Base Bob's Avanti AstroPlane model

[Marconi]

Bob, here is my model of your A/P at 36' feet to the feed point.

1. is the Free Space model I started with and showing the Average Gain results.

2. is Bob's model over Real Earth at 36' feet to the feed point and using (0.005, 13) for Average Soil.

 

[Marconi]

I agree Bob, this model suggest that Avanti appears to have never changed the A/P to 40 channels.

I hope the mast length is close, I made it 1.50" inches in diameter. This model also shows to be inductive and shows resonance to be 26.9 MHz. IMO, this is remarkably close to what you indicate seeing.

I posted an antenna view with notes for the wire dimensions I used. I also posted the <1.50:1 SWR bandwidth you mentioned. I used several images of the BW curve with the cursor on 1.50 SWR...above and below resonance.

Below is a PDF showing the match at resonance = 26.900 MHz.

 

[Marconi]

Bob, here is an overlay of your A/P over Real Earth with 3 different mast lengths in the antenna and extending below. All masts are 1.50" in diameter.

176" = 2.81 dbi
197" = 2.83 dbi
220" = 2.85 dbi this is what DB found to produce the maximum gain.

 

[bob85]

Your vswr curve is similar to my antenna Eddie,
mine is not linear like yours, it rises slowly either side of minimum then rises more sharply towards 1.5:1, my long coax would explain why my curve is wider & flatter,

My mast above the isolator is very close to 18ft & tellescopic,

i guesstimated that will be close to an electrical 1/2wave & give least current below the hoop when you figure in some electrical shortening when the mast is part of the antenna,
maybe i could find the best length mast with my field strength meter,

At first i was not pleased with your gain & pattern, then i remember the other models i-10K vector etc are on 36ft poles not at the same low tip height so maybe its not so bad.


Thanks for doing the models

 

[Marconi]

Your vswr curve is similar to my antenna Eddie,
mine is not linear like yours, it rises slowly either side of minimum then rises more sharply towards 1.5:1, my long coax would explain why my curve is wider & flatter,

Bob, if I made the SWR bandwidth curve using landscape rather than portrait...it might have looked flatter and better.

I agree your feed line will make a difference just as you described. Somehow I misunderstood your report to suggest the SWR for your Avanti A/P showed no SWR below 1.50:1 on your inline meter.

 

[bob85]

It did not have vswr below 1.5:1 anywhere when i first put it up but it was not the antenna or feedline causing the elevated vswr readings,

it was the radio going a little unstable but not full high vswr icon mode,

the high vswr icon problem is common with FT100 & 100d especially when folk try using them in a mobile,
Yaesu did some ugly factory modifications that don't work.,

i did some experimenting & found my own cure that does work but never removed the tuner to see what vswr was like until you asked me where minimum vswr is.

 

[Marconi]

At first i was not pleased with your gain & pattern, then i remember the other models i-10K vector etc are on 36ft poles not at the same low tip height so maybe its not so bad.

Bob, I just discovered I posted the wrong model for you above. No wonder you were disappointed in the gain.

Earlier, I made the model (Bob's AstroPlane Specs w197"M 36') and that is what I posted. I should have posted (Bob's AP Specs w197"M ISO 36') instead. Don't ask me to explain what happened to the poor model I posted...I have not tried to figure out its failings...it is destined for the trash bin.

Yesterday I was looking at my A/P models. I saw a model with your name in the title and that reminded me that I once had a thought...I never answered your question in this thread about tip height. Bob, this just popped into my mind. At some point later, I remembered saying to myself...I never made the model set to 55' feet comparing a 5/8 wave to the A/P at the same tip height.

Sorry, I must be getting old.

 

[Marconi]

It did not have vswr below 1.5:1 anywhere when i first put it up but it was not the antenna or feedline causing the elevated vswr readings,

I was confused by the comments above and I think you explained my confusion later. In re-reading it now and in light of the fact you had some radio problem...a month later I wonder if you still see low resonance close to 26.965 MHz?

 

[bob85]

The radio has not had the high vswr icon / pa oscillation since i fixed it Eddie, vswr is still low on your band,

i am still happy with how the astroplane performs when its isolated 1/4wave below the hoop, imho at least as good as my 5/8wave at the same tip height,

i hear better than most of my locals with higher antennas,

since i will be raising the astroplane at least 20ft i would be interested in how it compares to a 5/8wave on a 36ft mast at the same tip height,
with the astroplane isolated 1/4wave below the hoop as i have it setup now..

