Scott McClements wrote:
> I also put together a 18 foot boom/ 8 element NEC4 model using the
> ARRL LPCAD program. My gain figure for the LPDA were a little higher
> (5.5dBi), but I agree with what is shown here. Also note, its no
> contest on the F/R ratio.
>
> Now, before we fire up the LPDA crowd again - when the LPDA array's
> boomlength gets to around ~36 feet or greater with 20 elements, and
> covering only 14-30Mhz, the LPDA starts to kick serious butt. You
> start to see gain around 7.5dBi, but more importantly the F/R ratio is
> up around 25dB across all the bands (OWA Yagi style). Cebik has a
> model his site on a 52 foot boom / 22 elements that is around 8.6dBi
> and the F/R peaks around 37 dB (!!!) on 20 meters.
So.. if we talk about 14-30 MHz
18-20 ft boom -> 5.5 dBi
36 ft boom -> 7.5 dBi
52 ft boom -> 8.6 dBi
Assuming a symmetric pattern in E and H plane (yes, I know that's not
actually the case, but we can scale later), and assuming 100% efficiency
and approximating G= 41000/(beamwidth^2), we can get approximate half
power beamwidths:
5.5 dBi = 3.6 -> 107 deg
7.5 dBi = 5.6 -> 85 deg
8.6 dBi = 7.2 -> 75deg
I got Octave and gnuplot installed and working again, so time to model...
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