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How to connect an aerial antenna to a telescopic antenna?

Discussion in 'General Electronics Discussion' started by dietermoreno, Jul 31, 2013.

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  1. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    I thought of a project to learn about antennas and maybe improve FM reception (and later give me free TV).

    How to connect an aerial antenna to a telescopic antenna?

    This might be a very stupid question; I'm sorry if it is.

    I think I can have better FM reception if I build and errect a home made antenna on my balcony, but my LW/MW/SW/FM receiver when I read the manual it says that the telescopic antenna is for FM, it says that when no antenna is connected then only a ferrite loop stick is used for LW/MW/SW, and it says that when an antenna is connected to the coax input it is only for LW/MW/SW.

    So would the only way to connect an FM antenna be to some how connect it to the telescopic antenna?

    Like would I solder a wire from the feedline center conductor to somewhere on the telescopic antenna?



    Well the idea for the antenna is 5 clothes hangers, a 2x4 wood stud, some twine to tie the 2x4 to the balcony so it can rotate, and a feedline.

    The idea for the clothes hangers is of the 5 clothes hangers, one of them is oriented vertically and it is soldered to all the other clothes hangers and it is nailed to the 2x4 and it is a conductor with the clothes hanger stripped of its paint at the places it will be soldered to the elements and the feedline, and the other 4 clothes hangers are the elements, which are horizontal, and rotating the 2x4 changes the direction that the 4 elements are perpendicular to.




    If this is successful, the next project would be building a high VHF TV antenna of the same exact design just shorter elements for reception of Channel 2 digital which is actually Channel 12 analog in Chicago area, and it could also have one long element for low VHF for reception of Channel 6 analog which is actually an FM broadcast station.


    I don't think UHF is really possible to DIY because with UHF every inch of wire can make the difference between a tuned and an untuned circuit so I would have to have a feedline going to each element and by the time I do that I could just buy an antenna for about the same price.
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    Antennae are built so that their size is quite specific, depending on the wavelength of the signal determines the optimal length of the antenna.

    You would not want to connect them together, but you might be better of raising them up so they get better signal access, for that you can just attach them to a pole and leave that up.

    Connecting the two together would yield equal or worse signal quality to either on its own.

    Making your own out of coat hangers and stuff probably wont be that successful either, as you would need to add impedance somewhere, most antennae are either 75 or 300 ohms (Im not 100% sure on "digital" ones but they should be about the same)

    Honestly you would be better off spending 25-40 bucks on a generic antenna.
     
  3. dietermoreno

    dietermoreno

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    0
    Dec 30, 2012
    So then better luck on the TV antenna because every TV has a coax antenna input unlike most radios today don't even have a coax antenna input, or if they do it is a short wave radio that can also receive the other bands and the antenna input is only for short wave.
     
  4. xChuckx

    xChuckx

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    Aug 1, 2013
    You wouldn't want to connect an FM antenna to a telescopic antenna... You could disconnect the telescopic antenna from the radio and connect a 50ft 75 Ω coax to it... the coax shield would need to be grounded to the radio and the center conductor connected to your FM antenna input.... add the antenna on the other end of the coax and raise it in the air see how it goes... also check out Yagi antenna designs on the ARRL websites... there are antenna generators that can give you an estimate on lengths etc... you could also build a simple fm antenna tuner to adjust impedance... add a switch for LW/MW/SW/ on same ant etc. for long wire etc..

    good luck
     
    Last edited: Aug 1, 2013
  5. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012

    Well then I guess I could try it with a cheap radio for $3 at Good Will (clock radio) instead of a LW/MW/SW/FM receiver if I'm going to have to remove the telescopic antenna so that if I mess up I just throw it out and buy another clock radio for $3.

    I've taken the clock radio apart before and seen that the FM antenna wire logically is connected to a solder connection labled "FM ANT". So all I would have to do is solder the coax conductor to the FM ANT connection inside the clock radio and then put up an antenna outside.




    While were on the subject of FM, does anyone know why when using an analog tuner like a clock radio uses, for the close stations there is a loud spot around the left of the center frequency, a silent spot around the center of the center frequency, and another loud spot to the right of the center frequency, but the loud spot to the right of the center frequency sounds distorted?

    Is this a weak far away station in the middle interfering and for analog tuner it receives the station from frequencies far from the center frequency comming in over unused frequencies?

    The clock radio only has one speaker so its not a stereo signal.

    This is the case for the close stations 95 WIIL Rock (12 miles, 50kw), Star 105.5 WZSR (5 miles, 1.4kw), 103.9 The Fox WFXF (10 miles, 2.5kw), and 96.9 The Drive WWDRV (10 miles, 8.3 kw).
     
  6. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    Sorry I can't find the edit button for some reason right now.

    When I bothered to Google stereo multiplexing used by FM broadcast I found out that the stereo signal actual has the bandwith duplicated into two side bands and that's why changing the analog tuning slightly changes the reception because the "tuning on the left hand side" is the lower side band, the "tuning on the right hand side" is the upper side band, and the "deadspot in the middle" is the amplitude modulation center frequency of the double side band carrier supressed stereophonic signal.

    So even though the clock radio only has one speaker, it appears that it has a stereo decoder that is connected to only one speaker and recombines the stereo signal into a mono signal.

    So the reason that there are 3 strong spots and 2 dead spots in the spectrum of a strong local station signal is because the far left strong spot is the mono sum signal, the far left dead spot is the guard band between the sum and difference signals, the left strong spot is the lower side band of the difference signal, the right dead spot is the modulation center frequency of the difference signal, and the right strong spot is the upper side band of the difference signal.

    The reason that the lower side band is higher fidelity than the upper side band is that more bandwidth is required in the frequency division mulitiplex to get all the way to receiving the upper side band.



    Edit: weird, now this reply has the edit button but the one above it has no edit button.

    It appears that admin has the power to disable the edit button on posts if he doesn't want them to be edited and that is a clue to not post a reply or else be banned again.



    Edit 2: Well I think that actually the Lsb is not always superior fidelity with all modulations. I think the LSB in FM stereo mulitplex has superior fidelity, but I think the Usb in receiving a mono signal at all in FM has superior fidelity than the LSB( that is the USB being 200khz above the center frequency and the LSB 200khz below the center frequency). I'm not sure why the USB has superior fidelity in that case.
     
    Last edited by a moderator: Aug 13, 2013
  7. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    Dont misunderstand the sideband system. There are NO sidebands as such as part of the transmitted FM signal.
    AM has sidebands. FM doesnt
    The DSBSC that is used in FM stereo is all part of the signal encoding to produce what is called a baseband signal. This baseband signal is then used to modulate the FM transmitter.

    No, the demodulator in a mono FM receiver just filters everything above 15kHz so it doesnt even see the stereo channels part of the modulation. there is no recombination etc


    No, the forum software automatically removes the ability to post after ~ 24 hours.
    this gives you time to edit your post within a short time to fix typo's etc but not to edit /delete posts after a period of time.
    up to ~ 8 months ago there was no time limit on editing of posts. Then we had a clown who "went off the deep end" and deleted a large majority of his posts in several threads which totally destroyed the threads. So an edit time period was added to the forum system


    all irrelevent, as per my earlier post

    cheers
    Dave
     
    Last edited: Aug 13, 2013
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