GIZMOTCHY ANTENNA REVISITED 6 METER

[Happy_Hamer]

I will add this partial parts list to the mix here for the elements.

The 10/11 meter element have to obviously be cut down for 6 meter,

the 10/11 meter elements are as follows,

1/2 inch diameter tubing is 48 inches long

3/8 inch diameter tubing is 64 inches long

For 6 meter they need to be as follows,

1/2 inch diameter tubing is 28 3/4 inches long

3/8 inch diameter tubing is 36 inches long

So far this seems easy enough

 

[Happy_Hamer]

Well I finally got all the components cut down to size for 6 meter based on the list from Giz (See Attached)

It was pretty straight forward so I am not going in to detail about cutting the tubes down to size. Once we cut the tubes to proper length we had to cut the slits back into the ends so it can tighten to the hub.

But the thing that concerned me was that I still have to tighten the 1/2" element tubes to the hubs. On the 11 meter assembly the automotive hose clamps would "strip" out trying to tighten so they would stay on the hub.

So I went in search of better clamps and ended up at Menard's. There is not much of a choice for clamps out there. I ended up with more automotive style hose clamps. This time though, we made a change.

The elements from Giz has two slits cut in the bottom of the tube, we cut two extra slits for a total of four slits. Our thoughts were that it would "squeeze" the hub tighter. (See Images)

IT WORKED!!! We assembled it with minimal effort to tighten down. When shook violently, the clamp held the element on very well.

 

[Robb]

Xnt.

Did you cross drill into the beam to keep the hubs themselves from rotating too?

Do you have an MFJ-259B to help dial this puppy in?

What dimensions did you choose for the spacing? Gizmotchy or Henry HPSD's - or maybe a computer optimizing program?

 

[Happy_Hamer]

Final assembly was just looking at the picture in the assembly instructions

Not really much detail, like adjusting the gamma. Do you adjust the center rod or the shorting bar? or both?

Attached are the pictures of the final assembly and the results on the MFJ meter.

You can see with no adjustments the antenna SWR was at 1.8 at 50.122 MHz with an impedance of 18 ohms. I was able to get a 1.5 at 49 MHz but still 17 ohms of impedance.

It was 104 here today with high humidity so we stopped after we seen we were in the "ball park".

More to come........

 

[Moleculo]

You need to raise the antenna up a bit and see what the analyzer says. Maybe you already did that...can't tell from the pic?

 

[Happy_Hamer]

That was a plan because with this tripod i was able to get maybe 7 foot from the ground to the boom. Getting things cut to size and assembled was my first task.

Here is a question though, let's say I do not adjust anything and raise it higher in the air, I ASSume the impedance would drop even further?

You need to raise the antenna up a bit and see what the analyzer says. Maybe you already did that...can't tell from the pic?

 

[Happy_Hamer]

Just to keep everyone up to speed, here is how I assembled the antenna;

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

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 do I move to adjust SWR? the length of the tube or the height of the shorting bar? Or Both?

 

[Robb]

I'm no expert on beams. But when I set up the Sirio 4 element I use, I was told by someone who did this before to rest the beam on the reflector and then point the beam straight up. This allows you the freedom to make the adjustments easier - and it does. I secured the beam with the mast and on the other end of the mast to a clamp and the fence - so it wouldn't fall when trying to adjust it. Then I used the MFJ analyzer to adjust the Gamma. I first slid the gamma rod in and out until I got the lowest SWR. Then I moved the slider bracket back and forth on the gamma rod and the element until I got a flat match. Got the same readings after I put it up too.

Just sayin . . .

 

[Captain Kilowatt]

Here is a question though, let's say I do not adjust anything and raise it higher in the air, I ASSume the impedance would drop even further?

I believe you will find the impedance will go UP a bit.Proximity to the antenna tends to drive the impedance down.

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 do I move to adjust SWR? the length of the tube or the height of the shorting bar? Or Both?

The real answer is YES.

Actually you should adjust the shorting strap for an impedance of somewhere near 50 ohms while disregarding the reactance and then adjust the length of the tube to cancel out the reactance. These adjustments interact somewhat so it can get tedious and you may even have to adjust the spacing between the tube and the element if nothing works for you at all.

I'm no expert on beams. But when I set up the Sirio 4 element I use, I was told by someone who did this before to rest the beam on the reflector and then point the beam straight up.

That is the best way to decouple the antenna from the effects of being close to the ground. things may still change a bit when the antenna is in the final operating position but the change will not be as drastic as if the antenna was in a normal configuration.