1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Has anyone tried this FM diversity antenna circuit design from the "Electronics Now" magazine?

Discussion in 'Radio and Communications' started by thebestofall007, May 7, 2016.

  1. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
    Hello ETO, this is my first post, but I'm a big radio buff (YEP, I STILL LISTEN TO BOTH AM AND FM a lot in this digital age ;) ). I came across a project in the November 1993 edition of the "Electronics Now" magazine in the following link: http://www.n5dux.com/ham/files/pdf/Diversity Antenna.pdf where you build an automatic antenna switcher that allows diversity tuning on car radios that have only one antenna input (It's not just a Y adapter, either). It has a bill of materials list, circuit layouts, the PCB pattern for those who want to make their own circuit board, and instructions on how to tune it. I would like to build this circuit because I have a Toyota where the factory radio had diversity tuning and the two antenna inputs in the back, but that unit has long quit working, and most aftermarket headunits do not have diversity tuning, which is a big letdown. I know diversity tuning works because I have heard the radio reception of radios that had it, and it's a shame such a great technology didn't catch on with the newer aftermarket headunits. If you have installed car stereos and still listen to the radio, you know the problem.

    Anywho, Is there anyone here who has tried this circuit design and gotten it to work? How did it go? Do you have any tips? I am asking because while it looks promising for my application, I do not want to spend a lot of money on something I'm not sure would work due to the the fact that I can't find a lot of documentation for it online (I find this article all over, but no people who have put it together), and a little insight on this project would help tremendously.

    Thanks in advance!
     
  2. bountyhunter

    bountyhunter Well-Known Member

    Joined:
    Jul 17, 2009
    Messages:
    1,560
    Likes:
    81
    Your URL links to some index page.
     
  3. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,324
    Likes:
    585
    Location:
    Peterhead, Scotland
    ONLINE
    The link works OK for me.
    JimB
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!

    I also have Windows 10 with its Edge browser that goes to the index page on many links to a detailed link. Using Internet Explorer as the browser does not fix it.

    EDIT: If I click on the link I get to the index page. But if I copy the link and paste it into Edge browser it goes to the project properly.
     
    Last edited: May 7, 2016
  6. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
  7. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
    The link worked for me. It must be because I am using Linux Mint and Firefox. I have another link you might want to try: http://manualzz.com/doc/7071170/diversity-antenna

    Let me know how it works, please.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    Your new link works fine when I click on it with Windows 10 and its Edge browser. I tried the old link again just now and it opened the index page again.

    I disagree with needing diversity for a half-decent FM radio design. A good FM tuner has a good "capture ratio" where it captures only one signal in a mess of multipaths and it also has good AM rejection. A cheap radio will have flutter and distortion.
     
  9. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
    I am using an alpine deck for the radio with the capture ratio of 2db. I would like to use this circuit because my car, a 96 Toyota Celica, actually has two antennas out of the factory, the fender mount antenna, and a window antenna embedded in the back hatch window, and I wanted to take full advantage of them both. I already tried using a y adapter to combine the two, but it actually made the reception worse.
     
  10. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,324
    Likes:
    585
    Location:
    Peterhead, Scotland
    ONLINE
    A rather simplistic view there AG.

    Multipath is multipath and no amount of quality on the part of the receiver will sort it out.
    If the direct wave and the reflected wave cancel out, there is no signal and you cannot receive something which is not there.

    In answer to the OPs question, I have no experience of this circuit and so I cannot comment on its effectiveness.
    I do not know your experience or capabilities, but there is a lot in this circuit which if not quite right will stop it from working correctly.


    JimB
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    I listen to FM radio a lot and live near a major airport. A cheap or even medium quality radio produces "flutter" (cancellations due to multipath) and distortion but my hifi system does not. Both use a simple piece of wire as the antenna. I have never heard flutter on my car radio and have not heard multipath distortion for many years.

    A long time ago I had an Eico kit vacuum tubes hifi that was pretty good but in those days the capture ratio and AM rejection were not great. The antenna was the best Yagi the manufacturer made and it was on a rotor. I could turn the antenna to the strongest reflection of an FM station to reduce but not completely eliminate multipath distortion. The antenna was so sensitive that it could pickup two stations on the same frequency individually at different directions very far away.
     
  12. bountyhunter

    bountyhunter Well-Known Member

    Joined:
    Jul 17, 2009
    Messages:
    1,560
    Likes:
    81
    Combining signals from two different antennas is tricky because the distance changes the time phase of the signal and it can cause cancellation instead of addition.

    IMHO, using two antennas is a major pain and just using one good one is way easier.

    I reviewed the article on the device and it looks extremely complicated. I also wonder how likely it is that two mediocre antennas located about six feet apart would have a "bad" signal on one and a good signal on the other.

    Car reception is always problematic because the receiver keeps changing position with respect to the signal source. That means the antenna has to be as omni directional as possible which means (of course) highest chance of getting a multipath signal.

    Digital signal processing could be used to "take out" signals of the same frequency that arrive later but it would be complicated. I doubt they are going to put that kind of money into a car radio when FM is basically turning into talk radio and sports anyway.
     
    Last edited: May 8, 2016
  13. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
    As for decent antennas, I am using a spring steel whip fender mounted antenna as the main antenna and it works wonders, as the power antenna that came stock with the car was shot and the previous owner just unhooked it anyway, so I went to the junk yard and got an antenna off of a 95 grand am that happened to fit perfectly with a little modification to the mounting hardware (even looks stock, too!). The window antenna works well, too, but not as good as the fender one I put in, as it seems to be more directional.

