5/8 wave matching network

[w1vtp]

I guess I should have included the math based on that spreadsheet data that I did.

K = Constant factor

Freq  = The frequency for which the antenna is being designed

Feet = Length of element being cut.

Radial length = K of 575 divided by Frequency of interest 18.15 MHz = 575/18.15 MHz = 31.68 feet (Radial length)

Sorry for the confusion

Al

[KD6VXI]

I ran some numbers this evening out of boredom.

Length of radiator, 395 inches
Length of (4) radials,  163 inches

Mounted 1.5 meters above ground.

At 18.12 mhz,  72.86 ohms with - 296.8 ohms of reactance.

That's 2.607 uH.  

I'm including plots.   Above real soil equating to Bakersfield,  Ca dirt.

I also ran it as a quarter wave.   It comes in at 32.39 ohms with app 4 ohms of inductive reactance.   And only down 1.8 db.   And a 1.5 swr.   

Seems like a lot of aluminum to get less than 2 db...   And a matching network.


--Shane
KD6VXI

[WB4AM]

I ran some numbers this evening out of boredom.

Length of radiator, 395 inches
Length of (4) radials,  163 inches

Mounted 1.5 meters above ground.

At 18.12 mhz,  72.86 ohms with - 296.8 ohms of reactance.

That's 2.607 uH.  

I'm including plots.   Above real soil equating to Bakersfield,  Ca dirt.

I also ran it as a quarter wave.   It comes in at 32.39 ohms with app 4 ohms of inductive reactance.   And only down 1.8 db.   And a 1.5 swr.  

Seems like a lot of aluminum to get less than 2 db...   And a matching network.


--Shane
KD6VXI

Hello,

Less then 2 db vertical antenna is more then not having an antenna at all if one really wants to get on 17 meter when no other means of an antenna is possible! 

Personally I have never ran any of these antenna programs.  Never had an opportunity to.  How actuate are they in the real world.

Are there any actuate antenna programs for free?  I would like to mimic the one I had built and then play with the numbers.

Thanks Shane for running these numbers.  Have you tried to run the numbers for the same antenna above ground, say 30 feet or so?

Ken

[KD6VXI]

The program I'm using is mmana gal.   It's free,  and not the most accurate.

Yes,  changing height will change things,  especially  pattern and reactance present.   Shorter radials exacerbate the issue.

I can post more pics when I get home,  say of higher elevation.

--Shane
KD6VXI

[Steve - K4HX]

The NEC and MineNEC based modeling programs are generally very accurate when used properly. There are some gotchas and known errors. These are easily avoided.

I've used CocoaNEC to do much of the design for this antenna system.

http://amfone.net/Amforum/index.php?topic=21534.0


And the modeling came in handy in designing my phased Beverage antenna system.

http://www.amwindow.org/misc/huzantennas/antennas2014.html


And some short antennas for 160 meters.

http://www.amwindow.org/tech/htm/160smallants.htm