[Elecraft] EFHW

[Igor Sokolov]

A certain inductance places at a correct place along the 80m HW will 
make multy band EFHW. Here is the example 
http://myantennas.com/wp/product/efhw-8010p/

73, Igor UA9CDC

12.02.2017 1:50, K9MA пишет:
> On 2/11/2017 13:03, Brian Pietrzyk wrote:
>> Now comes the fantasy thinking... What about making it an end fed 
>> multi band by either putting traps in the 80m end fed or better still 
>> adding on a couple of fan EFHW wires for 40 and 20? Anyone tried 
>> this? How would the efficiencies compare to their centre fed trap or 
>> fan dipole counterparts respectively? 
>
> That won't work, because the shorter wires will present a much lower 
> impedance, and essentially short out the half wave wire. The whole 
> idea of the EFHW is that the high feedpoint impedance reduces ground 
> system current to practically zero.
>
> A trap might work, but might not be compatible with keeping the 
> antenna very light.  A QRP trap could be pretty small, I suppose, but 
> it still might be hard to support the wire with the extra weight on it 
> using a lightweight pole.
>
> However, an EFHW will work on harmonics, though the pattern changes.  
> A 40 meter half wave works quite well on 20, but I'm not sure an 80 
> meter half wave would be all that great on 20, especially with a 
> single support.  The free space patterns of long wire antennas are 
> shown in the ARRL Antenna Book.  As frequency goes up, more lobes 
> appear in the pattern, and the main ones get closer to the axis of the 
> wire.  For example, a full wave antenna has a cloverleaf pattern, the 
> lobes about 55 degrees from the wire axis, with nulls broadside.  For 
> a 2 wavelength wire, there are 8 lobes, the main ones 35 degrees from 
> the wire axis.  These patterns will, of course, be modified by the 
> effects of ground and the fact that the wire probably won't be 
> straight, but the free space patterns give some idea of how the 
> antenna will radiate. Modeling these antennas is very easy, and gives 
> much more accurate results.
>
> Note that the pattern of an EFHW (full wave, etc.) is NOT the same as 
> that of a center fed dipole operated at even harmonics.
>
> 73,
>
> Scott  K9MA
>
>