This is my ASTROPLANE copy avanti AV-101, ALL manufactured in IRON.
I get better signal than a dipole, a loop and a slim-jim.
)
woww!!
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Difference in AstroPlane vs. New Top One per Eznec5
- Thread starter Marconi
- Start date
woww!!
I see similar types of gain values in the regular CB antennas too, all except for the Gain Master.
Bob I can't get your idea with the feed point at the base of your A/P 3/4 wave antenna to show a good match...without the use of some form of matching device.
FWIU the tap point on a 3/4 wave radiator at 27 mhz is about 30" - 33" above the base, and no altering of the two down radials, to make the radials closer to the mast, or bowing a little bit toward the mast will work to overcome this mismatch...like it does on the A/P. However, the 3/4 wave radiator with 2 slanted up radials that are straight will work perfectly well and give a good match if the hub is smaller than the A/P, and we use a gamma match.
I found the best compromise offset hub size for my model's radials from the base of the radiator is 3/4" of an inch offset on both sides connected to the radials, and less is worse and more is worse.
View attachment Bob's bottom fed .75w Astroplane idea.pdf
Last edited:
woww!!
Nospec, our models are pretty close over a Perfect and infinite ground plane. What do you show over real Earth?
Here are some reports from my model: View attachment AstroPlane model.pdf
I see the little red box on the antenna as the base of the radiator...is that the feed point? You will see my FP set with a red circle at about the same spot.
What is the green cone on the mast represent?
Our data is also pretty close too. Are you using 4nec2?
If that is 4nec2, do you have access to the segment file and the currents of each segment including the phase? I would like to compare currents if you could email me you file. I will PM you my email address.
Good to see somebody that can model, and welcome to the forum.
Marconi
Since the GM was marketed to compete against 5/8 wave ground planes it has its gain figures referenced against the 5/8 wave ground plane rather than the 1/2 wave dipole.
Some of us are curious if Sirio had the time to confirm the specifications in question were free space gains and if you had a chance to conduct the simple 4 wire test on your Sigma models to determine if they are reliable?
Some of us are curious if Sirio had the time to confirm the specifications in question were free space gains and if you had a chance to conduct the simple 4 wire test on your Sigma models to determine if they are reliable?
I have not received a response from Sirio as yet. I don't recall when I sent it, but I'm still waiting. I've sent Sirio maybe 3-4 messages via their contact service, and I have only received 1 response todate. I think there are some questions that they don't answer due to company policy. I'm pretty sure you guys are right on this subject however, and the dbi values are in free space. My issue with Eznec on this point is...
I can not get the models for my CB vertical antennas to show over 2.57dbi at 0* degrees in free space unless I set the model over perfect and infinite ground.
Regarding your 4 wire idea to be mounted collinear above a S4, Donald I did that back on 09/20/13 and posted it in the link below.
Here is the link to my post #26 on the 20th: http://www.worldwidedx.com/cb-antennas/159435-ghz24-what-your-opinion-sigma-4-a-4.html#post443546
Below is the model I posted earlier. This time I added the version over Real Earth, so you can see there is some collinear effects going on. The models below shows you what I wanted to try and explain before, when I asked for your model. The post on 09/20/13 did not have currents turned on, and I did not realize that at the time. I wanted to call that to your attention, so I asked if we could resume the topic, and here we are I hope.
You will notice here that I turned the currents on and off for the model.
View attachment Collinear S4 w .50w above.pdf
Does this look like what you saw with your collinear S4, with a 1/2 wave radiator above it using the four wires?
Is this what you were talking about when you told us the Eznec collinear model failed?
Last edited:
Yes Marconi, that is the design I was talking about. You'll notice it now shows about an extra 1.5 db gain over the stock antenna. You may also notice you can add these four wires to any 1/2 wave ground plane and produce about the same gain.
What you absolutely cannot do is add this 180 degree phase shift and 1/2 wave element on top of a 3/4 wave Sigma type radiator. Exactly what EZNEC is showing to provide gain, removes gain in the field because the 180 degree phase shift cause 50% of the second 1/2 wave to buck the phase of the cone.
To add a 1/2 wave on top of a 3/4 wave that already has phase correction taking place in the lower 1/4 wave, requires a 90 degree phase delay. That is what works in the field. There is no way around the fact that EZNEC only sees the Sigma as a 1/2 wave and nothing could prove that more untrue than seeing a 90 degree phase shift provide maximum gain in the field.
What you absolutely cannot do is add this 180 degree phase shift and 1/2 wave element on top of a 3/4 wave Sigma type radiator. Exactly what EZNEC is showing to provide gain, removes gain in the field because the 180 degree phase shift cause 50% of the second 1/2 wave to buck the phase of the cone.
To add a 1/2 wave on top of a 3/4 wave that already has phase correction taking place in the lower 1/4 wave, requires a 90 degree phase delay. That is what works in the field. There is no way around the fact that EZNEC only sees the Sigma as a 1/2 wave and nothing could prove that more untrue than seeing a 90 degree phase shift provide maximum gain in the field.
OK Donald I just want to be sure I fully understand what you're telling us here. If I add a 1/2 wave radiator to my S4 model, like I did above, and I make the phase setup 1/2 the size...are you saying that I should see improvement, because that is what your field results show?
I'm saying that what works in EZNEC on this experiment is off by 100% when compared to the phase shift required in the field. You' collinear model shows what is expected anytime we add these four wires to a 1/2 wave ground plane.
