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Single vs. Stacked UHF Antennas

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  • Single vs. Stacked UHF Antennas

    Over the past several weeks I've been testing two different single UHF antennas (Antennas Direct XG91 and Channel Master 4228) against two horizontally stacked UHF antennas (Triax Unix100). The Unix100 and the XG91 (also listed as 91XG) are very similar antennas. The stacked Triax antennas provide the most directional setup while I would list the single XG91 as the second most directional and the 4228 slightly behind the XG91. I currently have the XG91 mounted about 2.5 feet below the Triax stack (pic below).

    One of the Indy analog LPs is in the process of moving from ch. 65 to ch. 19. Last evening the new transmitter fired up and began testing its signal. The station is now up to 150kW with a directional signal but I'm in one of the full-power beams. The station, WDNI-LP 19, is broadcasting from a tower 10 miles south at 165 degrees (azimuth). With a little tropo enhancement this morning, I was curious if I could null this station enough to receive Cincinnati's WXIX-19 @ 101 miles and at 123 degrees. By rotating the antennas to 119 degrees, I was able to find the best null position. The results are pictured below. The first pic is from the single antenna and the second pic is from the stacked array. The single antenna barely produced any co-channel interference from WXIX, while the stack was able to produce some nulling of the WDNI signal to allow some reception and visible video from WXIX. At times I was able to see WXIX through WDNI, including a commercial for Cincinnati FM station, WKRQ, Q102.

    This test pretty much sums up my results over the past several years with the stacked antenna array. In my experience, nulling co-channel interference (analog or digital) is very important in being able to DX and decode DTV signals.

    Steve
    Last edited by indysteve; 12-05-2008, 09:11 AM. Reason: Update on XG91/91XG

  • #2
    Originally posted by indysteve View Post
    This test pretty much sums up my results over the past several years with the stacked antenna array. In my experience, nulling co-channel interference (analog or digital) is very important in being able to DX and decode DTV signals.
    I totally agree with you. Directivity is, IMHO, going to be even more important after February 17th.

    I like the 4228, but it is not as directional as my chicken-wired dish. The 4228 has a wider beamwidth and receives a lot more signal off the back side. As consumer dishes are now out of production and so difficult to obtain, stacking XG91-type UHF yagis will likely become more common among serious DXers.

    Thanks, Steve, for the good information and photos.
    Last edited by Danny; 11-28-2008, 09:06 AM.
    Danny
    Shreveport, LA
    Mexico/Latin America TV DX ID Tips http://www.tvdxtips.com
    Submit and read DTV Stats http://www.tvdxexpo.com/dtvdxrecords.html
    TV and DTV DX Photographs http://www.tvdxexpo.com
    My Photographs of 100 Mexico TV DX Local IDs http://www.tvdxexpo.com/100mexicotvids.html
    More than 1,100 TV logs since 1994

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    • #3
      "I like the 4228, but it is not as directional as my chicken-wired dish. The 4228 has a wider beamwidth and receives a lot more signal off the back side. As consumer dishes are now out of production and so difficult to obtain, stacking XG91-type UHF yagis will likely become more common among serious DXers."

      I just put up a 4228 (8 Bay) after using a Winegard 9095 for about 8 years. I was surprised at the amount of signal off the backside. Some stations the 9095 received better and some the 8 Bay receives better - I guess I'd call the overall performance equal between the two even though the rear rejection of the 8 Bay is a disappointment. But now I wonder - would an XG91 do better???

      Comment


      • #4
        With digital, three things will be important in any antenna to be used for DXing. First, there's directivity. Second, directivity will be important, and, last, but not least, directivity will have to be considered!

        The biggest challenge to DXing an ATSC signal is that one cannot possibly ID an ATSC station unless it "rules it's channel", i.e., appears at one's receiver stronger than any/all other signals in that channel. (As opposed to NTSC signals where some of our best catches result from seeing call letters "under" other stations that may be as much as 20dB stronger than the DX at the antenna terminal).

        With regard to the 4228 and it's low F/B ratio (common to all bowtie arrays), I wonder if "stagger stacking" could work with this type of antenna as well.

