Modified Vector 4000

[bob85]

Eddie I don't remember the details of when you experimented with the sigma4,
I remember you cleaning it & ending up ill and me feeling it was partly my fault,

I did see the changes I described, my ideas on why have changed over the years as I have said before,

so far nobody has made a model of the cone that will show radiation due to unbalance at the top of the cone,
the same unbalanced condition that causes the short leg of a j-pole to radiate,

i don't even know if its possible to remove the upper monopole & still have the same unbalanced condition in NEC by terminating just the central monopole.

 

[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 ?

Bob, I would like to know your answer to my question.

 

[bob85]

cmc can cause coax placement to effect swr, it could be because you are lifting the coax nearer the antenna & away from the roof.

 

[Alexis Mercado]

cmc can cause coax placement to effect swr, it could be because you are lifting the coax nearer the antenna & away from the roof.

Hi again Bob. Like I said before, coax is hanging down, about 16 feet without touching the mast, about 40 feet of coax is laying on the roof and about 10 feet from edge of roof running inside tower to the coax relay box .

 

[bob85]

Alexis,
its possible to have some current flowing anywhere in the system when you have them connected on a relay box,
having the roof under the vector won't help with tuning moving as you raise the antenna,

if you are measuring swr through the relay box all bets are off as to what it could do to readings taken in the shack.

If its working with decent swr & signals & no rfi where you want to use it you are OK.

 

[freecell]

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

106.3' = line loss attenuation @ 27.365 of 0.684 dB. for 3.485 wl line. With R=57.4 and +jX=36.1, transline input R=51.7, jX=29.4. TX SWR=1.77:1 ANT SWR=1.96:1. Assuming 100W. input, PWR LOSS is 17.2W./% & power delivered to antenna load (NOT RADIATED) is 82.8W./%. Total transline loss + capacitive reactance and SWR LOSS is 0.821 dB.. Total power RADIATED FROM THE ANTENNA will depend upon radiation efficiency, i.e., Rrad / Rrad + Rloss = Reff %.

 

[Marconi]

106.3' = line loss attenuation @ 27.365 of 0.684 dB. for 3.485 wl line. With R=57.4 and +jX=36.1, transline input R=51.7, jX=29.4. TX SWR=1.77:1 ANT SWR=1.96:1. Assuming 100W. input, PWR LOSS is 17.2W./% & power delivered to antenna load (NOT RADIATED) is 82.8W./%. Total transline loss + capacitive reactance and SWR LOSS is 0.821 dB.. Total power RADIATED FROM THE ANTENNA will depend upon radiation efficiency, i.e., Rrad / Rrad + Rloss = Reff %.

FC, IMO and for CB level enthusiasts these details are likely truly an "enigma" as noted in Merriam-Webster below.

https://www.merriam-webster.com/dictionary/enigma

 

[Marconi]

For those that were wondering what my measurements on this antenna are......Here you go. The vertical whip is 29 feet 7 and 1/4 inches long from the bottom of the connector bracket to the tip of the whip. The four radial arms are 81 and 1/2 inches long from end to end. The loop is 129 inches in circumference. The gamma is simply adjusted for lowest VSWR. Sorry I did not measure the gamma and I did use a home made Teflon gamma match with a weatherproof HN connector.

You may notice this last version of the antenna is more sturdy. I used the parts from two Vector 4000 antennas so that I could double up the lower sections and cut the flimsy top sections off. The four black plastic arms that hold the radials in place are also taken from two antennas. The ends were cut and then two pieces were screwed together with 4-40 hardware to make them longer.

The antenna was tuned on 11 meters and still provides under 2:1 VSWR on 10 meter SSB. The gain and bandwidth with the larger loop seems better to me and certainly exceeds what is possible with a 5/8 wave. The main advantage of the gamma match versus a coil with a tap is that a gamma allows you to tune out both capacitive reactance and inductive reactance. The coil only allows you to adjust the inductive component.

Donald, can you tell me what frequency this Vector was using?

 

[Shockwave]

Donald, can you tell me what frequency this Vector was using?

Yup, I had a buddy connect a Perkin Elmer RF Generator to his vertical 50 miles away as I tuned this antenna for maximum signal. The generator was operating on 27.12 MHz. I made several mistakes with this antenna that resulted in it only being installed for about a month before it was removed and thrown behind the barn as scrap parts.

First was I tuned it too low, barley 20 feet off the ground, close to a tree and only 10 above a roof gutter. Then I assumed I would be able to establish a stable test signal from that RF generator 50 miles away. Signal strength was no problem but stability sucked when trying to measure down to a db. Doing absolutely nothing, revealed the signal could fluctuate on its own by several db at times. Then there is the issue with trying to keep the cone resonant with its shorter radials and wider loop, while still covering over the entire first 1/4 wavelength of the inner radiator.

Sad to say this attempt appears to be another waste of time and is why those large loop modifications, never made it into the FM versions of this antenna.

 

[Marconi]

Sad to say this attempt appears to be another waste of time and is why those large loop modifications, never made it into the FM versions of this antenna.

I found similar results trying to make the loop larger, it was no-way-no. Based on your comments, I don't think I will waste my time on this idea again either.

Thanks!

 

[El Kabong]

I'm in the process of assembling mine now. Got the 4 ring brace arms coming from England. Only source I could find. I have the ant assembled by eye to the specs in the "manual" as listed. Leaning against a tree, bottom on the ground I get a 1.5 SWR. When the arms arrive, and before the weather turns, I will haul it up on the roof and fine tune the gamma. Any suggestions on how to get a stock Vector to see a flat match?

 

[Alexis Mercado]

El kabong

What type of roof you have ? I had issues with my Vector 4000 because I had a concrete roof made of concrete and rebars. It was a pain in the ass to tune it. First I tuned it on a 10 feet mast on the backyard. When I installed it on the roof SWR went up had to tune it again. I could tune it back to 1.1 but as I raised the mast, SWR went up again. I was told here o. This forum that the rebars could influence.

After many attempts playing with the Gamma and last section, I could achieve SWR of 1.0 on channel 1. After raising it about 16 feet above roof, SWR went up to 1.3. Coax was strapped to the mast. Resonant frequency shifted to channel 28. After some suggestions here on this thread, I left the coax hanging from the antenna, without strapping it to the pole and the SWR went down to 1.1. I left it right there. No more attempts.

 

[El Kabong]

Wood roof over wood beams. Almost flat. No way I will let my coax hang free. All that weight on three small solder areas.

 

[Marconi]

Alexis, I will model your idea with my NV4K and see if rebar in your roof messes with the model...just for grins.

 

[Alexis Mercado]

Alexis, I will model your idea with my NV4K and see if rebar in your roof messes with the model...just for grins.

Thanks Marconi.