If you can add a 180 degree phase shift and 1/2 wave element to the Sigma and show gain in EZNEC, this proves beyond a doubt that EZNEC interprets the Sigma as a 1/2 wave radiator with NO significant in phase radiation from the cone.
The fact that we have to reduce the phase shift in half to make the antenna have gain in the field shows there is significant in phase radiation from the cone that cannot be ignored by using the 180 degree phase shift that EZNEC suggests.
The fact the antenna in the field has virtually no change in gain from the stock version when used with a 180 degree shift shows the radiation from the cone is comparable to an open 1/4 wave radiator.
I base this on the fact that it takes 1/4 wave of the added top 1/2 wave to cancel the productive radiation from the cone while the second 1/4 wave of the added 1/2 wave merely returns the antenna to its original gain when used with a 180 degree phase shift.
If you can add a 180 degree phase shift and 1/2 wave element to the Sigma and show gain in EZNEC, this proves beyond a doubt that EZNEC interprets the Sigma as a 1/2 wave radiator with NO significant in phase radiation from the cone.
The fact that we have to reduce the phase shift in half to make the antenna have gain in the field shows there is significant in phase radiation from the cone that cannot be ignored by using the 180 degree phase shift that EZNEC suggests.
The fact the antenna in the field has virtually no change in gain from the stock version when used with a 180 degree shift shows the radiation from the cone is comparable to an open 1/4 wave radiator.
I base this on the fact that it takes 1/4 wave of the added top 1/2 wave to cancel the productive radiation from the cone while the second 1/4 wave of the added 1/2 wave merely returns the antenna to its original gain when used with a 180 degree phase shift.
Last edited:
Donald, here is what I get when I compare my Big Hair 5/8 wave collinear to my Sigma 4 with a collinear .50 wave above.
View attachment Collinear .625w vs. S4 collinear with .50w.pdf
I understand that this S4 does not work as this model indicates in you real world testing, but this shows me the collinear S4 is about the same as a full 5/8 wave collinear.
View attachment Collinear .625w vs. S4 collinear with .50w.pdf
I understand that this S4 does not work as this model indicates in you real world testing, but this shows me the collinear S4 is about the same as a full 5/8 wave collinear.
You do have the model of the Sigma built the way I suggested and it is working in EZNEC with a phase delay that is much too long to work in the field. The point here was to prove that EZNEC needs to see a 1/2 wave phase shift and that can only be the case if it misses just about all of the cones phase corrected radiation.
The collinear model I suggested was built only to clearly demonstrate this fact by using a phase shift design whose electrical length and total unfolded physical length would be virtually the same. The shorted stub phase delay does radiate on this antenna and distorts the radiation pattern badly.
This makes that collinear Sigma model unsuitable for comparison to other collinear models not suffering from a phasing network that is radiating and causing heavy distortion in the pattern. They should also be compared in free space to eliminate ground gain variables and distortion in the pattern from those ground reflections.
The idea here was to find a way to test what EZNEC was telling me about how much of the antenna it thinks was radiating, its phase and relative magnitude. Adding a known 1/2 wave radiator on top and adjusting the phase delay in the field for maximum gain in the distance is an ideal real world test for this.
The radiation current and phase distribution across an end fed 1/2 wave is a given we can take as common knowledge. Adding it to the top of another antenna in question and peaking the gain in the phase shift will identify the relative magnitude and phase of the entire radiator below this phase delay.
If the Sigma cone was just transmission line or had low amounts of in phase currents radiating from it, that means it's just a fancy looking 1/2 wave J-pole. It also means the phase to drive the second collinear 1/2 wave must be completely inverted the full 180 degrees. Just like EZNEC suggests.
Since the gain peaks with an electrical 1/4 wavelength or 90 degree total phase shift, that proves the cone is producing fairly strong radiation currents that effectively combine with the upper element in the far field. When I consider this along with the CST data, I have conclusive proof the Sigma is a "non apparent collinear". Needless to say all the EZNEC models we have seen on the Sigma have been nothing less than misleading too.
The collinear model I suggested was built only to clearly demonstrate this fact by using a phase shift design whose electrical length and total unfolded physical length would be virtually the same. The shorted stub phase delay does radiate on this antenna and distorts the radiation pattern badly.
This makes that collinear Sigma model unsuitable for comparison to other collinear models not suffering from a phasing network that is radiating and causing heavy distortion in the pattern. They should also be compared in free space to eliminate ground gain variables and distortion in the pattern from those ground reflections.
The idea here was to find a way to test what EZNEC was telling me about how much of the antenna it thinks was radiating, its phase and relative magnitude. Adding a known 1/2 wave radiator on top and adjusting the phase delay in the field for maximum gain in the distance is an ideal real world test for this.
The radiation current and phase distribution across an end fed 1/2 wave is a given we can take as common knowledge. Adding it to the top of another antenna in question and peaking the gain in the phase shift will identify the relative magnitude and phase of the entire radiator below this phase delay.
If the Sigma cone was just transmission line or had low amounts of in phase currents radiating from it, that means it's just a fancy looking 1/2 wave J-pole. It also means the phase to drive the second collinear 1/2 wave must be completely inverted the full 180 degrees. Just like EZNEC suggests.
Since the gain peaks with an electrical 1/4 wavelength or 90 degree total phase shift, that proves the cone is producing fairly strong radiation currents that effectively combine with the upper element in the far field. When I consider this along with the CST data, I have conclusive proof the Sigma is a "non apparent collinear". Needless to say all the EZNEC models we have seen on the Sigma have been nothing less than misleading too.
Last edited: