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

The short ones.

The long ones.

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!

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.

http://forum.tvfool.com/attachment.p...1&d=1491962552

http://forum.tvfool.com/attachment.p...1&d=1483891000

http://forum.tvfool.com/attachment.p...1&d=1491962883

http://forum.tvfool.com/attachment.p...1&d=1492047489

http://forum.tvfool.com/attachment.p...1&d=1491963344

A lot of good reports from users in strong signal areas.

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/

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.....

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

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.....

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.

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!

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."

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.

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.

http://forum.tvfool.com/attachment.p...1&d=1492288237

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!!

Diagram revised:

http://forum.tvfool.com/attachment.p...1&d=1492351076

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.

http://forum.tvfool.com/attachment.p...3&d=1492047521

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."

http://forum.tvfool.com/attachment.p...1&d=1492362159

Definitely a pair of directors in front of the Tetrapole.

http://forum.tvfool.com/attachment.p...1&d=1492655892

http://forum.tvfool.com/attachment.p...1&d=1492655892

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

http://forum.tvfool.com/attachment.p...1&d=1492658157

http://forum.tvfool.com/attachment.p...1&d=1492659580

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.....

My guess would be the same.
To make it cheaper, not better.
More profit.
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:

http://forum.tvfool.com/attachment.p...1&d=1492307620

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.

http://i496.photobucket.com/albums/r...G_0144_1_1.jpg

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!

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!

http://forum.tvfool.com/attachment.p...1&d=1492728873

http://forum.tvfool.com/attachment.p...1&d=1492728873

Rca ant751
 

Yeah, I think we're preaching to the choir here. And each time I've seen new advertisements of this antenna, RCA ups the receiving distance. On their website, it has always stated approximately 40 miles. Now it's up to 70 with the removal of some critical elements, no less! Well, my advise is to hang on to your original 751s or grab one if you see it before they replace them all with the "new and improved" 7511. But it will be interesting to see your comparisons with the new GE Indoor Attic Antenna and RCA 7511, rabbit73. I'm going to take a crap shoot and say the GE will equal or perhaps outperform the RCA 7511 by a small margin. How 'bout a wager???

I have been having a lot of fun with it. At my present location an indoor antenna is necessary for OTA reception. We also have basic cable, but I love to play with antennas and make antenna measurements.

I started experimenting with antennas when I was 8; I'm now 84. I have built many ham and TV antennas, and am still fascinated by the magic.

The GE Attic Antenna 34792 comes requiring assembly; this video showed me what to expect:
https://www.youtube.com/watch?v=1qYucg3JXzA

The signals are quite strong here, so I can get away with an indoor antenna on the ground floor, in spite of buildings and trees in the signal path. The GE antenna has more gain on UHF than on VHF-High; the UHF section is a yagi with a curved reflector, but it only has a folded dipole for VHF-High. As a result, although channel 13 is listed on my report almost as strong as the UHF signals, it is a lot weaker at the tuner because the antenna has less gain on VHF than UHF.

I have added an RCA TVPRAMP1R preamp to help 13, but I have found that the antenna location indoors is critical because of multipath reflections. Even though the signal might be strong enough, the tuner might not be able to decode it because it has reduced signal quality from multipath reflections.

Notes and photo of antenna added to screen shot of Sony Diagnostics Screen:

http://forum.tvfool.com/attachment.p...1&d=1486828373

http://forum.tvfool.com/attachment.p...1&d=1492732056

Rca ant751
 

I share your enthusiasm and fascination with OTA TV and radio as well. I don't have a tech background like you and ADTech, but I really enjoy the mysteries of what has turned into a hobby for me. That's why I was so thankful I came across TV Fool one day while surfing the web. And then receiving the helpful replies from you has been greatly appreciated, rabbit73. Thanks for the input on your new GE antenna. It will be interesting to see how it compares with the RCA7511 and how quickly others respond to it. In the meantime, I'm also looking at a couple of antennas from Antennas Direct, as they have good reports for both indoor and outdoor reception. I'm sure I'll have many more questions, so as they say, "stay tuned." I'll be back.....

