Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

To 7/8 or NOT to 7/8, that is the equastion

Below are the same model overlays with various radiator lengths I did earlier in Free Space. This time I did them over Real Earth.

Here I compare the various length antenna radiators with no mast, with an isolated (ISO) mast, and with a mast directly connected to the antenna.

You will note the similar trends in the patterns, gain, and angle results that my previous Free Space models indicated. Click here; is a link to the Free Space models: http://www.worldwidedx.com/threads/...at-is-the-equastion.189729/page-3#post-529597

Again all of the models with shorter radiators show better patterns, and a bit better performance at low angles to the horizon, however notice the overlays with the mast directly connected to the antennas show less differences in gain and angle for all the various length models. This surprises me that the antenna models with mast attached directly to the antenna did not show as much difference in maximum gain or angle for my other Vector models reported in this thread with various lengths. However, these are just models and these findings need to be tested in a real world situation to be sure.

In my real world testing however...I don't think I was ever convinced with as much difference as others report...just using my radio. Click Real Earth models noted below.
 

Attachments

  • IMG.pdf
    268.5 KB · Views: 25
Last edited:
Voltage fed antenna, almost an entire full wavelength contained within the antenna, I wouldn't expect the mast to have any influence on the gain or elevation because for the antenna system as a whole it is doing very very little other than providing a support and I would summise that any effect was due to its presence and coupling rather than any function of RF grounding.

What happens when you do the same model but say lower the top of the mast fractionally or add an insulator so it isn't actually part of the antenna system?
 
M0GVZ said:
Voltage fed antenna, almost an entire full wavelength contained within the antenna, I wouldn't expect the mast to have any influence on the gain or elevation because for the antenna system as a whole it is doing very very little other than providing a support and I would summise that any effect was due to its presence and coupling rather than any function of RF grounding.

What happens when you do the same model but say lower the top of the mast fractionally or add an insulator so it isn't actually part of the antenna system?
Click to expand...

M0GVZ, I don't consider the New Vector 4K to be a voltage fed antenna, so we differ on that issue.

IMO models over Real Earth should include the mast in the model. Some folks suggest, among other things, that the mast needs to be isolated (ISO) from the antenna in order to help reduce any ill-effects from errant currents...so I made these 4 different radiator length models for your comparison;
with a mast,
with no mast,
and with an isolated mast.

M0GVZ, I didn't post the supporting models over Real Earth earlier because the file is quite large. The models captioned with ISO at the end of the title are "isolated" models...just as you suggested above.

Note the distinctions and difference in the red line currents on the mast in the antenna view, and compare.

I made a 5" inch space between the top of the mast and the bottom of the antenna and titled them as "....ISO"

The 30+ page file is attached below.
 

Attachments

  • IMG.pdf
    1.5 MB · Views: 19
Last edited:
  • Like
Reactions: M0GVZ
Marconi said:
M0GVZ, I don't consider the New Vector 4K to be a voltage fed antenna, so we differ on that issue.

IMO models over Real Earth should include the mast in the model. Some folks suggest, among other things, that the mast needs to be isolated (ISO) from the antenna in order to help reduce any ill-effects from errant currents...so I made these 4 different radiator length models for your comparison;
with a mast,
with no mast,
and with an isolated mast.

M0GVZ, I didn't post the supporting models over Real Earth earlier because the file is quite large. The models captioned with ISO at the end of the title are "isolated" models...just as you suggested above.

Note the distinctions and difference in the red line currents on the mast in the antenna view, and compare.

I made a 5" inch space between the top of the mast and the bottom of the antenna and titled them as "....ISO"

The 30+ page file is attached below.
Click to expand...
hi Marconi, ok how about a 2 antenna comparison between the current Vector 4K & a 28.6' over real ground &including mast?
 
