Crossed Yagis
Crossed Yagis analyzed using 4nec2.
Hi-VHF 8-El. Yagi design is from on-line K7MEM calculator:
http://imageevent.com/holl_ands/yagis/hivhf
Since the K7MEM designs are NOT optimized for wide-band use, usable Gain is only
realized on Ch7-10, with reduced F/B and F/R Ratios on Ch7.
ALL of the below K7MEM 8-Element Cross Yagis have POOR and inconsistent
suppression of the Left Hand Circular Polarized (LHCP) signal across the Hi-VHF Band.
Much better LHCP suppression was found in the Offset Crossed Yagis (see other album):
http://imageevent.com/holl_ands/circularpolarized/offsetcrossedyagis
When RHCP signals are reflected (e.g. multipath), it changes to a LHCP signal, which will be
SUPPRESSED by antenna's Cross-Polarization Loss. Hence importance of LHCP suppression,
also known as Cross Polarization Loss (CPL = RHCP - LHCP).
Note that Polarized Gain figures do NOT account for the DOUBLING of Transmitted Power (H+V),
which results in TWICE as high a receive signal power level when RHCP is effective. The 4nec2
program assumes a fixed amount of power input to a "standard" RHCP antenna, which splits
that power into Horiz. and Vert. components. At the receiver, the two components are summed
together via the interconnecting Transmission Line. But DTV uses TWO transmitters.
When/If circular polarization optimization parameters are added to nikiml's optimizations
scripts, re-optimizing the entire antenna might be able to improve on below performance.
Date(s): 24 Jan 2012. 1 - 3 of 3 Total. Shared |
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 | 1.
HiVHF 8-El Crossed Dipole-Pair Yagi (3 Feb 2011)Hi-VHF 8-Element Cross Yagi with Right Hand Circular Polarized (RHCP) Dipole-Pair active driver elements
analyzed using 4nec2. Dimensions of K6STI's Dipole-Pair (w/o Yagi) were optimized using nikiml's
optimization scripts, presuming QICT (Quarter-Inch Copper Tube) element size.
Although Gain, SWR & RHCP were very good across Ch7-10, Cross Polarization Loss
was only good on a limited range of frequencies.
Since the K7MEM designs are NOT optimized for wide-band use, usable Gain is only
realized on Ch7-10, with reduced F/B and F/R Ratios on Ch7. |
| 2229 Visits
25 Images
Shared Album | |
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 | 2.
HiVHF 8-El Crossed FD's Yagi - TL=QWL (4 Feb 2012)Hi-VHF 8-Element Crossed-Folded-Dipoles (FD's) Yagi [Coincident, NOT Offset] interconnected by
a Transmission Line that is a Quarter-Wavelength long. |
| 1478 Visits
26 Images
Shared Album | |
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 | 3.
HiVHF 8-El Crossed Dipoles Yagi - TL=QWL (4 Feb 2012)Hi-VHF 8-Element Yagi with Crossed-Dipoles [Coincident, NOT Offset] interconnected by
a Transmission Line that is a Quarter-Wavelength long. |
| 1454 Visits
26 Images
Shared Album | |
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