UHF 2x2-Bay Bowtie (NO Reflector), NARROWER WIDTH with Bay-Bay Separation = 10-in and 2-in Vertical Spurs on Whiskers, analyzed using 4nec2. This smaller version is as much as 3.5 dB lower Raw Gain than an Optimized full-size version without Vertical Spurs.
Since an in-window mount was the target application, AWG10 wire size was assumed.
a) UHF 2x2-Bay Bowtie (Narrower) with Two Transmission Lines from a common SOURCE Wire was Optimized (using nikiml's Python Scripts). Bowtie-Bowtie Separation was FIXED at 9.0-inches, with all FIVE other parameters as VARIABLES. Maximum constraints were imposed on Whisker Length and Feedline Separation to also limit overall antenna width. Width=38.5-in, Height=14.0-in.
BowLen=8.5-in (AWG10 Elements), VertSpurs=2.0-in, BowSep=9.0-in, TineSep=5.0-in, BowSwp=0.0-in. FeedSep=2.0-in (AWG10), Left/Right Bay Separation YBay=20.0" (Center-Center). Two Transmission Lines: Impedance=450-ohms, Length=11 (to 12) inches (Balun to Feedlines).
b) UHF 2x2-Bay Bowtie (Narrower) with Horizontal Harness from a common SOURCE Wire was Optimized (using nikiml's Python Scripts). Bowtie-Bowtie Separation, Whisker Length & Tine Separation was as determined in para a) above. Harness Separation between the two Transmission Lines (determines Impedance), distance BEHIND Bowties and Bowtie Feedline Separation were all VARIABLES. Width=38.25-in, Height=14.0-in.
Substituting thinner AWG12 (without re-optimizing dimensions) will slightly increase SWR (from under 2.0 to under 2.6), with no change to Raw Gain.
Raw Gain is about 2.5 dBi higher on the broad maximum across the higher frequencies than it is on 470 MHz. This is frequently desired to overcome higher Balun, Coax and (if no Preamp) RF Splitter Loss on the higher frequencies. Note that Horizontal Harness acts as a REFLECTOR....which is why it is important to make sure that it is on the BACKSIDE of the (NO Reflector) Antenna. With a Reflector, it MAY turn out it needs to be on the FRONT (like CM4228/CM4228HD).
Minimizing SWR wasn't easy....changing SOME dimensions by more than about 1/4-inch can change SWR.
Hi-VHF Raw Gain with the Horizontal Harness (Reflector) adds about 0.5 dB Gain more than the 2xTL version, with about 3.5 dBi. However, the SWR is excessive, which may or may not degrade performance on weak stations.
Date(s): 2 Mar 2013. Album by holl_ands. 1 - 33 of 33 Total. 2435 Visits.
enlarge 104KB, 1018x1024 1 UHF 2x2-Bay Bowtie - NO Refl Narrowed, Two 450-ohm Transmission Lines Bay Ctr-Ctr=10-in, Vertical spurs=2-in 3D View
enlarge 211KB, 1152x536 2 UHF 2x2-Bay Bowtie - NO Refl Narrowed, Two 450-ohm Transmission Lines Each Electrical Length = 11 (to 12) inches Front View [1 big square = 2.5-inches]
enlarge 35KB, 791x1024 3 UHF 2x2-Bay Bowtie - NO Refl Narrowed, Two 450-ohm Transmission Lines 4ned2 File
enlarge 168KB, 1152x692 4 UHF 2x2-Bay Bowtie - NO Refl Narrowed, Two 450-ohm Transmission Lines UHF Raw Gain = 8.3 to 11.4 dBi (For 12-in Harness Lengths)
enlarge 208KB, 1152x692 5 UHF 2x2-Bay Bowtie - NO Refl Narrowed, Two 450-ohm Transmission Lines UHF SWR (300-ohms) Max = 2.9 at 698 MHz (For 12-in Harness Lengths)
