Any Astro Plane Fans ?

[bob85]

Eddie,
I don't think we need a great match in order to explore what I was asking you to do with the mast,

we don't need the pages of current log posting, I probably would not understand it all anyway,

if you say the trend in current magnitude on mast & upper 1/4wave is as I think it should be or is not as I think I will take your word on it,
I don't think your here to deceive me,

I would be looking for an answer to why that is so.

 

[HomerBB]

Homer, I made a model of this idea without any real understanding of the model that Henry reported. I read his claim and saw his graph, but I did not see any model, just a graph of some results. I'm not criticizing the report, I'm just saying I saw no model to try and duplicate...so I can't be sure of my model. I will post it in another post.

I can't be sure, but I think Henry used a feature in Eznec Pro 4, that DB used the feature in 4Nec2. DB posted some of his results which looked impressive, but I also recall Henry giving DB a caution in the use of the feature as well. I have seen no more such modeling.

I asked you to model a 5/8^ with both radials and a cone once. I can't find the model you did, but I know it sucked.

 

[HomerBB]

page 41 Homer
http://cb-antennas.com/wp-content/uploads/2013/12/Sigma-IV-1.01-Jan-2015.pdf

Thanks!
I will read it again (it's been a while) and try to dig out the part where the ground plane was put under the Sigma.

 

[bob85]

Heres what My temporary tied to fence astroplane looks like,
the fence is coming down soon & the antenna will be moved out into the field,

 

[HomerBB]

Looks great!

 

[Marconi]

Great setup Bob. I pictured your location with a small garden out back with a big apple tree nearby.

I just finished doing some comparison work on my Old Top One Free Space model I posted earlier. I did 4 iterations making the mast inside the antenna 1" inch longer. My intentions were to compare the tabular currents log values and confirm your prediction that as the mast length below the hoop becomes more effective the currents on the radiator should increase.

I used a snipping tool to capture the side by side images for the antenna and the currents on my wire #1, the radiator and everything is small. I don't know how well this file will look after I scan and upload to the forum, but here it is.

This is just a test.

If I can't see these results, then I will do the post again and make the images on a single page each. I also posted the original model results again...if you need to check it.

The antenna image shows how long the mast is in inches.

The tabular currents log shows the currents and phase on wire #1 the Old Top One radiator. Wire #2, noted is a wire for the top hat element.

Bob, sorry these images are not like a high pixel camera image, but you can use the PDF file zoom feature.

Let me know if this does not give us a clue that your claim is right. I base my assumption on the fact that I also see the Eznec Average Gain results improve as the mast was made a little longer. It went from -0.04 to -0.02 in the short range I've posted.

I will analyze these effects on the mast currents too and get back...if this idea helps.

 

[bob85]

Eddie,
you have seen this location before 10+ years ago,
its where i had my cabbage patch, i have plenty of space for antennas,

the other place did have a small garden, about 85ft x 60ft with apple trees & conifirs near the antenna,

this place is lower ASL but its a better location for radio,

i see the trend in your models,
as the mast gets longer current in the upper 1/4wave is rising & gain increasing,

its only a tiny change undetectable on air but 1" is a tiny incremental increase,

can you check mast current to see if it is falling as upper 1/4wave current is rising ?

can you find a sweet spot that as you pass the trend reverses & current in the upper 1/4wave starts to fall again ?

i don't know how much work is involved making the incremental adjustments Eddie,

if its a lot of work, maybe try larger increments to save time & effort,

Thanks

 

[Marconi]

I asked you to model a 5/8^ with both radials and a cone once. I can't find the model you did, but I know it sucked.

Homer, sorry I forgot to post the model results.

I don't remember the 5/8 wave model.

Henry is right there looks to be improvement adding radials to the base of the Sigma4 and my model shows a little increased gain. Adding radials might also have other positive effects too.

However, my model does not show anywhere near 2 db of gain in the far field using Eznec normal processes.

Homer, you need to talk to DB about this modeling idea. I'm not even sure what they call this new function, at least it is new to me.

 

[HomerBB]

Oh, no, Marconi. Sorry, I wasn't clear.
This was momths ago in private email correspondence. But, as I think about it, I was toying with a caged monopole idea where there were 4 radials on a square plate and asked you if you'd model a 5/8^ with upturned radials. It fell apart, as I recall.

 

[Marconi]

Eddie,
you have seen this location before 10+ years ago,
its where i had my cabbage patch, i have plenty of space for antennas,

the other place did have a small garden, about 85ft x 60ft with apple trees & conifirs near the antenna,

I think I saw an image of your parents place. Is this the same place?

i see the trend in your models,
as the mast gets longer current in the upper 1/4wave is rising & gain increasing,

its only a tiny change undetectable on air but 1" is a tiny incremental increase,

Bob, the length of the mast is a little over 17' feet, and I think this is close to resonance for that diameter of tubing. So, I'm likely right near the tipping point. It is like tuning a gamma match.

I did not save any of the models except for the original FS model I posted earlier.

I did convert the FS model to check the model over Real Earth and everything was fine at that 206.867" inch length. I also realized that I did not change the segment counts as I increased the mast length 1" inch at a time. However, the change was pretty small compared to the overall length, so I doubt it made much of a difference. It needs to be double checked though.

I don't remember for sure but I also made the mast 20" to 30" inches longer and the model crashed. I did not check that out, but it could be a segment error crash. I took the error as passing the sweet spot and stopped working on the model. I was having an A-Fib attack and I went to bed.

 

[Marconi]

Oh, no, Marconi. Sorry, I wasn't clear.
This was momths ago in private email correspondence. But, as I think about it, I was toying with a caged monopole idea where there were 4 radials on a square plate and asked you if you'd model a 5/8^ with upturned radials. It fell apart, as I recall.

Homer, I don't remember a thing. That model sounds like a EzBob model however.

 

[HomerBB]

Found it. I know it's off topic. Couldn't resist.

Homer, here is my effort at your idea.

I didn't add a hoop at the top, but the new redials are 53" tall by 3" off-set from the center of the radiator on both sides. I did slanted the radials out to 15" off-set at the top, and that extended their length to a little more than 54", but I did not save the model. The gain dropped a fraction however, but I read that to indicate the model was likely improved just a very little bit.

I see very little difference in the pattern shape, except this radial modification does look to press the high angle lobe down a little, which is good.

I also noted that the current levels in the originally model with horizontal radials only, did loose some current magnitude. That current looks to have been transferred into the new radials, which is good because Eznec shows they are now in phase currents, and that is good.

I checked the effects on the match, and it did show to be improved there too, so that is good.

All and all I don't see much advantage for the effort, even when slanted out at the top a bit to look more like the Vector. But, it would look different.

Good luck,

Eddie

 

[Marconi]

can you check mast current to see if it is falling as upper 1/4wave current is rising ?

can you find a sweet spot that as you pass the trend reverses & current in the upper 1/4wave starts to fall again ?

That is my next step after I'm able to find a sweet spot like you mentioned.

i don't know how much work is involved making the incremental adjustments Eddie,

Increasing the mast length in the FS model is just making two changes. As I noted somewhere I should have also change the segment lengths as I went along...so that would require two more changes...not hard to do.

Maybe tomorrow when I'm out of this funky feeling.

 

[Marconi]

Found it. I know it's off topic. Couldn't resist.

Right off the bat I see a big no-no in modeling with Eznec...modeling tapper is said not to work too good.

I think "Mikey" did it.

 

[HomerBB]

Right off the bat I see a big no-no in modeling with Eznec...modeling tapper is said not to work too good.

I think "Mikey" did it.

It was done back in 2015.