NEC2 model of 40m loaded cubical quad
 

Hi - I am trying to play around with modeling a loaded 40 meter
cubical quad. To start I made a single loop the size I wanted (about
2/3 full size) - I then looked at the impedance on 7.1Mhz. I added a
load (inductance) to bring the loop to resonance on 7.1Mhz. I then
created some parasitic elements - a director and reflector. I used the
same value load for these elements. Now, can I just adjust the lengths
of the wires to tune the feedpoint impedance and directivity and leave
the value of the load alone? Or is there some reason I will need to
adjust those values too? I placed the load opposite the feedpoint,
FYI.

-Scott, WU2X

NEC2 model of 40m loaded cubical quad
 

On Dec 14, 11:16�am, Scott M wrote:
Hi - I am trying to play around with modeling a loaded 40 meter
cubical quad. To start I made a single �loop the size I wanted (about
2/3 full size) - I then looked at the impedance on 7.1Mhz. I added a
load (inductance) to bring the loop to resonance on 7.1Mhz. I then
created some parasitic elements - a director and reflector. I used the
same value load for these elements. Now, can I just adjust the lengths
of the wires to tune the feedpoint impedance and directivity and leave
the value of the load alone? Or is there some reason I will need to
adjust those values too? �I placed the load opposite the feedpoint,
FYI.

-Scott, WU2X

Hi Scott, Seems to me since this is a quad that your goal is maximum
gain or F/B. As such, I would adjust the loads and element spacing
keeping the element lengths constant, until you have the current
distribution in the elements optimum for your goal. Then check the
source impedance, and if it is not too bad, devise a way to match.
Suggest that instead of a single load opposite the source, use two
loads, should help with current distribution. Good luck.

Gary N4AST

NEC2 model of 40m loaded cubical quad
 

Gary,

I wrote some code to automate the optimization of the quad for my
goals - but my code only deals with element length, so I am hoping
that I don't need to add more code to manipulate the value of the load
too.

-Scott, WU2X


On Dec 14, 5:23*pm, wrote:
On Dec 14, 11:16 am, Scott M wrote:

Hi - I am trying to play around with modeling a loaded 40 meter
cubical quad. To start I made a single loop the size I wanted (about
2/3 full size) - I then looked at the impedance on 7.1Mhz. I added a
load (inductance) to bring the loop to resonance on 7.1Mhz. I then
created some parasitic elements - a director and reflector. I used the
same value load for these elements. Now, can I just adjust the lengths
of the wires to tune the feedpoint impedance and directivity and leave
the value of the load alone? Or is there some reason I will need to
adjust those values too? I placed the load opposite the feedpoint,
FYI.

-Scott, WU2X

Hi Scott, *Seems to me since this is a quad that your goal is maximum
gain or F/B. *As such, I would adjust the loads and element spacing
keeping the element lengths constant, until you have the current
distribution in the elements optimum for your goal. *Then check the
source impedance, and if it is not too bad, devise a way to match.
Suggest that instead of a single load opposite the source, use two
loads, should help with current distribution. *Good luck.

Gary N4AST

NEC2 model of 40m loaded cubical quad
 

It will be much easier to make the two elements exactly the same
in terms of wire lengths, and just increase the load for the
reflector element.

Tor
N4OGW

NEC2 model of 40m loaded cubical quad
 

On Dec 14, 10:03�pm, Scott M wrote:
Gary,

I wrote some code to automate the optimization of the quad for my
goals - but my code only deals with element length, so I am hoping
that I don't need to add more code to manipulate the value of the load
too.

-Scott, WU2X
- Show quoted text -

OK, for modelling purposes, you can keep the load constant, and vary
the element lengths. From a practical standpoint, if you have this
beast up in the air, tuning is easier with a tapped inductor.

Other factors that will effect the gain and F/B are the element
spacing, and how high you can get the thing. Practically, these are
not things you can change easily.

I just did a quick 2 element 66% (reflector) quad in a diamond
configuration with 17' spacing on EZNEC, and got a 10.25 dbi gain at
35 degrees. F/B about 13 db. Feedpoint impedance was 44+j0 with a
678pf shunt capacitor. The element lengths were the same on both,
varied loads to get max gain and best match. The center of the
diamond was 50' up.

Gary N4AST