[TowerTalk] verticals and radials

[Grant Saviers]

I've read the referenced K5IU paper several times and always come back 
to this issue:  How much does it matter that the currents are unbalanced?

Modeling in 4.2 of my measured 8x .25wl long 10ft elevated radial 
currents, which have 3:1 variation (average soil), shows a small 
fraction of a db shift of same gain and elevation pattern as 
symmetrical. So if 4.2 is to be believed (some say not), it isn't worth 
"fixing" my imbalance.  I haven't noticed a performance asymmetry.

For resonant elevated radials, modeling with 1, then 2, etc shows the 
pattern is little affected beyond 2.  Even for an extreme case of 4 all 
in "half the pie".  For that case, the result is 2.35db F/B and +1db 
gain in the radial direction over 8 symmetrical.  Not great but maybe 
useful. DXpeditions have used a single radial as an opportunity to 
create a favored direction in the pattern.

A little modeling of my T with towers in the model shows that they have 
a larger effect than unbalanced currents on the pattern symmetry.  I 
suspect this is the case for most QTHs with towers, buildings, power 
lines, etc in the near field.

It's possible my analysis is missing something, if so, I'm sure I'll be 
advised there is contrary data.  I think there is no correlation between 
these results and what happens in buried radial systems.  Also, my T is 
75' of vertical and 2x 33ft top hats and fed near its resonance Z with a 
TLT.  Designs with skewed feedpoints for direct 50 ohm feed or very 
short radials may yield very different modeling results. As N6LF showed 
in his studies, my 8 radials should be shorter than 1/4wl for a slight 
increase in gain.  Or conversely, elevated radial resonance doesn't 
matter much as the number increases beyond 4.

My measured radial currents sum to the vertical. The MFJ RF current 
meter I used must be calibrated on the bench, on all ranges at the test 
power level and expected currents.

Also, it is important in these discussions and measurements to separate 
antenna efficiency which is highly dependent on the radial system from 
far field gain/pattern which depends on the soil/salt water properties.

Grant KZ1W

On 1/21/2022 15:52, Dave Sublette wrote:
> I have followed this thread with interest.  I am surprised that nobody
> seems to have considered the following:
> 
> Several months ago I was given a link to a couple of papers by K5IU and
> someone else, who I forget, about RF currents in radial systems.
> 
> This information is available in the "Lowband DXing" manual.
> 
> Briefly, with full sized quarter wave radials, measured RF currents were
> found to be unequal in each radial.  I have had a full quarter wave 160
> meter vertical made with Rohn 45 and a broadcast insulator section 27 feet
> above ground operating for more than 30 years. I had 8, full quarter wave
> radials suspended 27 feet above ground, sloping to 10 feet at the ends.
> The whole antenna footprint is over an acre.
> 
> So, having read the paper, I climbed to 27 feet and measured the RF current
> in each radial.  Much to my surprise, only two of the radials carried the
> bulk of the current.  The rest hardly had any at all.
> 
> The article recommended using one eighth long radials and tuning the
> reactance out with a coil in series with the shield of the feedline and the
> connection of the radials.   So, I took down my full sized radials and
> replaced them with four, one eighth wavelength radials and a matching
> coil.  Modeling shows capacitive reactance of 160 ohms for these shortened
> radials, 14 uh at 160 meters.  That's what I wound and it works perfectly.
> The RF currents in each of the radials is now equal and the sum of the four
> currents is equal to the current flowing in the driven element. I don't see
> any improvement or degradation since changing the radials.
> 
> Here is the bottom line to me.  I have this vision of everyone going to all
> the expense and labor (considerable labor!) to either bury or suspend
> quarter wave radials and the result would seem to be less than optimum.
> The efficiency and pattern should be affected by unequal currents flowing
> in the radials.
> 
> In light of this info and my experience,  this discussion has missed the
> mark.
> 
> I might add that in neither case , short or long radials, the angle of
> slope of each radial with respect to the others was not equal.  Nor did I
> go to any trouble to try and tune them to exactly the same frequency.
> These differences might contribute to the unequal currents, but didn't seem
> to affect the shortened radials at all.
> 
> Offered in a spirit of curiosity and hoping to learn.
> 
> 73,
> 
> Dave., K4TO
> _______________________________________________
> 
> 
> 
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk