Software for calculating feed impedance

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VK3LU
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Software for calculating feed impedance

Post by VK3LU » Thu Sep 10, 2015 8:11 pm

Does anyone know if there is software available that can calculate the feedpoint impedance (and reactances) of a ground mounted vertical of fixed height at various frequencies?

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Nev
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Re: Software for calculating feed impedance

Post by VK4JAM » Thu Sep 10, 2015 9:40 pm

Hi Nev,
Try the following:

http://www.arrl.org/files/file/Antenna% ... 0W8WWV.pdf

It may point you in the right direction.

73
Andrew

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Re: Software for calculating feed impedance

Post by VK4TI » Fri Sep 11, 2015 8:29 am

If using a std design then the impedence will be easily available , simply measuring it when built will aid in matching but what objectives ?

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Re: Software for calculating feed impedance

Post by VK4TJ » Fri Sep 11, 2015 1:45 pm

If I understand your question correctly, MMANA-GAL will do it. Dunno about a graph plot - maybe it does, but I have not found it yet, being a "baby steps" user of the software still.
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John VK4TJ

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Re: Software for calculating feed impedance

Post by VK3LU » Sat Sep 12, 2015 11:10 am

Thanks all for your suggestions.
I am on holidays at the moment on VK4 time, hence the sluggishness of my reply :beer:
Perhaps I should explain my query.
If a 40m ground mounted vertical is used on other bands, there is a wide variation in feed impedance; high on 80 and 20, low on 40 and 15 etc. This can make life difficult for a 4:1 voltage balun at the feed point. Losses etc.(The antenna is to be fed with an auto matcher at the base)
The idea occurred to me that if the vertical was cut for say 8.5mHz then the variation in feed imp. on the bands would be less, the antenna being "in between ", neither high nor low Z.
That is why I asked about any relevant software.
Or am I nuts?

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Nev
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Re: Software for calculating feed impedance

Post by VK4TI » Sat Sep 12, 2015 4:03 pm

Have a read about the 43ft vertical . mine performs very well and cost not much

http://www.ad5x.com/images/Presentation ... 43RevA.pdf
of course grounding systems help but need not be complicated or costly

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Re: Software for calculating feed impedance

Post by VK3LU » Sat Sep 12, 2015 8:11 pm

Thanks,
I had a look at EZNEC a few months ago and found it rather complicated to say the least. It will need a lot of reading and fiddling I suspect.
When I am back home I will have a try at MMANA-GAL.
I hope it is more user friendly.
Of course I could buy an antenna analyser and have a play with some aluminium tubing :thumbup:

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Nev
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Re: Software for calculating feed impedance

Post by VK4TJ » Sun Sep 13, 2015 5:48 am

MMANA-GAL will probably get you up and going faster. The key is to find a .maa file from somebody else :-)
Quite a few ship with the base install, but there are even more in the files section of the Yahoo group.
Even if you have to alter the dimensions, height above ground etc. to suit your particular requirements, having somebody else do the hard work saves having to get your head around X,Y & Z coordinates.

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John VK4TJ

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Re: Software for calculating feed impedance

Post by VK3AUU » Sun Sep 13, 2015 6:39 am

EZNEC is easy. You just need to put in the x,y and z coordinates of each element. If you give me the dimensions of everything I will do it for you. Imclide all the ground wires too. Send to my email address VK3auu@dcsi.net.au

David

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Re: Software for calculating feed impedance

Post by VK3LU » Sun Sep 13, 2015 2:28 pm

Thanks John and David,
I read the article by AD5X and it has me interested. I was thinking of something shorter than 42 feet but it would have higher angles of radiation I would imagine.
I would like to mount it on the metal roof of a shed of 6X14 metres but the Leader of the Opposition might have a say about that. }:[
When I get home I will spend some time on it, but at the moment it holiday time!!

