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Old 11-Apr-2017, 7:17 PM   #1
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Rca ant751

Which elements on the boom of the RCA ANT751 are for UHF and VHF High reception? I've had good use of this antenna for some time now, but was a bit confused as to which are being used for the various TV frequencies; especially since it does not have a reflector behind the UHF elements as is typical. Any help would be appreciated. Thanks! OTAFAN
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Old 12-Apr-2017, 12:59 AM   #2
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Quote:
are for UHF
The short ones.

Quote:
VHF High
The long ones.
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Old 12-Apr-2017, 1:29 AM   #3
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Rca ant751

Well, that's interesting ADTech. So, there's 3 short UHF antenna elements in front and 4 long VHF High elements, although there is a gap between the first 3 longer elements and the last longest element at the far back of the boom. Any idea what that gap is for? And with so few elements on the ANT751, it really is quite a good performer across the TV frequencies. At least it has been for me. Any idea what its secret for success has been? Thanks again for your help!
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Old 12-Apr-2017, 1:53 AM   #4
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One secret is that the UHF driven element is a tetrapole, in the original version of the 751.

RCA likes to change the design in mid stream without changing the model number, usually to meet a price point with the loss of some performance.

Another secret is that the VHF section is an LPDA.

Another secret is that it is an original Winegard design.











Quote:
And with so few elements on the ANT751, it really is quite a good performer across the TV frequencies.
A lot of good reports from users in strong signal areas.

Quote:
Any idea what that gap is for?
Ask holl_ands. He does computer modeling of antennas. You can find him here:
http://www.avsforum.com/forum/25-hdtv-technical/
or here:
http://www.digitalhome.ca/forum/186-...h-development/
Attached Images
File Type: jpg RCA ANT751CES2009bL_1.jpg (89.2 KB, 723 views)
File Type: jpg Winegard UHF Tetrapole2.jpg (121.3 KB, 709 views)
File Type: jpg Stub Illustration2.jpg (110.8 KB, 702 views)
File Type: jpg 0.75 wave folded dipole.JPG (53.8 KB, 1269 views)
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Last edited by rabbit73; 13-Apr-2017 at 1:40 AM.
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Old 12-Apr-2017, 2:36 AM   #5
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Smile Rca ant751

Wow, thanks for the antenna primer, rabbit73! I appreciate better now my antenna set up. BTW, I called RCA earlier and asked them the same question I posed on this forum. The CS Rep told me in no uncertain, but friendly terms, that they could NOT answer my question because it was "proprietary information." ???!!! I pressed them for an answer since their antenna was a yagi design and had been around for nearly a century, but to no avail. I didn't understand the secrecy in this case. But tight lipped they remained. So, thanks again to TV Fool for revealing the mysteries of TV antenna theory for dummies like me! You folks are very much appreciated!! OTAFAN now more enlightened.....
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Old 12-Apr-2017, 2:45 AM   #6
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The UHF section is a yagi, but the VHF section is not a yagi, it is a LPDA.
https://en.wikipedia.org/wiki/Log-periodic_antenna
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Old 12-Apr-2017, 3:15 AM   #7
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Smile Rca ant751

Yes, understood rabbit73. I see that this antenna is a combination that I didn't know about before. You certainly have clarified the issue. Unfortunately, RCA wasn't able to educate me further in this good hobby of mine. But as long as we have TV Fool.....
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Old 13-Apr-2017, 8:26 PM   #8
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Quote:
BTW, I called RCA earlier and asked them the same question I posed on this forum. The CS Rep told me in no uncertain, but friendly terms, that they could NOT answer my question because it was "proprietary information." ???!!! I pressed them for an answer since their antenna was a yagi design and had been around for nearly a century, but to no avail. I didn't understand the secrecy in this case. But tight lipped they remained.
I can GUARANTEE you that they were tight-lipped because they didn't have a clue as to the correct answer. FWIW, the antenna is manufactured for VOXX (owner of the old RCA trademark) by Winegard. It is a derivative of their old HD7000R antenna which was discontinued a few years ago but then was relaunched last year with a feature that allows extra metal to be bolted on to make it convertible between a 2-uhf or a 7-UHF model.
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Last edited by ADTech; 13-Apr-2017 at 8:35 PM.
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Old 13-Apr-2017, 10:11 PM   #9
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Smile Rca ant751

