.64λ Homebrew

[HomerBB]

I made my first 43 div contact with the .64 homebrew today.

Peter_43WR789-----Melbourne,AU and I got connected on .385 and QSY .405

Conditions could have been better, but I felt good about it under the circumstances of being in a DX drought my way.

 

[Marconi]

I made my first 43 div contact with the .64 homebrew today.

Peter_43WR789-----Melbourne,AU and I got connected on .385 and QSY .405

Conditions could have been better, but I felt good about it under the circumstances of being in a DX drought my way.

I'm having the same here on the Gulf Coast of Texas. I can hear one sided DX, but the signals are weak.

I talked to Hawaii yesterday on my Starduster. I could hear Australia in the back ground, but I just couldn't reach that far. It has been sort of quiet here too.

Maybe around dusk time I'll hear Western Europe in here again.

 

[HomerBB]

Up on the platform working on the antenna again.

 

[Needle Bender]

I hope those diagonal platform braces are strong!


________________

I used to think I was smart, but now that I'm briliiant, I realize I'd be stupid to think I'm that intelligent.

 

[HomerBB]

They'll do. They're the same as those bracing the bottom post of the mast.

 

[2RT307]

Um, just don't try to get me up there, Homer! I am fluffy, but I don't bounce.

Looking good!

73,
RT307

 

[HomerBB]

You can throw the tools up to me.

Worked on the antenna some more, and not so sure I've noted any improvements from the analyzer standpoint.
I put on a cap hat just to see if it made any measurable difference. It has an overall diameter of 14".
I had to work at an acceptable shortening length for the antenna vertical, and ended up a mere 10" shorter than previous to installing the thing.

I also went back to a smaller nearly square coil modeled from the Shockwave antenna coil - 4.5" tall x 4" OD x 6 exact wraps. This is around the vertical rather than off to the side as I usually do. It may get changed . . .

I sat on the platform with the antenna at 18.5' and attempted to tune it with the single 1/2λ coax until I felt I was too tired to continue and said good enough for now. 27.400 was a 1.2 SWR, R43, x8 when working there.

So here's the result with the antenna at 34' elevation, and using first the 6 x 1/2λ coax. and then measuring from the shack.
I scoped the P/U pole out an additional 15.5' and climbed down to take some measurements.

Here they are:

------------1/2λ x 6 coax -------------------------------------------------- at Shack end of coax run

2.0 --- 24.214 --- R27 -- X13 ------------------------------------------ 26.262 --- R72 -- X41
1.5 --- 26.439 --- R44 -- X20 ------------------------------------------ 26.647 --- R48 -- X20
1.2 --- 26.965 --- R40 -- X6 ------------------------------------------- 1.0 -------- R46 -- X2
1.1 --- 27.185 --- R42 -- X2 -------------------------------------------- 1.2 -------- R51 -- X10
1.1 --- 27.400 --- R45 -- 0 ---------------------------------------------- 1.4 -------- R62 -- X16
1.0 --- 27.555 --- R47 -- X3 -------------------------------------------- 1.5 -------- R66 -- X29
1.5 --- 28.728 --- R39 -- X15 ------------------------------------------ 28.210 --- R74 -- X14
2.0 --- 29.374 --- R25 -- X5 -------------------------------------------- 28.600 --- R82 -- X35

Best:
27.732 -- 1.0 R55 X0 --------------------------------------------------- 26.983 -- 1.0 R46 X1

 

[High Voltage Mobile NJ]

I worked on this thing some more today trying to prove to myself it could be done.
Here is what I did and the results.

First using this coil:

2.0 R= 28 X= 21 --------- 28.713
1.5 R= 56 X= 21 --------- 28.108
1.2 R= 61 X= 7 ----------- 27.804 (lowest)
1.2 R= 53 X= 9 ----------- T5
1.2 R= 50 X= 11 ---------- 27.405
1.3 R= 52 X= 14 ---------- 27.185
1.5 R= 61 X= 22 ---------- 26.869
2.0 R= 110 X= 0 ---------- 26.244


Second using this coil:

2.0 R= 28 X= 20 ---------- 28.769
1.5 R= 53 X= 23 ---------- 23.243
1.1 R= 51 X= 5 ---------- 27.706 (lowest)
1.1 R= 52 X= 8 ---------- T5
1.2 R= 49 X= 10 ---------- 27.405
1.3 R= 51 X= 14 ---------- 27.185
1.5 R= 59 X= 22 ---------- 26.884
2.0 R= 110 X= 0 ---------- 26.249


