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 holl_ands | Home > Chireix Zig-Zag Antennas > Hi-VHF+UHF Stealth Hawk  
Hi-VHF+UHF Stealth Hawk
"Stealth Hawk" modifications to the 2-Square Chireix antenna were analyzed using 4nec2, based on some postings by ota_canuck:
http://www.digitalhome.ca/forum/showthread.php?t=123803

Two variants are analyzed: lower element Swept Back (bottom elements on Chireix splayed outward) and also Swept Forward (X29).
Date(s): 25 Apr 2010. 1 - 4 of 4 Total. Shared
UHF_HiVHF Stealth Hawk - 0.2-in Elements
1. UHF_HiVHF Stealth Hawk - 0.2-in Elements  (20 Apr 2010)
UHF + Hi-VHF Stealth Hawk analyzed for three different configurations:
1) holl_ands "best so far" dimensions: 9.5-in at 45-deg angle Top & 30-deg angle Bottom and 0.75-in Gap at Top & Feedpoint,
2) XAuto's dimensions in his 4nec2 file, all 10-in at 19.67-deg angles and 0.75-in Gap at Top & Feedpoint.
3) ota_canuck's first drawing with 7-in Top at 30-deg angle, 8-in Bottom at 22-deg angle and 0.75-in Gap at Top & Feedpoint.

Widening the Top Gap to 2-in was also tried, and although there was a small SWR improvement, it did NOT improve Gain.

Note that Stealth Hawk is derived from a 2-Square Chireix, except bottom two elements are splayed directly outwards.

UHF Azimuthal Pattern is poorly formed, resulting in low gain.
Hi-VHF is low gain and very poor SWR.

A Vertical Dipole is a better omni-directional antenna.
A Six-Whisker Bowtie (or a 2-Bay) is a MUCH better bi-directional antenna.
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UHF_HiVHF Stealth Hawk - AWG10
2. UHF_HiVHF Stealth Hawk - AWG10  (25 Apr 2010)
UHF + Hi-VHF Stealth Hawk (AWG10 Elements) analyzed using AWG10.

Presuming equal lengths for all elements and assumed angles, it was not possible to cover the entire UHF band.
The following are useful alignments that cover the lower, middle and higher channels respectively:

A. WL=10.0-in at 45-deg, BL=10.0-in at 30-deg with Top & Feedpoint Gaps=3-in:
UHF: > 2dBi on Ch14-42 with SWR < 2.7 and HiVHF: 1.7-1.8 dBi with SWR 7.0->5.8

B. WL=9.75-in at 45-deg, BL=9.75-in at 30-deg with Top & Feedpoint Gaps=3-in:
UHF: > 2dBi on Ch14-45 with SWR < 2.8 and HiVHF: 1.7-1.8 dBi with SWR 7.3->5.9

C. WL=9.5-in at 45-deg, BL=9.5-in at 30-deg with Top & Feedpoint Gaps=3-in:
UHF: > 2dBi on Ch16-47 with SWR < 2.8 and HiVHF: 1.6-1.8 dBi with SWR 7.9->5.9

D. WL=9.0 at 45-deg, BL=9.0-in at 30-deg with Top & Feedpoint Gaps=3-in:
UHF: > 2dBi on Ch20-51 with SWR < 2.8 and HiVHF: 0.8-1.8 dBi with SWR 12->6 [Note loss of Gain and higher SWR on Ch7-8.]

E. WL=8.5 at 45-deg, BL=8.5-in at 30-deg pushed UHF coverage even higher and had a Gain HOLE on Ch7 - NOT recommended.

F. WL=8.0 at 45-deg, BL=8.0-in at 30-deg pushed UHF coverage even higher and had a Gain HOLE on Ch9 - NOT recommended.
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UHF_HiVHF Stealth Hawk X29 - 0.2 Element
3. UHF_HiVHF Stealth Hawk X29 - 0.2 Element  (25 Apr 2010)
UHF + Hi-VHF Stealth Hawk (X29 Mod) analyzed using 4nec2, based on dimensions in a post by ota_canuck and named after the X-29 aircraft:
http://en.wikipedia.org/wiki/Forward_swept_wing

However, since 0.38-in "equivalent round diameter" for 3/4-in wide Tape elements was too large to model well in 4nec2, 0.2-in diameter was assumed.
[Actually the UHF Gain function blew itself up to smithereens....]

Variable Zdrop was employed to determine "optimum" distance (1-in) for mounting the lower element below the feedpoint...although differences were small.

Hi-VHF Gain and SWR are improved wrt swept back version, although it is still Excessive on some Hi-VHF channels.
The small dimensions result in UHF Gain being pushed to the upper part of the Band.
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UHF_HiVHF Stealth Hawk X29 - AWG10
4. UHF_HiVHF Stealth Hawk X29 - AWG10  (25 Apr 2010)
UHF + Hi-VHF Stealth Hawk (X29 Mod) analyzed using 4nec2.

Although it was not possible to cover the entire New UHF Band, the following choices cover nearly the whole band,
except a few channels on either the top or the bottom of the band:

A. Top: 9.5-in at 45-deg. Bottom: 9.5-in at 30-deg with Zdrop=-1.0-in, Gaps=3-in and AWG10.
UHF: 2-4 dBi on Ch14-47 with SWR < 2.4. Hi-VHF: 1.4-1.5 dBi with Excessive SWR=7.3->5.3.

B. Top: 9.25-in at 45-deg. Bottom: 9.25-in at 30-deg with Zdrop=-0.5-in, Gaps=3-in and AWG10.
UHF: 2-4 dBi on Ch18-51 with SWR < 2.4. Hi-VHF: 1.4-1.6 dBi with Excessive SWR=9.3->5.7.

Note that although the Azimuthal Pattern is well controlled at Hi-VHF, it's double-lobed at UHF, with reduced gain along the X-axis.
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