Thanks much for the follow-up ADTech! Very interesting indeed. Between your replies and rabbit73 info provided, I've become much more enlightened as to how my antenna set up works. Since OTA TV has always been my go to for viewing, I've increasingly grown curious as to how it all works. TV Fool has been extremely helpful in directing me to continue my life long learning in this field. And both you and rabbit73 have always been willing to answer my questions. I can't thank you enough and I'm sure I echo many on this forum. BTW, I found a place on the RCA web site where one could post questions to an RCA Engineer. So, nothing left to loose I emailed them and to my surprise, I just received an answer to my initial question. And the response was.....exactly what you first said here in this thread--shorter elements UHF and longer VHF High. So, to be fair to RCA (or rather VOXX), I was able to get something out of their "proprietary information!" But I think I will keep posting my future questions first on this forum. I know I will get help here. Best to you ADTech!
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Old 14-Apr-2017, 6:09 PM   #10
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Rca ant751

P.S. I received another reply from RCA Engineer which was appreciated and obviously they are willing to discuss their antenna in spite of CS claiming "proprietary information," as I mentioned above. But they referred to the ANT751 as a "Yagi style." Rabbit73 said the back of the antenna used for VHF High was an LPDA. So, I'm now a bit confused again as to which is which??? Any follow up would help. Here is the comment from RCA regarding the gap between the two last elements on the back of the boom:


"The longer element is called a reflector element and its length and distance from the other elements is a calculation based upon factors such as gain, front to back ratio, the bandwidths that the antenna is designed to receive, and the pattern desired by the antenna designer for the antenna reception. In a traditional Yagi style antenna, the reflector is typically longer than the other elements in the antenna."
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Old 14-Apr-2017, 6:39 PM   #11
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The UHF section is a simple UHF Yagi structure with a parasitic element that is probably there to flatten the bandwidth.

The VHF section, is not a Yagi as the two rear most elements are connected to each other with phasing lines which excludes that section from being a conventional Yagi but is rather a log-periodic design. The two long elements clipped to the underside of the boom are probably there for the same reason as the parasitic element on the UHF side.

I haven't tried modelling the antenna (not my cup of tea) but I did test it on my backyard antenna test range late last summer and compared it to several other antennas. Might have to dig out those spreadsheets and see what things look like.
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Old 15-Apr-2017, 8:31 PM   #12
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Quote:
The UHF section is a simple UHF Yagi structure with a parasitic element that is probably there to flatten the bandwidth.

The VHF section, is not a Yagi as the two rear most elements are connected to each other with phasing lines which excludes that section from being a conventional Yagi but is rather a log-periodic design. The two long elements clipped to the underside of the boom are probably there for the same reason as the parasitic element on the UHF side.
I agree.

The two long elements on the underside are parasitic directors for VHF-High, which would make the four rear elements a hybrid called a log-yagi for VHF-High.

Attached Images
File Type: jpg RCA ANT751elements.jpg (110.3 KB, 982 views)
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Old 16-Apr-2017, 12:16 AM   #13
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Smile Rca ant751

A picture says a thousand words! And I also found it helpful to read this:

https://en.wikipedia.org/wiki/Log-periodic_antenna

Thanks again rabbit73! I owe you guys a cup of coffee or a free prize at Antennas Direct!!
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Old 16-Apr-2017, 2:09 PM   #14
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Diagram revised:



I suspect that the insulated UHF parasitic element in front of the UHF driven element Tetrapole is actually a pair of side-by-side directors that you also see in high gain UHF yagis by other manufacturers. The Tetrapole, AKA 3/4 wave folded dipole, has two current loops that allow the use of pairs of directors in front of it for maximum gain. But, I can't be certain until I have a 751 in front of me to confirm it.



You can see the idea of director pairs in Winegard patent 3,518,693. The patent drawing shows pairs of directors, but the patent text claims "a plurality of director elements."

