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Old 2011-07-20, 12:14 AM   #1
re_nelson
 
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Default Winegard HD769 design (phasing lines)

I'm revisiting my Winegard HD7696P antenna which has been stored away for several months.

I'm curious about its design and a possible flaw (or perhaps it's due to my ignorance). After removing the balun cartridge, I used an ohmmeter to better understand how it's designed.

On the UHF lines, there was no continuity between the two sides nor was there a short to the boom. Each of the elements did show continuity as expected on the proper side of the line.

VHF was another story. Although the boom was isolated, I was surprised to see a short between each side. If you'll examine the PDF file for the HD769 series, you'll see the VHF elements alternating top/bottom on the rear of the boom with the lines passing through each element join point.

Electrically, it doesn't make sense to me that there's a short between the VHF lines (but not on the UHF lines). So that's why I'm posing this situation to the antenna design and research people who frequent this forum.
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Old 2011-07-20, 12:24 PM   #2
300ohm
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Quote:
VHF was another story. Although the boom was isolated, I was surprised to see a short between each side.
Its not a flaw and its quite common to have the back elements of a LPDA shorted. My CM1221 vee boom is shorted at the back.

For an extreme example, look at post 301 here :
http://www.digitalhome.ca/forum/show...107706&page=21

Youll note that the driven element, reflector and directors are ALL shorted together thru the boom. The antenna models correctly and in real life works fine.

Why it works is that RF waves are different than direct electrical current. Of course for it to work properly, it must be designed specifically that way. Just willy nilly shorting elements usually results in disaster, heh.
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Old 2011-07-20, 04:07 PM   #3
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Quote:
Its not a flaw and its quite common to have the back elements of a LPDA shorted.
Well...that's not the answer I was hoping for.

As I mentioned in my first post on this subject, the Winegard HD7696P was taken out of storage for a series of shootouts against the similar size AntennaCraft HBU-44. Unlike my previous A/B comparision made in the attic, this was made outdoors with each antenna hoisted atop a 3 meter ladder. The relative gains were measured with a Sencore SLM-1456 with a focus on the VHF performance. Five measurements were averaged for each antenna to eliminate any point-in-time wobbles.

HD7696P
Code:
+----+--------+-----+-----+-----+------+----+
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!
!    !        !POWER!     ! CCN !      !QLTY!
!    !        !dBmV ! dB  ! dB  !      !    !   
+----+--------+-----+-----+-----+------+----+
!  8 !8VSB    !-16.8!     ! 29.9! <10-9!PASS!
!  9 !8VSB    !-22.6!     ! 27.8!1x10-6!PASS!
! 11 !8VSB    !-14.2!     ! 33.2! <10-9!PASS!
+----+--------+-----+-----+-----+------+----+
HBU-44
Code:
+----+--------+-----+-----+-----+------+----+
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!
!    !        !POWER!     ! CCN !      !QLTY!
!    !        !dBmV ! dB  ! dB  !      !    !
+----+--------+-----+-----+-----+------+----+
!  8 !8VSB    !- 8.5!     !>36.0! <10-9!PASS!
!  9 !8VSB    !- 9.3!     ! 34.6! <10-9!PASS!
! 11 !8VSB    !- 6.8!     !>36.0! <10-9!PASS!
+----+--------+-----+-----+-----+------+----+
The HD7696's measured gain is down anywhere from 7.4 to 13.3 compared to the HBU-44. (I didn't bother to post the UHF figures since they were pretty close, with the Winegard winning on a few channels and the HBU-44 beating its competitor on others).

Given the large disparity in performance (not just raw power but also MER), I thought I had stumbled onto a cause when I detected that short on the VHF lines into the balun cartridge housing. I'm still at a loss to explain why this particular HD7696P, which has published VHF gains comparable to its YA-1713 cousin, shows such subpar values.

And for the record, I also measured the gains on a consumer television (Sylvania branded) signal quality meter. Those numbers also squared with the Sencore values. For example, RF-9 showed 87% with the HBU-44 but a mere 62% with the HD7696P.

Last edited by re_nelson; 2011-07-20 at 04:52 PM. Reason: Noted brand of consumer television
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Old 2011-07-21, 10:26 AM   #4
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Thanks for posting this comparison. So I guess I might have chosen the wrong antenna. If I ever desire to do so, "upgrading" to an HBU55 might yield better results for me on rf7 WNGS. I'm already getting excellent peformance out of my Winegard 7697 but WNGS is still my weakest station. I was considering a ten elemen single channel 7 yagi, but I guess switching to and HBU55 might get me over-the-hump as well. I'm even more nervous about when CKVR goes on-the-air in digital on Aug 31 on rf10.

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Old 2011-07-22, 06:18 PM   #5
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Quote:
...its quite common to have the back elements of a LPDA shorted.
And what 300ohm previously stated has been confirmed by Hans Rabong, Technical Service Manager for Winegard:

The HD7696P antenna will read a DC short with an ohm meter between the two sides of the VHF phasing lines because there is a 3" rivet holding the reflector elements and plastics to the boom. The way the antenna is tuned the RF signal is not affected by this DC short. On the YA-1713 the hardware is different and you will not have the short.
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Old 2011-07-22, 08:26 PM   #6
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I would be very nervous about connecting that type of antenna to the old early 1960's style TVs that had the hot chassis ground with the selenium rectifier power supply, heh.
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Old 2011-07-22, 08:34 PM   #7
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Hee hee the old arm tinglers!
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Old 2011-07-22, 11:28 PM   #8
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Wonder if replacing that rivet with a non-conductive fastener would improve the antenna's VHF performance? I've noted the VHF performance is not that great. I suspect having a short like that would tend to modify the gain curves of the antenna, possibly causing resonance where it shouldn't be and somewhat nulling out part of the desired band.
Will have to have a closer look at this, I didn't notice this when I installed the antenna last year.
-C.
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Old 2011-07-24, 05:41 PM   #9
re_nelson
 
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Wonder if replacing that rivet with a non-conductive fastener would improve the antenna's VHF performance? I've noted the VHF performance is not that great.

