CocoaNEC EZNEC Model

[Happy_Hamer]

Is there a EZNEC "guru" that can check out the antenna project we have in the ham radio antenna section please?

http://www.worldwidedx.com/amateur-radio-antennas/114078-gizmotchy-antenna-revisited.html

I do not understand the program and I am on a Mac.

Thanks

 

[Henry HPSD]

Hello!

I dont truly understand what your question is regarding enzec, the post gives me the idea
You are asking about the gamma-match details?

The rod thickness of the gamma-match should be 1/2 size of the radiating element and the length approx 0,05 wl long.

If the antenna would be a "scale" model of the 11 meter version the boom would be roughly
half the size (eg 27versus 50 Mhz) its not 12 foot compared to 9 foot.
Futher more the element thickness should be roughly 1/2 size of the 11 meter version.

If you do insert the model into eznec make sure you include the boom and mast..
if i recall correct they didnt do that on the 2 meter model, while they should have done that on 2 meters BC is very important.

The best i actually remember: i believe they had to change the entire antenna in order to get some normal gain/fb. That says enough.

Anyway if you do have any questions about enzec feel free to mail me.

Kind regards,

Henry
www.dx-antennas.com

 

[Henry HPSD]

Hello!

I dont truly understand what your question is regarding enzec, the post gives me the idea
You are asking about the gamma-match details?

The rod thickness of the gamma-match should be 1/2 size of the radiating element and the length approx 0,05 wl long.

If the antenna would be a "scale" model of the 11 meter version the boom would be roughly
half the size (eg 27versus 50 Mhz) its not 12 foot compared to 9 foot.
Futher more the element thickness should be roughly 1/2 size of the 11 meter version.

If you do insert the model into eznec make sure you include the boom and mast..
if i recall correct they didnt do that on the 2 meter model, while they should have done that on 2 meters BC is very important.

The best i actually remember: i believe they had to change the entire antenna in order to get some normal gain/fb. That says enough.

Anyway if i did miss any other enzec questions please feel free to forward them,

Kind regards,

Henry
www.dx-antennas.com

 

[Happy_Hamer]

I guess I was talking about the spacing of the elements as well. Like noted on the 2 meter, the elements were optimized because the original directions assembled it "wrong"

So on this 4 element 6 meter it shows the elements all at 35 inches apart, which seems a little odd to me????

 

[Happy_Hamer]

As for the boom diameter, the 10/11 meter and 6 meter both use a 1 1/4 inch diameter boom.

The Boom for the 4 element 10/11 meter is 12 foot and some change, the boom for the 6 meter is 9 foot. They all use the same "hubs" on all three antenna, 2 meter 6 meter and 10/11 meter.

I appears the gamma match plate (where the SO-239 is) is the same for the 10/11 and 6 meter. The tubes for the gamma are the same diameter tubing, just different lengths which I have also posted that info in the post.

The element diameter for 10/11 meter are both 1/2 inch and 3/8 inch diameter

So using that info, are the directions for the 6 meter "optimized" from GIZ or do I need to change it somewhat like what was done with the 2 meter?

I do not know how to use eznec to see if that is true or should I just use the Giz 6 meter assembly directions and be done with it?

 

[Henry HPSD]

just did a quick run and got up with over 9,1 dB in forward gain and 13 dB in front to back.
So it is a lot better than the 2 meter version but probarbly the FB could be improved abit..
have to take a look into that when time permits.
Didnt include the gamma-match in the model yet..will do that next time aswell.

Dont think the gain can be improved..9,1 is already quite an amount from a 6foot boom on 6 meters.
The antenna seems to be resonant a bit low in freq (49,8Mhz) though the gamma-match will take care of that.

Kind regards,

Henry

 

[Happy_Hamer]

Dont think the gain can be improved..9,1 is already quite an amount from a 6foot boom on 6 meters.

Kind regards,

Henry

THANKS, although it is a 9 foot boom, maybe you meant to type 9 foot but put 6 foot?

I have a bit more info if that will help.

The 1/2 inch element tubes are 28 and 3/4 inches

The 3/8 inch element tubes are 36 inches long

So one just has to assemble in the normal telescoping fashion to get the required lengths.

Here is a partial 6 meter list

 

[Henry HPSD]

indeed 9 foot, rougly 2,7 meters boomlength.
Had that 6 meters thingy in my mind..

Regards,

Henry

 

[Moleculo]

That gain really does seem pretty good for 4 elements. I'm pretty sure the F/B can be improved with spacing changes, but the EZNEC model will have to prove it...

