.64λ Homebrew

[Marconi]

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

I went back to change the Top Hat dimensions to 7.5" radius and found that I left them 10" like the original ones on the I-10K. You're right, you didn't say they were each 14" long, but that is only 7", so I'll make the radials 7".

That still makes my Top Hat a few inches larger, and when fixed that will help shorten the length and raise the frequency some...assuming this presentation idea is close to corrected.

I'll change the model that I referred to as your modified version and post it up. I could be wrong, but I don't think it will make a huge difference that will get the results up anywhere near 27.732.

Homer, I realize you could disagree with me here, because you were right there during your testing and I'm just assuming, but I based it on these model results. This is the reason I asked you which result you thought were probably best.

BTW, I'm curious, what was your reason for adding the loops, and connecting the Top Hat elements?

Would you agree that might make the hoop look electrically bigger to the antenna?

 

[HomerBB]

I went back to change the Top Hat dimensions to 7.5" radius and found that I left them 10" like the original ones on the I-10K. You're right, you didn't say they were each 14" long, but that is only 7", so I'll make the radials 7".

That still makes my Top Hat a few inches larger, and when fixed that will help shorten the length and raise the frequency some...assuming this presentation idea is close to corrected.

I'll change the model that I referred to as your modified version and post it up. I could be wrong, but I don't think it will make a huge difference that will get the results up anywhere near 27.732.

Homer, I realize you could disagree with me here, because you were right there during your testing and I'm just assuming, but I based it on these model results. This is the reason I asked you which result you thought were probably best.

BTW, I'm curious, what was your reason for adding the loops, and connecting the Top Hat elements?

Would you agree that might make the hoop look electrically bigger to the antenna?

It is my understanding that the outer circumference connected loop will make the hat look bigger electrically.
I used the hat I did because that's the way it was on the lamp shade I got it from . . .

 

[Marconi]

OK, here is the FIXED model and I was wrong. The fix did make that much difference, and the higher frequency looks to be the best.

Now, not-with-standing the error I made, I can still crow a little. I think you may have been trying to tune to 27.400, and the results at the end of your 1/2 wave x 6 feed line, your best antenna result shows 27.732. That's not too far from the 27.600, my model shows, now is it.

I just had to brag a little, even though I made an error.

View attachment Homer's Top Hat model FIXED.pdf

 

[Marconi]

Here are the patterns with gain and angle for Homer's models with the error vs. the one that I fixed by setting the frequency at the resonance for the match, 27.600, which made for a better gain of .16 dbi.

View attachment Homer's Top Hat model with frequency fixed.pdf

 

[Marconi]

It is my understanding that the outer circumference connected loop will make the hat look bigger electrically.
I used the hat I did because that's the way it was on the lamp shade I got it from . . .

You're right Homer, that is my understanding also.

As you say, there isn't any good reason that a body can get a 2-way radio and get on the air, and not have to break the bank buying an expensive antenna. You just have to use your head and have a lot of creativity.

Homer proves it every day.

 

[HomerBB]

Thnx, Marconi, that looks a lot better.
What if you added 14.5 inches to the over all length?

From the radials up I am 22' 2"

 

[Marconi]

Thnx, Marconi, that looks a lot better.
What if you added 14.5 inches to the over all length?

From the radials up I am 22' 2"

That would be hard to figure with the antennas being different to start. Element diameter is a very sensitive area to mess with, but when I tried it on the model I call Homer's Modified model, the frequency drops down into 25.000 mhz, if I did it right.

I'll try it again tomorrow in case I made a mistake. This effect might be similar to the cause for why I thought for sure there would not be much change earlier. I learned something new tonight, that I had never considered.

I also don't think I can model your particular antenna because of the issue we talked about the other day that is similar to the Wolf antenna. The only thing we see here tonight was a trend that is similar and that is not so hard to track, but it is not a perfect comparison even if I tried to take some credit in that regard.

 

[Marconi]

Thnx, Marconi, that looks a lot better.
What if you added 14.5 inches to the over all length?