Third using second coil and adding 10" to length to compensate for the portion of the vertical beneath the radials:

2.0 R= 27 X= 19 ---------- 28.814
1.5 R= 51 X= 23 ---------- 28.293
1.1 R= 60 X= 0 ---------- 27.754 (lowest)
1.1 R= 51 X= 6 ---------- T5
1.2 R= 48 X= 9 ---------- 27.405
1.3 R= 50 X= 13 ---------- 27.185
1.5 R= 59 X= 21 ---------- 26.859
2.0 R= 108 X= 0 ---------- 26.225


AT THE SHACK END OF THE FEEDLINE:

homer you are a genious now !!!!! you just figured it out .
keep your coil always in the focal point of the radiation which the antenna faces . that aluminum coil is the way to go anyway . the other way you had was creating another frequency wave , thats why you had alot or reactance . id lower the antenna down about 4 to 8 inches now so you will resonate more on channels 1 through 40 , unless you talk higher up.
awsome job !!!!!!

 

[W5LZ]

Two questions.
Is it possible to move the radial plate further down the support pole so that the actual connection of the top of the coil is further down the vertical element. That's to remove any metal from the center of the coil.
And the second question is what is the circular thingy hanging under the radials on the right side of the picture, a choke?
- 'Doc

 

[HomerBB]

Thanks HVNJ.

Doc, I am still experimenting, so the possibility exists to lower the top of the coil, however that would mean compressing the coil more seeing the bottom can't go any farther South.
That could be a good thing. And, yes, that is a choke you see.

 

[W5LZ]

What I'm getting at is that the vertical element being inside the coil does affect the impedance of that coil, increases it to some extent. Getting it out of the coil eliminates that variation.
- 'Doc

 

[HomerBB]

What I'm getting at is that the vertical element being inside the coil does affect the impedance of that coil, increases it to some extent. Getting it out of the coil eliminates that variation.
- 'Doc

Yes, Sir, I get you.
I may have that to do as I'm still experimenting with it. It was not, nor is it the first choice for coils any longer, but because the Shockwave antenna utilizes it I wanted to try it and see where it took the antenna.

I took some much more gradual readings of the antenna in its latest configuration today @ 34' elevation:

29.350----2.0----R24--X4
29.250----2.0----R25--X2
29.150----1.9----R26--X5
29.050----1.8----R28--X8
29.000----1.7----R29--X10
28.950----1.7----R30--X12
28.900----1.7----R32--X12
28,850----1.6----R34--X14
28.800----1.1----R57--X2
27.950----1.1----R57--X0
27.900----1.1----R56--X0
27.850----1.1----R57--X0
27.800----1.0----R56--X0
27.750----1.0----R54--X0
27.700----1.0----R53--X2
27.650----1.0----R51--X3
27.600----1.0----R50--X3
27.550----1.0----R48--X3
27.500----1.0----R46--X2
27.450----1.1----R45--X1
27.400----1.1----R45--X1
27.350----1.1----R44--X0
27.300----1.1----R43--X0
27.250----1.1----R43--X0
27.200----1.1----R42--X2
27.150----1.2----R42--X3
27.100----1.2----R41--X4
27.050----1.2----R41--X5
27.000----1.2----R40--X5
26.950----1.2----R40--X6
26.900----1.3----R40--X6
26.850----1.3----R39--X7
26.800----1.3----R39--X9
26.750----1.3----R39--X10
26.700----1.4----R40--X12
26.650----1.4----R39--X13
26.600----1.4----R40--X15
26.550----1.5----R41--X16
26.500----1.5----R42--X18
26.450----1.5----R43--X19
26.400----1.5----R44--X21
26.350----1.6----R45--X23
26.300----1.6----R47--X24
26.250----1.6----R49--X26
26.200----1.7----R51--X27
26.150----1.7----R55--X28
26.100----1.7----R58--X29
26.050----1.7----R61--X30
26.000----1.8----R65--X30
25.950----1.8----R69--X30
25.900----1.8----R73--X30
25.850----1.9----R79--X29
25.800----1.9----R84--X26
25.750----1.9----R90--X22
25.700----1.9----R95--X15
25.650----2.0----R100-X0

 

[Marconi]

You can throw the tools up to me.

