Avanti Sigma4: An alternative view point

[CDX-007]

thats great cdx what do you think the chances are of taking a picture of that baby?

I tried but the crappy 3megapixel camera just doesn't capture much more than sky.

Imagine walking out into a big field or park with:

1) a five (10')section, 45' telescoping mast
2) a 1" diameter, 36" long iron stake, one end sharpened & a 6" washer
3) guy wire & dacron line
4) insulators
5) 88' of RG-213
6) an Imax 2000
7) your radio & swr meter

Hammer the stake 18" into the ground leaving 18" of solid stake above ground to keep the bottom of the mast from moving around, plus helping to support the mast upright while guying the bottom 10' section in place with dacron non-metallic line.

Place the tight-fitting 6" washer around the bottom of the iron stake to prevent the mast from sinking into the ground and slide the mast over the stake and guy by 3-4 dacron lines from the top of the mast bottom section 10' up.

Now you have a mast sitting upright and guyed at ten feet alongside of which you may now stand a ladder.

Climb up and install the Imax, attaching the 88' of RG-213 to it and tape well for strain relief.

Add a 23' length of guy wire (including an insulator at the far end) to the top U-bolt on the Imax and let it hang with enough Dacron line from the insulator to reach the ground at a ~45° angle once fully elevated to 45'.

Now elevate the top section of mast ~8'.

Add three 9' guy wires (including insulators at their far ends) to the guy wire ring at the top of the 40' (4th) section of mast. Add enough dacron line to the end insulators to reach the ground for guying at ~40° angle when fully elevated.

Elevate the remaining 3 middle sections of mast 9' each and pull the three 9' guy wires/ dacron out to about a 40° angle and set with stakes or lawn corkscrew type dog leash holders into the ground.

Pull the single 23' guy wire & dacron line out to about a 45° angle and tie off on the ground with another stake.

Drape the 88' of 213 from about the 20' high point on the mast, out and down to the radio about 40' away from the mast.

Now you have my approximate set-up.

Clear as mud?

Thread hijack possibly over.

 

[HomerBB]

As I said earlier, I put the Qv4k up to right at 35' at the feed point. I removed the isolation from between the mast and the vertical antenna radial and put a ten foot metal mast pipe up into the bottom 13 3/4" of the antenna. The rest of my mast is wood. What I have is a nearly 9' (1/4 wave) length of mast in direct contact with the antenna from feedpoint downward. I experienced no significant SWR change from when it was 10' above earth and isolated from the mast. I continue to use a coax choke on the feedline.

SWR @ 10' and isolated:

28.755 ------- 1.5:1
28.305 ------- 1.4:1
27.855 ------- 1.2:1
27.555 ------- <1.1:1
27.405 ------- 1.0:1
27.205 ------- <1.1:1
26.965 ------- 1.2:1
26.515 ------- 1.8:1
26.065 ------- 2.2:1
25.615 ------- 2.6:1
25.165 ------- 2.8:1

SWR @ 35' and not isolated from a 19' section of mast:

28.755 ------- 1.5:1
28.305 ------- <1.4:1
27.855 ------- <1.2:1
27.555 ------- <1.1:1
27.405 ------- <1.1:1
27.205 ------- 1.1:1
26.965 ------- 1.3:1
26.515 ------- 1.8:1
26.065 ------- 2.4:1
25.615 ------- 2.8:1
25.165 ------- 3.0:1

I put the other 5/8 up on the roof this evening, but need some time to tune it in - SWR is high. Also, unlike I previously thought, it may prove challenging to get it to 35' where it is. I am at 25' right now, Perhaps by the weekend I'll be ready for some comparisons. As it is now, the Qv4k is eating its lunch in an unfair mismatched setup.

 

[1342]

I tried but the crappy 3megapixel camera just doesn't capture much more than sky.

Imagine walking out into a big field or park with:

1) a five (10')section, 45' telescoping mast
2) a 1" diameter, 36" long iron stake, one end sharpened & a 6" washer
3) guy wire & dacron line
4) insulators
5) 88' of RG-213
6) an Imax 2000
7) your radio & swr meter

Hammer the stake 18" into the ground leaving 18" of solid stake above ground to keep the bottom of the mast from moving around, plus helping to support the mast upright while guying the bottom 10' section in place with dacron non-metallic line.

Place the tight-fitting 6" washer around the bottom of the iron stake to prevent the mast from sinking into the ground and slide the mast over the stake and guy by 3-4 dacron lines from the top of the mast bottom section 10' up.

Now you have a mast sitting upright and guyed at ten feet alongside of which you may now stand a ladder.

Climb up and install the Imax, attaching the 88' of RG-213 to it and tape well for strain relief.

Add a 23' length of guy wire (including an insulator at the far end) to the top U-bolt on the Imax and let it hang with enough Dacron line from the insulator to reach the ground at a ~45° angle once fully elevated to 45'.

