considering an M400 starduster. whats the deal?

[Marconi]

A few tips to watch for when installing an AstroPlane. A vohm meter can be your friend, so use it with this antenna in particular. When fully constructed the AP will show continuity between every element in the antenna including the feed point shield to center conductor. I know it will look wrong to you, but there is no exception to this fact in this antenna.

If you are able to detect any intermittant readings with your vohm meter then check all physical connections, including where the mast you provide attaches to the hub. Physical connections means the stud connections in the ends of tubing. Make sure they are tight and do not turn or wiggle and carefully make sure these elements are set fully into the insularor looking devices if your antenna is a knockoff. The original AP has a metal to metal compression fit for the side opposite the feed point and studs are not used in this case.

In the knock off AP with insulators mounted to both sides of the mounting hub studs in the ends of the tubing are used to secure. These points may show good continuity and still be loose, so check these points where studs are crimped fit inside of tubing. Even if any of these points are a bit loose fitting and you are able to get them screwed into the hub brackets and they show good on a vohm meter the antenna will probably work OK, but you may find it producing a lot of TVI and/or bleedover with neighbors and maybe even with your own household stuff.

The potential for bad spots that need to be checked are in the stud ends of the two elements that hang down below the hub bracket and the shortened top element where you may find both ends that have studs installed. All of these little stud devices set in the ends of the tubes are crimp fit to be tight and they do come loose in some cases and this is difficult to detect unless you take the antenna apart or otherwise have problems with the antenna. I bet a lot of these antennas have been destroyed over the years just due to this problem not being easy to detect and the antenna unexplainably acting bad.

When the AP antenna is right I find it to be one of the best matching CB antennas on the market and they do a very good job of not causing interference like TVI and bleedover, but again if you notice such problems---check the physical connections throughout the antenna closely.

Replace all screws, washer, and nuts with stainless and this antenna should last even in bad weather areas for many years.

Another area of concern are where the manufactures have flattened tubing at the bottom ring, these points tend to break over time with the motions of wind and weather.

When in stalling the AP make very sure that the bottom hoop is well away from anything, not just reflective metal. Avanti and other manufactures note of "WARNING" in there install instructions about the bottom hoop being less than 4' feet away from any large mount like a tower or other reflective surface including guy wire setups, but IMO even 4" is too close. At one point during a recent install of my AP at 20' feet to the hub, with the bottom hoop being about 12' feet to the ground---my antenna tune acted badly. I found this problem was because I had my I-10K lying on the ground 12' feet below the AP. I was amazed at this response so far away from the hoop and that is worth noting.

You should find the AP to be a very effective antenna and will compare equal or better than most if the antenna tips are the same height above ground. I also find the AP is very responsive to local horizontal signals and even so this may account for a little less vertical signal response on you RX meter. I think this may just be a near field issue and not so obvious in the far field. I have not been able to actually realize the same horizontal response with DX when switching between antennas, but this little antenna is none-the-less a really good DX workhorse---so maybe this horizontal affinity the AP seems to exhibit may be making that difference too. If you are not able to rapidly switch between antennas to check this out you probably will not be able to make such an observation however, but I believe these facts can be duplicated.

I personally believe the AP to be a remarkable antenna in many respects, but unless you get it up as high to the tip as another you wish to compare it too, it is likely only mediocre at best locally---except for DX and it will work DX very well at just about any reasonable height above ground.

 

[Marconi]

As others have noted the radials are not insulated at the hub. They are supported lower down the radial away from the mast by insulated spacers or rods; for mechanical and rf stability. The radials are resonant and if the spacing away from the mast changes so does the tuning. The starduster when properly tuned has the same amount of current flowing in the radiator as the radials. As for the name you choose to use to describe the Starduster that's open : 2 1/4 wave elements same as the old 1/4 droopy Groundplane,the original coaxial vertical and the newer coaxial bazooka
designs. I believe that the Starduster was designed with the radials at the angle they are was an attempt to raise the impedance of the antenna closer to 50 ohms. The radials also act as a sleeve with the large diameter at the bottom of the radials producing a high impedance point. The earlier vertical coaxial dipole designs suffered from bad feedline radiation due to the sleeve being pipe or alum of 2 inches in dia. Reason being the ratio of the feedline dia to the sleeve was not great enough to produce the high impedance needed at the bottom of the sleeve for the antenna to operate correctly.
The only improvement i can think of would be to increase the number of radials on the Starduster to simulate a complete sleeve. Have any of you
seen the ISOPOLE brand of 2m/440 antennas same theory with more decoupling.

I once built a coaxial vertical for 10 meter FMand had to use 4" alu for the sleeve to reach acceptable decoupling. It is really great to see all the discussion on antennas.

