Any Astro Plane Fans ?

[Needle Bender]

Eddie,
i don't know the exact measurements of the mast...

...no idea where resonance is either, only that minimum vswr is lower in frequency than i want, 27.500 would be ideal.

Take 3.5" off the height of the bell and about about 1" off the top hat, and about 17' 2" of mast with the coaxial choke at the end of the mast should get you handgrenade close, but I'd start with shortening the mast & top hat.

 

[VictorPapa]

I have no scientific formula as I am a man of simplicity.

What I did was use an antenna calculator to get the size of a 1/2^ @27.2 Mhz and a 1/2^ @ 145 Mhz.

27.2 = 5.51m
145 = 1.03m
1.03 ÷ 5.51 = 0.18693285
Next I took the dimensions of the Astroplane and multiplied them by 0.18693285.

Sure, Homer, i mean the s/d factor, excuse. A pipe of 3/4 " thickness is on 11m different than on 2m. Biggest problem is the mounting bracket and the distance to the mast.

Victor

 

[HomerBB]

Sure, Homer, i mean the s/d factor, excuse. A pipe of 3/4 " thickness is on 11m different than on 2m. Biggest problem is the mounting bracket and the distance to the mast.

Victor

I am using the help of these fellows who model to iron out those details.

So far, I am only speculating.

 

[bob85]

Eddie.
Just noticed you thought i liked 5/8 groundplanes,
its true i own a few and have owned many in the past,
I liked them until i bought my 1st sigma4,

Since i found out WHY a 5/8 has a little more gain than a 1/2wave on the same pole i have been saying theres nothing special about 5/8waves,
The problem is nobody makes a low loss durable 1/2wave.

I have two verticals that for me outperform a 5/8

I owned other antennas in the past i wish id kept hold of that i never tested at the same tip height,
I think you can guess what they are.

 

[Marconi]

Eddie.
Just noticed you thought i liked 5/8 groundplanes,
its true i own a few and have owned many in the past,
I liked them until i bought my 1st sigma4,

You are right Bob, I stand corrected.

The first 5/8 wave I ever owned was the I-10K and I thought it did good, but when I finally started comparing antennas I realized after a while they were all about the same...when you get the current maximums close or equal in height.

I'm happy you finally got a chance to revisit the A/P and see the results I've been claiming for years.

 

[bob85]

Eddie

i have owned more 5/8waves than anything else,
the only one that holds any interest for me is the gainmaster even though in our test the 1-10k had a small edge in tx & rx to most locals, i like the bandwidth and neat copact looks.

i like the astroplane partly because its an unusual design
DC short & coils to burn out,
& partly because it works very well if you put it at the same tip height as other antennas.

 

[Tib2K]

The A/P model I just did to Tib2K's specs shows resonance at 27.100 MHz recorded at the feed point. If the antenna is as old as I suspect, then it was probably cut for 23 channels, and this was right in the middle of the band at that time.

Do you think that the AV-101A was cut to center on the new 40 channel band? (its production run started 1979)

 

[bob85]

Tib2K,
which are you calling the 101A ?

the one you have there is the late version same as mine,
they are clearly not cut for low vswr on higher frequencies unless we both have mast/coax current issues screwing the vswr curve up,

i owned the old version for a while in the early 80's,

my old timer buddy was one of if not the first cber in my area way before any cb shops opened over here,
he had an astroplane up in the early to mid 70's up to him passing in the 90's,
his was the same as the early one i owned with expanded upper tubes,

i don't think they changed the length of the elements,
i have some pictures of the old version with a tape measure beside it when i find the flash drive the pics are on,

i have no time at the moment to experiment with mine to find out why its lowest vswr low in frequency, & don't know where its resonant.

 

[Tib2K]

Tib2K,
which are you calling the 101A ?

I have a 1978 AV-101

The Avanti AV-101A appears to be a revision. I assume it came after 1978.

 

[Marconi]

my old timer buddy was one of if not the first cber in my area way before any cb shops opened over here,
he had an astroplane up in the early to mid 70's up to him passing in the 90's,
his was the same as the early one i owned with expanded upper tubes,

Is the Top Hat the upper tubes you refer to Bob?

I've noticed some old ads showing atrist renderings that look like the A/P with different Top Hat construction, maybe using tubing instead of SS wires like your antenna. The SS wires remind me of the wire tips on the Moonraker.

i have no time at the moment to experiment with mine to find out why its lowest vswr low in frequency, & don't know where its resonant.

The model I made using Tib's dimensions shows resonance of 27.1 at the feed point. If the model is close to accurate the A/P antennas you and Tib have were probably pre 1979 and were still being cut for 23 channels. I think the 40 channel idea came up about that time or maybe 1976-1977.

I have an old HyGain SP500 manual dated 1975 that shows they were still making their antenna for 23 channels. When they went to a 40 channel design they added 3" inches to the radiator. They also made changes in the tubing distribution for the radiator over time. Mainly making the tall base section smaller at some point.

My last CB Magazine is dated Jan 1976 and all the radios were 23 channel models.

The ad below from CB Tricks is noted to be dated Feb 1978, and this antenna is for 40 channels according to the specifications. However the article itself shows copyright 1977. Some of the text is missing and I don't see the model noted as AV-101A and this one is the last ad in a string of ads on the CB Tricks Website.

I would be interested to know if Avanti made any adjustments to the dimensions after the 40 channels came out?

This is not history and does not answer much...the dates are probably off a bit.