Now elevate the top section of mast ~8'.

Add three 9' guy wires (including insulators at their far ends) to the guy wire ring at the top of the 40' (4th) section of mast. Add enough dacron line to the end insulators to reach the ground for guying at ~40° angle when fully elevated.

Elevate the remaining 3 middle sections of mast 9' each and pull the three 9' guy wires/ dacron out to about a 40° angle and set with stakes or lawn corkscrew type dog leash holders into the ground.

Pull the single 23' guy wire & dacron line out to about a 45° angle and tie off on the ground with another stake.

Drape the 88' of 213 from about the 20' high point on the mast, out and down to the radio about 40' away from the mast.

Now you have my approximate set-up.

Clear as mud?

Thread hijack possibly over.

thanks for trying cdx now i see why they say a picture is worth a thousand words!lol

 

[CDX-007]

Geez, I hope you didn't count all that! :blink:

Maybe I'll try to borrow back the one I used to capture the I-10K & P-500.

 

[jazzsinger]

I'm wondering how a mirror image (downward) radial cone + a tuned (3/4?) section of mast might add to the performance, making it a semi-center-gamma fed 1.5wl dipole.

Perhaps an experiment for a 3 meter version first!

I'm not sure how well it would work,but i bet at 27 mhz the neighbours would f@cking love it.54 feet of total eyesore.compared to that Laura Bush would look pretty.

 

[CDX-007]

Yeah, but either way, only the down-firing radial cone would add to the already big aerial appearance if it was mounted on a 30' mast.

 

[Shockwave]

I'm wondering how a mirror image (downward) radial cone + a tuned (3/4?) section of mast might add to the performance, making it a semi-center-gamma fed 1.5wl dipole.

Perhaps an experiment for a 3 meter version first!

Oddly enough I did experiment with a second set of downward radials on the Sigma and saw the signal drop. If I took the second set of radials any lower then horizontal the test signal went down. If I folded the second set of radials upward, between horizontal and the first set, I saw the slightest increase. It also added directional lobes without the loop on the second set. Not worth the extra mechanical design.

 

[CDX-007]

Interesting about the lower radial cone having to be non-inverted for gain. I guess since it's not separated like a dipole it was canceling/ out of phase.

Did you test the additional lower at distance or mostly near-field?

Makes me wonder if there could be a worthwhile real world increase on 11m.

 

[Shockwave]

CDX, I think the extra set of downward radials on a Sigma makes the gain drop because the portion of mast directly under the antenna radiates some energy that is in phase. This would be based on the same reason the upward cone confines the out of phase radiation of the first 1/4 wave on the main radiator. Extra horizontal radials seemed to do nothing because they do not cancel radiation (in phase or out of phase) and the Sigma is not looking for a reflection under it. All of my tests to this point have been far field from about 40 to 50 miles.

One possible area of improvement may be to construct some type of wire mesh screen around the cone to confine a higher percentage of out of phase radiation. Just like the fourth radial added some gain on the Vector from the original Sigma, this could help further. Very old prior art work contained in the Sigma patent showed this wire mesh cone dated from 1939! Who would have guessed the basic design has been around that long?

This diagram did not show a matching network and obviously the gamma would complicate a mesh. It may have to be pulled inside the mesh cone or a void in the mesh for the gamma could be tried. It's unlikely the added gain would be worth the cost to mass produce this mesh design. However there are plenty of us that would make any reasonable attempt to add any gain to our antennas.

 

[Shockwave]

Interesting about the lower radial cone having to be non-inverted for gain. I guess since it's not separated like a dipole it was canceling/ out of phase.

Did you test the additional lower at distance or mostly near-field?

Makes me wonder if there could be a worthwhile real world increase on 11m.

I also wanted to add that your thoughts about dual cones and a dipole are supported by sound RF theory dating back to at least the cold war era. If you form a dipole from a pair of cones, with the cones flaring outward from the center feedline, it makes a very broadbanded dipole without a loss in gain. It can be orientated either vertical or horizontal.

The infamous "Russian Woodpecker" generated one of the worlds most powerful RF signals for over a decade using a massive array constructed from dipoles of this design. The "tower" stands over 500 feet tall and over 1/4 mile long. It was used to operate an HF over the horizon radar system. It's major side effect was that it jammed up a good slice of the center of the HF spectrum worldwide!

This was a serious issue during the 70's and 80's. While the end of the cold war would eventually see these things come to an end, another incident played a role in stopping the "Woodpecker". Against the advice of engineers working at the Chernobyl nuclear power plant, a test was conducted to see how the reactor would respond at reduced output with an interrupted main cooling system.

