AstroPlane up and Testing

[Starduster]

i think i have one exactly like that eddie ,

starduster,
thanks for posting the great pics, im drooling
have you thought about trying the alternative symetrical configuration shown in the patent where the upper 1/4wave is an extension of the mast rather than offset?
an aluminum plug in the mast drilled to take the the 1/4wave would look ok imho, i wonder if it would clean up the lobsided pattern also shown in the parent.

How would a person go about testing the radiation pattern? I see avanti used a scaled down antenna at a higher frequency for that test.

 

[Marconi]

SD'r with this view and the rule your modified is fine. In fact it looks more symmetrical that the original or the TopOne.

If you use the modified hub on your beam, it looks like there is room for the stock mast to boom bracket to clear whether you decided to make one or not.

 

[bob85]

starduster,
i agree with the idea that the radials may be better positioned how you have them central to the mast and apreciate your efforts in building and testing the idea, as you can see from the pic i could not test that without making a longer bracket

i would expect that rotating the antenna would show any asymetry in pattern, how much you would see on a field strength meter or signal meter on a distant receiver i don't know

 

[Starduster]

Did the additional testing with my copy of the Astroplane verses The Original Equipment of Manufacture
Three plots were made as follows:

1) AP OEM
This is the factory designed stock antenna SWR curve as indicated by the blue line on the chart.

2) AP COPY 5/8 R
This is my original copy with all elements at the same length as the NOS factory original. On this antenna I used 5/8” lower radials down to the spreader bar and ½” radials from the spreader to the loop on the antenna bottom. Indicated by the red line on the chart. Note: I could not get a SWR reading lower than 1.2 with this set up.

3) AP SD COPY 1/2R
This is my original copy with all elements at the same length as the NOS factory original. On this antenna I used 1/2” lower radials all the way down to the loop on the antenna bottom like the OEM antenna. Indicated by the green line on the chart.
For some reason it was difficult to get the X reading on the meter to be stable at frequencies between 27.440 and 27.695 They kept jumping from 0 to some other number and would not settle down.

The data sheets are also shown.

There are some more differences in the copy design 2&3 above verses the OEM design as follows;

1) The lower elements are on a center line with the mast. The OEM antenna has the mast offset. As talked about earlier in the thread.

2) The lower 10” of the upper radial is ¾” d. The OEM is 5/8”d.

3) The top hat differs in that all horizontal radials of the copy are in the same plane, not stacked and they are ¼” d. aluminum rods instead of 1/8” d. stainless steel rods. This made the top element somewhat of a guess for length.

Some conclusions on the SWR curve are;

1) The Copy antenna is more broad banded than the OEM This is probably an insignificant amount although clearly not any worse than the OEM. Could be due to the symmetrical element/mast layout or perhaps the larger diameter tophat stingers.

2) The diameter of the lower elements seams to make a significant frequency shift in the SWR curve. Probably due to the Z- ??

3) A 1:1 reading could not be achieved with the 5/8 d. radials. However other than the frequency shift and overall higher SWR the curve shape look about the same as the ½” d. radials.

4) Next step will be to try and get the Curve to shift up in frequency closer to 27.205. not sure what direction to take to accomplish that though. Maybe try the straight element again.

What is the purpose of the round cage like ball as seem on some of the old ground plane antennas? I think it was for static or noise reduction. Does anyone think that that may work on the AP with a straight radial instead of a tophat?
Comments or suggestions are welcome as always.

 

[W5LZ]

A few points.

Doing radiation pattern testing as a 'scaled' higher frequency? Yes, it works. There are enough variations in doing that sort of testing that the 'general' results are comparable, but not exactly comparable. The general characteristics of the radiation pattern will 'follow through'. Then you get to make compensations for the typical propagation for the frequencies used in testing and for the actual band of use when they are called for.

From the results shown, I would say that all three antennas are comparable, do the same things. The frequency difference between the specific "R+/-J" results are about as 'comparable' as you can get, not really all that much difference in general. The differences can be accounted for by the variations in designs/constructions. 'Centering' the 'resonant' frequency, or placing it where you want it to be, can be/is handled like tuning any other antenna. Simplest method would be to lengthen/shorten the 'top' element, I would think.

