[Elecraft] Inverted-L (was OT: Vertical antenna)

Mon Dec 20 20:06:05 EST 2010

"I personally would not consider elevated radials that are non-resonant"

I guess I'm having a difficult time with that comment.  You can have a 
resonant system without the elevated radials themselves being 
"resonant"  ... i.e, any two of them acting like a resonant dipole.  If 
the elevated radials are shorter than a 1/4 wavelength, all that is 
required is that the vertical section be a little longer than a 1/4 
wavelength to compensate.  If the radials are longer than a 1/4 
wavelength, the vertical section needs to be shorter than a 1/4 
wavelength for resonance.

Elevated radials are kind of like the lower half of a vertical 1/2 
wavelength dipole except that it is "fanned out" for symmetry, and if 
the radials are longer or shorter than half of a 1/2 wavelength dipole 
the feedpoint simply behaves similarly to an off-center fed dipole.  You 
can prove this to yourself with EZNEC ... start with a vertical section 
longer than 1/4 wavelength and see what length radials you need to have 
a resonant feedpoint.  Then do the same thing with different lengths of 
vertical sections and see the effect on radiation pattern.   I can tell 
you that it isn't a direct function of radial resonance.

I could be wrong, but I don't see any need at all for the radials to be 
"resonant" on their own.  You want system resonance and generally 
speaking, for radiation effectiveness you want as long a vertical 
section as you can manage.  You might want to choose a vertical section 
somewhat longer than a 1/4 wavelength and radials correspondingly 
shorter than a 1/4 wavelength in order to take advantage of that 
"off-center feed" aspect I mentioned in order to get a 50 ohm match.

The only situation where resonant radials might be required is if you're 
trying to decouple whatever is on the other side of the radials.  In 
that case, the radials act like a choke to keep current on the feedpoint 
side of the resonant radials.  You can see that effect with EZNEC as well.

73,
Dave   AB7E

On 12/20/2010 5:25 PM, Don Wilhelm wrote:
>    Mel,
>
> I personally would not consider elevated radials that are non-resonant -
> but then all of my antennas are resonant.
>
> I could consider something "balanced", like a 43 foot vertical having 43
> foot elevated radials and being fed with parallel feedline to the
> location of the tuner.  I would equate that to a dipole having 43 foot
> elements on each side of the feedline, but oriented in a different
> fashion to take advantage of things like the low angle radiation of a
> vertical antenna.
>
> I am not on the edge of salt water, so the great low angle "advantage"
> of a vertical is not available to me.  I recently bought a (used) GAP
> Titan DX antenna, and installed it - it pales in comparison to my modest
> height resonant dipoles, and I have made comparisons with DX stations as
> well as distant domestic stations - the horizontal dipoles always are
> better.  I was expecting better results for the vertical on DX, but
> failed to find it.  (anyone want to buy a GAP Titan DX for about half
> the price of a new one?).
>
> 73,
> Don W3FPR
>
>
>
> On 12/20/2010 6:56 PM, Mel Farrer wrote:
>> It is a matter of loss or lack of it.  If you look at the takeoff patterns of a
>> vertical antenna on a perfect ground and then with increasing loss, the pattern
>> is modified to have increasing less energy on the horizon.  However, this is the
>> loss factor, not necessarily due to lack of resonance.  As one removes the
>> antenna network from direct ground, and substitutes radials, several things
>> happen.  IF, and that is a big IF, the amount of coupling to ground is
>> maintained with non resonant radials or resonant radials are used, eff and match
>> will remain .  Example, a mag mount antenna or a ground plane vertical with
>> three or four resonant radials works fine and any elevation.  Just a point of
>> thought.
>>
>> Mel, K6KBE
>>
>>
>>
>>
>>
>>
>> ________________________________
>> From: Steve Ellington<n4lq at carolina.rr.com>
>> To: Guy Olinger K2AV<olinger at bellsouth.net>; Vic K2VCO<vic at rakefet.com>
>> Cc: elecraft at mailman.qth.net
>> Sent: Mon, December 20, 2010 3:44:28 PM
>> Subject: Re: [Elecraft] Inverted-L (was OT: Vertical antenna)
>>
>> Guy:
>> Very interesting....
>>
>> Some of your comments were verified in a recent QST article.
>>
>> Mar 2010 - QST (Pg. 30)
>>
>> An Experimental Look at Ground Systems for HF Verticals
>> The author experimented with resonant vs nonresonant radials on the ground
>> and found performance improved when the radials were cut to electrical
>> resonance vs just measuring them with a tape.
>>
>> Given this, it stands to reason that if the same radial field is used by a
>> multiband vertical on a higher frequency, the high current point would be at
>> some distance from the antenna's base thus reducing efficiency.
>>
>> Now here's the question....
>> Folks assume ground radials to be (non resonant) but that isn't the case. So
>> what would be the best solution for a multiband antenna with ground radials?
>> Well if we follow this idea, we would need multiple 1/4 wavelength radials
>> for each HF band for best performance.
>>
>> My inverted L is 50' up and 150' out. I use a separate elevated counterpoise
>> for each band. I've found that a ground rod and some buried radials have
>> virtually no effect. I just use them for lightning protection.
>>
>> Steve
>> N4LQ
>>
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