Attached Images
File Type: jpg RCA ANT751elementsRev.jpg (118.5 KB, 901 views)
File Type: jpg WinegardPatentDirectorPairs.JPG (174.3 KB, 619 views)
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Last edited by rabbit73; 16-Apr-2017 at 5:04 PM.
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Old 20-Apr-2017, 2:40 AM   #15
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Definitely a pair of directors in front of the Tetrapole.



Attached Images
File Type: jpg RCA ANT751 Unfolding1.JPG (75.3 KB, 569 views)
File Type: jpg RCA ANT751 Unfolding2.JPG (69.0 KB, 577 views)
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Old 20-Apr-2017, 2:53 AM   #16
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CAUTION, there is a new version being sold, and they are using the photo of the original ANT751; very misleading.

RCA Suburban Mini Yagi Digital Outdoor Antenna with Mast, now model ANT7511

Differences:

1. The mast clamp is now ahead of the rear element
2. There is only one VHF director
3. The 4 shorting stubs have been replaced with 2 small-diameter wires, each 5-1/2" long
4. The Tetrapole has been replaced with a long dipole driven element; 6-1/2" long on each side
5. The UHF director pair in front of the Tetrapole has been replaced with a conventional director, for a total of 3 directors, each 7" long



Attached Images
File Type: jpg RCA ANT7511.jpg (190.2 KB, 653 views)
File Type: jpg RCA ANT7511cu.jpg (160.0 KB, 644 views)
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Last edited by rabbit73; 20-Apr-2017 at 7:35 PM.
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Old 20-Apr-2017, 8:55 AM   #17
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Unhappy Rca ant751

So.....I'm guessing that RCA's newest revision of their popular ANT751 or rather now, 7511, could be a step back in performance? What was their thinking here? And why mess with success??? I suppose we'll have to wait for in field testing by you guys and others who happen to purchase it. Fingers crossed for those who have yet to use it. Well, rabbit73, you certainly deserve another cup of coffee on me or prize from Antennas Direct, or both! Let me know I'm good for it.....Thanks so much again for going the extra mile here.....
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Old 20-Apr-2017, 1:58 PM   #18
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Quote:
So.....I'm guessing that RCA's newest revision of their popular ANT751 or rather now, 7511, could be a step back in performance?
My guess would be the same.
Quote:
What was their thinking here?
To make it cheaper, not better.
Quote:
And why mess with success???
More profit.
Quote:
I suppose we'll have to wait for in field testing by you guys and others who happen to purchase it.
I would love to be able to compare it with the original 751, but I don't have one. I thought I was getting an original 751 when I ordered it. Even if I had both, I wouldn't be able to make a good comparison at my present location as I previously was able to do like this:



With the setup above I was able to use a steady OTA signal and switch back an forth between the two antennas with an A/B switch while reading my signal level meter.

I do plan to compare it with my GE attic antenna for indoor reception, and I still have a signal level meter, or two.

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Last edited by rabbit73; 20-Apr-2017 at 2:48 PM.
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Old 20-Apr-2017, 7:25 PM   #19
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Unhappy Rca ant751

Well, I understand we all need our paycheck at the end of the day, including the bossman! But if sales off Amazon are any indication of the 751s success, I guess RCA must figure you can never have enough??? And they obviously have cut corners on their 7511 revision to the probable downgrade of their product for their customers. So it goes. BTW rabbit73, I would be very interested in your testing results of the new GE Indoor Attic Antenna. Feedback on Amazon has been surprisingly good. Please post when you can. Thanks, as always, for your generous support and help on TV Fool!
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Old 20-Apr-2017, 10:56 PM   #20
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Not only are the companies that are selling the ANT7511 using the image of the original ANT751, but the box for the ANT7511 has images of the original ANT751. The worker that pasted the ANT7511 sticker on the box, put it on at an angle, so that it is possible to see the printing ANT752Z.

My guess it that first RCA wanted a smaller box, so they made the boom in two pieces. Then, they said why stop there, let's see what we can remove to cut costs even more, so the ANT7511 was born......Ugh!



Attached Images
File Type: jpg RCA ANT7511 Box3.jpg (158.0 KB, 550 views)
File Type: jpg RCA ANT7511 Box2.jpg (111.6 KB, 553 views)
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