 

[HomerBB]

Fellers, I have long time said my AP did as well as my 5/8^ GP at same tip height. I look forward to a model like this.

 

[Marconi]

The radio has not had the high vswr icon / pa oscillation since i fixed it Eddie, vswr is still low on your band,

Thanks, Bob. I wasn't sure. I have two A/P models at 36' feet to the FP bracket, and they both have your name in the title. They are both a little different in the radial dimensions. I need to know your specific dimensions. I know you've posted them, but I don't want to re-read these posts trying to find what you've posted

One model is (Bob's AP Specs w197"M ISO 36') and it shows:
1. has the 2 top radial wires #8/#9 at 45.5005" x 0.50" inches.
2. has the 2 bottom radial wires #10/#11 at 45.5081" x 0.50" inches.
This model shows me resonance at 26.9 MHz.

The other model (Bob'sAP Specs w197"M ISO 36'a) and it shows:
1. has the 2 top radial wires #8/#9 at 45.5004" x 0.50" inches.
2. has the 2 bottom radial wires #10/#11 at 44.0567" x 0.50" inches.
This model shows me resonance at 27.2 MHz.

My radial hoop is also 29.50" x 0.375". If this is different let me know.

i am still happy with how the astroplane performs when its isolated 1/4wave below the hoop, imho at least as good as my 5/8wave at the same tip height.

Can you be more specific with the 1/4 wave dimension below the hoop, including the diameter? I have the mast at 197" x 1.50" inches from the mounting bracket to the end below the hoop about 0.45 wavelength.

My models show good results from 197" to DB's longer dimension at about 220" inches for the mast below the hoop. I've used 1.50" inch mast on this model.

i hear better than most of my locals with higher antennas,

I have reported the same advantage for my New Top One and my Maroni 4x a similar design using an A99 radial hub, mobile L-bracket, and 4 x 102" stainless whips.

since i will be raising the astroplane at least 20ft i would be interested in how it compares to a 5/8wave on a 36ft mast at the same tip height,
with the astroplane isolated 1/4wave below the hoop as i have it setup now..

I was going to compare tip heights for this A/P to my new model for the SP500 model both about 55' feet to the tip. For a couple of days I have been studying that 5/8 wave model and now I question why the currents on the radiator are so low in current maximum compared to a HWCF dipole. The magnitude of the currents flowing on the matching device wires on the SP500...are noticeably higher. Then I checked my I-10K model and I see about the same thing. No wonder they both show such low gain.

So, I compared the tip height idea using NV4K. First I would like to confirm your dimensions again knowing your antenna is low in resonance.

Fellers, I have long time said my AP did as well as my 5/8^ GP at same tip height. I look forward to a model like this.

Homer, I figured I had a good 5/8 wave model, but like I said above...I now question all my 5/8 wave models that have the physical matching device added.

I've had a bad couple of days over the weekend. IMO, this suggests to me that a good match might not always mean a good thing...if the antenna sucks otherwise.

Bob, the two models below might suggest why your A/P shows to be lower in resonance than expected.

 

[bob85]

Its not low in frequency Eddie, i have low vswr all across your band,
our band is 27.60125 ch1 -- 2799125 ch40 its a little high on our band

The mast above the isolator is in two parts, bottom section is about 8ft x 1.9",
upper section is 12ft x 1.5" telescopic so i can adjust mast length above the isolator to minimise mast currents, set to 18ft total length.

 

[Marconi]

Fellers, I have long time said my AP did as well as my 5/8^ GP at same tip height. I look forward to a model like this.

Here are the overlays and models at a similar tip height. I posted overlays too.

 

[bob85]

If you are happy the models are pretty accurate i think im right in rating the astroplane at least as good as my 5/8waves Eddie,

 

[HomerBB]

See if I got this right.
#1 is best descending from there.

1. Nv4k
2. Bob's AP
3. Spec AP
4 .625
5. .50 (EFHW)
All at the same tip height.
The Nv4k about 1.5dbi over the EFHW.