Homer's Qv4k Redo

[homerbb]

I have been redoing the Qv4k.
I have it in a temporary testing location, and even that will be changing. Due to work schedule and rain I have o quit for today. First time up it is a 2.2:1 on 40 and a 1.6:1 on 1. It is currently tuned below ch1 it seems. I made QSO with WR54 in Colorado. I'll keep you posted with photos.

[homerbb]

Assembly notes on the Qv4k:

I started with the tubing for the vertical element. Here it is assembled to full length.



I used these 4' fiberglass rods coupled together with pieces of tubing to form the radials.





The ring is formed from a 10' joint of PEX tubing cut to the necessary length to form a ring of 31" diameter. The PEX I covered with aluminum tape the same as the radials to provide conductive skins. The ends of the PEX tube were solidified by inserting a short dowel in them, and connected together with a conduit coupler.



The bottoms of the radials were connected to the vertical mast by means of electrical terminals, while the tops were connected to the ring and kept rigid by means of spaces made of a wire/rope spool and PVC nipples.




It lies in the backyard awaiting the Gamma match to ready it for tuning.



The gamma is made of a 1/2" ID tube 17.25" long, and a 3/8" x 36" rod insulated by a piece of PEX tube.The upper tube cap does double duty as the spacer, a rubber stopper.





The Gamma is installed and a stand-off strap made of 3/4" x 1/8" aluminum strap helps hold the rod and tune the antenna.





In the air for tuning.

[Sandbagger]

I admire your ingenuity in fabricating the tricky items on a complex antenna like this one from common materials. But I have to wonder how well tape wrapped elements would work over time.

I'm anxious to hear how well it performs. I used to have an Avanti Sigma 4 and for me, it was the best performing omni I ever had. I've heard mixed reviews from others, and there's been quite a few heated debates on several forums trying to decide exactly what type of antenna it really is and what the true gain figures are. Not a lot of consensus though......

[homerbb]

I hear ya. The foil is a temp solution. I intend to redo that part of the antenna if the cost is effective to the performance on trial.
I have heard of it lasting years . . .
Either I'll save for the tubing, or strip oax of its braid and put that to work under heat shrink..

[cbrown]

The coax under heat shrink sounds good, but I think the heat shrink would drive the cost up.

[homerbb]

Yes, it would. I will look for the heat shrink where I found some a while back very cheap.

I put the Qv4k up as shown in the photo using the dimensions of:

Length of vertical -------------- 29' 8" (accidental length)
Radial lengths ------------------ 108"
Gamma Match --------------------- 17.25" tube, 36" x 1/4" rod
tap point of Gamma to vertical -- 30" up from bottom of Gamma
rod set ------------------------- 1" off bottom of Gamma

SWR:

28.755 -------------------------- 2.5:1
28.305 -------------------------- 2.0:1
27.855 -------------------------- 1.2:1
27.405 -------------------------- 1.0:1
27.205 -------------------------- 1.0:1
26.965 -------------------------- 1.05:1
26.515 -------------------------- 1.4:1
26.065 -------------------------- 1.1:1
25.615 -------------------------- 1.1:1
25.165 -------------------------- 1.0:1

Next I used the dimensions from the Vector 4000 specs:

Length of Vertical -------------- 27' 10"
Radial lengths ------------------ 106.75"
Gamma Match --------------------- 17.25" tube, 36" x 3/8" rod
tap point of Gamma to vertical -- 27" up from bottom of Gamma
rod set ------------------------- 4" off bottom of Gamma

SWR:

28.755 -------------------------- 3+
28.305 -------------------------- 1.7:1
27.855 -------------------------- 1.0:1
27.405 -------------------------- 1.1:1
27.205 -------------------------- 1.5:1
26.965 -------------------------- 1.5:1
26.515 -------------------------- 1.3:1
26.065 -------------------------- 1.5:1
25.615 -------------------------- 3+
25.165 -------------------------- 3+

Needless to say that wasn't looking too good, so:

Length of vertical -------------- 28' 10" (compromise length)
Radial lengths ------------------ 106.75"
Gamma Match --------------------- 17.25" tube, 36" x 3/8" rod
tap point of Gamma to vertical -- 30" up from bottom of Gamma
rod set ------------------------- 7" off bottom of Gamma

SWR:

28.755 -------------------------- 2.6:1
28.305 -------------------------- 1.9:1
27.855 -------------------------- 1.15:1
27.405 -------------------------- 1.0:1
27.205 -------------------------- 1.0:1
26.965 -------------------------- 1.0:1
26.515 -------------------------- 1.2:1
26.065 -------------------------- 1.2:1
25.615 -------------------------- 1.0:1
25.165 -------------------------- 1.0:1

The weather has shut down any movement on the antenna for now. I don't know what to think of the odd SWR wavy shape, but I'm hoping that getting the antenna higher in the air away from the house will help me to see a more customary curve. I am wondering what it will take to get the curve further up the band toward 10 meters. I want it for 11 meters, but favoring a curve toward 10 meters.