        High directivity will be even more important for successful DXing on VHF-high band, as the channels will be packed (even in non-urban areas) and VHF antennas are not usually as directional as UHF designs.

        Rob
        Comparing Sporadic-E skip to skip on the AM and shortwave bands is like comparing apples and oranges.

        Comparing tropo to skip is like comparing apples and bacon cheeseburgers.

        Comment


        • #5
          Originally posted by Robert Grant View Post
          High directivity will be even more important for successful DXing on VHF-high band, as the channels will be packed (even in non-urban areas) and VHF antennas are not usually as directional as UHF designs.

          Unfortunately, the larger, highly directional VHF antennas once made by Channel Master (Quantum and Crossfire) and Winegard (Chromestar) have been out of production for years. My understanding is that the last of the best VHF antennas, the Delhi-Wade-General Instrument-Jerrold VIP-307, has also been discontinued.

          I realize that those antennas were large in part because of the long elements required to receive the low-band. However, I'm not aware of any currenty-available *exceptional* high-band yagis.
          Danny
          Shreveport, LA
          Mexico/Latin America TV DX ID Tips http://www.tvdxtips.com
          Submit and read DTV Stats http://www.tvdxexpo.com/dtvdxrecords.html
          TV and DTV DX Photographs http://www.tvdxexpo.com
          My Photographs of 100 Mexico TV DX Local IDs http://www.tvdxexpo.com/100mexicotvids.html
          More than 1,100 TV logs since 1994

          Comment


          • #6
            Originally posted by Danny View Post
            However, I'm not aware of any currenty-available *exceptional* high-band yagis.
            The Funke high-band antennas used by some WTFDAers are not currently on Funke's site, so I assume they are no longer available. I think those were exceptional performers.
            Danny
            Shreveport, LA
            Mexico/Latin America TV DX ID Tips http://www.tvdxtips.com
            Submit and read DTV Stats http://www.tvdxexpo.com/dtvdxrecords.html
            TV and DTV DX Photographs http://www.tvdxexpo.com
            My Photographs of 100 Mexico TV DX Local IDs http://www.tvdxexpo.com/100mexicotvids.html
            More than 1,100 TV logs since 1994

            Comment


            • #7
              And the 4228 is now the 4228HD. Not sure I care for the changes.

              Anyone have any thoughts on how decent the gain is of the XG91?

              Comment


              • #8
                Originally posted by antennanut View Post
                Anyone have any thoughts on how decent the gain is of the XG91?
                Here are some sites you might check out.
                http://www.hdtvprimer.com/ANTENNAS/comparing.html

                http://www.highdefforum.com/local-hd...8-vs-xg91.html

                http://home.indy.rr.com/challengerul/antenna.html

                During the past couple of years, the CM 4228 (now the 4228HD) and the XG91 (also known as the 91XG) have been two of the most talked about antennas around. I've used and tested both, and each has pluses and minuses. YMMV.
                Last edited by indysteve; 12-08-2008, 10:26 AM.

                Comment


                • #9
                  Thanks for the links. Reading of the antenna variety is something I definitely enjoy!

                  Comment


                  • #10
                    I have two of the old style CM4228 antennas on my roof and it's amazing how reception differs between the two of them. One is about 5 feet higher than the other, and they're about 20 feet apart on the roof. Both have the same length of RG-6 coax.

                    The taller one picks up most of the stations in Sacramento transmitting from the Walnut Grove site 65 miles away strong enough to be received 100% of the time. The lower one does not. Signals are often below the cliff edge and I get "No Signal". On the other hand, the four stations transmitting 35 miles away from the hills above Fremont, CA, are much stronger on the lower antenna than on the higher one, and so is the station transmitting from Mt St. Helena 70 miles away.

                    This just proves that location and height have a lot to do with how well you receive certain stations. For those who write to the various groups about having problems receiving specific stations, I advise them to try moving the antenna higher or lower, or horizontally a few feet, to see if it helps. In many cases they reply that it solved their problem.

                    My question for all of you DXing experts is... why does reception and signal levels vary so much over just a short distance? Often a change of just a few feet is all that's needed to take a station from "No Signal" to an excellent signal.

