[600MRG] NDB Antenna Calculator

[Frank Lotito]

Ed -I think you may have lost sight of something - A "DC" measurement of coil resistance does not mean anything of consequence w.r.t. to RF losses in an inductor. I assume when you used the term "multimeter" you meant a DC measuring instrument like a VOM, VTVM?

 Besides skin effect losses, there are additional losses that show up at RF.  These additional losses will not show up with a plain DC resistance measurement. For that matter, coil inductance at 1000 Hz (a common measurement frequency for many low-$$ R-L-C instruments) also means little w.r.t. inductance at the operating frequency, and definitely for harmonic frequencies.  For example, I am sure we recall from the old days "dipping out a plate choke" to verify that at the amplifier's operating frequencies the choke does not become series resonant, or take on a capacitive nature at or near the operating frequency.  

Have fun, be safe - 

73 Frank K3DZ / WH2XHA     

________________________________________
From: 600MRG <600mrg-bounces at w7ekb.com> on behalf of Edward R Cole <kl7uw at acsalaska.net>
Sent: Sunday, September 27, 2015 3:10 PM
To: sbjohnston at aol.com; 600mrg at w7ekb.com
Subject: Re: [600MRG] NDB Antenna Calculator

I played with it and get quite a bit lower radiated power than my
other calculations.  I do not know the coil Q so tried some values
and see R change accordingly.  So I am guessing if I measure the coil
resistance with a multimeter I could find the Q backwards by
adjusting the value of Q till R reads what I have measured.

What I am getting is RP =1.97w.  I previously measured ground
resistance with my modified MFJ analyzer as 20-ohms.  My previous
calculations gave radiation resistance as 0.83.  This calculator
gives is as 0.34 ohms for coil Q=100

I can only guess that the model is a single wire inverted-L.  My
antenna has three parallel wires in the vertical section and two in
the horizontal top section.  I would guess that would increase the
top capacitance and lower the Q of the antenna.  I did my previous
modeling with EZ-NEC demo v.5.0.

73, Ed - KL7UW

At 08:34 AM 9/27/2015, sbjohnston at aol.com wrote:

>
>One of the Australian 630 meter enthusiasts, VK5ABN, has created an
>online antenna calculator based on published equations for
>Non-Directional Beacon antennas.  These are similar to many of our
>amateur antenna efforts.  See message copied below...
>
>Steve WD8DAS and WH2XHY
>
>- - - - - - - - - - - - -
>
>G'day,
>
>FYI: I've created a web page using equations found in "NDB Antennas" by
>John R. Pink. to calculate and evaluate antenna parametric. It can be
>found on
>
>http://ping.net.au/index.php?mode=antcalc
>
>Here you will also find a link to the original article. This is work in
>progress, so please let me know if you find any errors or have
>suggestions for improvements.
>
>I found it very useful in aiding me to improving the performance of my
>MF antenna.
>
>Enjoy,
>
>73, Berndt
>VK5ABN
>
>
>- - - - - - - - - - - - -
>
>
>
>
>
>
>
>_______________________________________________
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com


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