Modified Vector 4000

[Marconi]

Bob, I did a search on QRZ.com and found this post in their forum, but the links and the PDF files don't work anymore.

Does this thread look like something you might have checked-out regarding Eznec Feed Line features.

Antennas, Feeds, Myths and Facts

 

[bob85]

I used to read what Cecil Tom & the other guys would argue about years ago Eddie,
i don't remember that particular thread but i may well have read it, i read quit a lot back in the day,
arguing about the conjugate match was one i remember, not the details but the arguing back & forth.

not read much about antennas for quit a while now.

 

[Marconi]

not read much about antennas for quit a while now.

Me to Bob, I was just trying to find some discussions that I could understand on Feed Lines. I did a search on QRZ.com and what I found was very old...and all the links were dead ends.

Sorry if I keep repeating myself. Forgive me, I get to rambling sometimes, and I can't remember whether I've posted a thought or was I just thinking about posting a thought.

 

[Alexis Mercado]

Hi again. Today I could install my Sirio Vector 4000 on top of my house. It is about 12 feet above the house. House is 10 feet tall.

When adjusting on the back I did it on a 10 feet tall pipe with my MFJ Analizer. Here are the readings with 14 feet of RG-8x cable with a velocity factor of 82 according with specs. Using that info. and the formula to cut cables to a 1/2 wave, it gave me 14 feet.

Here are the numbers:

SWR ——- Frequency —R———-X

2.0 ———27,635 ———24 ———1
1.5 ———27,375 ———31 ———0
1.1 ———26,985 ———45 ———5
1.5 ———26,705 ———47 ———1
2.0 ———26,495 ———38 ———29

Bandwidth: 1,140 KHz

This bandwidth a little bit tighter than the 1,400KHz Sirio specs specifiy.

Here are the measurements:

L1= 36 5/8”. L2 = 25.0”. L3= My bad, I didn’t measure it, I had to make little adjustments from the factory recommendations, but I did measure the whole length of the radiating element , which is 25’, 8” .

Here comes the interesting part. When I took this antenna up to the roof ( flat concrete roof ), I took measurements again with the analizer, and bandwidth changed.

SWR——— Frequency———— R——-X

2.0————-28,335——————41——32
1.5————-27,850——————37——40
1.1————-26,583——————48——-0
1.5————-26,923——————31——-5
2.0————-26,460——————27——-12

Bandwidth: 1,875 KHz

By the way, I had to adjust L2 ( Gamma Match ) from what is recommended in the manual to 24.25” to drop the SWR to an acceptable 1.2. For some reason, when installing it above the house, things changed.

But, when measuring with the station SWR meter, readings are different, probably because it is measuring readings of the components between antenna and SWR meter, things like amplifier, antenna tuner and RCS-4 Ameritron Remote Antenna Switch . Bandwidth Goes up dramatically. Here are the readings with the station SWR meter.

SWR————Frequency

2.0—————-28,545
1.5—————-28,285
1.15—————26,975
1.5—————-26,195
2.0—————-25,775

Bandwidth = 2,770 KHz

Since I have a big difference in bandwidth, will this difference from the 1,400KHz affect the performance of the antenna?

 

[Marconi]

Since I have a big difference in bandwidth, will this difference from the 1,400KHz affect the performance of the antenna?

Alexis, I once used a RCS-4 Ameritron Remote Antenna Switch, and it had me chasing my tail. I gave up and stopped using it. It probably didn't have a thing to do with the equipment however.

All I can say about your numbers above, and the questions you note about the bandwidth change is: IMO you are likely dealing with heavy losses somewhere, and CMC could be part of the issues you need to be checking.

Noticing big changes in antennas on raising is not generally a good sign, and not all antennas respond the same either. I think it is a good idea to match in situ whenever possible, and sometimes being very close to the ground is not productive. I've always considered the Simga4 design type to be very steady in this regard.

However, I had an Sigma4 that on 1 occasion, of numerous installs over time, where I discovered the gamma was not positioned precisely between the two radials as it should be. The skewing in that case was about 1/2" or less off center. I assumed it got bumped at some point and I had a real problem tuning the antenna, and then seeing the match change on raising. Something at least to check out. I think I've already posted something about this experience sometime back.

 

[Marconi]

Hi again. Today I could install my Sirio Vector 4000 on top of my house. It is about 12 feet above the house. House is 10 feet tall.

When adjusting on the back I did it on a 10 feet tall pipe with my MFJ Analizer. Here are the readings with 14 feet of RG-8x cable with a velocity factor of 82 according with specs. Using that info. and the formula to cut cables to a 1/2 wave, it gave me 14 feet.

Here are the numbers:

SWR ——- Frequency —R———-X

2.0 ———27,635 ———24 ———1
1.5 ———27,375 ———31 ———0
1.1 ———26,985 ———45 ———5
1.5 ———26,705 ———47 ———1
2.0 ———26,495 ———38 ———29

Bandwidth: 1,140 KHz

What frequency were you tuning for?

Did you hit your target?