                    Larry
                    SF

                    Comment


                    • #11
                      While I am certainly no expert at DXing, or anything else for that matter, I do have some RF experience. My experience has been that the higher you go in frequency the more pronounced the effect is that you are talking about. For example, with VHF low band, say 6 meter amateur radio band, you may have to move quite a distance to improve reception. Move up to VHF high band and again moving to improve signal can be an improvement, but often not as much is needed as lower in frequency. Continue up to UHF 440-470 mHz, 800 mHz, or further still to 1.9 gHz and even moving a couple of inches can make a dramatic improvement in signal. The other issue that I have seen is analog vs. digital modulation differences. With analog you can work with a modest signal, but with digital it seems to be more of an all or nothing effect. With ATSC reception, for the ,ost part, you either have a great signal or nothing. I do realize that you can get pixelization on ATSC, but for the most part it is either great or not there.

                      Comment


                      • #12
                        Listen to a distant FM station on your car stereo and listen to the fading as you move just a foot or two when stopped for a red light - it might go from full stereo to gone and back again. That simply enforces rule #1 - You cannot have too many antennas.

                        Comment


                        • #13
                          With a little tropo enhancement in the area earlier this morning, here are a couple examples of reception between the single UHF antenna (91XG or XG91) and stacked UHF antennas (Triax Unix 100 W/B).

                          The first picture shows decoding of WAVE-DT 47, Louisville @ 110 miles, azimuth at 172 degrees, using the stacked antennas. This station has to make it through local LP analog WBXI-CA 47 @ 12 miles, azimuth at 187 degrees. With the narrow beamwidth of the stack, it nulls enough of WBXI to receive WAVE-DT. The second picture shows the same digital receiver (Zenith DTT900) connected to the single antenna via the use of an A/B switch.

                          The third picture shows decoding of WXIX-DT 29, Newport, KY/Cincinnati, OH @ 101 miles, azimuth at 123 degrees, using the stacked antennas. This station has to fight with semi-local and full-power WTTK-29, Kokomo, IN @ 29miles, azimuth at 18 degrees. The fourth picture shows the Zenith DTT900 attempting to decode WXIX-DT. It did display the PSIP and just barely decoded a few frames of video.

                          On the other hand, I do find that on occasion the single antenna will outperform the stack, but not very often. Directivity is one of the keys, especially in receiving distant (DX) stations when co-channel interference is present.

                          Steve

                          Comment


                          • #14
                            Thanks, Steve. Once again, IMHO, directivity is going to be a lot more important with DTV DX. Channels 7-51 are going to be packed with short-spaced DTVs.
                            Danny
                            Shreveport, LA
                            Mexico/Latin America TV DX ID Tips http://www.tvdxtips.com
                            Submit and read DTV Stats http://www.tvdxexpo.com/dtvdxrecords.html
                            TV and DTV DX Photographs http://www.tvdxexpo.com
                            My Photographs of 100 Mexico TV DX Local IDs http://www.tvdxexpo.com/100mexicotvids.html
                            More than 1,100 TV logs since 1994

                            Comment


                            • #15
                              This antenna called "Sabre"was used till around 10-15 years ago in the Channel Islands
                              south of the UK to pick up Uhf signals from the mainland
                              for local rebroadcast by commercial TV from a high powered station
                              around 100 miles away.

                              http://tx.mb21.co.uk/features/sabre/index.shtml

                              There were several sources of co channel interference and the antenna
                              could selectively place nulls when the tropo "interference" came up.
                              Very advanced for its time,introduced in the late 70's.Would be useful with
                              DTV now.

                              There are a lot of old BBC Research and Development reports as well here
                              of interest

                              http://www.bbc.co.uk/rd/pubs/reports/index.shtml

                              going back to the 1960's.

                              Report from 1976 number 33 is interesting,receiving an Indian Uhf
                              TV satellite sidelobe at 860MHz(I remember this ! one could just about get
                              a very weak picture with a 6 ft mesh antenna)

                              Reports 1977-10 and 1978-08 talk about the BBC system of receiving
                              signals in the Channel Islands with large Uhf dishes and also via a large
                              number of log periodic Uhf antennas,

                              Think the link to the Channel Islands is now via fiber optic cable with satellite
                              as a backup.

                              Happy Reading!

                              Hugh

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