Rca ant751
 

P.S. I just noticed your Signal Diagnostics Screen report. Your SNR is 34, but your signal strength is 57. You have a Sony TV, but on my Samsung if I had an SNR of 34, my signal strength would be 100%. I'm uncertain about this other than Samsung does it different than Sony. Any thoughts? Thanks.

The signal strength scale on TVs is just a relative scale; the scale will vary from brand to brand, and it isn't even the same on my different model Sony TVs.

The important thing is that you can use it for comparisons, like how weak can a signal be and still be received. Or you can use it for aiming an antenna while watching signal strength and signal quality as defined by SNR and uncorrected errors.

I used my signal level meter to calibrate the signal strength scale of my KDL32R400A:

http://forum.tvfool.com/attachment.p...1&d=1492737324

In the screen shot channel 16 measured 57 on the Sony, which is equal to -2 dBmV which is equal to -51 dBm. Channel 16 on my report is listed as having a signal power of -29 dBm, so the signal at the tuner is 22 dB weaker than listed. The signal is weaker inside because of the building and tree loss. but it is made a little stronger because of the antenna gain (on UHF). The report assumes that a simple dipole antenna is used; that is the reference for a 0 dB NM signal.

Rca ant751
 

I found an initial answer to the question I posed to rabbit73 above regarding how the "new and improved" RCA ANT7511 would compare to the previous versions of the ANT751. It was a reply from holl_ands on the AVS Forum in a thread on the antenna subsection back on 12/28/2016. Here is what he said:

IF you provide detailed Measurements and multiple PHOTOS (incl. a RULER in the Photo), then I can TRY to model ANT-7511 ES (or most any other Antenna of interest). But I haven't published 4nec2 Results for ANT-751 because Log-Yagi's (ditto YA-1713) do NOT model very well on the upper frequencies wrt Gain and SWR for ANT-751 was "off"....I suspect I need pricey NEC4 Engine to model the Cross-Over Feedlines and hopefully eliminate these shortcomings.

UHF portion of ANT-751 and ANT-7611 ES are SLIGHTLY different...but not by much and SAME number of UHF Elements....so, probably about the same UHF Gain....as given in Spec Sheet for HD-7000, from which the UHF part of ANT-751 was derived:
http://manuals.solidsignal.com/HD7000R.pdf

My simplified 4nec2 model for the ANT-751R/EZHD calculated 6.3 dBi (Minimum at band edges) to 7.5 dBi (Max Mid-Band) Hi-VHF Gain. When I removed the most forward Hi-VHF Director to emulate the ANT-7511 (although without SAME Element Spacings) it is reduced to 5.6 dBi (Minimum at band edges) to 7.0 dBi (Max Mid-Band). So only 0.5 to 0.7 dB reduction in Hi-VHF Gain.

FYI: Slightly higher Hi-VHF Gain numbers (esp. on upper Channels) were found when I OPTIMIZED 3 and 4-Element Hi-VHF Yagi's [which tend to provide more Gain than Log-Yagi's, esp. on higher frequencies], using Folded-Dipole Active Elements designed for Hi-VHF Band....rather than going THROUGH the UHF Folded Dipole Active Element, as done in the ANT-751 Log-Yagi [UHF Dipole and TWO Hi-VHF Active Elements form a 3-Element LPDA structure]...which is clearly causing some minor degradation, esp. on Ch12/13:
http://imageevent.com/holl_ands/yagis/hivhf3elfdyagiopt
http://imageevent.com/holl_ands/yagis/hivhf4elfdyagiopt

Here is where I actually found the above comment:

http://www.avsforum.com/forum/25-hdt...ntenna-related

So it appears from his findings that there is a small loss in gain from the RCA ANT7511 to the ANT751, if I'm reading him correctly. Any thoughts?

Rca ant751
 

P.S. The above quoted comment is specifically found in the HDTV Technical section on the AVS Forum.

