Avanti Sigma4: An alternative view point

[CDX-007]

Finally got the 5/8 into the air last night as the sun fell. Preliminary results are encouraging, but limited. Ears within 20 miles seem good and reports from other stations indicate I may be doing as good, perhaps better with this antenna over the Qv4k.

If this proves true I believe the cause will have to be because I have not optimized the Qv4k due too not having the proper equipment. The construction of a 5/8 wave is much more basic and falling into a good design is much easier.

I will begin to compile data in terms of audio reports, and S unit readings here and to other stations. i know radio S/RX meters are not precision instruments, but I believe they are usable references when they are from stationary stations on the same radios each time.

Some modifications to the 5/8 were done before I sent it up: after a lot of wind here in the area I decided it needed some changes to avoid disaster.

I'd like to see you try 23' (.64) next!

 

[CDX-007]

On a regular basis, I can talk to 360 in Squaw Valley, Ca.

He's approx 4K feet.

I'm at 6000 feet, and we talk. At will. I'm on a (how I found the thread) Sigma IV.

He runs a 3 element beam, homebrew I BELIEVE!

Amplitude, Altitude and Attitude. AAA of CB.

--Toll_Free

Hey Toll Free, what frequency do you use when you two are talking and when are you typically on?

You're not that far from me, maybe we could QSO. If not on 11 then maybe 20m-80m.


...and you'll have to explain that "Pidgeon" thing

 

[HomerBB]

I'd like to see you try 23' (.64) next!

It is at 22.5 ft now, however I had to redo it after a severe storm snapped the vertical in two. It reads a little long for the tap point it is at. Perhaps I could move it out 6" and retap.

I would have reported findings by now but have had some radio issues and can not trust the results until I get it sorted out. The reference radio is out of commission.

I've got to find the money to put a reliable radio in line.

 

[CDX-007]

It is at 22.5 ft now, however I had to redo it after a severe storm snapped the vertical in two. It reads a little long for the tap point it is at. Perhaps I could move it out 6" and retap.

I would have reported findings by now but have had some radio issues and can not trust the results until I get it sorted out. The reference radio is out of commission.

I've got to find the money to put a reliable radio in line.

Homer, do you think you have enough accumulated info on the 5/8 to draw a decent comparison to a .64 if you resurrect it by increasing it to 23'? Actually it should be right about 22' 10" for .64 @ 27.375 to offset the average diameter of the tubing.

You might want to feed it with a 10 turn coil at ~2" diameter and close to center tapped, though you might find resonance a little closer to the ground side, perhaps even only 2-3 turns up.

I'm sorry to hear about your radio melt-down, what happened?

I found this on ebay and have to share it, it's all you'd need for awesome SSB performance. (AM receive is incredibly good but AM TX operation requires a VERY tinny sounding mic to get decent performance without bass overdrive, such as an Echomax 2000 which works very well, especially w/o the echo crap.)

ICOM IC-751A HF XCVR - eBay (item 160497880786 end time Oct-31-10 14:26:54 PDT)

You could possibly get it for well under the average closing bid of $500-$600 due to the loose shaft possibly scaring away less courageous bidders.

The VCO(VFO) knob Shaft is easy to tighten.

I had to help a friend tighten his up, just remove the knob with a small allen wrench in the hole under the rubber grip and the other knobs, and screws along the edge of the face plate, then you'll find one more screw to remove behind the VCO/VFO knob.
REMOVE THE FACE SLOWLY & CAREFULLY BECAUSE THERE ARE WIRES GOING TO THE SWITCH-BUTTONS TO THE IMMEDIATE RIGHT OF THE VCO KNOB!

Simply tighten the hex nut on the shaft. It's really quite easy and should require about 10 minutes for the entire procedure including reassembly.

You'd love the incredible receiver clarity, and my TX sound quality with a Yaesu MD-100 desk mic constantly gets me unsolicited but highly complimentary audio reports.

Here are test results which show it scoring higher in some ways, such as 10KHz rejection (one CB channel) than even the newer Yaesu FT-2000 and Icom 7800:

Drake ICOM Yaesu receiver dynamic range measurement

I preferred, and kept, my Icom IC-751A while letting go of my Kenwood TS-940SAT & Yaesu FT-990, even though those are also very nice radios.