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Nev
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Re: Software for calculating feed impedance

Post by VK4TI » Sun Sep 13, 2015 2:54 pm

you could use a 32'6"vertical but it is not as versatile however it does offer a good signal on 40 m , 15 with some tricks and perhaps another smaller vertical for 10 and 20m as well ? , or if you have some trees then a 43ft sloper perhaps

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Re: Software for calculating feed impedance

Post by VK3XL » Mon Sep 14, 2015 12:57 pm

Hi Nev... hope you are enjoying your holiday up north.
I have not tried any of these non resonant verticals myself but have done a bit of reading about them. It seems that the length needs to be something that will not produce a very high impedance on any band you want to use it on.
Some common lengths that come up regularly are:

43 feet - used from 80m to 6m
31 feet - used from 40m to 6m
24 feet - used from 20m to 6m

Hope that helps.
Catch you on 80 meters when you get back.
73 Mike

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Re: Software for calculating feed impedance

Post by VK3XL » Mon Sep 14, 2015 1:10 pm

found this quote in reply to someones question fr non resonant verticals

And the answer is: In 2 years, 37,000+ QSO's, 223 countries, 5 Band DXCC. All with a 31' , S9 Vertical, using the metal roof as the radials, with a Balun Design 4:1 Unun, and an AT-AUTO Tuner. which tunes it better then 1.2:1 on all bands 10-80m.

I think you said you have an AH4 tuner and want to use the shed roof as the groundplane now you just have to get the 31 foot vertical past the minister for war..... good luck
73 Mike

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Re: Software for calculating feed impedance

Post by VK3LU » Mon Sep 14, 2015 1:42 pm

Hi Mike,
Thanks for the info. Interestingly the 24ft vertical is almost a quarter wave on 10mHz.
It makes me think about the trapped vert I made for 30/20. It's physical length is 21ft 6in.
I wonder what the radiation angles are for the 31 and 24 ft verts? The 31 ft seems to work according to the quote you posted.
I suspect the shorter verts have higher angles...perhaps.

Anyway, I'm on holidays. I will think of you when it's beer o'clock.

Cheers
Nev
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Re: Software for calculating feed impedance

Post by VK3XL » Mon Sep 14, 2015 3:01 pm

sun is up isn't it? ....





damb I need to add more charecters... that should do it
73 Mike

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Re: Software for calculating feed impedance

Post by VK2AVR » Wed Sep 16, 2015 11:19 am

VK3LU wrote:I wonder what the radiation angles are for the 31 and 24 ft verts?
I suspect the shorter verts have higher angles...perhaps.
EZNEC simulation seems to indicate that the angle of radiation is not changed much.

See pic comparing a 10m tall vertical (full size @ 7MHz) with a 6m tall vertical (40% shortened). In both cases I left the ground plane as infinite real ground (a reduced ground plane will definitely change matters). Vert1 is the full size, primary is the shortened. So the shortened antenna has 1dB more gain above 45 degrees (it is getting closer to being an isotropic radiator), but below 45 degrees they are within 0.1dB.
shortened vertical.jpg
What has changed with the short vertical is the antenna impedance is screwed up. So you will need an ATU, loading coil, or capacitive hat. Loading/matching has the potential to cause loss, so your performance decrease comes from losses not a change in radiation angle. Loading (with a coil or hat) also narrows the bandwidth.
Geoff
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Re: Software for calculating feed impedance

Post by VK3LU » Wed Sep 16, 2015 6:45 pm

Thanks Geoff,
That chart makes trying out the 21ft6in 30/20 vertical I made worth a try. I don't know why I have never used it :oops:
I still think the 43 ft vert is the best choice from what I have read.
But I can't do a thing about it up here in VK4 :beer:

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Nev
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Re: Software for calculating feed impedance

Post by VK4TI » Wed Sep 16, 2015 7:22 pm

"VK3LU"Thanks Geoff,
That chart makes trying out the 21ft6in 30/20 vertical I made worth a try. I don't know why I have never used it :oops:
I still think the 43 ft vert is the best choice from what I have read.
But I can't do a thing about it up here in VK4 :beer:

Cheers
Nev "

It's quite amazing how poorly people judge the height of a thin camo painted vertical , out council claims a 10m limit and in 7 years never a problem even with huge 6m antennas covering much of the house roof
Maybe digital TV has an advantage with no tvi so no complaints ?

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