From the radials up I am 22' 2"

That would be hard to figure with the antennas being different to start. Element diameter is a very sensitive area to mess with, but when I tried it on the model I call Homer's Modified model, the frequency drops down into 25.000 mhz, if I did it right.

I'll try it again tomorrow in case I made a mistake. This effect might be similar to the cause for why I thought for sure there would not be much change earlier.

I also don't think I can model your particular antenna because of the issue we talked about the other day that is similar to the Wolf antenna.

 

[HomerBB]

Alrighty. You've been really helpful so far.

 

[HomerBB]

OK, here is the FIXED model and I was wrong. The fix did make that much difference, and the higher frequency looks to be the best.

Now, not-with-standing the error I made, I can still crow a little. I think you may have been trying to tune to 27.400, and the results at the end of your 1/2 wave x 6 feed line, your best antenna result shows 27.732. That's not too far from the 27.600, my model shows, now is it.

I just had to brag a little, even though I made an error.

View attachment 7050

Yes, you did pretty good all things considered. I appreciate it, too.

 

[HomerBB]

I went back to change the Top Hat dimensions to 7.5" radius and found that I left them 10" like the original ones on the I-10K. You're right, you didn't say they were each 14" long, but that is only 7", so I'll make the radials 7".

I might add that my radials are exactly 108" long each - 9"
total vertical length 22' 2" above radials (10" below radials in the mount)
top hat 7" radius (14" diameter)
coil 4.5" length x 4" OD

 

[Marconi]

Thnx, Marconi, that looks a lot better.
What if you added 14.5 inches to the over all length?

From the radials up I am 22' 2"

I see that you are asking me to make my model the same length as your antenna in question. I tried it late last night and posted that the frequency dropped down into the 25.000 mhz range, but it was late and I must have made a mistake somehow. I did the attached this morning and it is much better. I did not, however, add any length to the radials. That may make the model go down some more in frequency, but I hesitate to guess, because I've been guessing wrong of late.

The following models are: 1st one is the model I made similar to your mods and it is scanned at 27.205 showing resonance at 26.8. The 2nd one is the same model, but I did the frequency scan set at 26.850. Not much difference except for the frequency change.

The currents look great at 50' feet, so I moved the antenna down to 36' feet and added another model for something else to consider as I think you might be at 35.5' feet. See 3rd model attached.

Check out the difference in current flowing on the mast with the change in height, it is significant...maybe by 5 times more. I have never really done any real world testing on this idea, but for a long time I've sensed something that I did not understand...when raising my antennas. Before I was able to model, I could only discuss the idea with words, but now I think this might suggest some real world testing could be useful. For me this issue is about TVI problems and I test it using a field strength meter set up on or near my station. On my digital field strength meter I use a shorted coaxial antenna about 15' feet long, and it's very sensitive to RF in the shack.

View attachment Homer's idea adding 14.5''.pdf

 

[HomerBB]

It certainly appears that I have something to gain by moving it up higher. Certainly some potential TVI to lose.

 

[Marconi]

It certainly appears that I have something to gain by moving it up higher. Certainly some potential TVI to lose.

Again, I have not tested this idea in the real world, but if you can tell in your work, or sense maybe it's like I did, then let's talk about that. I would like to know more of how modeling relates to what is really likely to happen compared to the real world.

Are you at about 36' feet in your testing? And if so, can you detect any stray currents at your station however minimal? Do you have a field strength meter that is sensitive and works?

BTW, making the radials 108" improves the gain about .25 dbi, the match improves as well, and resonance remains even closer to 26.850. I can't post it, because I forgot to save the file.

 

[HomerBB]

I am at 34.5 feet feedpoint.
When I add guys to the mast I'll try to scope it up some more. It isn't so easy for a light weight like me.
In a previous configuration, it displayed TVI into an old cathode tube TV when the amp was employed on high mode, in low mode nothing, but I haven't tried it with the last configuration.
I do have one or two field strength meters around here, so I may try that approach. I would have to tape/zip tie the key to do it as my wife would not touch the radio for anything short of the gold in Fort Knox. She considers this stuff her rival and my mistress.
If she only realized it neither nags nor talks back, and is friendlier than man's best friend. . .