 

[Happy_Hamer]

Well I downloaded cocoaNEC 2.0 for a Mac

cocoaNEC

Now if I can just figure out how to use it

 

[Captain Kilowatt]

That gain figure of 9.18 dBi is about what one would expect from a four element array. It's only 7 dB over a dipole and a good four element should be able to provide that easily.Cushcraft's A503S which is a three element yagi has 8 dBi on a 6 foot boom with a F/B of 20 dB and the A505S is a five element yagi on a 12 foot boom and has 10.8 dBi gain and a F/b of 24 dB so the gain figure for the Giz looks about right but the F/B could be a few dB better.

 

[Happy_Hamer]

That gain figure of 9.18 dBi is about what one would expect from a four element array. It's only 7 dB over a dipole and a good four element should be able to provide that easily.Cushcraft's A503S which is a three element yagi has 8 dBi on a 6 foot boom with a F/B of 20 dB and the A505S is a five element yagi on a 12 foot boom and has 10.8 dBi gain and a F/b of 24 dB so the gain figure for the Giz looks about right but the F/B could be a few dB better.

That is what I am hoping with some modeling, to me the 35 inch spacing for each element set seems "generic" to me

 

[Captain Kilowatt]

Agreed. Usually the reflector is spaced a bit further from the driven element than the first director is. Playing with spacing will also affect the feedpoint impedance a bit too.

 

[Happy_Hamer]

Well look at the assembly thread now, you will see where it is using only the assembly directions from Giz with no other adjustments :thumbdown:

http://www.worldwidedx.com/amateur-radio-antennas/114078-gizmotchy-antenna-revisited.html

 

[Happy_Hamer]

OK Henry HPSD,

I hope you have read my thread with this antenna assembly thus far?

You sent me a PM and said to ask you the specific question so we can get this set up.

Here we go

The 6 meter giz antenna I modified is as follows;

The boom is 1 1/4 inch O.D., it is 8 foot 11 3/4 inch long

The elements are assembled in a telescoping fashion.

The first part of all the elements are 1/2 inch O.D tubing. and are 28 and 3/4 inch long.

Inside each element is a 3/8 inch O.D. tubing that is 36 inches long.

Once the 3/8 tubing is inside the 1/2 inch tubing the element lengths are as follows

ELE 1 = 53 inches
ELE 2 = 54 inches
Driven ELE = 58 and 1/4 inch
Ref = 59 inches

When the elements are measured, the directions say measure from the bottom of the element to the top of the element. So "technically" there is an extra 1/4 inch on each one because the hub it attaches to is 1/4 inch thick. Am I correct in assuming that?

The spacing of the elements are as follows. From center element to center element is 35 inches spacing on each one from the first element to the reflector. I measured the left over of the boom after the reflector, it is 2 inches.

The Gamma Matches are as follows;

The spacing from the center of the gamma tube to the center of the driven element is 3 and 1/4 inch on both vertical and horizontal.

The outer tube of the gamma is 3/4 inch O.D. tubing that is 4 and 1/2 inches long.

Inside the the outer tubing is 5/8 inch O.D. nylon tubing with a 1/2 I.D and is 4 and 3/4 inch long. The inner gamma tube is aluminum 1/2 O.D. and the length is 5 and 1/2 inches long

Giz inserts that piece of aluminum 1/2 inch O.D. tubing inside the nylon and epoxies it so it has 1 inch of the aluminum tube sticking out the top of the nylon.

Then they insert a 3/8 inch O.D. aluminum tubing that is 6 inches long for the vertical side of the antenna inside the 1/2 inch tubing to telescope to a length of 9 and 1/2 inches long where it connects to the shorting rod.

The horizontal side of the gamma is identical except the 3/8 tube that connects to the shorting rod is 7 inches long, it is still telescoped to the shorting rod the same 9 and 1/2 inches.

I get a 1.8 SWR at 50.122 mHZ and 18 ohms impedance.

I get a 1.5 SWR in the 49 mHZ range with 17 ohms impedance

Can you use the above information to model the antenna and see what results you show and possibly see if the model would show a way to improve?

Also I am confused with the gamma lengths, how can both vertical and horizontal be a total length of 9 and 1/2 inch long? I understand the 6 inch tube and 7 inch tube could make a difference, but what to I move to adjust SWR? the length of the tube or the height of the shorting bar? Or Both?

Any help is appreciated