Ideas?

[Sandbagger]

May 23, 2011 22:32:35 GMT -5 homerbb said:

Yes, it would. I will look for the heat shrink where I found some a while back very cheap.

I put the Qv4k up as shown in the photo using the dimensions of:

Length of vertical -------------- 29' 8" (accidental length)
Radial lengths ------------------ 108"
Gamma Match --------------------- 17.25" tube, 36" x 1/4" rod
tap point of Gamma to vertical -- 30" up from bottom of Gamma
rod set ------------------------- 1" off bottom of Gamma

SWR:

28.755 -------------------------- 2.5:1
28.305 -------------------------- 2.0:1
27.855 -------------------------- 1.2:1
27.405 -------------------------- 1.0:1
27.205 -------------------------- 1.0:1
26.965 -------------------------- 1.05:1
26.515 -------------------------- 1.4:1
26.065 -------------------------- 1.1:1
25.615 -------------------------- 1.1:1
25.165 -------------------------- 1.0:1

Next I used the dimensions from the Vector 4000 specs:

Length of Vertical -------------- 27' 10"
Radial lengths ------------------ 106.75"
Gamma Match --------------------- 17.25" tube, 36" x 3/8" rod
tap point of Gamma to vertical -- 27" up from bottom of Gamma
rod set ------------------------- 4" off bottom of Gamma

SWR:

28.755 -------------------------- 3+
28.305 -------------------------- 1.7:1
27.855 -------------------------- 1.0:1
27.405 -------------------------- 1.1:1
27.205 -------------------------- 1.5:1
26.965 -------------------------- 1.5:1
26.515 -------------------------- 1.3:1
26.065 -------------------------- 1.5:1
25.615 -------------------------- 3+
25.165 -------------------------- 3+

Needless to say that wasn't looking too good, so:

Length of vertical -------------- 28' 10" (compromise length)
Radial lengths ------------------ 106.75"
Gamma Match --------------------- 17.25" tube, 36" x 3/8" rod
tap point of Gamma to vertical -- 30" up from bottom of Gamma
rod set ------------------------- 7" off bottom of Gamma

SWR:

28.755 -------------------------- 2.6:1
28.305 -------------------------- 1.9:1
27.855 -------------------------- 1.15:1
27.405 -------------------------- 1.0:1
27.205 -------------------------- 1.0:1
26.965 -------------------------- 1.0:1
26.515 -------------------------- 1.2:1
26.065 -------------------------- 1.2:1
25.615 -------------------------- 1.0:1
25.165 -------------------------- 1.0:1

The weather has shut down any movement on the antenna for now. I don't know what to think of the odd SWR wavy shape, but I'm hoping that getting the antenna higher in the air away from the house will help me to see a more customary curve. I am wondering what it will take to get the curve further up the band toward 10 meters. I want it for 11 meters, but favoring a curve toward 10 meters.

Ideas?

I don't know if this helps or not, but I do remember some interesting characteristics that my old Sigma 4 used to exhibit. One was that the SWR used to rise much sharper on the higher side of the low SWR point (going up in frequency) than it did going below the low SWR point. If the SWR was best at 27.115, I could drop 1 Mhz (26.115) and still be below 2.5:1. But by 28.115, it was over 3:1. Don't know why this was, but it sucked for me, as I had hopes of using it on both 10 and 11 meters without needing the tuner.

The other thing I noticed is that setting the gamma capacitance affects bandwidth. If you set it for the absolute lowest SWR at the lowest center SWR frequency, then the bandwidth is not as good (SWR rises quicker as you dial away from the center). Conversely, if you back off the gamma to something like an SWR of 1.3:1 at the center point, the bandwidth widens.

[homerbb]

Now that is some useful information. I will keep that in mind as I try to tune it after i make the move. I want to be able to use it for 10 meters when I get my ticket. I'll try what you've suggested and see how it goes.

[homerbb]

SWR:

28.755 -------------------------- 1.2:1
28.305 -------------------------- 1.0:1
27.855 -------------------------- 1.0:1
27.405 -------------------------- 1.15:1
27.205 -------------------------- 1.2:1
26.965 -------------------------- 1.25:1
26.515 -------------------------- 1.1:1
26.065 -------------------------- 1.35:1
25.725 -------------------------- 2.0:1
25.615 -------------------------- 2.3:1
25.165 -------------------------- 3+

More later. Chores first.