That 'caged ball' thingy is a combination of corona/static ball and capacitive hat. They can be useful in a number of ways (including 'looks'). If one of those 'qualities' is needed or desired, use one. If not, then don't.
The shape being 'rounded', with no 'points' or sharp edges, is a good thing for capacitive hats, because of possible coronal discharges 'liking' those 'sharp' or 'pointy' things. That's not a huge biggy, but very nice to remember, saves a lot of 'snap/crackle/popping'.
Keeping things at least 'sort of' symmetrical is a fairly good idea because it cuts down on the variations in the resulting radiation patterning, which is the whole point. A little bit of asymmetrical'ness isn't going to make a lot of difference overall. Considering all the other 'variables' in the typical antenna and how/where it's mounted, it probably isn't going to make much difference. That 'frugality' thing would probably be the biggy.
- 'Doc

 

[Marconi]

Did the additional testing with my copy of the Astroplane verses The Original Equipment of Manufacture
Three plots were made as follows:

1) AP OEM
This is the factory designed stock antenna SWR curve as indicated by the blue line on the chart.

2) AP COPY 5/8 R
This is my original copy with all elements at the same length as the NOS factory original. On this antenna I used 5/8” lower radials down to the spreader bar and ½” radials from the spreader to the loop on the antenna bottom. Indicated by the red line on the chart. Note: I could not get a SWR reading lower than 1.2 with this set up.

3) AP SD COPY 1/2R
This is my original copy with all elements at the same length as the NOS factory original. On this antenna I used 1/2” lower radials all the way down to the loop on the antenna bottom like the OEM antenna. Indicated by the green line on the chart. For some reason it was difficult to get the X reading on the meter to be stable at frequencies between 27.440 and 27.695 They kept jumping from 0 to some other number and would not settle down.

The data sheets are also shown.

Very nice work Starduster, I envy you---being able to working hard with something you enjoy.

With all elements being the same length as the NOS blue line, I would expect the larger diameters stuff to trend toward lowering of frequency, like the AP Copy 1/2 R (green line) did even though it only had a larger top hat. That might be expected.

The AP Copy 5/8 R had larger tubing in different spots including the top hat and yet the frequency went higher, and was higher even than the NOS. That surprises me unless the length of the 1/4" top hat was made too short to accommodate your estimate, like you intimated in #3 of your differences section below. I would have expected the (red line) Copy 5/8 R to be the lowest in frequency just base on the facts and because with larger tubing it needs to be shorter that the NOS in order to maintain resonance.

There are some more differences in the copy design 2&3 above verses the OEM design as follows;

1) The lower elements are on a center line with the mast. The OEM antenna has the mast offset. As talked about earlier in the thread.

2) The lower 10” of the upper radial is ¾” d. The OEM is 5/8”d.

3) The top hat differs in that all horizontal radials of the copy are in the same plane, not stacked and they are ¼” d. aluminum rods instead of 1/8” d. stainless steel rods. This made the top element somewhat of a guess for length.

We can see differences, but they are not significant except for the frequencies and even that is not much, well within bandwidth range. Bandwidth range is a bit low compared to my Top One and I’m not sure yet why that is. I have not really studied my AP stuff from last summer because it worked fine and I could not tune it like the other antennas I was comparing.

How long did you make the 1/4" Top Hat radials? Whatever it was going shorter didn’t seem to affect the frequency like I would expect with the 1/2 R. I don't get that, seems it should be higher. I guess we can't fuss to much seeing as the 5/8 R antenna is resonant almost perfect to the middle of CB band. Isn't that what you saw the very first bat-out-of-the-box with that antenna? I would set that one and forget it, and the bandwidth being near 2 mhz is perfect. That is what Avanti touted on their ad stuff, if you can find it anymore.

Some conclusions on the SWR curve are;

1) The Copy antenna is more broad banded than the OEM This is probably an insignificant amount although clearly not any worse than the OEM. Could be due to the symmetrical element/mast layout or perhaps the larger diameter tophat stingers.

2) The diameter of the lower elements seams to make a significant frequency shift in the SWR curve. Probably due to the Z- ??

3) A 1:1 reading could not be achieved with the 5/8 d. radials. However other than the frequency shift and overall higher SWR the curve shape look about the same as the ½” d. radials.

4) Next step will be to try and get the Curve to shift up in frequency closer to 27.205. not sure what direction to take to accomplish that though. Maybe try the straight element again.

Well Starduster, you may be right, but at this point and with no real way to tell, maybe you should wait and see how the Copy 5/8 R works on-air and compare it to the original and/or you first Copy 1/2 R---if that is possible. I would do that before you consider changing the top element to a full 1/4 wavelength. On-air you may find something else to consider and that may take a little time. I think you have worked good and hard. You need a break. You will find if you go too fast now, you may miss something---and like me, I always regret something later going too fast.

