Modified Vector 4000

[Marconi]

Thanks Marconi.

Alexis, I did not have enough segments to use my Vector 4K model over an all metal roof object. I wanted to see if the antenna was effected in such a situation.

I see the roof producing some benefit in gain for the model when on the roof. I can't say you will be able to realize if this happens or not.

1. is in Free Space over the metal roof showing the model Average Gain Test = 1.

2. is the same model as #1, except it is over Real Earth and the roof at 25' feet to the feed point.

3. I removed the metal shed and added a mast to the ground. I did have to re-tune the model a bit, and I had to add isolation to the model when I added back the losses over Real Earth.

That said, I have run several Starduster antennas over all these years and I never had any problems with the match, and I installed those antennas at many different heights and locations in my yard.

My SD'r model acts just like the real antenna and it loves to be up there high.

 

[bob85]

i just finished modding an old vector 4000 for 6mtrs,


if its not raining tomorrow i will see how it tunes.

 

[nav2010]

Looks very good.

 

[HomerBB]

@bob85, it looks great.
My homebrew tunes right up.
Curious about your dimensions....

 

[bob85]

Homer
its not tuned yet but it won't be far from where i want it on 50mhz,
i have not allowed for the change in wavelength/diameter ratio or the fact im using the fatter sections of the vector so it will be a little long electrically which is ok,

monopole 179" from hub to tip
radials 57.5"
hoop 18" diameter

i don't like the spreaders up there so i will modify a spare set & swap them later.

 

[HomerBB]

I also did not make adjustments to the lengths for larger diameters of tubing. It did tune fine. I will measure my components to see how mine line up with yours. I built mine for mid band up through 53 to 54 as most of the repeaters and simplex around here operate there.
Keep us posted.

 

[Marconi]

Homer
its not tuned yet but it won't be far from where i want it on 50mhz,
i have not allowed for the change in wavelength/diameter ratio or the fact im using the fatter sections of the vector so it will be a little long electrically which is ok,

monopole 179" from hub to tip
radials 57.5"
hoop 18" diameter

i don't like the spreaders up there so i will modify a spare set & swap them later.

Bob, if you tell me the height of the bottom of the dog bone bracket from the feed point in inches, I will try an model of this 50 MHz idea.

I also need the tubing diameters for the 3 elements you posted above.

How far is the center of the feed point from the center of the radial hub?

 

[bob85]

Eddie its a cut down vector 4000, same hub, my radials are beefed up at the bottom like a sigma4 from another project, i will swap them for stock sirio legs later,,

gave it a quick tune in the rain with the minivna earlier 1.2 @50mhz & below 1.5 from 49-50.8mnz but the rig is not happy,
its dark cold wet & muddy outside so a job for another day.

 

[freecell]

Eddie its a cut down vector 4000, same hub, my radials are beefed up at the bottom like a sigma4 from another project, i will swap them for stock sirio legs later,,

gave it a quick tune in the rain with the minivna earlier 1.2 @50mhz & below 1.5 from 49-50.8mnz but the rig is not happy,
its dark cold wet & muddy outside so a job for another day.

looking into the line from the tx line input, what are you measuring for X and Z?

 

[nav2010]

I've just built a coaxial half wave dipole for 6m to talk to Bob85. First mistake: My upper element is 143cm long and so is the coaxial lower element, my isolation pole is also 143cm long which meant my choke overlapped the isolation pole and the mast and yes you guessed it - the choke coupled with the mast and detuned it. Second problem, any rain on the choke and it sends the swr to hell, probably lowering the impedance so that I start radiating on the coax underneath the choke and the mast although I didn't notice CMC in the shack, chances are they were there though. I've now stopped the choke coupling with the mast via a rubber bung and i've taped the choke to hell and back to keep water from it. So much so it lowered the impedance of the choke slightly and I had to retune the antenna. All in all they work and that's it. Do anything to the choke and lower coax leg including coughing on it and it changes the resonant frequency. Not a fan I'm afraid.

 

[nav2010]

A better idea Bob85 would have been two aluminum radiators @ 143cm each with a spacer between, run the coax up inside the lower radiator and center feed my elements then choke the antenna at the base of the lower radiator just like I did with my fake27 HWD.

 

[Marconi]

Here is what I come up with Bob, at about a wavelength high.

 

[HomerBB]

@nav2010
I've used one of these,



To wrap the coax choke in. This was on the insulating tube at the bottom of the lower element of the dipole.
I then mounted a SO-239 on the box for attaching the feedline.

 

[bob85]

freecell
i only got it in the ballpark with the analyzer, i can't find my calibration jumper so used a vswr meter,
best i saw on the analyzer was z=47 x=9 through a random length of rg213, just enough to reach the house doorway & keep the laptop/analyzer dry.

if it drys up today i will have another play.

 

[nav2010]

@nav2010
I've used one of these,

View attachment 41978

To wrap the coax choke in. This was on the insulating tube at the bottom of the lower element of the dipole.
I then mounted a SO-239 on the box for attaching the feedline.

I've just put the antenna up with an vswr of 1.3:1 There is rain forecast today so I'll see if the tape protects the choke from lowering the impedance. I didn't have this problem on my half wave dipole I made for 11m, I used two aluminum radiators which were centre fed and the coax ran up the middle of the lower leg, it was isolated and choked at the base of the bottom radiator. The choke on my 11m version didn't have as much work to do and was basically a CMC choke. This particular choke on the 6m dipole performs two tasks, firstly it sets the resonant length of the lower radiator at 143cm and it also stops CMC. The trouble is of course if your choke sets your resonant length of the lower radiator (the braid of the coax) any change in impedance of the choke changes the electrical length of the whole antenna. This is why I don't like them.