Ah, yes; I remember that thread:

first post by kram1
http://www.avsforum.com/forum/25-hdt...l#post48491929

post by kram1 showing two boxes

He said he bought the 751, but he bought the 7511

http://www.avsforum.com/forum/25-hdt...l#post48525657

http://forum.tvfool.com/attachment.p...1&d=1492886569

post by kram1 showing ANT7511 up

http://www.avsforum.com/forum/25-hdt...l#post49316025

http://forum.tvfool.com/attachment.p...1&d=1492887539

post by holl_ands that you quoted

http://www.avsforum.com/forum/25-hdt...l#post49348785

The gain figures that holl_ands gave are only estimates, but I am inclined to agree with him. He is very good at antenna modeling, but isn't able to model LPDAs with great accuracy because of software limitations.

I made some measurements indoors to compare the GE 34792 Attic Antenna with the RCA ANT7511 Antenna. They are not exactly antenna test range measurements that an engineer would do, and they are not quite as accurate as I used to be able to do when I mounted two antennas side-by-side on my car and used stable LOS signals. But, I think they are useful because I used my Sadelco DisplayMax 800 Signal Level Meter in the single channel scan mode.

The meter makes many measurements across a TV channel during a single channel scan, as a spectrum analyzer would do, and calculates the average of all the measurements. I used an RCA TVPRAMP1R preamp and a splitter to feed the meter and my Sony KDL32R400A TV.

http://forum.tvfool.com/attachment.p...1&d=1493406880

The GE antenna did a little better on channel 7, even though it only has a folded dipole for VHF. The RCA antenna did better on channel 13, as would be expected with 3 VHF elements.

UHF comparison coming soon.

http://forum.tvfool.com/attachment.p...1&d=1493419398

The GE antenna is much better on channel 16, and a little better on 29, than the RCA ANT7511 (at this location). The RCA doesn't look like it would be suitable for UHF after repack, but please keep in mind that my measurements indicate how the antennas performed at my location and it might not be an accurate indication of the actual gain of the antennas.

Rca ant751
 

Wow, rabbit73.....you're THE MAN! Excellent testing especially given indoors and limits of your current situation from what you used to be able to door with your outdoor set up. And unfortunately, the updated RCA 7511 doesn't appear to compete with the newer indoor GE Attic; as compared to it's very successful former RCA 751. My advise would be to grab a long box 751 if you can find one while you still can! Thanks a million, rabbit73! We're fortunate to have your expertise and input on TV Fool!!

Thanks for your kind words; glad you enjoyed it. It was an interesting project for me, because many people can only have an indoor antenna.

Now I'm wondering how a 751 would compare with a 7511.:)

I found an RCA ANT751R on ebay with free shipping. The seller showed a photo of the long unopened box, so I was fairly certain it would be the original. It was the original when it arrived, and he sent it Priority Mail.

Most of the other sellers show a stock image of the unfolded 751, but no photo of the box, so it is hard to tell if is a 751 or 7511 especially when they use various UPCs.

The UPC on my ANT751R box is 0 44476 06452 4. Unfortunately, the UPC bar code on the short 7511 box is the same.:eek:

So, I guess the most reliable indicator is the box length, because the boom for the 7511 comes in two pieces, but the boom for the longer 751R is in one piece.

I compared the 751R with my GE Attic antenna as a standard. The VHF signals were a little weaker that day, but it is the comparison that counts.


The 751R is a LOT better than the 7511 on channel 16, but not as good as the GE. The GE Attic Antenna is designed for indoor use only. It's not rugged enough for outdoor use.
Good advice.

The RCA antennas are kind of messy to unfold; they have a coating of oil that comes off on your hands. The thin flat elements are easier to unfold with gloves on because they have sharp edges.

Might have some interesting test data after tomorrow.

I had to bail out of the office late this morning to get back home while I could and I'll be land-locked for a couple of days due to local flooding southwest of St Louis. On my way out, I grabbed all (hopefully) my gear to set up my backyard impromptu test range along with a number of antennas. Once I get it set up and running, I'll be able to do relative gain and antenna pattern testing.

I happen to have a 2014 RCA 751R, a recently purchased WG7000, and I picked up both a new 7511 as well as an ANT705Z from a local Walmart on the way home. In total, I have about 18-20 different models to run through the process including a little gem that Santa brought me this winter, an AAronia BicoLOG-5070 (http://www.aaronia.com/products/antennas/BicoLOG-5070/) reference antenna that came complete with performance data. <grin>

Hopefully I grabbed everything I need....