Did it surprise you that the 5/8 R was working at 27.200 mhz when the other day you couldn’t figure why it changed? What did you do different? I bet it had to do with the feed lines. Maybe it would be a good test to change the line to some random length on the 5/8 R, and see what, if any, affect it has on your scans. Please don't do it before you do some on-air work first and get a feel for what it does. Going fast is great and gives us a lot to talk about, but we don't want to miss the on-air testing.

The symmetrical stuff is really good IMO, but you might not be able to tell with the testing you are doing. Where that counts is the positive affects it can have on pattern.

What is the purpose of the round cage like ball as seem on some of the old ground plane antennas? I think it was for static or noise reduction. Does anyone think that that may work on the AP with a straight radial instead of a tophat?

Comments or suggestions are welcome as always.

I got and opinion, but you don’t want to hear it.

You did good.

 

[Starduster]

I need to make sure that I am explaining the top hat diferences correctly. the length of the horizontal rods are the same as the OEM 23" tip to tip, only the diameter of the rods is different. The OEM being 1/8" and the copy being 1/4". The estimated length comes in for the top element. As shown below the tophat rods are stacked on the OEM and mine are all in the same plane due to the hub that I use. So I set my top element length at 48-1/2" to the center of the hub.
I am now experimenting with the length of the top element trying to get the center frequency up a little.
I am noticing something going on here and it is kind if a radical thought. I'll post after more investigation.
The antenna is getting alot of skiip contacts if you can count that, but direct contacts are a better for evaluation. After all in theory you could make a skip contact with a hand held. There is not a lot of CB activity around here so it kind of makes it tough.

 

[Starduster]

Very nice work Starduster, I envy you---being able to working hard with something you enjoy.
The key is to be able to make changes quickly. It only takes about 3 minutes to get the antenna down to make changes. I like to share the results and get opions so you guys are as much a part of it as I am. This is greatly apreciated.

The AP Copy 5/8 R had larger tubing in different spots including the top hat and yet the frequency went higher, and was higher even than the NOS. That surprises me unless the length of the 1/4" top hat was made too short to accommodate your estimate, like you intimated in #3 of your differences section below. I would have expected the (red line) Copy 5/8 R to be the lowest in frequency just base on the facts and because with larger tubing it needs to be shorter that the NOS in order to maintain resonance.

Me too.

We can see differences, but they are not significant except for the frequencies and even that is not much, well within bandwidth range. Bandwidth range is a bit low compared to my Top One and I’m not sure yet why that is. I have not really studied my AP stuff from last summer because it worked fine and I could not tune it like the other antennas I was comparing.

I do have a theory on this but it needs further testing before I open my mouth.

How long did you make the 1/4" Top Hat radials? Whatever it was going shorter didn’t seem to affect the frequency like I would expect with the 1/2 R. I don't get that, seems it should be higher. I guess we can't fuss to much seeing as the 5/8 R antenna is resonant almost perfect to the middle of CB band. Isn't that what you saw the very first bat-out-of-the-box with that antenna? I would set that one and forget it, and the bandwidth being near 2 mhz is perfect. That is what Avanti touted on their ad stuff, if you can find it anymore.

Yes I did see that right off the bat. But I could not get the SWR down to 1:1 with the antenna mentioned.


Well Starduster, you may be right, but at this point and with no real way to tell, maybe you should wait and see how the Copy 5/8 R works on-air and compare it to the original and/or you first Copy 1/2 R---if that is possible. I would do that before you consider changing the top element to a full 1/4 wavelength. On-air you may find something else to consider and that may take a little time. I think you have worked good and hard. You need a break. You will find if you go too fast now, you may miss something---and like me, I always regret something later going too fast.

I here you.

Did it surprise you that the 5/8 R was working at 27.200 mhz when the other day you couldn’t figure why it changed? What did you do different? I bet it had to do with the feed lines. Maybe it would be a good test to change the line to some random length on the 5/8 R, and see what, if any, affect it has on your scans. Please don't do it before you do some on-air work first and get a feel for what it does. Going fast is great and gives us a lot to talk about, but we don't want to miss the on-air testing.

I also am thinking feed lines. The early test may of been flawed. that is why I changed it.

The symmetrical stuff is really good IMO, but you might not be able to tell with the testing you are doing. Where that counts is the positive affects it can have on pattern.

Agree but that is hard to test.

I got and opinion, but you don’t want to hear it.

Let me take a stab at it; Marketing hipe?

You did good.

Thanks. Also see my other post today about the top hat.