73

 

[HomerBB]

the radio on ebay looks nice, and would be great to have should I find the money. For now I'll have to do some swapping around and put the mobile in the shack if I can't do otherwise.
I lack the skills, and equipment, to be sure of repairs on the radio I have now. I lost the 1969 finals and a mosfet upgrade is about the only worthy replacement that I know of. I may try to tackle it, or else I'll look around for another rig. Problem is, anything I do will mean having to become accustomed to what I am experiencing on a different rig in order to get some comparison. I have an old Super Star that is the noisiest recieve I've ever had, and someone who had it before I got it screwdrivered the SSB so I can hardly stand to fool with it on both accounts, and don't want it in the mobile, either.

I am so close to .64 length it would be easy enough to go there. I will look at that closer over the next couple of days.

 

[CDX-007]

Well, what the heck happened to your radio? What rig were you using for a base?

Figure out a way to grab that 751A and you'll always wonder what took you so long!

... If not I'm tempted to find some extra duckets and grab it for myself, then I'll have one for the mobile.

 

[HomerBB]

Well, what the heck happened to your radio? What rig were you using for a base?

Figure out a way to grab that 751A and you'll always wonder what took you so long!

... If not I'm tempted to find some extra duckets and grab it for myself, then I'll have one for the mobile.

Okay, I skipped a step or two in the explanation of my radio woes. I was using a very good and reliable DX88HL in both the shack and the mobile. I was asked if I'd trade one of the 88's for a Magnum Delta Force. I played with the idea for a few days and , IMO, did the dumbest thing. I traded. I thought that the Delta Force ability to go back and forth as a 10 meter/11 meter unit would stand in good for when I got my ticket (planned for this winter). Well, the Delta Force was a let down on modulation after the 88, so I went in and turned up the radio. It blew the very weak voltage regulator. Put another in - both of them 754's. It blew that one, too ( I know. lesson learned. hindsight. . . DF's are power weanies ). So I ordered some 817's. That held, but it forthwith blew the finals. I know how great some feel the Magnum DF is, however I don't think it stacks up to the durability of my 88's, nor their modulation and power capabilities.

My first mistake was not thinking of the difference in the radios in terms of comparing the antennas. For now, I've brought the 88 from my SUV into the shack and will run the old Gold Faced Super Star 3900 out in the mobile. A little learning curve on this 88 on the base antennas and the results can be posted.

What a deal.

2 - 3 months from now and I probably could see some light on the 751A you're looking at. It's the wrong monetary cycle for me right now.

As an aside, the Qv4k remains a compelling piece of work. I mounted it on my shed for storage purposes as it is so long and I did not want to dismantle it risking any changes to it going back together. I put my old Cobra 87GTL out there with an old Courier power desk mic, too. Only 10' up to the coax connector the SWR remains usable, I talk well locally, and any DX I'm hitting from the mobile or the base antenna at 35' to feedpoint I can hit with the Qv4k.

 

[CDX-007]

Okay, I skipped a step or two...

My first mistake was not thinking of the difference in the radios in terms of comparing the antennas. For now, I've brought the 88 from my SUV into the shack ... A little learning curve on this 88 on the base antennas and the results can be posted.

So I take it there's no going back to the old 88, and that it was the one which you were using for your test readings?
Will you be able to duplicate the receiver / S-meter with the other 88?

I imagine you have a few weak contacts you are somewhat familiar with which will give you an idea of the general comparison between antennas...?

There will always be another 751A, that one was priced particularly friendly due, I'm sure, to the fear of mechanical issues. I know I wouldn't have given it another thought if I hadn't already dealt with a loose VCO/VFO knob and knew how easily it can be tightened.

Good luck with the Magnum 'DF', perhaps you can beef it up to reliable condition.

 

[HomerBB]

I'll do fine with the other 88. just get readings for a week or two on it, record them, and fly the other antenna.

 

[CDX-007]

I'll do fine with the other 88. just get readings for a week or two on it, record them, and fly the other antenna.