That's gratifying to learn that I'm not the only one letdown by the VHF performance of the Winegard HD7696P, especially since the published gain figures at within fractions of a dB for the stellar YA-1713.

The brass colored rivet is readily visible at the rear of the boom. Pop the black plastic cover at the end and you'll see the connection referred to by Hans Rabong.
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Old 2011-07-24, 08:17 PM   #10
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Except for channel 13, the gain figures quoted are a bit higher for the HD7696P on vhf. But looking at the pictures, about half the HD7696P's boom is for uhf, so thats about 55 inches of boom for vhf compared to YA 1713's 100 inches.
The LPDA and Yagi formulas show that packing more elements into a shorter boom space doesnt compensate enough for the use of a shorter boom versus a longer boom (to a point) with less elements.

The vhf directors in front of the uhf corner reflector, and some on the uhf corner reflector itself, may help or hinder vhf reception depending on which direction the signal is coming in at. So overall, except maybe in special circumstances, the HD7696Ps quoted vhf gain figures have to be fairly overstated compared to the YA 1713.

The quoted uhf gain figures arent so hot either. At SS, the price difference between the HD7696P and the YA 1713 is $41. So in most cases, the YA 1713 combined with a UVSJ and a four bay bowtie or G1483 is going to have better performance for the buck. Spend an additional $12 and combine with a 91XG.
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Old 2011-07-24, 10:32 PM   #11
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Quote:
The quoted uhf gain figures arent so hot either. At SS, the price difference between the HD7696P and the YA 1713 is $41. So in most cases, the YA 1713 combined with a UVSJ and a four bay bowtie or G1483 is going to have better performance for the buck. Spend an additional $12 and combine with a 91XG.
After experimenting with a number of different combinations, I've found that for me at my location, the ultimate off-the-shelf 2-unit configuration is the 91XG and the Y10-7-13 (slightly edging the YA-1713). The C5 is also a contender for high-VHF if size is a factor and it utterly trounces the disappointing VHF performance of the HD7696P.

For a single U/V unit, the HBU-44 has beat the two others I've tried in a similar class: CM-2018 and HD9696P.

All of the usual caveats apply (distance, direction of signals, terrain and space for mounting), so YMMV.
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Old 2011-07-26, 04:06 AM   #12
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Greetings:

I can't believe I've stumbled across this discussion.

About 2 yrs ago, I purchased a 7698P.
It seemed to perform well, but after a couple mos, my signal meter would drop to zero, usually when it was windy.

I decided to ohm it out and would get a dead short to the boom, when wiggling it.
I don't remember exactly where it was, but I do remember that it was caused by a hanging chad, that wasn't punched out properly.
I drilled out the rivet, reamed out the hole and used a bolt/ nut instead.
Problem solved.

And yes, iI saw it, when I removed the plastic end cap.


Hope this helps.
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Old 2011-07-26, 10:01 PM   #13
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What's strange is that the Winegard 7082 & 7696 have virtually identical VHF-HI specs but the 7082 is equivalent to the YA-1713 from my informal testing.

Never tried the 7696, but surprised it doesn't seem to live up to Winegards usual standards.
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Old 2011-07-31, 03:18 AM   #14
re_nelson
 
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Default Replacement HD7696P vastly improved on VHF

The HD7696P that I obtained in November 2010 was a real letdown in terms of its VHF performance. My findings on the Sencore were confirmed on other devices with diagnostics as well. I just attributed the subpar VHF traits to inflated published gain values by Winegard and let the matter lie dormant for months.

The query about the short circuit on the VHF phasing lines (but not the boom) ultimately reached Hans Rabong at Winegard. He was interested enough in the situation to ship me another HD7696P for comparison.

The difference was dramatic. I measured VHF gains improvement ranging from 5.5 dB to 7.8 dB on the replacement HD7696P compared to the original antenna (using the same balun cartridge on each). The UHF side was the same (varying only +/- 0.5 dB across the whole band). I can now state that the published VHF gain values for the HD7696P are accurate and that this U/V combo equals (or slightly exceeds) the YA-1713 on channels 8, 9, 11 and 12 that are in my market.

I did a careful visual inspection of the original vs. replacement HD7696P and can't account for the remarkable difference. Prior to shipping the original back to Winegard, are there any suggestions of what to look for that might account for such a notable variance?
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Old 2011-07-31, 06:03 AM   #15
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Quote:
I did a careful visual inspection of the original vs. replacement HD7696P and can't account for the remarkable difference. Prior to shipping the original back to Winegard, are there any suggestions of what to look for that might account for such a notable variance?
Theres gotta be some difference, heh.

Its possible that you have a short or shorts on some of the elements before the end of the boom. Since the phasing line is shorted, a meter is not the answer, only close visual inspection.

Are the element lengths and spacings the same ?
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