Thanks for posting further testing results rabbit73! Very interesting indeed.

My amateur sense and experience with the RCA751 here at my location, and the nearly 5000 posts on Amazon from users all over the country have indicated its good to excellent performance in a variety of terrain. When RCA removed several elements from their new 7511, especially the UHF Tetrapole and VHF LPDA (I hope I wrote correctly here?), even a dummy like me could figure there would be a compromise in performance.

But what is surprising is how good the GE Indoor/Attic performed in your location, compared to both the RCAs. The GE is getting good reviews on Amazon. And I see they now have an outdoor version of the same antenna. It might be worth further investigation???

I'll be very interested in ADTechs findings when he posts them too. I feel like I'm back in school and really enjoying both you "professor's" lectures!! I'm doing a lot of homework, but ever learning. Thanks to you both again for sticking with this thread!

Thanks; I didn't know about that. Is it the GE 29884 Pro Outdoor/Attic Mount Antenna? Click on Outdoor 70 mile version:

https://www.amazon.com/GE-33692-Atti...00DNJZ58M?th=1

http://forum.tvfool.com/attachment.p...1&d=1493690763
My guess is the reflector design helps the UHF gain a lot. The directors look like director pairs as in the Winegard patent. But, I haven't figured out the driven element that looks like a long dipole instead of a tetrapole or how the UHF yagi and the VHF dipole are combined. I'm not quite ready to open it up to find out, but the urge is getting very strong.

Please keep in mind what I said above. My measurements indicate how the antennas performed at my location, but they might not be a reliable indicator of the actual gain of the antennas.
This "professor" is still learning too, even after 76 years of antenna experiments.

Rca ant751
 

Yes, your link to the GE Outdoor Antenna is right. There is also a review of it on You Tube posted sometime in early March of this year. I don't have it in front of me, but I'm sure you could find it on their website. I watched it a couple of weeks ago and it was interesting. The few reviews of it on Amazon so far, are promising.

Adtech mentioned the RCA ANT705Z. It looks very much like the GE Outdoor. Walmart has it on their web site. I'll be interested to see what his evaluation of it is.

If you decide to open your GE Indoor up and discover its mysteries, I'll be interest, rabbit73.

Yes indeed, I'm hooked on OTA TV and radio!

Anxious for the professor's next lectures!!

Found the 29884 video; thanks.
https://www.youtube.com/watch?v=R_XAO14gSms

The G.E. 29884 Pro Outdoor/Attic Mount Antenna looks promising
but all that plastic........is cause for concern. With our intense
sunshine and 120f degree heat, I can visualize that plastic falling
apart, cracking and warping after a year or two of service.
A similar antenna, available at Walmart.com uses far less plastic,
and costs a bit less. Cannot help but wonder how it would perform
versus some of the other antennas, including the G.E. 29884.

https://www.walmart.com/ip/RCA-Attic...enna/146879296

Inside the GE 34792 Attic Antenna
 

Well, here it is:

http://forum.tvfool.com/attachment.p...1&d=1494003938

http://forum.tvfool.com/attachment.p...1&d=1494003938

I have used the conventional terms for top and bottom of the board. The top is where the components are mounted and the bottom is where the ground plane is located. In actual use, the coax connector faces down.

The GE 34792 Attic Antenna includes a REAL UVSJ, not shorting stubs, to keep the UHF and VHF signals separated before combining. Each section of the antenna has its own balun. The UVSJ and the well designed reflector are responsible for the good performance of this antenna.

Here is a circuit of a UVSJ by SM0HX (amateur radio callsign for a ham in Sweden). The UVSJ UHF/VHF Separator-Joiner belongs to the filter family of Diplexers. All UVSJs are Diplexers, but not all Diplexers are UVSJs; Diplexer is the more general term. A HLSJ is also a Diplexer, but for VHF-Low and VHF-High.

http://forum.tvfool.com/attachment.p...1&d=1494003938

The UHF highpass filter section has 3 series capacitors and 2 shunt inductors. The VHF lowpass filter section has 3 series inductors and 2 shunt capacitors.

Here are the curves for the Radio Shack UVSJ:

http://forum.tvfool.com/attachment.p...1&d=1494006989