Modified Vector 4000

[Alexis Mercado]

Here is the picture of the isolator installed

 

[Alexis Mercado]

Since I had some attenuation on RX, I decided to take the isolator off and leave it installed with RSC- antenna switch. It’s working fine like that, with SWR of 1.2 on channel 28 and a bandwidth of 1,850 KHz

Specs says SWR @ resonant frequency should be equal or less than 1.2 on resonant frequency which in my case is channel 28 and bandwidth @ SWR of 2.0 or less should be 1,400KHz. I have a Bandwidth of 1,850, pretty close to specs but I will have to deal with it.

The tip of the Vector is around 2 feet below the Gain Master. Practically RX and TX are practically the same. But I did noticed something, people from south ( Brasil, Argentina, some locals , ) can be heard better with the lower Vector thanks the higher GM. Maybe it’s location dictates that difference.

In my “ less than optimal” conditions ( 16 foot above a concrete flat roof ) , I set the L3
( top section ) to 28 3/4” and L2 to 24 3/4” .

Maybe I should try it at 6 feet above roof top because at that height is where I get the best readings and compare performance on both 16’ and 6’ high. It will take me some days to let you know.

 

[freecell]

I use TMS LMR240 & LMR400 exclusively for 2 reasons.

1. the loss at these frequencies (27.185) is only .64 dB per 100 feet. I appreciate the advantages of using virtually lossless lines. Line attenuation is the killer, not VSWR.
2. where the rf shielding attenuation for conventional coaxial feedlines with a single shield conductor seldom exceeds better than > 40 dB, LMR240 and LMR400 are manufactured with a dual shield which provides increased levels of rf shielding attenuation to better than > 90 dB.. That eliminates a lot of "unwanted" coupling.

Additional Information: https://www.worldwidedx.com/threads/rg-8x-vs-rg-8u-coax.88215/page-3#post-747593

 

[Alexis Mercado]

Today I made some final adjustments and could achieve this with LMR-400 cable, 45.56’ of coax from RCS-4 control switch to remote coax relay box in the tower, and 60.74’ from relay box to Vector 4000 @ 16 feet above roof. SWR reading taken with a SWR/Watt meter at the station.

SWR———FREQUENCY
2.0—————27,985
1.5—————27,665
1.1—————27,245 ( Channel 25 )
1.5—————26,765
2.0—————26,295

Bandwidth = 1,690 KHz

This SWR is the lowest I could achieve. I’ll leave it right there.

By the way, I could get a Mini 1300 analyzer that could measure + and - X . Here are the reading taken today as well . By the way, I used one 12.5” RG-58 short jumper and a 7’3” LMR-400 jumper. Both practically gave me the same readings @ 6 feet above roof.

SWR——Frequency———R————-X
2.0————27,985———25.6—— + 3.3
1.5————27,530———34.1—— - 1.8
1.0————27,040———50.9—— - 0.4
1.5————26,665———62.8—— + 16.7
2.0————26,365———57.4—— + 36.1

Bandwidth = 1,620 KHz

 

[Alexis Mercado]

Hi Bob. Do those number look right ?

 

[bob85]

it looks typical of what happens when you tune near the ground then raise the antenna higher.
did you see the change in signal that you talked about earlier ?

 

[Alexis Mercado]

it looks typical of what happens when you tune near the ground then raise the antenna higher.
did you see the change in signal that you talked about earlier ?

No, I did not noticed the attenuation I had before. Maybe it was the line isolator, the jumper I used to connect it to the Vector, I don’t really know. Even when I had higher SWR, I didn’t have attenuation without line isolator installed.

For short, adding the isolator gives me some kind of attenuation.

 

[Marconi]

it looks typical of what happens when you tune near the ground then raise the antenna higher.
did you see the change in signal that you talked about earlier ?

Bob, here is my model of the NV4K at 8.5' above the Earth, showing a good match. When I raise this model to 36' feet the match hardly changes, but the gain does change dramatically.

I recall that my S4 antenna match was always very stable on raising, and I probably was suprised at that too at some point considering ohter antennas like the 5/8 wave vertical match always seemed to need a bit retuning on raising.

Just my modeling experience compared below for the NV4K. BTW, these models have no choke to mitigate CMC's, and there is no sign of currents on the mast as noted. The models are Isolated however, but if I added a feed line then maybe that would tell us if the model needs CMC mitigation.