 

[bob85]

No Eddie,
upper tubes are the upper sections of the two 1/4wave flared members,

i have seen the advertising drawings with what looks like tubular hat elements, i think it mentions that in the patent too but the ones i have seen all had stainless wire hats,

Mine is an av101 same asTib2k's,
no idea how to date it but its not the early astroplane i had years ago,

i assumed that the changes on avanti antennas came after A/S bought avanti out in august 1981,
40ch rigs came in mid 70's maybe 76,

most of the antennas we got here were the early versions, 1981/2 is when avanti stopped been stocked in my local shops,

40ch rigs came in mid 70's maybe 76

i don't know who we could ask nowadays,
the avanti guys are either silent key or not interested in talking about old CB antennas.

 

[Marconi]

Here is my new A/P model based on Tib's dimensions.

1. is the model with a mast portion (1" wire #45) that is 198.195" inches inside the antenna, and extending below the bottom hoop 108" inches. It has a full 1" inch mast below connected to Earth and is likely typical of most installations I would do.

Note: this model is resonant at the feed point on 27.1 MHz. It also shows some currents on the supporting mast.

2. is the same antenna with a 4" inch insulator (ISO) at the bottom of wire #45 and a supporting 1" inch mast below that is not attached to the antenna.

3. is an overlay of both antenna patterns for comparison.

 

[bob85]

Eddie,

if I had used a 1" diameter mast just the part that is inside the antenna my NOS astroplane would be snapped in the wind already,
astroplanes are designed for 1-1/4 to 1-3/4" masts, the diameter of the mast inside the antenna effects impedance,

your vswr curve with 1" mast never reaches low vswr, avanti claim ( 50-52ohm vswr less than 1.2:1 )
I have that but not on the frequency I would like,

does the isolation 1/4wave below the hoop reduce current in the mast & increase current in the upper 1/4wave improving low angle gain as I think it should, do you think that is what your model shows Eddie ?,

if im correct you should be able to tweak the mast length above the isolator maximising current in the upper 1/4wave,

i see no benefit in increased bandwidth if its coming from mast & coax braid currents reducing low angle gain & increasing potential for noise and rfi,

Thanks.

 

[Marconi]

Eddie,

if I had used a 1" diameter mast just the part that is inside the antenna my NOS astroplane would be snapped in the wind already,

astroplanes are designed for 1-1/4 to 1-3/4" masts, the diameter of the mast inside the antenna effects impedance,

Bob, I figure since you have winds strong enough to do as you suggest, the A/P with its much smaller aluminum tubing 3/8", 1/2", and 5/8" elements would likely be a twisted mess long before the 1" inch pipe gave way. And like somebody said the A/P has a large footprint to catch wind.

I mentioned that I used 1" inch in the model simply because my push-up pole has a 1" x 10' top section. I can't use tapper on the P/U pole using Eznec, so I used the tip diameter for the mast length. A couple of key strokes can change that diameter in short order.

At different times over the years I've installed my Top One with:
9' x 1" square aluminum tube,
10' x 1.25" fence rail,
2.75" x 12' feet of heavy wall cast aluminum army surplus mast with a 12" x 1" pipe in the top.

I saw changes in the match just like you tell us. However, I could not tell a difference in how the antenna worked...the difference were just too small of a difference. Probably similar to the difference you see between the two model overlays I posted above.

I will check out the tabular currents log and get back.

your vswr curve with 1" mast never reaches low vswr, avanti claim ( 50-52ohm vswr less than 1.2:1 )

Since the match was close, I have not fiddled with the model to try and get the match closer to perfect. DB has reported about the same match as I'm seeing here, with a value for R a bit high (60+ ohms) for his models. Maybe by now he has figured out a solution and will be willing to share the process and his results with me. Then I will fix the model. If that doesn't happen, sooner or later I will get to a solution.

I have Old Top One models with a near perfect match, but this model is new where I followed Tib's exposed dimensions for the original AstroPlane. Prior dimensions given and sourced in the manual were not exposed tubing dimensions...and the results were disappointing. I have not fiddled much with this model since I created it on 07/09/17.

Thanks Bob, I will try and follow up on your other points later today.

 

[Marconi]

your vswr curve with 1" mast never reaches low vswr, avanti claim ( 50-52ohm vswr less than 1.2:1 )
I have that but not on the frequency I would like,

IMO reading SWR using over a 100' feet of low loss feed line, I'm surprised you were not seeing even lower SWR readings with increased bandwidth. I use to read my SWR and analyzer on the Old Top One at the end of a working feed line too. I may have tried a tuned 1/2 wavelength jumper once with bad results as I recall, but for me the analyzer at the feed point was not practical.

With Eznec the model shows the match at the feed point and that will result in possible differences in match from a real antenna with a long feed line. My Antenna Work Sheets often show more backwidth with a long feed line.

i see no benefit in increased bandwidth if its coming from mast & coax braid currents reducing low angle gain & increasing potential for noise and rfi,

I've heard every little bit of gain helps and I guess that goes for the other results too. Have you setup your antenna without isolating the mast so you can compare the difference?

if im correct you should be able to tweak the mast length above the isolator maximising current in the upper 1/4wave,

This will take some modeling and checking out the tabular currents log in order to compare for your comment here. You could be right.

I seem to recall Homer telling me that DB has a graph or something that shows his model with varying effects in mast lengths inside and projecting below the hoop. Maybe Homer or DB will give us a heads-up rather than us having to read volumes of posts trying to find this info.

I will still take a stab at the idea, but it won't be as fancy and it won't be in color like DB's 4Nec2 produces.