[homerbb]

There are changes that were made to the Qv4k that has resulted in movement in the SWR that I find favorable. Primarily, the changes were made to the 4 radials - length and diameter of the elements - and to the gamma match. Also, the length was reset to 29' 1".

The above posted SWR was where I landed with those changes while the antenna was mounted on the temp testing pole very near the house and close to the ground, if I recall around 14' from the earth.

This is a view of the changed radials: 90" from where they bend away from the center vertical to the tip ends, and 3/4" diameter.



Closer up while the antenna is laying on its side you can see the close-ups of the changes to the Gamma Matching setup. The dogbone is now set at 36" up from the feedpoint of the antenna, the gamma tube is now 17" x 3/4" OD, the rod is 36" x 3/8" and pulled out from the tube 25.5" which brings the tap point around 19". Additionally, between the rod and the tube there is a nearly snug fitting dielectric tubing running the entire inner length of the tube.



Here is a snapshot of the Qv4k sitting above the Yagi on the tip-over mast just as the sun is setting.



After the antenna went up higher into the air, sitting just above the yagi about a foot, the SWR curve shifted upward some.

Here it is currently from the 2.0:1 reading upward:

26.515 -------------------------- 2.0:1
26.965 -------------------------- 1.2:1
27.205 -------------------------- 1.0:1
27.405 -------------------------- 1.0:1
27.855 -------------------------- 1.0:1
28.305 -------------------------- 1.2:1
28.755 -------------------------- 1.2:1

I do not know where the SWR goes upward from there as I ran out of frequencies on the DX88HL.

Street view:

[homerbb]

The Qv4k has given me several days of radio pleasure.
What I notice about this antenna is its great ears. Close in local is as expected, but what I am finding is the improvement in being able to hear stations beyond 40 miles regularly which has challenged me from my QTH. I had also feared that I would not experience the low TOA expected from this antenna and have to resort exclusively to the Yagi for very long distance DX contacts. I haven't been disappointed with its performance, yet. When the band is open I am talking to Colombia, South America, Hawaii, and Australia on the Qv4k. The 4 element Yagi still demonstrates more gain directionally, but I am able to hear and be heard where I have not been able on an omni from my location. We all know that DX depends on conditions above all else, but when experiencing RX/TX differences with this omni after redoing it to what I did before on it, I have to say that it has been worth my while to get back to it.

[Sandbagger]

May 30, 2011 23:47:51 GMT -5 homerbb said:

The Qv4k has given me several days of radio pleasure.
What I notice about this antenna is its great ears. Close in local is as expected, but what I am finding is the improvement in being able to hear stations beyond 40 miles regularly which has challenged me from my QTH. I had also feared that I would not experience the low TOA expected from this antenna and have to resort exclusively to the Yagi for very long distance DX contacts. I haven't been disappointed with its performance, yet. When the band is open I am talking to Colombia, South America, Hawaii, and Australia on the Qv4k. The 4 element Yagi still demonstrates more gain directionally, but I am able to hear and. be heard where I have not been able on an omni from my location. We all know that DX depends on conditions above all else, but when experiencing RX/TX differences with this omni after redoing it to what I did before on it, I have to say that it has been worth my while to get back to it.

My Sigma 4 was a skip magnet. I always attributed that to the reportedly higher angle of radiation (Which also helped me to climb out of the hole I was in at my old QTH). I used to talk occasional AM skip with a barefoot Uniden HR2510 (12 watts). I was never disappointed with the performance of that antenna. It was mounted about 25' above the ground, and it was still only about 1.5 - 2 S units less than the Astro Beam mounted on my 45' tower. It was the best omni I ever ran in the 70's and 80's.

[homerbb]

It seems to be in fine form for DX alright. it just may be a keeper.

[cbrown]

May 31, 2011 7:05:19 GMT -5 homerbb said:

It seems to be in fine form for DX alright. it just may be a keeper.

It looks great, and keep up the testing. Nothing much could touch a Sigma IV back in the days.

[homerbb]

I have an analyzer on the way from a friend, so I hope to learn more about this antenna from its use. For now, getting a few more feet of elevation under it will likely be my next move.

[cbrown]

Height was always might with those antennas. I'd always try and get it at least one full radio wave above the mount.

Let us know what the analyzer shows when you get it.

[homerbb]

I will. I'm anxious to see myself.