[600MRG] Estimating Rr for non-confirming verticals

Sun Jul 19 17:40:38 EDT 2020

Of course the calculations are interesting.  But the only need to 
determine Rr and R is for calculating EIRP (legal requirement for operating).

I made a coil base on best guessing 10-inch dia. by 11-inch long with 
1/4 inch winding spacing.  I believe that calculated to around 650uH 
and I am using 2/3 of the turns (~400uH) to get resonance (measured 
with modified MFJ-269B): Z = 20 +/-j8.  I found the 50-ohm match by 
trying taps above the ground (2-1/2 turns).

As WD2XSH-45 I ran 100w shown on Bird with 100H element and measured 
1.40 RF amps at the transmitter 50-ohm output.

Inverted-L is down so not QRV at this point (need to retune from 495 
to 475 KHz) and plant new radials.

73, Ed - KL7UW

At 01:18 PM 7/19/2020, Rik Strobbe wrote:
>Hello Ben, all,
>
>he 6pF/m for the vertical section is for a 'thin wire', the ladder 
>line will have a larger capacitance, as you assumed.
>This will reduce the radiation resistance a bit as you will have a 
>bit more 'vertical picofarads'.
>But  wouldn't worry too much about that.
>The dimensions of your antenna are similar to my 472kHz antenna (14m 
>high, 23m topload), and despite the fact that the location is far 
>from perfect (many birch and oak trees up to 30m high surrounding 
>the antenna) it works.
>Running 200W I worked many European stations up to 2200km and even 2 
>US stations (N1BUG and NO3M).
>
>73, Rik  ON7YD - OR7T
>
>________________________________________
>Van: Ben Gelb <ben at gelbnet.com>
>Verzonden: zondag 19 juli 2020 21:56
>Aan: Rik Strobbe
>CC: Roger Graves; Neil Klagge; Posting 600m 600mrg
>Onderwerp: Re: [600MRG] Estimating Rr for non-confirming verticals
>
>Thanks all.
>
>The VK1SV calc appears to use the 5pf/m (top load) and 6pf/m
>(vertical) approximation for C (formulae 2b and 3b) in Rik's writeup.
>Haven't spent anymore time on the 472khz calc to figure out what it is
>doing... but perhaps will get back to it time permitting.
>
>Now, I went and measured the loading coil w/ LCR meter and measured
>332uH. Also used an air-coil calculator to compute expected value (10"
>dia, 4.25" long, 33 turns) and got 312uH. So fairly close, so pretty
>confident within 10% anyway.
>
>This would imply ~340pF of capacitance from the antenna (vs. 272pF
>predicted by VK1SV calc). So about 68pF more than predicted. If I
>consider that the horizontal component of the ladder line section
>traverses approx 13m or so and blindly apply the 5pF/m value, that
>comes out to 65pF.. which is pretty close (actually, its a bit too
>close, since I probably haven't established antenna height within
>better than 20% accuracy...). Perhaps next thing is to measure height
>a bit more carefully.
>
>Once the pFs are adding up, I guess next question is to think about
>what it means to have "top load" distributed across the diagonal
>section of vertical. Presumably this means that the segments of
>vertical closest to the ground "see" the greatest amount of top
>capacitance (and probably have higher current and therefore an outsize
>share of the radiation resistance). Seems like for a true diagonal,
>should be fairly straightforward to come up w/ an average and use that
>to figure Rr.
>
>
>On Sat, Jul 18, 2020 at 2:03 AM Rik Strobbe <rik.strobbe at kuleuven.be> wrote:
> >
> > Neil is right, it is ;-)
> >
> > I found out that using this formulas results is a relative small 
> error (in most cases < 10%) compared to simulation with MMANA.
> >
> >
> > 73, Rik  ON7YD - OR7T
> >
> >
> > ________________________________
> > Van: 600mrg-bounces at mailman.qth.net 
> <600mrg-bounces at mailman.qth.net> namens Roger Graves <ve7vv at shaw.ca>
> > Verzonden: zaterdag 18 juli 2020 7:44
> > Aan: Neil Klagge
> > CC: Posting 600m 600mrg
> > Onderwerp: Re: [600MRG] Estimating Rr for non-confirming verticals
> >
> > Hi Neil! Thanks, those could well be the formulae.
> >
> >
> > On Jul 17, 2020, at 8:34 PM, Neil Klagge <w0yse at msn.com> wrote:
> >
> > Hey Roger, I think the ON7YD calculations for Rr were based on 
> his Capacitance formulas from this page
> >
> > http://www.strobbe.eu/on7yd/136ant/#CapTop
> >
> > Sent from Neil's iPad....
> > ________________________________
> > From: 600mrg-bounces at mailman.qth.net 
> <600mrg-bounces at mailman.qth.net> on behalf of STEVE MCDONALD <ve7sl at shaw.ca>
> > Sent: Friday, July 17, 2020 6:13:18 PM
> > To: Roger Graves <ve7vv at shaw.ca>
> > Cc: Posting 600m 600mrg <600MRG at mailman.qth.net>
> > Subject: Re: [600MRG] Estimating Rr for non-confirming verticals
> >
> > Neil has a nice methodology page here that can be used to find 
> Rr, or get you in the ballpark:
> >
> > https://w0yse.webs.com/wg2xsvpage.htm
> >
> > Steve  VE7SL
> >
> >
> > ----- Original Message -----
> > From: Roger Graves <ve7vv at shaw.ca>
> > To: Ben Gelb <ben at gelbnet.com>
> > Cc: Posting 600m 600mrg <600MRG at mailman.qth.net>
> > Sent: Fri, 17 Jul 2020 17:51:44 -0600 (MDT)
> > Subject: Re: [600MRG] Estimating Rr for non-confirming verticals
> >
> > Ben,
> >
> > Thanks for the link to the other calculator.
> > I ran my antenna dimensions in both and got similar values to 
> what you reported.
> >
> > The 472 kHz calculator is estimating a greater topload capacity 
> (and lower required inductance) for the same antenna dimensions.
