Avanti Sigma4: An alternative view point

[bob85]

i don't remember how long i had it set when it was up at 73ft other than it was longer than a stock sigma4, the last time i had one up using the skinny sirio monopole between 12ft and almost 36ft to the hub the monopole ended up arount 30ft from hub to tip maybe a little longer,
its nothing like tuning a groundplane, feet and inches mean squat to me with this style antenna,
i look for best distant signals while maintaining a low vswr,
ALSO if they work as i suspect and i am manipulating takeoff angle ( very possible ) you will have to find out what works best for you by trail and error with distant stations, preferably staions you can only just hear or cannot hear on a 5/8wave.
i would not bother with hats ect as they change current distribution along the monopole and the vector is all about relative current phase between radials and monoplole imho.

 

[CDX-007]

...i would not bother with hats ect...

Ahhh, music to my ears!

Thanks Bob, When you wrote "73 ft" were you referring to the hub height or the top?

 

[bob85]

hub height in an open field

 

[CDX-007]

hub height in an open field

Whoa! Very high! I take it that was only a temporary set up and not what you're able to have at the home QTH?

 

[bob85]

that was at my parents where i had all my antennas up at that height for years.

 

[CDX-007]

that was at my parents where i had all my antennas up at that height for years.

Tower, I'll bet. I'll be able to possibly get a 60' base height if I can find decent enough guy points. I really don't want it to come in contact with the 12Kv lines running down the side yard. Might scratch the aluminum

 

[Marconi]

not much info available on the saliut, why they call it a 3/4wave when its 9.5 mtrs long is beyond me, even taking into account the electrical shortening as the radials are swept upwards it still don't tally, its virtually identical to the 7/8 vector,

http://www.cbtricks.com/ant_manuals/cte/sigma4_copy.pdf

Yep Bob, that is why I asked 007 for physical measurements.

Here are the same Salitu LW150 documents I have. You will note the front page has dimensions that your CBTricks link does not show. Since the thing is all screwed together it has a fixed length except for the top element which is adjustable.

There are hand written numbers included here that convert cm to inches. I was referring to the printed information only.

Never mind the measurements 007, I don't want to get an argument started over this outdated antenna.

 

[CDX-007]

Yep Bob, that is why I asked 007 for physical measurements.

Here are the same Salitu LW150 documents I have. You will note the front page has dimensions that your link does not so, but they are incomplete. Since the thing is all screwed together it has a fixed length except for the top element which is tunable.

There are hand written numbers included here that convert mm to inches. I was referring to the printed information only.

Never mind the measurements 007, I don't want to get an argument started over this outdated antenna.

Don't give me that, yes you do!

Thanks, Marconi. I'll get measurements and post them later. 73

 

[bob85]

don't knock the extended version eddie, its been the best performer to date, it has yet to be proven that the new version does what is claimed

 

[HomerBB]

Homer, lowering the plastic disk that supports the radials will not hurt the performance of the antenna although it may make adjusting your gamma harder. In fact the lower the disk is the less RF voltage will be across it. Placing the plastic supports too high on the radials can cause them to arc over the insulator at high power.

Thanks for this tidbit. I just drilled a hole though the plastic disc, as you see, and continued on with the matching.

 

[CDX-007]

don't knock the extended version eddie, its been the best performer to date, it has yet to be proven that the new version does what is claimed

...so do you advise I should go the full 7/8 wave?

 

[Shockwave]

I would advise going very close to the 7/8 wave but not quite 7/8 wave. This is an area I've done lots of testing with. Even with fairly large deviations in the size of the cone structure, the .82 wavelength radiator almost always shows me the most gain on the horizon.

 

[Marconi]

don't knock the extended version eddie, its been the best performer to date, it has yet to be proven that the new version does what is claimed

You're right Bob, the longer idea model should be compared by somebody and for sure if they are able to also give us a report comparing the New Vector 4000.

My comment sounded worse than I intended. I was thinking about the three antennas I ordered back in 2003 that were poorly made using a base element that was fluted. I can only assume they were made by CTE. I think I've told this story before about the two guys complaining the antenna had no ears. I think Shockwave confirmed for me that CTE did make some of these antennas using the fluted material in the base and this was the point of my comment.

I certainly would encourage CDX007 to test the longer idea after he gets the stock setup working good, whatever the stock setup is. Does anyone have any ideas how to setup his LW150, the instructions are not very helpful. It reads for setting as follows: "The adsustment (sic) of the aerial must be done moving the slide top stub upwards (sic) or downwards (sic), in order to obtain the minimum reading on the SWR meter." Based on the description here, I assume they are talking about the gamma length adjustment. My instructions show the tip element is 120 cm or 47.28". Since the rest of the main radiator is all preset with screws I guess that part of the antenna is fixed, so the overall length is the length suggested and this is the part I was really asking CDX007 about. I have never forgotten about all the grief I got for selling those crappy antennas and I never really got an answer as to why they had no receive unless they just made the antenna too long.

