[Antennas] Re: full wave INV-L for 160m

Wed Mar 5 08:35:08 EST 2008

> At 10:33 PM 2008年03月04日, Igor Sokolov wrote:
>>I would make it a bit longer then 3 quarters and then bring to resonance 
>>with the serial capacitor. That will make the impedance higher and 
>>improve efficiency of the antenna somewhat. MMANA is a good tool for 
>>modeling and understanding what is going on.
>>>>73, Igor UA9CDC
>>>> Roy, K6XK, is right. The only function of the horizontal wire is to 
>> bring the antenna to resonance. The antenna is basically a short vertical 
>> radiator loaded by the horizontal wire, and the minimum total wire length 
>> needed to bring it to resonance is a quarter wavelength. The next length 
>> that works is three-quarter wavelength, not full wavelength.
>>>> Keep it simple!
>> 73, Brian KF2YN
>> The 3/4 wl version impedance is pretty close to 50 ohms at resonance, so 
> you shouldn't need to lengthen it to get the impedance up. However, the 
> presence of an extra horizontal half-wave of wire (beyond the first 1/4 
> wl) will radiate a very significant horizontally polarized signal, mostly 
> straight up, since the current maxima in this section is essentially equal 
> to the current in the vertical section at the feedpoint. In addition, the 
> low angle pattern of the 3/4 wl version isn't very omnidirectional, with a 
> broad null off the open end of the top wire which is down about 6-9 dB 
> from the broadside signal.
>> Keep it simple by staying close to 1/4 wl, unless you want to favor NVIS 
> operation. Of course, if you just want NVIS, use a dipole and save the 
> pain of installing the ground system.
>> 73, Terry N6RY
Terry all you said is true. Anyway my experience shows that one needs both 
high and low angles. Here 3/4 WL antenna is a good trade off. Making it 
longer then 3/4WL and bringing impeadance closer to 75 or even 100 Ohm gives 
you better efficiency especially where ground losses are high. Matching 
higher impeadance antenna to 50 Ohm cable is pretty easy when we talk about 
just one band matching. In my case ground loss can be as high as 30-40 Ohm 
which makes 50 Ohm antenna pretty inefficient (less then 50% efficiency).
73, Igor UA9CDC