> > The VK1SV calculator page says it uses formulas from an ON7YD 
> webpage, but my scan of that did not reveal which formulas might be used.
> > The 472 kHz calculator says nothing about what formulas it is based on.
> > So it is not possible to compare the models.
> >
> > When you measure the inductance of your loading coil, which 
> calculator's prediction came closest to what you measured?
> >
> > I like the VK1SV calculator better b/c it does not try to 
> estimate the coil loss. What I can measure is the total system R, 
> which is the sum of (at least) ground loss, coil loss, and antenna 
> radiation resistance (which can be neglected given the size of the 
> other losses at MF/LF). That is the value that the VK1SV calculator 
> requests. IDK what my ground loss by itself is, which is what the 
> 472 calculator requests.
> >
> > Roger
> >
> >
> > > On Jul 17, 2020, at 3:50 PM, Ben Gelb <ben at gelbnet.com> wrote:
> > >
> > > Thanks all for replies.
> > >
> > > A couple of clarifications that might not have been clear from 
> my first e-mail.
> > >
> > > - Though the dipole is fed with ladder line, it is being fed as a
> > > T-top vertical (i.e. ladder line conductors shorted together at the
> > > base) when used on 630m.
> > > - I've had no issue feeding the antenna and getting it on the air.
> > > Have been QRV for the last week or so.
> > > - My question is about estimating Rr (in order to estimate EIRP).
> > >
> > > Thanks Roger for the calculator link and validating that my thought
> > > process seemed reasonable at least (if it makes sense to at least 1
> > > other person maybe not hopefully lost). :)
> > >
> > > Interestingly, I use this calculator:
> > > http://www.472khz.org/pages/tools/antenna-simulator.php
> > >
> > > Result for 12m height, 28m top load length T-top do not give same Rr
> > > from the two calculators.
> > >
> > > VK1SV: 0.236 ohm
> > > 472khz: 0.385 ohm
> > >
> > > That is a pretty significant difference! Any idea which one is right
> > > (or what I did wrong)?
> > >
> > > 73,
> > > Ben
> > >
> > > On Fri, Jul 17, 2020 at 3:28 PM Roger Graves <ve7vv at shaw.ca> wrote:
> > >>
> > >> Hi Ben,
> > >>
> > >> Your idea to just use the vertical portion of the ladder line, 
> the height of the top hat, for the vertical section length sounds 
> good to me. That and the length of the top hat should give a good 
> approximation.
> > >>
> > >> FWIW, I use the calculator at 
> http://people.physics.anu.edu.au/~dxt103/calculators/marconi.php
> > >> It has been quite useful for me to get predictions for the dB 
> improvement expected from various changes (height, top hat length, 
> ground R) to see what might be worth doing and not worth doing and 
> how much power might be needed to get to 5W EIRP.
> > >>
> > >> Once you have your new antenna resonated with a loading coil, 
> you can measure the inductance of the coil and compare that to what 
> the calculator came up with for the L. You could then adjust the 
> size of the top hat in the calculator to get it to show your actual 
> inductance and then see how much the Rr and EIRP changed. That 
> would, theoretically, give a better estimate. But there are so many 
> complicating factors that the estimate is just a "ball park" 
> estimate I would think.
> > >>
> > >> Looking forward to hearing the signal on 630m.
> > >>
> > >> 73,
> > >> Roger
> > >>
> > >>
> > >> On Jul 17, 2020, at 2:12 PM, Ben Gelb <ben at gelbnet.com> wrote:
> > >>
> > >> Hi all -
> > >>
> > >> I decided to try feeding my HF dipole (ladder-line fed) as a vertical
> > >> on 630m. I did so, and it works. But I'm wondering a bit about how
> > >> best to estimate Rr, given that the ladder line feed is not actually
> > >> vertical. The first 20 ft or so are close to vertical, followed by a
> > >> roughly 40ft slanted section (45 degrees-ish, though not a straight
> > >> line since it is not held taught - so it follows a catenary curve).
> > >>
> > >> Top load is 93.8'.
> > >>
> > >> That is what I mean by "non-conforming".
> > >>
> > >> So the question is how to reason about this antenna in service 
> of Rr estimation.
> > >>
> > >> Since the whole antenna is pretty small relative to a wavelength,
> > >> perhaps I can get pretty close by decomposing the antenna into its
> > >> vertical and horizontal components? The vertical component (at least
> > >> ignoring that the 45 degress section actually has a nonlinear shape)
> > >> would basically be the height of the dipole feedpoint.
> > >>
> > >> The horizontal component of the ladderline section I imagine would add
> > >> to the effective capacitance of the top loading from the dipole
> > >> (though its more like "mid load" since its not at the top). Perhaps I
> > >> can estimate the increase in effective *top* loading length by
> > >> measuring apparent C of the antenna at the feedpoint - and backsolve
> > >> the equivalent *conforming* T-top antenna (w/ save vertical component)
> > >> that would yield that capacitance. Then use the Rr result for that
> > >> antenna.
> > >>
> > >> Other thoughts?
> > >>
> > >> I could also learn how to use antenna modeling software. But sort of
> > >> fun to try to think about how you might get there intuitively.
> > >>
> > >> 73,
> > >> Ben N1VF
> > >> ______________________________________________________________
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com 