Worked on the antenna some more, and not so sure I've noted any improvements from the analyzer standpoint.
I put on a cap hat just to see if it made any measurable difference. It has an overall diameter of 14".
I had to work at an acceptable shortening length for the antenna vertical, and ended up a mere 10" shorter than previous to installing the thing.

I also went back to a smaller nearly square coil modeled from the Shockwave antenna coil - 4.5" tall x 4" OD x 6 exact wraps. This is around the vertical rather than off to the side as I usually do. It may get changed . . .

I sat on the platform with the antenna at 18.5' and attempted to tune it with the single 1/2λ coax until I felt I was too tired to continue and said good enough for now. 27.400 was a 1.2 SWR, R43, x8 when working there.

So here's the result with the antenna at 34' elevation, and using first the 6 x 1/2λ coax. and then measuring from the shack.
I scoped the P/U pole out an additional 15.5' and climbed down to take some measurements.

Here they are:

------------1/2λ x 6 coax -------------------------------------------------- at Shack end of coax run

2.0 --- 24.214 --- R27 -- X13 ------------------------------------------ 26.262 --- R72 -- X41
1.5 --- 26.439 --- R44 -- X20 ------------------------------------------ 26.647 --- R48 -- X20
1.2 --- 26.965 --- R40 -- X6 ------------------------------------------- 1.0 -------- R46 -- X2
1.1 --- 27.185 --- R42 -- X2 -------------------------------------------- 1.2 -------- R51 -- X10
1.1 --- 27.400 --- R45 -- 0 ---------------------------------------------- 1.4 -------- R62 -- X16
1.0 --- 27.555 --- R47 -- X3 -------------------------------------------- 1.5 -------- R66 -- X29
1.5 --- 28.728 --- R39 -- X15 ------------------------------------------ 28.210 --- R74 -- X14
2.0 --- 29.374 --- R25 -- X5 -------------------------------------------- 28.600 --- R82 -- X35

Best:
27.732 -- 1.0 R55 X0 --------------------------------------------------- 26.983 -- 1.0 R46 X1

Homer, since the tuned lines do not seem to be doing what you thought would result in the beginning, which of the two "Best" readings above do you consider to likely be most accurate?

IMO, connecting the ends of those 14" stingers would tend to make the Top Hat a lot longer than just the 28" diameter would suggest. I would be surprised if only a 10" reduction in radiator length would reinstate the original resonance, but I could be wrong.

You may have already changed your antenna, but I would like to better understand the effects of the mode you made, since you used a style of Top Hat that I believe will present a lot more capacitive affect than you might think.

Of course I don't have your antenna modeled, but I have a tuned up I-10K with the trombone matcher attached. It also has a typical Top Hat, and it is resonant at 27.205 mhz with a low SWR match. I will add a hoop to the tips of the Top Hat, lower the radiator 10" similar to what you did, and then I'll report my modeling results, for Antenna View, SWR, and Source...which represents the match at the feed point and we'll see which way resonance goes in a similar situation using modeling.

 

[Marconi]

Marconi's models for Homer Top Hat version his 5/8 wave

Here are four models, modeled over Eznec5's real Earth feature. The first is my I-10K model with a trombone matching device that allows the antenna to appear tuned at 50' feet in height. I have added the dimensions to the models, and each model shows the Antenna, SWR chart, Source Data which shows SWR, R, and X values at the feed point.

Model #2, is a generic Exnec model of a 5/8 wave without a matcher added to provide us with the natural match. This is done to indicate that such an antenna needs a matcher, and suggest to us what we might expect with any 5/8 wave radiator and suitable ground plane attached at 50' feet high.

Model #3, is model #1, with hoop added to 4 x 14" Top Hat radials. The radiator length has not yet been adjusted so as to show the net affect of adding a Top Hat similar to what Homer added.

Model @4, the radiator is shortened by 10", with the Top Hat noted for #3, which I consider to likely be close to the modifications that Homer made to his antenna. This is of course no-with-standing the absence of a feed line or two that Homer is using.

View attachment Homers Top Hat idea..pdf

 

[HomerBB]

IMO, connecting the ends of those 14" stingers would tend to make the Top Hat a lot longer than just the 28" diameter would suggest. I would be surprised if only a 10" reduction in radiator length would reinstate the original resonance, but I could be wrong.

You may have already changed your antenna, but I would like to better understand the effects of the mode you made, since you used a style of Top Hat that I believe will present a lot more capacitive affect than you might think.

The entire diameter o the top hat is 14", the radius is 7.5".
Do model it and let's see.