What increment length adjustments were you making that got you to the best match above?

 

[Alexis Mercado]

Hi again Marconi. Since I had a SWR change on the roof, I did had to tune again on the roof. I was tuning for channel 20.

What I am going to do is to bypass the RCS-4 remote switch and see what happens. Regarding the Gamma Match, I made sure it was centered.
I incremented the Gamma Match adjustments by around 1/4” up or down.

By the way, I did use a line isolator and bandwidth jumped to 4,644KHz measuring from the SWR meter, with the analizer bandwidth went down a little to 1,730KHz. Here are the numbers with the line isolator installed at the feed point:

With SWR meter at the station

SWR———-Frequency
2.0—————30,013
1.5—————28,780
1.0—————27,524
1.5—————26,057
2.0—————25,368

Bandwidth: 4,644 KHz

With analizer measured directly with a 14 feet RG-8x jumper

SWR———-Frequency———R———X
2.0—————-28,505————31——-21
1.5—————-27,705————37———4
1.0—————-27,355————50———8
1.5—————-26,730————51———21
2.0—————-26,285————41———30

Bandwidth: 2,220 KHz

 

[Alexis Mercado]

By the way Marconi, I forgot to mention that before buying the Vector, I had a HyGain SPT-500 installed on the same mast going through the antenna switch, same coax, same things and I didn’t have the bandwidth issue.

 

[Marconi]

By the way Marconi, I forgot to mention that before buying the Vector, I had a HyGain SPT-500 installed on the same mast going through the antenna switch, same coax, same things and I didn’t have the bandwidth issue.

I can't explain Alexis, I can only try and remember the experiences I had with my S4 some years ago.

I was given the S4 by a long time local friend named Bill. Bill got it from another friend, and it was a "demo" installed at his CB business back in the days when Antenna Specialists was promoting their new Sigma 4 antenna.

It was laying in Bill's back yard in 2 pieces, but otherwise it was fully assembled. I took it home and added the top section to the bottom section, and the match was good on a 5' testing mast.

So, I raised it up to about 20'-25' feet, worked it for a while, and got a few very good responses (unsolicited signal reports).

When it was low to the ground it messed up some electronics at my house, but on raising the RFI went away for me. I also had no complaints from neighbors...like I'd had with some other antennas back around that time, so I was aware of interference back then in a very primitive sorta' way.

I found the antenna match to be very steady on raising. I never did a lot of testing on it up higher, because it was so tall. I also recall the bandwidth was a lot less compared to my SD, A99, Imax, CLR2, and possibly a few others.

So, I cannot explain the very broad-bandness you've reported above. I also know that Sirio reports their NV4K showing about 1.4 MKz <2.00:1 SWR bandwidth plus the gamma on my S4 was physically very small...so I figured that had some limiting effects on tuning range too.

I never owned a Sirio, but I've read a few guys claiming the NV4K BW was pretty narrow.

That did not surprise me however, I figured taller antennas of the time, were what folks were talking about...when they made claims about High Gain antennas seen in magazine advertising. That seemed to fit nicely and make some sense with the old stories we heard about beams..."if you want maximum gain you have to sacrifice some rejection." Now-a-days I see this idea has got some merit with my Eznec CB vertical models as well.

I can only guess that the very wide BW you've reported has to do with some substantial losses in your system somewhere.

 

[Marconi]

When adjusting on the back I did it on a 10 feet tall pipe with my MFJ Analizer. Here are the readings with 14 feet of RG-8x cable with a velocity factor of 82 according with specs. Using that info. and the formula to cut cables to a 1/2 wave, it gave me 14 feet.

Here are the numbers:

SWR ——- Frequency —R———-X

2.0 ———27,635 ———24 ———1
1.5 ———27,375 ———31 ———0
1.1 ———26,985 ———45 ———5
1.5 ———26,705 ———47 ———1
2.0 ———26,495 ———38 ———29

Bandwidth: 1,140 KHz

Unlike my S4, the Sirio gives you almost exact dimensions at frequency of choice for the important areas in tuning and setup.

I've have the Sirio New Top One antenna (A/P knockoff) and it uses a gamma match to fine tune. I find those dimensions given, when correct with all other dimensions given, will produce a resonant and well matched antenna at the frequency of choice. I saw this on the first attempt at setting the NTO up and raising it up in the air to working height. I installed this antenna several different times and I don't recall ever having a problem with the match at any reasonable height.

When you made your 14' foot tuned jumper of RG8x did you test it for resonance using your analyzer after doing the math to get the tuned length?

I case you have not made changes to your current setup on the roof and all of the system is still in tact as noted above, and TRY adding this 14' foot jumper back to the current setup at the radio-end, this time, and report what happens.

 

[Dr_DX]

Hi again Marconi. Since I had a SWR change on the roof, I did had to tune again on the roof. I was tuning for channel 20.

What I am going to do is to bypass the RCS-4 remote switch and see what happens. Regarding the Gamma Match, I made sure it was centered.
I incremented the Gamma Match adjustments by around 1/4” up or down.