73 RCB

IMO, RCB describes very well what is likely going on with the Starduster. This may also account for the reason the radial angle of the SD'r is much steeper than the claims of antenna guru's stating that 40 degrees slope is the magic angle needed to achieve a 50 ohm match with a resonant 1/4 wave radiator.

Personally I think there's more gain to be had with a steeper angle. I also think this might be why there is a little off set in measurements of the physicals. Maybe it is a way to get back to a better match. To support this idea about the angle, I find that my knock-off, which has a considerably larger radal angle at 38 degrees, does not seem to perform as well as the original SD'r which I measure to be close to a 26 degrees angle.

 

[loosecannon]

marconi,

i agree with everything you said about the astroplane copy.
why shouldnt i; we discussed this antenna to death in another forum.

you, me, and a guy called tech833.
did we ever actually agree on what type of antenna it is? LOL! J/K
(lets not get THAT discussion going again!!!)

i think you knew me by a different name on that rather oppressive forum.
(the name kid vicious ring any bells?)

it would be pretty cool to actually make a DX contact with you some time.
i get texas in here sometimes, and thats just with my inverted V on the roof.

what freq do you hang out on when DXing?


take it easy,
LC

 

[Marconi]

Sure LC, I remember the discussion on CF with you and 833. I don't remember all of the details, but I think I was probably arguing for raising the AP up as high to-the-tip as any of the other antennas 833 had rated in his report.

For years before and in that thread the issue about the AP had always been that it only worked well when it was installed low to the ground. I disgreeded back then and for sure now---with that observation and that the antenna also worked well if mounted up high. Maybe I even raised an issue, as I understood it, regarding the likely confusion being connected with the ideas and purpose of the design noted in the Patent, and/or for sure promoted by Avanti and others back in the day.

But Kid with that said, I have since learned a lot and one thing is for sure---what happens in my back yard with my antennas is not always what goes on everywhere---and that is a hard fact to sell considering we hear so much CBBS on these forums.

I hang out on lsb 36 - 39 depending on the traffic. Mostly on 36 & 38 when DX is rolling. I'm in Houston, most of the time. When DX is working I mostly go these days as Ole Grandpa after my daddy who is still working that starduster down south of Corpus Christi. Folks tell me they can't tell our voices apart and sometimes when we are together.

 

[loosecannon]

basically i just kept raising my "top one" higher and higher into the air trying to see if it ever lost any ability way up there.
it did not!

i started with the tip at about 35', then went up to 44', then to 54'.

i based my results on how i received certain stations that were known to be running the same equipment from the same location.
each time i moved the antenna, i left it there for a month or so before changing it.

each time i raised it, the stations came in better.
i cant say there were big S unit increases, but there were increases.

by the time i got to 54' to the tip i could be king of the channel when running power, and the ears kicked ass.

my new antenna just arrived today, so the fun begins tonight when i get home from work.

hope to catch you out there some time.
LC

 

[Marconi]

Yep LC, I have found the same to be true with the AP and have argued that if you get the tip up as high as say the I-10K or the Sigma IV the AP may be as good and sometimes even better than both.

I just ran a few weeks of such comparisons and have averaged out the results to make it easier to analyze my results. These comparisons were done with the antennas side by side using a switch box. This may not be the moar acceptable way to compare antennas, but at the time conditions were a bit variable at the time and this made the work difficult. I tried to do this using just one mast and feed line, but I found I was not fast enough to make changes to the antennas so I did them side by side.

1. SR 7/28/09 is comparing Sigma IV vs. 1-10K both at the same feed point height of 23'9".
Sigma averaged 56 Sunits / 8 contacts = 6.2.
I-10K averaged 52 Sunits / 8 contacts = 5.8.

2. SR 8/01/09 is comparing the same antennas with the antennas has high as I could get each. The I-10K was 27' to the feed point and the Astroplane was 33'10". The AstroPlane in the report had a full 1/4 wave element in the top instead of the shortened element with a top hat.
I-10 averaged 57 Sunits / 7 contacts = 8.1.
A/P averaged 50 Sunits / 7 contacts = 7.1.

3. SR 08/03/09 is comparing the Sigma IV vs the AstroPlane with the regular tip in the top of the antenna and both tips were at 45'8".
Sigma averaged 33 Sunits / 5 contacts = 6.6.
A/P averaged 35 Sunits / 5 contacts = 7.

At this point I had to remove all of my antennas because of a remodel of my home. I am thru now and I plan to get back to some more testing soon.

I would post the reports, but I have not scanned all of them to my hard disk yet. I have the first one and when I get the others I will try to remember to fix that.