Cool!

...and now a

for the more mechanically minded among us;

I'm thinking of using a 1" diameter solid fiberglass rod to insulate the 'SigVectalute IV,ooo' from the mast by installing .1875" wall, 1.375" diameter, mast section 12" into the bottom then cutting it off as it leaves the base of the aluminum antenna and adding a 14" piece of 1" solid fiberglass rod about 6" into each mast half as an insulator, exposing about 2" of fiberglass rod at which point I'll have the coaxial common-mode-current choke and an RF isolation coil in the DC ground wire. That is as much RF isolation as I can figure out how to accomplish.

I'm wondering if 1" fiberglass rod would be strong enough to support it in ~60mph wind?

- It seems strong enough to tow a truck but I just don't have the experience nor FEA info to know if I'm 'setting it up for a fall'.

Anyone have experiential / empirical knowledge of the strength of 1" solid fiberglass rod, especially within this type of application?

 

[bob85]

i would use more overlap but 1" solid fiberglass rod should hold a vector, the 1"rod will be way stronger than the bottom tube of a vector
the upper sections of the old style vector lay down or break off much above 50mph to reduce windload,
if it was built stiffer with 100+mph wind survival id use a stronger rod.

 

[BOOTY MONSTER]

i guess i need to set a day aside to read this entire thread from beginning to end . LOL

anyhow , does a gamma have to be used for the tuning of the vector ? what would happen if the gamma was taken off and a coil was put at the base of the vertical and taped ?
would it tune ?
would the ground elements no longer "add to the vertical radiation" of the antenna ?

im guessing theres a good reason why a gamma is used rather than other tuning methods for the sigma style antennas , but id like to know why . thanks .

 

[HomerBB]

Beats me, Booty, but as finicky as this antenna is I'd be hesitant to try it. I've thought of the same, but decided not to attempt it. My thinking is that this antenna is sophisticated beyond the simplicity of a 5/8 where the ground plane is offset against the vertical, similar to a dipole. However, someone else will have to fill in the holes in my thinking on this.

As for me, I ain't gonna do it . . . yet.

 

[CDX-007]

Interesting thought. Being the Gamma Match is capacitive, I presume an inductor would throw your phase reverse of where you need it for the Vector 4000 phased collinear design to function correctly.

I also had an horrendous thought;

The Sirio Gain-Master is a center-fed, capacitive coupled radiator, 5/8 dipole,
so,
what if one were to take a...

Jo Gunn Pistol

...a gamma-fed, center-fed ½ wave dipole (read DC grounded Starduster) and insulated the radiator from DC ground along with extending the radiator & radials each to 5/16 wave, then adjusted the Gamma for ~zero reactance, (adding a cmc choke & 1:1 balun) shouldn't that function similarly to the new Sirio Gain-Master center-fed 5/8?

- Just a thought :blink:

 

[Marconi]

007, I think you meant to type 5/8 wave rather than 5/16 wave.

My model of the 5/8 wave with slanted 5/8 wave radials makes strange looking patterns both over real Earth and in free space. They are nothing like the Gain Master. The gain and angle shows to be great however, but just like the Starduster the radiator and the radials are not in phase...like the Gain Master.

So, if my model is close to correct, the 5/8 wave with 5/8 wave radials does not make a pattern similar to the Gain Master. The antennas do look similar by design, but I can't fathom a guess why the patterns are so different...just to say the phase is different. The Starduster looks similar to this long 5/8 wave idea of yours, and I know it works fine at 1/2 wave, so I don't know why the 5/8 wouldn't also.

NM5K here in Houston designs and models his Imax in a similar fashion as you describe and it too shows improved gain. I have posted his models in my album: http://www.worldwidedx.com/members/...ing-10-meter-verticals-nm5k-demo-version.html.

By the way I have just modeled the original Sigma 4 to meet almost all specs except I left the radials as a single .50" wire. I just posted it to my album and it has the hoop as a circular hoop and not square as earlier models showed: http://www.worldwidedx.com/members/marconi-albums-henry-s-sigma-4-modified-specs-resonance.html