 

[bob85]

Eddie
tuning a vector at 2ft above my ground here then raising it up to 12 & 18ft moves the tuning up in frequency,
tuning at 36ft then raising to 73ft the change was less but still moved up,

Alexis is tuning over a concrete roof full of rebar,

i don't know of any cb vertical that is not effected by height above ground or other conductive body if you start by tuning low down then raise it higher,

the mast & coax could be playing some part too.

 

[Marconi]

Bob, I haven't touch a real antenna for several years, and I never said I had my S4, 2 feet above the Earth.

The models I just posted is all I have that suggests my opinions on this mater. Again the model I started with above was at 8.5' feet above the Earth, and I simply raised it up to 36' feet and posted both models to compare. My models are what they are, but I did try and run the Average Gain Report in Free Space...so I have some indications that Exnec is not playing with an unreliable input of the dimensions, and the feed point is close to where it belongs for such a model, and that is according to what error checking by Eznec determines in this case.

Except for one time with my Sigma4 when the gamma match got bumped out of position directly between the two radials where it was supposed to be carefully centered...that match never changed as much as is being suggested here...as I raised the antenna over several different installations over time.

That always impressed me with my physical S4 antenna. My old Startduster use to go up and down at different heights too...and I was had a solid match too.

My old and best A99 did on occasion change upon my on raising. but I blamed that on possible radiation on the feed line and mast. I could also see it ill-effect performance and that did not make my happy.

The only thing I ever saw change noticeably was the signals at different heights.

On my AS Sigma4 I once added a choke with ferrite cores in the cylinder built for 11 meters by Palomar, with connectors on both ends, and I also made a couple of coaxial chokes. None made any difference on this antenna that I could tell.

 

[freecell]

The feedpoint of an elevated monopole above real ground directly impacts both impedance and pattern parameters. The elevation angle polar projection is a representation of the dielectric lines of force created by antenna current looking for a low resistance ground return path. This shapes the geometry of the pattern. The ensuing circuit is capacitive in nature. The value of capacitance present is highest when ground mounted and decreases as the feedpoint is elevated, resulting in the electrical length of the antenna becoming more inductive, lowering the resonant frequency of the system.

 

[Marconi]

Bob, here is the Vector in Free Space showing the Average Gain Results = 1.

 

[Marconi]

The feedpoint of an elevated monopole above real ground directly impacts both impedance and pattern parameters. The elevation angle polar projection is a representation of the dielectric lines of force created by antenna current looking for a low resistance ground return path. This shapes the geometry of the pattern. The ensuing circuit is capacitive in nature. The value of capacitance present is highest when ground mounted and decreases as the feedpoint is elevated, resulting in the electrical length of the antenna becoming more inductive, lowering the resonant frequency of the system.

FC, every thing you say here could be true and fact, but these two models do not show very much capacitance or inductance in the match.

I never saw a lot of difference in the match on raising my Sigma 4 antenna back in the days when Bob and I collaborated the better part of a month testing my Antenna Specialists Sigma 4. He was always concerned that I could not produce the results he thought I should, and in the end he told me that the Sigma 4 was not capable of producing the results that his Vector Hybrid did for him in any way.

That did surprise me when he finally told me that. He may well deny any of this, but this is what I remember.

FC, before I got sick, you talked about a model that I assumed you had. I asked you to publish that Eznec model so I could look at what you were describing in words. I'm still waiting, or am I just dead wrong about you being able to model using Eznec?

 

[Marconi]

Is this FreeCell, it is on his FaceBook network page.

See his link on his WWDX post in his signature area.

 

[Alexis Mercado]

Today I taped the coax cable at 6 feet high to see what happened. About half inch of coax was taped to the mast.

Before that, coax cable was hanging down not touching the mast. Antenna height and conditions remained the same. See post 619 for you to compare.

Resonant frequency shifted up and bandwidth broadened a little as well. SWR went up one decimal point.

These are the reading from my SWR/Power meter.

SWR—————-Frequency
2.0———————-28,100
1.5———————-27,795
1.2———————-27,435
1.5———————-26,665
2.0———————-26,100

Bandwidth = 2,000 KHz

According with this info, Is it correct to assume I have CMC ? Will this CMC will affect antenna performance anyway , even if coax cable is hanging down and not touching the mast ?