 

[loosecannon]

interesting results marconi.

one of these days i will have the space to run a sigma IV.
ive always wanted one.

i dont hear of too many people doing it, but i think the vertical radiator should be bound in place inside the ring.

kind of like the mast and the hoop on the astroplane.

the sigma IV's have a reputation of breaking and i think this idea would help.

ive never owned one though so i could just be blowing smoke. LOL
LC

 

[Marconi]

interesting results marconi.

one of these days i will have the space to run a sigma IV.
ive always wanted one.

i dont hear of too many people doing it, but i think the vertical radiator should be bound in place inside the ring.

kind of like the mast and the hoop on the astroplane.

the sigma IV's have a reputation of breaking and i think this idea would help.

ive never owned one though so i could just be blowing smoke. LOL
LC

LC, some years ago when I got my hands on my Avanti, a 3 - radial Sigma IV, I put it up an a 10' mast to check it out. I receive it already assembled by the original owner, but in two large pieces. The bottom in tact and the radiator minus the bottom section. I did nothing more than put the two pieces together an talked on it for a while. I did notice the antenna see resonant best a bit higher in frequency than I expected, but the nice BW took care of working the CB band just fine. A bit later I did try to tune it down frequency a bit, with not success, so I left if alone until just recently. That is another story for another thread for another time maybe.

One day I was away from home and when I got back my Sigma IV was gone. The coax was on the ground and led over into my neighbors yard and wento over the fence. That is where I found the antenna---luckely it was in perfect shape. I then put the antenna back into two pieces and stored it away in my garage. I recently resumed my antenna work after maybe 15 years and I found that one element about the 3rd down from the top had been bent a bit either in the fall or by the wind that must have carried it off of the mast and into my neighbors yard.

That said, I believe the Sigma is quite strudy as it is and if you added something to guy the hoop to the main mast it might prove determintal to its operation, because the hoop is one of those points in the antenna where a lot may be going on that affects directly how the pattern developes. Maybe it would not be noticable to the eye or other senses, but I would just leave it alone, structural improvement or not.

The simple fact is that every owner/user of this fine antenna I have ever heard or read about says: "...it works fine or it is the best antenna I've ever owned." IMO this suggest to me that it is a very complicated and sensitive antenna in construction and that because of that it defies all predictions for using a radiator that is that long. I even think the same might be true of the AstroPlane, but I have heard of guys guying that hoop too and attaching it to the supporting mast, but I don't know the results other than it made the antenna mover about less in the wind. Maybe these guys did not even check to see if their mode made a difference or not.

 

[BOOTY MONSTER]

ill just go ahead and embarass myself ....

if the weather isnt severe or if it was taken down if/when hurricanes were comming in , is there any reason the sirio vector 4000 shouldnt perform similar to the sigma 4 ? most complain about its potiental to break in bad weather .

Sirio Antenne - Products

theres an assembly PDF under technical details if anyone is interested ...

 

[bob85]

booty,
in our tests the original 31' vector outperforms the sigma4,
if you take it down anytime you expect 35mph or higher winds it may survive but i would not bet on it,

after 20+ years of the same design sirio recently changed the antenna, the latest version is shorter than the original 31' version so it should be a little more sturdy,
it also has significantly longer radials than the original which used the same radial sleeve length as the avanti and other sigma copies,

sirio claim the new upgraded configuration produces a lower angle of radiation, sirio have an rf anechoic chamber and proper test equipment, did they put it to good use? i dont know,

i have not had the chance to test the new version but i have in the past observed significant changes in signal strength at distances of 60miles+ when altering sleeve to monopole length ratios and retuning,

it is also claimed from more than one source that sleeve length can be used to control elevation/angle of maximum radiation in skirted/sleeve monopole antennas,
sirio's claims may have some merrit,

the only way to find out is do your own tests with both versions.

 

[Marconi]

Hey Bob, I just posted my last three Signal Reports comparing my Sigma IV to my I-10K and my AstroPlane in my post above. I don't believe you have seen these yet. I was really surprised to see how well the AP performed when the tips were close to equal heights. Conditions are better now and DX has been sparse to non-existent up until today and conditions were just terrible. All the locals were sounding like they were off frequency and DX was so strong the locals sounded like they were 100's of miles away. Tonight conditions are very good and now I'm copying stations nearby up to a 100 miles or so. That is nice.

I also just added the choke to my Sigma that I described to you earlier. I sense less noise when it is quiet, but according to the Signal Reports I have just recorded and comparing them to signals back in August---I am not seeing improved signals---and that confuses me considering I seem to be hearing better.