Man all great info here!! Now I know what I am gong to do. Save a bit and try the new vector. Sounds like at the height I am wanting to use it at that it will work quite well. Height will be between 20-30ft to feedpoint. Will have to just get one I suppose and see for myself. If it works like the tornado did I'll be happy. I've 2 1/2 wave dipoles up now to 35-40ft to the feedpoint, both horz. and they work great for dx. I just need a vert. now to get back my locals out at 30-50 miles. The A99 at 30ft to the feedpoint didn't hack it. Not sure if it's the fiberglass or what but the noise issue I have seems to be about 2 s-units stronger with the A99 vs. what the tornado read at the same height. And I was very easily able to make it to 50 miles on SSB every night pretty much. Glad all this info was posted and now I can proceed with what I think will be the best suited setup for my needs. Thanks again for everyone's input!!
 
Needle Bender said:
hi Marconi, ok how about a 2 antenna comparison between the current Vector 4K & a 28.6' over real ground &including mast?
Click to expand...

Attached below is an overlay of the two antenna setups as you suggest, plus I added the Vector set at the length for the Sigma4 and my Sigma 4 with 3 shorter radials...all at 36' feet with a mast over real Earth.

There just isn't much difference like Sirio suggested to us in their promotion for their New Vector 4000.
 

Attachments

  • IMG.pdf
    100 KB · Views: 26
Last edited:
Vector 4000....

ssaM8PT.png


Moxon at same 36ft height...

wf2ZrHS.png


No contest really for DX....
 
Wonder what an imax 2000 would look like at 36' 45' 55' 65' and 72' at coax connection point at base?
 
Marconi said:
Attached below is an overlay of the two antenna setups as you suggest, plus I added the Vector set at the length for the Sigma4 and my Sigma 4 with 3 shorter radials...all at 36' feet with a mast over real Earth.

There just isn't much difference like Sirio suggested to us in their promotion for their New Vector 4000.
Click to expand...
oops, Marconi it looks like you accidently had a momentary bout of needle bender slysdexia, I often get things wackbirds ;) - from the pattern & the "26.8" at the upper left, me thinks you programmed 26.8 not 28.6 :eek:
It appears that 'magic' .8 or so wavelength provides the fullest pattern from 8 to 40 degrees, sacrificing maybe .3-.5dB around 8 degrees to gain 3-4dB(!) around 30 degrees. I guess I'm just not fully convinced that a low TOA at any expense is the best option for an all-around vertical omni for local-semi-local/Dx performance. ...and if I were opening a thread about horizontal directionals, I'd much prefer a QUAD over a moxon, but this thread is focused on the differences in the marijuan... er uhm, Sigma/Vector/Tagra/LW150 etc. design
 
Marconi said:
I was just taking a wild guess at what I thought you asked.
Click to expand...
And I have to reiterate, I greatly appreciate your efforts, I'mfinding this extremely helpful. I have a nearly completed 7/8 resting in the backyard and a new V4K awaiting mods & assembly, once I finish moving & musical storage locations. Would you mind adding a 28.7' pattern to the mix? - Also, what dimensions did you use for the Sigma pattern?
 
I posted three Vector models. I also posted a Sigma 4 model to specs. All with masts attached.

1. 28.6' model is the Vector extended as your suggested, The black line is the Primary model
2. 26.8' the stock Vector and is blue

I should not have added the last two models. Forget the comparisons I added with the S4 length idea for the last two, green and red patterns. Black and blue are the two colored line patterns that apply to your question...as I understand it.

Needle Bender said:
Also, what dimensions did you use for the Sigma pattern?
Click to expand...

Sigma 4 model is 331" x .75" inches used for the overall radiator length, and 90.5" x .50" inches used for the overall length of the three radials.

Needle Bender said:
Would you mind adding a 28.7' pattern to the mix?
Click to expand...

NB, I will add the 1" to the "Vector 28.6' with mast" model that is set at 28.6' inches already...the black line in the overlay patterns above. Do you really think one inch will make a difference that matters? I would be surprised if it did. The Vector model also has a 5" inch diameter top hat that is not included in the overall radiator length, but is part of the model.
 
Last edited:

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back