It turns out they shouldn't have done that. The reactor had already shown signs that it could not be controlled at extreme low output levels. Nevermind tampering with the cooling and bypassing the protection systems simultaneously. Chernobyl exploded with the over the horizon radar system located within eyesight from it. An excellent photo section of the radar antenna can be seen here English Russia » “Duga”, the Steel Giant Near Chernobyl

PS. How would you like to connect your 40 meter rig into that antenna?

 

[jazzsinger]

I also wanted to add that your thoughts about dual cones and a dipole are supported by sound RF theory dating back to at least the cold war era. If you form a dipole from a pair of cones, with the cones flaring outward from the center feedline, it makes a very broadbanded dipole without a loss in gain. It can be orientated either vertical or horizontal.

The infamous "Russian Woodpecker" generated one of the worlds most powerful RF signals for over a decade using a massive array constructed from dipoles of this design. The "tower" stands over 500 feet tall and over 1/4 mile long. It was used to operate an HF over the horizon radar system. It's major side effect was that it jammed up a good slice of the center of the HF spectrum worldwide!

This was a serious issue during the 70's and 80's. While the end of the cold war would eventually see these things come to an end, another incident played a role in stopping the "Woodpecker". Against the advice of engineers working at the Chernobyl nuclear power plant, a test was conducted to see how the reactor would respond at reduced output with an interrupted main cooling system.

It turns out they shouldn't have done that. The reactor had already shown signs that it could not be controlled at extreme low output levels. Nevermind tampering with the cooling and bypassing the protection systems simultaneously. Chernobyl exploded with the over the horizon radar system located within eyesight from it. An excellent photo section of the radar antenna can be seen here English Russia » “Duga”, the Steel Giant Near Chernobyl

Makes you wonder if a second upward cone at the base of the mast would do for the mast radiation what the antenna cone does for the antennas radiation and again add more horizontal gain.

 

[CDX-007]

So it sounds to me like the bottom 1/4 wave of the main radiating element is radiating out of phase and being captured by the in-phase radiation of the radial cone, thus providing another additional 1/4 wave in-phase element in a relative collinear fashion, plus acting as a feed system for the upper 1/2 - 5/8 wave part of the antenna, but doing so in a manner which lowers the TOA below that of a single 1/2 - 5/8 antenna.

If this is close to being anywhere near accurate it seems the next logical step would be a full wave main radiating element with a 1/2 wavelength radial cone to extract the gain & flat - downward TOA equivalent of a 1/2wl above a 1/2wl collinear.

 

[Shockwave]

So it sounds to me like the bottom 1/4 wave of the main radiating element is radiating out of phase and being captured by the in-phase radiation of the radial cone, thus providing another additional 1/4 wave in-phase element in a relative collinear fashion, plus acting as a feed system for the upper 1/2 - 5/8 wave part of the antenna, but doing so in a manner which lowers the TOA below that of a single 1/2 - 5/8 antenna.

If this is close to being anywhere near accurate it seems the next logical step would be a full wave main radiating element with a 1/2 wavelength radial cone to extract the gain & flat - downward TOA equivalent of a 1/2wl above a 1/2wl collinear.

OK, I'm impressed. After speaking with the Sirio engineer and confirming this confinement and replacement of out of phase radiation, I wondered the same thing and built a model. The weather here has been poor the last few days so I haven't run any field tests yet. Earlier test where I extended the radiator and radial length showed the gain began to drop as the radiator went past .82 wavelength with radials just over 1/4 wave. It is quite possible that there just may be a null in gain when extending these lengths before a second peak in gain is seen fully extended. We shall see soon enough.

 

[CDX-007]

OK, I'm impressed. After speaking with the Sirio engineer and confirming this confinement and replacement of out of phase radiation, I wondered the same thing and built a model. The weather here has been poor the last few days so I haven't run any field tests yet. Earlier test where I extended the radiator and radial length showed the gain began to drop as the radiator went past .82 wavelength with radials just over 1/4 wave. It is quite possible that there just may be a null in gain when extending these lengths before a second peak in gain is seen fully extended. We shall see soon enough.

Were the radials over 1/4 wave including the ring/4 or PLUS the ring/4?

What changes to the Gamma do you expect will be required to match the full (1.5wl?) wave?

Hmmm, being a 3/4 wave x 2, I wonder if it could be possible to direct feed with a 1:1 balun at the point 3/4 wave down from the top since a 3/4wl is a ~50-72 ohm load?

- Maybe a .75wl - 1.25wl piece of 75ohm (whichever is in phase with the bottom 1/4) up inside of/ into the lower 1/4 wave point/ feed point?

 

[Shockwave]

The radials were over 1/4 wave not counting the loop. Other then the length and value of capacitance I think the gamma will still work without much change. I think this would work best as a half wave over a half wave. I haven't had the best luck with 3/4 wave over 3/4 wave but I haven't tried center feeding it either like it seems you're suggesting.