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

[Don Wilhelm]

  Guy,

OK, I missed by a factor of 10.
I am using 2 elevated radials per band, and the physical direction is 
such the pairs are horizontally opposed - that should reduce the 
radiation from the radials to zero (or nearly so).

I first cut the radials 15% longer than the "formula" would indicate, 
and used my MFJ259B to determine the actual (X=0.00) resonance point.  
By changing the lentgth of the radial (one at a time), I was able to 
comee with a working antenna for 160, 80, and 40.

While my antenna works well fot me, it is not a universal solution.

73,
Don W3FPR


On 12/20/2010 10:15 PM, Guy Olinger K2AV wrote:
> 15 ohms miscellaneous in series with 32 ohm radiation resistance, only
> 3%?  Don't you mean 30%?
>
> What were the lengths of the elevated radials and how many?
>
> 73, Guy.
>
> On Mon, Dec 20, 2010 at 8:27 PM, Don Wilhelm<w3fpr at embarqmail.com>  wrote:
>>   Dave,
>>
>> If you read the radial tuning procedure in Low-Band DXing, you will find
>> that it "all comes out in the wash".  Yes, your statements are correct,
>> and in fact that is how I did mine. Although  I did not resonate my
>> vertical monopole against any ground plane - I simply cut the lengths to
>> what was stated in the article, and then cut each radial to resonate
>> with that particular length of the "monopole".  If the result was
>> slightly "off-center fed", so be it, the impedance and the resonance
>> point obtained were a good match for 50 ohm coax, and I left it at that.
>>
>> OK, so the ideal impedance of a vertical antenna is 32 ohms - I got
>> closer to 50 ohms which indicates a 15 ohm loss in signal efficiency.
>> It matches my feedline nicely, and I an willing to accept the the 3%
>> loss in efficiency that represents.
>>
>> The ground conductivity in my area is not the greatest, so I have
>> accepted the logical consequences of that fact.
>>
>> 73,
>> Don W3FPR
>>
>>
>> On 12/20/2010 8:06 PM, David Gilbert wrote:
>>> "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
>>>
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