 

[Marconi]

I need to make sure that I am explaining the top hat diferences correctly. the length of the horizontal rods are the same as the OEM 23" tip to tip, only the diameter of the rods is different. The OEM being 1/8" and the copy being 1/4". The estimated length comes in for the top element. As shown below the tophat rods are stacked on the OEM and mine are all in the same plane due to the hub that I use. So I set my top element length at 48-1/2" to the center of the hub.
I am now experimenting with the length of the top element trying to get the center frequency up a little.
I am noticing something going on here and it is kind if a radical thought. I'll post after more investigation.
The antenna is getting alot of skiip contacts if you can count that, but direct contacts are a better for evaluation. After all in theory you could make a skip contact with a hand held. There is not a lot of CB activity around here so it kind of makes it tough.

You are right SD'r, I was reading the top hat thing wrong, but the diameter should still cause the elements to appear longer. Plus for my top element on my TopOne I show the the straight element is 47" total and the wires are 23" like you show. If i'm right, then this may be the cause for your 1/2 R being low in frequency. I still don't get why this top hat does not seem to effect things similarly with the 5/8 R though.

Yep, not having local traffic does make checking things tough. I only record RX signals on my Signal Reports, because the few guys that are on regular here in the Houston area don't go for antenna checks, it is below there dignity. You are right DX is not a good indicator unless you can check with a flip of a switch, and work two antennas on a switch box. Even then I only do it for comparison reasons. It might not be good process using two separate antennas for comparisons, but if you don't you might miss some of the finer issues like conditions changing, tone or quality of audio, and signal. I have switched my antennas about before and I have never seen any difference that I could tell.

If you are not getting any traffic to compare, then I would continue with your ideas. I did not mean to appear to be so bossy. I would like to see what length you get with the straight 1/4 on the 5/8 R.

I had hoped you would try an answer to my last question in my post #81.

 

[Starduster]

If you are not getting any traffic to compare, then I would continue with your ideas. I did not mean to appear to be so bossy. I would like to see what length you get with the straight 1/4 on the 5/8 R.

I had hoped you would try an answer to my last question in my post #81.

Marconi,
I did not see any form of bossy in your replys. Although we never met or will never meet face to face, I view everyone here as a friend unless they tell me otherwise. A lot of times the spirt and/or meaning of the measage gets twisted when communicating with words only. If we all realize that then we all know not to take comments and such too seriously.

Your questions about coax length and straight elements will be answered as I too am curious.

 

[Starduster]

I was curious to see if the SWR would change when the curve/bend of the lower elements was changed so I moved the spreader brace that is located about half way down the legs and got these results. The first table is the antenna before starting and the second is the readings after moving the brace down about 6”.
While the SWR did not change much the X and R shows some differences. It appears that on the frequencies below the lowest SWR , R was pretty steady until nearing the end of the test range. On the frequencies higher than the lowest SWR X was steady at 0 for all but the highest test frequencies.
Would this be considered normal?
Comments please to help me understand this.

 

[KomaToast]

Nice job Starduater, you do good work.

I like all the old Avanti antennas, they made good stuff that worked well and didn't sell hype.

I converted an original Astroplane into an AstroBeam a few years back from memory from 1974 and the specs I found online.
It's a very picky antenna, if the boom sections which are only a few inches different in length are switched it will act like a bad ground plane with high SWR.
That's how I got mine so cheap back then, the original owner had the boom sections swapped and it wouldn't work. I put it together right and mounted it at 74 feet in the air.

 

[bob85]

starduster,
i would have expected to see a small drop in impedance with the the spreader moved down placing more of the radial closer to the mast, that does not seem to be what happened,

for seeing trends i prefere scans listed by frequency step rather than vswr points,
its not practical with the odd design of the astroplane but it would be interesting to see what the antenna measured over that bandwidth with an analyser connected right at the feedpoint,


nice work.

 

[Marconi]

Nice job Starduater, you do good work.

I like all the old Avanti antennas, they made good stuff that worked well and didn't sell hype.

I converted an original Astroplane into an AstroBeam a few years back from memory from 1974 and the specs I found online.
It's a very picky antenna, if the boom sections which are only a few inches different in length are switched it will act like a bad ground plane with high SWR.
That's how I got mine so cheap back then, the original owner had the boom sections swapped and it wouldn't work. I put it together right and mounted it at 74 feet in the air.

Hey KomaToast, how long was the mast inside the AstroPlane driven element?

Also how long was the top 1/4 wave portion of the same element?

Did you use the pig tail provided in the kit?

 

[Marconi]

Hey Bob, I agree with you about the step rate.