I agree that TX/RX are supposed to be reciprocal, but I can't figure out why I'm not seeing better RX signals also. I would think that should go along with what seems like a lower noise level. So, if I have eliminated some of the CMC that may have been emanating from my Sigma, then I'm hoping the reciprocal idea is also doing its thing. Of course I will repeat these comparisons just in case I was experiencing bad conditions.

Our weather is changing dramatically so changes in signals may be occurring and maybe that is why my recent signals are not as good as they were back in August. I'll plan to get back to my antennas soon. I have ordered some delrin material to better insulate my antennas and when that arrives I'll get started. Then I can raise the insulation idea up above the mast as both you and Master Chef suggest. I do think that is important to help prevent passive radiation between the radiator and ground even if I don't end up seeing results similar to you and Multimode 200. I'm going to first try it out on the A99, cause I can't find any of my Antenna Work Sheets on my A99, so I'll be starting over with my testing again. Sooner or later I will get it right, as practice makes perfect, so I hear.

Hang loose,

 

[bob85]

hello eddie,
its good to finally see the results for your sigma4 vs other antennas, i was kinda waiting with baited breath to see how it turned out, i dont know why as i was pretty confident if you got the sigma tuning even half right it would beat the other antennas mounted at the same feedpoint height, still good to see it where it belongs though lol

i dont doubt the astroplanes performance when mounted as the designers intended , i found a nice 60" piece of .070" wall 6061-t6 tube for my homebrew astroplane,
the hub you sent me will live to fight another day, i thank you,

if your choke is reducing receiver noise id suspect it is reducing common mode noise or other noise thats getting onto your coax and back into the antenna, if the sigma is still electrically connected to the mast i would not expect the choke to do much if anything for received or transmitted signals but as always i could be wrong,

keep us postedop:

 

[Marconi]

Well like I said some where today, I have some plastic coming and then I'll be able to insulate the Sigma and some of the others the right way.

I have been studying my Antenna Work Sheets and I am seeing the I-10K "R to X" problems with other antennas as well. I hope to get to the bottom of why that is too, but it will take more work and testing. I plane on trying to solve that issue if I can first, and then see how the insulation idea works out.

Stay tuned.

 

[loosecannon]

marconi,

if what we are presuming about how the A99 works by using the coax shield as a counterpoise; then if you were to isolate it from its mast, and use the RF choke at the feedpoint, but did NOT use the groundplane kit in this install, then you should see a high SWR right?

or am i confused again? LOL

LC

 

[Marconi]

marconi,

if what we are presuming about how the A99 works by using the coax shield as a counterpoise; then if you were to isolate it from its mast, and use the RF choke at the feed point, but did NOT use the ground plane kit in this install, then you should see a high SWR right?

or am i confused again? LOL

LC

LC, as I understand this issue concerning the A99, CMC, Isolation, Chokes, and no GPK, the choke and isolation alone would only have minimal responses in such a configuration if we excluded proper GP radials. This is because the system needs a return path for these currents and without the GP radials to provide that path, the CMC would just defeat the choke and flow on the shield anyway. I'm sure it is much more complicated that this, but others will have to speak to that.

In my limited experience on this issue I am lead to believe that the SWR may in fact show to be a bit higher if we are able to curtail the flow of CMC if we start out with a system that shows a very low SWR. I see this as if we might expect the feed point impedance to be reduced a bit from say 50 ohms when we stop CMC if they are bad enough to matter. These current might be exhibiting a better match at the feed point due to losses and if we reduce those losses, we might see the SWR go up a bit due to an increase in reactance creeping into the system. I've also been told that if we have a low loss system, feed line, and resistive load---that most of this type of problem will not happen. I'm still waiting for someone to be able to prove that to me and be convincing.

It is really hard to predict what a feed point impedance might be when we make a modification of some type to our antenna system and I can only guess that the SWR could also start out in a system a bit high and end up actually lower as a result of curing the CMC problem also. Just a guess though.

My mentor in radio, the man that got me started in all this business, was a retire Army Master Sgt. in charge of field communications training for nearly 25 years. He use to tell me when installing a 1/4 wave whip on an auto to always strive to achieve at least a 1.3:1 VSWR. He explained the natural match for such an element under proper installation conditions is approximately 38 ohms of resistance at resonance and with a suitable ground plane the effects would be to generate an approximate VSWR of 1.3:1, and if you pushed the system to show more than 38 ohms somehow you are just adding losses that show up as increased impedance via reactance and that part of the feed point impedance (reactance) does not radiate. You all have heard that from our friend 'Doc as long as I can remember, but you have to be paying attention to understand that.

I tend to believe that idea although, I like most prefer to see my SWR as low and as flat as possible with at least 1- 2 megs of bandwidth. I just wish I could definitively measure and prove that idea, because most will not even consider such an idea.