By the way, I did use a line isolator and bandwidth jumped to 4,644KHz measuring from the SWR meter, with the analizer bandwidth went down a little to 1,730KHz. Here are the numbers with the line isolator installed at the feed point:

With SWR meter at the station

SWR———-Frequency
2.0—————30,013
1.5—————28,780
1.0—————27,524
1.5—————26,057
2.0—————25,368

Bandwidth: 4,644 KHz

With analizer measured directly with a 14 feet RG-8x jumper

SWR———-Frequency———R———X
2.0—————-28,505————31——-21
1.5—————-27,705————37———4
1.0—————-27,355————50———8
1.5—————-26,730————51———21
2.0—————-26,285————41———30

Bandwidth: 2,220 KHz

Alexis,

What is the minimum coax length with your antenna @ height on the roof back to the first thing the coax plugs into? BTW, I would definitely use the Line Isolator.

 

[Alexis Mercado]

Dr_DX:

Coax length from antenna to antenna switch relay box is about 30 feet. From relay box to station, another 30 feet.

I noticed something. This antenna doesn’t like to be close to other antennas. When raised, the Vector’s loop get closer to a Mosley yagi on top of the tower. The longest element tip of the yagi was about 10 feet from the Vector vertical radiating element as well. Distance from tower to Vector 4000 is 20 feet.


Marconi:
As soon as I lowered the Vector around 6 feet height, according with the analizer, bandwidth lowered to 1,460 KHz. When I rotated the yagi to have it’s longest element tip as far as it goes from the vector, bandwidth went down to 1,340 KHz.

Now the SWR meter reading is 1.0, just below from channel 1.

See the picture below.

I tested all the equipments connected between transceiver to antenna ( SWR meter, antenna tuner, amplifier, RCS - 4 Ameritron antenna switch control box, antenna relay box inside the tower, coax and jumpers included, etc) . I would like to know why I have difference in the reading. Below on the left side of the picture, the first column readings were from the SWR meter and next to it, where it says MFJ, was done with the MFJ analyzer on the same frequency of the meter. Which one is more accurate ?

The readings on the right side of the picture were done with the analyzer as well and give me different readings, different frequencies and different bandwidth. Why is that ?

 

[bob85]

Alexis

The only time I have seen a similar wide vswr bandwidth with a vector style antenna is when using very lossy coax,

I got lucky with my Vector 4000 install but they can be prone to cmc like any j-pole type antenna compared to a 5/8 with proper radials,
having it connected to a switch that the other antennas are connected to means its possible current could be flowing in any or all coax & antennas connected to the box,

even when using a choke its still possible, a reactive choke can make cmc worse if you are unlucky & it resonates one of the common mode paths,

Vectors can be sensitive to changes in height above ground & mast length if you tune close to ground then raise them higher up,
placing one over a reinforced concrete roof could upset it too,

I run coax from the radio to my antennas & if that means having to unscrew the coax to swap antennas or to swap to another socket on the radio for a different band that's what I do, no switch boxes duplers/diplexers,

no measuring vswr through switches, amplifiers, duplexers/diplexers or anything that adds impedance discontinuities & reactance,

every antenna switch for CB or Ham radio I ever opened up including ALPHA switches are garbage inside or use regular relays.

My radio buddies think I am OCD about it all, which is true, once you go down the rabbit hole there's no turning back,

I think they just like wasting money on things to put inline with their coax so they can sit back & be lazy,

it gives them more time to talk about why their vswr is not right & how they can't hear the guy IM talking to & how noisy their RX is.

 

[Alexis Mercado]

Thank for your input Bob. I wanted to test the whole system in order to discard any problems with it. Now I know it was the proximity between the yagi and the Vector.

Now that I found the issue and fixed it, I’ll try again to tune the antenna where I wanted to work.

Sirio states in the tuning table that if you want it to resonate in channel 20, L3 should be set to 730mm = 58 3/4” and then the L2 ( gamma ) should be adjusted from 630mm to 640mm.

I did it like that but instead to resonate on channel 20, resonates just below channel 1. I played with the gamma match as Sirio recommends but what is does is that it remains on the same frequency , let’s say 26,885 and lowest SWR on that frequency . It can be 1.3, 1.5. 1.8, etc. Check with the analyzer for any dip on up and down but nothing. In other words, I can’t shift resonant frequency just by adjusting the gamma match.

 

[bob85]

Alexis
adjusting the gamma capacitor/rod can only cancel reactance,
it can't adjust the resistive part, you adjust R by sliding the gamma strap up or down,

remember that when measuring resonance ( not vswr ) through coax, the coax will cancell reactance in the antenna too,

causing x=0 to be somewhere other than where the antenna is resonant unless you are VERY lucky & the antenna is resonant on a frequency where the coax is an electrical 1/4wave or multiple electrical 1/4waves. ie 1/2wave 3/4wave 1wavelength etc,

tuning for x=0 through your coax does not mean the antenna is resonant,
it means the system ( coax + antenna ) are resonant.