CDX if helpful, I have another buddies gamma off of his LW150 that was marked. The sleeve is 15.125" to the plastic tip, the rod is 20.375' from the plastic tip to the end of the rod = 35.5" inches overall. There is another mark on the rod at 31.875" that looks like where the top of the dog bone was attached, but I can't be sure. This last mark makes the length between the bottom of the sleeve and the top of the dog bone to be in the area of 31.75" and that is a little short of my Sigma 4's 33" inch setting. Sigma4 instructions are not much more informative as to the actual rod length, just the dog bone location is noted at 33" inches. This is while the overall length of the antenna radiator is fixed by construction and the kit design.

Good luck CDX007.

 

[CDX-007]

I would advise going very close to the 7/8 wave but not quite 7/8 wave. This is an area I've done lots of testing with. Even with fairly large deviations in the size of the cone structure, the .82 wavelength radiator almost always shows me the most gain on the horizon.

You're right Bob, the longer idea model should be compared by somebody and for sure if they are able to also give us a report comparing the New Vector 4000.

My comment sounded worse than I intended. I was thinking about the three antennas I ordered back in 2003 that were poorly made using a base element that was fluted. I can only assume they were made by CTE. I think I've told this story before about the two guys complaining the antenna had no ears. I think Shockwave confirmed for me that CTE did make some of these antennas using the fluted material in the base and this was the point of my comment.

I certainly would encourage CDX007 to test the longer idea after he gets the stock setup working good, whatever the stock setup is. Does anyone have any ideas how to setup his LW150, the instructions are not very helpful. It reads for setting as follows: "The adsustment (sic) of the aerial must be done moving the slide top stub upwards (sic) or downwards (sic), in order to obtain the minimum reading on the SWR meter." Based on the description here, I assume they are talking about the gamma length adjustment. My instructions show the tip element is 120 cm or 47.28". Since the rest of the main radiator is all preset with screws I guess that part of the antenna is fixed, so the overall length is the length suggested and this is the part I was really asking CDX007 about. I have never forgotten about all the grief I got for selling those crappy antennas and I never really got an answer as to why they had no receive unless they just made the antenna too long.

CDX if helpful, I have another buddies gamma off of his LW150 that was marked. The sleeve is 15.125" to the plastic tip, the rod is 20.375' from the plastic tip to the end of the rod = 35.5" inches overall. There is another mark on the rod at 31.875" that looks like where the top of the dog bone was attached, but I can't be sure. This last mark makes the length between the bottom of the sleeve and the top of the dog bone to be in the area of 31.75" and that is a little short of my Sigma 4's 33" inch setting. Sigma4 instructions are not much more informative as to the actual rod length, just the dog bone location is noted at 33" inches. This is while the overall length of the antenna radiator is fixed by construction and the kit design.

Good luck CDX007.

All good info, Thanks guys, and I'll go ahead and ballpark it to .82, gamma set to 35.5" / 31.75" and the radials extended to 90.5" for starters, unless someone has a better recommendation for a better starting point for the radials.


Evidently the new Vector is only 3/4 wave and is using ~106.6" radials, would that be a better place to begin, then try the .82?

Shockwave, I presume .82 does NOT include the 16" of mounting tube below the radial hub.

 

[Shockwave]

CDX, I would set the radiator to .82 wavelength from the connector hub to radiator tip. From what I can determine in recent testing on VHF, 90.5" inch radials may be a good starting point on CB but it looks like longer gives more signal on the horizon. Right when you approach 1/4 wavelength radials seems to work the best. For example on 98 MHz. my radials are 30 inches.

I then shortened the radiator almost a half foot less then .82 wave in small increments at 98 MHz. and saw no increase in signal. The interesting thing is while I could detect no increase, I also could not detect any decrease in signal over that length. Testing in the far field at 50 miles is very difficult because the normal signal fluctuations over this path can often be larger then the changes in signal due to antenna adjustments.

Soon I plan on taking my best far field prototype and seeing how it responds in a more stable environment where the test signal is only several miles away. I hope there will not be significant changes at these distances and can continue minor adjustments and comparisons without the frustrating propagation fluctuations. If I see major changes in tuning I'll know this method is no good. Of course this prototype will again be compared out at 50 miles.

When you're looking for the slightest change in signal measuring in microvolts on a digital meter, propagation conditions can drive you crazy. Most of the adjustments on this design interact with each other and you really need to be able to detect the smallest changes to know what direction to move each part in. This sure is nothing like aligning a receiver with a signal generator connected to it. It's been helpful to keep a stock antenna tuned so that I can instantly swap them out on the mast and compare.