Hi-VHF Winegard YA-1713 Log-Yagi
Hi-VHF Band, 10-Element, Winegard YA-1713 Log-Yagi Antenna is investigated, using 4nec2 Antenna Simulation Software.
Ken Nist's EZNEC antenna simulation results for numerous antennas are summarized here: www.hdtvprimer.com/ANTENNAS/comparing.html.
In the VHF charts, the YA-1713 had severe loss across channel 13. However, this is NOT what is found in the ants.xls charts
(which only summarized center channel gain), see www.hdtvprimer.com/SIMS. Further investigation of the posted w1713a.ez NEC file
reveals it assumed DIFFERENT element sizes and other measurements than a recently purchased YA-1713. [Did W-G change it????]
Surprisingly, Ken Nist found 300-ohm impedance, vice 75-ohm for newer YA-1713 (holl_ands below) with different dimensions.
4NEC2 simulation results are presented for both antenna measurements, demonstrating which assumptions can be ignored and
which lead to severe loss across channel 13.
UPDATE (29Jan2009): Prelim On-Air Test (at 10-ft height) was conducted 70 miles SE from Mt Wilson, inserting an RF attenuator
to find audio & video degradation levels. If there truly is gain loss across Ch13, NTSC audio carrier should be more susceptible to loss.
However, NO DIFFERENCE was observed wrt either audio or video performance on Analog Ch13 compared to Analog Ch7, 9 and 11,
nor was there any noticeable difference between audio & video degradation levels on Ch13.
Hence the Ch13 gain loss found in overly simplified NEC simulations appears to be a modeling problem.
UPDATE (23Feb2010): Added 4nec2 sim runs for SemiChemE's Extended Boom modification.
Another On-Air Range test that did NOT find any frequency roll-off on Ch13: http://www.aa6g.org/Lp/tests.html
Date(s): December 30, 2008. 1 - 5 of 5 Total. Shared |
|
 | 1.
Ken Nist's w1713a.ez 4nec2 Results (21 Jan 2009 NEW)4nec2 simulation results for Ken Nist's w1713a.ez file (as found in ant.xls on www.hdtvprimer.com/SIMS).
Compared to VHF Raw and Net Gain charts (as posted on www.hdtvprimer.com/ANTENNAS/comparing.html).
Latest version of 4nec2 refused to convert w1713a.ez file. Thanks are due to <300ohm> for using EZNEC to convert the file.
Ken Nist's ant.xls and w1713a.ez files do NOT show Big Gain Loss across Ch13, as depicted in VHF Raw and Net Gain Charts on hdtvprimer.
w1713a.ez measurements (prior to 2006) are somewhat different than recently purchased YA-1713. [Different sub-contractor???]
Substituting larger radius elements measured in holl_ands YA-1713, a moderate Gain Loss is exhibited in upper half of Ch13.
Note that Ken Nist found 300-ohm impedance, vice 75-ohm for newer YA-1713 (holl_ands below) with different dimensions. |
| 2888 Visits
24 Images
Shared Album | |
|
 | 2.
YA-1713 - TL Simulating the Crossover (21 Jan 2009 UPDATE)Winegard YA-1713 is a 10-element, Hi-VHF Band (Ch7-13) hybrid Log-Yagi. Fol. results are for measurements from LATEST MODEL.
Third and second elements form a two-element Log Periodic Array "Cell" surrounded by a Yagi-type Reflector and seven Directors.
The Crossover Transmission Feedline between third and second elements is investigated to find the optimum simulation parameters.
In 4nec2, the TL Card stipulates the characteristic impedance (Zc) and length (Lc). When Lc=0, a direct connection line is assumed.
UPDATE (21Jan2009): Reran everything using latest 4nec2 version and final, very minor, tweaks to holl_ands measurements.
Very little change wrt earlier posting. Added Summary Charts.
Ken Nist's w1713a.ez file stipulated Lc equal to the distance between Element #2 and #3, equivalent to a direct connection,
rather than simulating how the feedline snakes around the boom, thereby changing the phase of the signal to Element#2.
Two SOURCE options were investigated: Element#3 and Balun Feed (Slide #19 onward), emulating the Balun location under Element #4,
being connected to Element#3 via another non-crossing transmission line (Zb, Lb).
SOURCE at 1:1 75-ohm Balun location had best Net Gain and lowest SWR (whether 75 or 300-ohm Balun).
LD1 Card emulated 50-pF Capacitor across Balun, but only resulted in a few tenths of a dB reduction in Gain Loss on Ch13.
EDIT (18Sept2010): Added Elevation Angle Gain Charts. |
| 2947 Visits
58 Images
Shared Album | |
|
 | 3.
YA-1713 with and w/o Boom Corrections (5Jan2009 UPDATE)Winegard YA-1713 modeled in 4nec2, based on actual measurements. Includes Max, Min & No Boom Corrections.
Due to Gain degradation and wild SWR fluctuations, I used NO Boom Corrections in all other investigations.
UPDATE (5Jan2009): Crazy SWR behavior was due to error in 4nec2 file (need meters vice inches for Lc!!!).
Also double checked antenna physical measurements--a few changed a couple sixteenths.
Revised runs show only small Gain & SWR differences after apply BoomCorr.
Excessive SWR will severely degrade Net Gain. [Note that Gain in SWEEPER is incorrect...see "Pattern" box for value.] |
| 3099 Visits
16 Images
Shared Album | |
|
 | 4.
YA-1713 Detailed Boom & Crossover (14 Jun 2010)Winegard YA-1713 with Detailed wire model for the Boom and Crossover feedline (instead of TL Card) analyzed using 4nec2.
Includes Boom Correction.
It does not appear that 4nec2 has sufficient numerical accuracy to model the tiny wire segments in Boom,
which is why Yagi's are normally modeled WITHOUT the Boom, using a Boom Correction instead.
HENCE THESE RESULTS CAN NOT BE BELIEVED!!! |
| 1994 Visits
20 Images
Shared Album | |
|
 | 5.
YA1713 with an Extended Boom (23Feb2010)Extended Boom on YA-1713 as per SemiChemE experiment adding six 24.125-in directors with 14-in spacing.
Spacing was determined by a recycled FM antenna with antenna elements shortened....so NOT optimized.
Also ran 4nec2 simulation runs with only three additional directors.
Gain increase was moderate across Ch7-11.
Due to modeling shortcomings identified in other NEC runs, Ch12-13 results are indeterminate.
The severe gain roll-off was NOT found in either the On-Air I conducted or in the fol. On-Air test: http://www.aa6g.org/Lp/tests.html |
| 2161 Visits
4 Images
Shared Album | |
| |
