investigation that it is in the radiator.
There are quite some beam antenna designs, where this is not the case.

Henry

Any antenna I have seen has the most RF current in the driver element and first director with negligible current in the reflector and further directors. I would like to see some directional parasitic antennas where most of the RF current is somewhere other than the driver or first director. Any examples?

Hello Captain Kilowatt,

I was not expecting an answer like that from a you as a person or as a staff member.
Either you did know ...but in that case an answer like:
"owh, yes...almost forgot! Tnx ! Indeed, sometimes most current lies in the prasitic elements like the 1st director.
Or you didnt knew ..: A possible answer could be : Heck, i didnt knew that...thanks for the update !

However, you have provided an answer in which you now seem to agree that it is not always the radiator. By doing so, you have changed your intitial statement.
Though you are asking me the same question, that isnt really logical is it ...

There are a couple of reasons why a person would do that.
But my best guess would be ....you didnt notice...that is what i am hoping.
If know this forum to be friendly, and accurate...
Changing things, or leaving things open for wrong interpertation...
That is for politics, im an ethousiast not a floraholic who want to be right.

Now, back to your question.
If the amount of current in director nr 1 is higher copared to the radiator the antenna often is a "50 ohms OWA" version.

Besides that first director, there are antennas where other parasitic elements have the highest amount of current.
So to your last question asked...yes there are.
But providing an answer should be usefull...helping...
If the possibility is there that the question asked will not remain the same, I respectfully will leave that question where it is.

Kind regards,

Henry

 

[Captain Kilowatt]

Hello Captain Kilowatt,

I was not expecting an answer like that from a you as a person or as a staff member.
Either you did know ...but in that case an answer like:
"owh, yes...almost forgot! Tnx ! Indeed, sometimes most current lies in the prasitic elements like the 1st director.
Or you didnt knew ..: A possible answer could be : Heck, i didnt knew that...thanks for the update !

However, you have provided an answer in which you now seem to agree that it is not always the radiator. By doing so, you have changed your intitial statement.
Though you are asking me the same question, that isnt really logical is it ...

There are a couple of reasons why a person would do that.
But my best guess would be ....you didnt notice...that is what i am hoping.
If know this forum to be friendly, and accurate...
Changing things, or leaving things open for wrong interpertation...
That is for politics, im an ethousiast not a floraholic who want to be right.

Now, back to your question.
If the amount of current in director nr 1 is higher copared to the radiator the antenna often is a "50 ohms OWA" version.

Besides that first director, there are antennas where other parasitic elements have the highest amount of current.
So to your last question asked...yes there are.
But providing an answer should be usefull...helping...
If the possibility is there that the question asked will not remain the same, I respectfully will leave that question where it is.

Kind regards,

Henry

Nothing wrong with my statement whatsoever Henry. I made a statement that you said was wrong. I then said that every antenna I have seen acted the way I said it did and thought that perhaps maybe I was wrong and asked for an example to help me understand what you were talking about better. Simply saying "Ooops I was wrong you are right" teaches me nothing. Agreed? Providing an example of such an antenna and a little explanation of currents and operation would indeed actually teach me something would it not?

Don't go thinking thatt there was more to the question that that. There was NOT.