    The device works by tracking the FM station's 19 khz pilot signal and "listens" through an audio input to gauge when to switch antennas. It doesn't simply combine the antennas like I did with the Y adapter and what you said with the time-phase relationship applied, and that's indeed why reception got worse in that case. This device however uses either one antenna or the other and switches them automatically. Remember when the article said that you can get bad reception when you stop at a light for example, and then move a short distance ahead and get the station back? If there were an antenna in a different location, there is a chance that it is getting better reception and switching to it would improve the reception, which is what the device does when it loses the pilot signal.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    The FM stations I listen to are music only and frequently they have one hour of music continuously without any ads. I do not listen to talk radio stations nor sports radio stations.
     
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,044
    Likes:
    541
    Location:
    AZ 86334
    In Commercial and Amateur Radio, we usually use two antennas and two receivers, and then use a "Voting circuit" that aut0matically selects the audio signal with the best SNR... Some VHF repeaters use multiple receiving sites, and seamlessly select the best signal to be repeated...
     
    • Informative Informative x 1
  16. bountyhunter

    bountyhunter Well-Known Member

    Joined:
    Jul 17, 2009
    Messages:
    1,560
    Likes:
    81
    Yes, I read it. That is what I am very skeptical about. I have my doubts it's cost and complexity will yield enough improvement to justify it.

    I found a better cure for music reception problems: a five hour MP3 music CD that runs containing the music I like and has zero ad content. Every piece of music ever recorded is on Youtube now, you don't even have to pay for music if you don't feel obligated to. IMHO, commercial radio passed the point of intolerable ad content many years ago.... and TV is peering over that precipice right now (the average TV show now has about 20 minutes of commercials per hour). The latest feature of TiVo is commercial "skip" where they set in markers on any recorded show that allows a one button instant skip over all junk to the next program point. Well worth the money....
     
    Last edited: May 9, 2016
  17. bountyhunter

    bountyhunter Well-Known Member

    Joined:
    Jul 17, 2009
    Messages:
    1,560
    Likes:
    81
    Around here there is no music worth listening to on the radio and ad/jabber content averages about 20 - 25 minutes per hour which I find completely intolerable.
     
  18. thebestofall007

    thebestofall007 New Member

    Joined:
    May 7, 2016
    Messages:
    21
    Likes:
    1
    OMG, you are so right on the commercial crap and that's why I hate TV, PERIOD. As for mp3 music: I have a 64 gig thumbdrive I bought for about $15 with over 3 days' worth of music on it, and growing. I have better use for internet than television when I can download my shows, even a whole series if I want, so it's not even much of a consequence if they cancel it like it was in years past. However, I am lucky to have some good non-commercial stations in my area that broadcast music I don't find on other stations, but unfortunately the signals aren't very powerful like the commercial stations. I'm also an avid DX'er.
     
    Last edited: May 9, 2016
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,437
    Likes:
    933
    Location:
    Canada, of course!
    Radio stations in Canada want to attract more listeners and keep the happy ones they already have. Then they can sell ads at a high cost to only a few advertisers. I think there are surveys that show the number of listeners. Therefore there are only a few short ads per hour and frequently no ads for an hour. I think the Canadian government regulates ads to be infrequent and short.
    Ads on radio stations in the US are completely different? US radio stations want to annoy and drive away listeners by having too many ads?
     
  20. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    9,908
    Likes:
    1,094
    All of this is funny. I used to be an avid FM listener and now I seem to prefer quiet. Car listening is only AM/FM I did. A 1982 toyota radio was really bad. Ant amp + external blaupunkt antenna really helped.

    In the house when it all worked I had anexcellent tuner and rotor where I managed 3 stations on one frequency depending on how the antenna was pointed.The tuner was a tecnics professional ST-9030.

    I add the carver TX1-11 Asymectrical FM charged couple decoder and multipath was non-existant.

    Antenna was aimed using the SCOPE out outputs as an audio source on the tuner.

    Added to that was the dbx 4bx dynamic range expander with impact restoration.

    The system was nice in its day. It currently needs major repairs.
     
  21. bountyhunter

    bountyhunter Well-Known Member

    Joined:
    Jul 17, 2009
    Messages:
    1,560
    Likes:
    81
    Yes. There is no legal restriction, however TV stations all do the same thing by convention at least on network (prime time). If you have Netflix you can see program length by era:

    1) The original Star Trek (late 60's) will show about 52 minutes length which means in that era, an hour show had about 8 minutes of commercial.

    2) Star Trek The Next Gen which was late 80's and early 90's was about 48 minutes long.

    3) Current TV shows run about 41 minutes per hour.

    NOTE: When they rerun old shows they still use the 41/hour time so that's why when they show an older program they have to chop more than ten minutes out of it to fit in the hour leaving what's left to be unintelligible.

    As for local programming: anything goes. The noon 1/2 hour Fox news runs about 12 minutes commercial/18 minutes program.

    As for radio: I use to listen to FM at work and the "normal" ratio on typical music station I heard (popular music) was about two songs followed by 5 minutes of commercials repeat ad infinitum. That is roughly 8/5 which is ridiculous and intolerable IMHO.

    What was really bad was the FM station that had a "commercial free" hour drive time show because for the six hours prior to it, they ran so many commercials that it seemed like there was no music at all.
     

Share This Page