Connect with us

Amplifier antenna question

Discussion in 'General Electronics Discussion' started by gabriel13, Feb 9, 2013.

Scroll to continue with content
  1. gabriel13

    gabriel13

    1
    0
    Feb 9, 2013
    I'm new to electronics... i have kind of a whimsical question... what would happen if i was to plug a telivision antenna into the headphone jack of... let's say, a guitar amplifier... would there be a signal, and if so, what frequency would it be on... or would it be on multiple frequencies?

    Gabriel
     
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Plugging anything into a guitar amplifier will only give audio frequencies. If the amplifier is sufficiently sensitive then you will hear mains hum and hash from switch mode power supplies. The difficulty is keeping this rubbish out of sensitive equirment.

    Radio and television programs are sent on frequencies far above what an audio amp can respond to.
     
  3. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012

    You can not plug a signal input into the signal output of an active circuit. A guitar amplifier is an active circuit.

    I think you mean you want to plug the television antenna RCA cable into the 1/4 inch jack input of the guitar amplifier by means of an RCA-to-1/4 inch adapter.

    I don't think that would work and that is why we invented the super heterodyne reciever because amplifiers (at least before transistors) can only amplify radio frequencies up to about 1,000 KHZ, and terrestrial TV in the U.S. uses VHF RF of somewhere below FM broadcast band like 60MHZ for channels 2-6 I think and uses VHF RF of somewhere above the Air Traffic Control band like 220MHZ for channels 7-13 I think and uses UHF RF of somewhere around 260MHZ for channels 14-38 and uses SUHF RF of somewhere around 300MHZ for channels 38-59 I think. I'm not sure I'm too lazy to Google it now, but a simple Google search would yield the frequency spectrum that terestrial television broadcast in the U.S. uses. but regarding your question, it doesn't matter what the RF is, all that matters is that the RF is greater than about 1,000KHZ so it won't work.



    Well I wouldn't be so certain about that... I have gotten AM radio on my guitar amp before using the coaxial cable as capacitance, using the pickups as inductance, using the tone control pots as variable resistors in place or varicaps, using the inductance of EM field around the unused wire in the TRS cable to induce the RF from the TRS cable to the wire of the TRS cable that is connected into the amplifier and induce RF from the guitar and the guitar strings and the cable are the antenna, (and there is enough dirt on the cable contacts to act as a crystal), and I recorded it and uploaded it to YouTube:




    I am also interested in his question because I don't have cable or satelite television.

    I live far way from TV stations (about 55 miles Northwest of the Chicago loop near McHenry, IL), so the sales man at RadioShack told me that I have to pay $300 for a 20 foot tall antenna to watch TV.

    Is this just marketing b.s. and a smaller antenna would be just fine if there was a way to amplify it?

    I have a question: using modern transistor theory and IC theory is there any transistor or IC amplifiers available that can accurately amplify RF in the terrestrial television broadcast band so that the weak signal coming from the rabbit ears can be amplified?

    Or is the answer a flat out no and that is why cable television and satelite television were invented?
     
    Last edited: Feb 11, 2013
  4. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    Pretty much everything you said up to the final comment quoted above was correct :)
    then you went askew ;)

    RF is RF it can be any frequency
    if RF started at ~ 1000 kHz (1MHz)
    1) then we wouldnt have all the AM broadcast stations from 550 kHz to 1000 kHz
    2) we wouldnt have all the ~200 - 600 kHz NDB navigation beacons ( NDB = Non Directional Beacon)
    3) we wouldnt hear on other equip all the 50/60 Hz AC mains radiated signals :)
    4) we wouldnt have all the ~ 10 kHz Loran and Omega transmitters that were/are used for transmissions to submarines
    5) we wouldnt be able to receive all the RF signals generated in the upper atmosphere
    often called atmospherics, more commonly known as whistlers and dawn chorus

    As you can see, Audio and RF signals do share a common section of the spectrum the difference is how they are produced.
    RF signals are the emission of photons from a conductor that has an AC signal in it - this is defined/known as an EM Electromagnetic wave

    can go deeper, but that will do for now :)

    Dave
     
    Last edited: Feb 11, 2013
  5. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    If your terrestrial signal is low, you will need a tall mast with the antenna high up to clear surrounding obstacles and a very sensitive amplifier at the antenna. Even then, the signal may not be good enough.

    Why not use a satellite?
     
  6. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    Thats only because the amplifier has crappy or nil RF suppression

    Dave
     
  7. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    As I said
    "The difficulty is keeping this rubbish out of sensitive equipment."

    If you have a weak signal, then a better antenna can help. An amplifier at the antenna to raise the signal level before the co-ax cable can minimise the degradation of the signal/noise ratio.

    Most TVs these days are pretty good and have a built in low noise amplifier An amplifier before the TV will not necessarily improve things. In the days of tube TVs a low noise transistor amplifier feeding the TV often improved things a lot.
     
  8. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    Oh, okay. So it performs as a component in an analog amplified radio reciever because it does not have components configured to cancel out RF, like humbucker pickups on a guitar are designed to cancel out RF, and still obviously humbucker pickups are not perfect as the video that I uploaded used a guitar with humbucker pickups.




    No I didn't say that RF doesn't go below about 1,000 KHZ. I said that RF can not be amplified on by the same amplifier that amplies audio, unless it is the case that it is in the medium wave band below about 1,000 KHZ. The medium wave band predated the super heterodyne reciever and that is why the frequencies were selected because of what RF ampliers of the day in the 1920s could amplify without using a lower IF, at least that is what Wikipedia says in its article on the super heterodyne receiver. So I was assuming that shitty guitar amps have no better frequency response to RF than amplification components in a 1930s super heterodyne receiver.

    Well in the video I made I am not even sure of the frequencies because I don't have a frequency counter and the only station identifier that I heard was WBBM, and this was all blindly tuning because my PC sound card can not monitor in real time and I didn't have an audio interface and I didn't have Pro Tools, but now that I have an M-audio interface and I have the Pro Tools SE that came with the interface for free, I will try again to record my guitar crystal radio reciever and I will make the antenna bigger too by buying some wire from the hardware store and winding the wire around the tip of the 1/4 inch TRS jack at where it is plugged into the guitar so that RF induced in the wire will be induced into the TRS.


    So if my guitar amp is a transitor amplifier and my TV is a CRT, will my guitar amp amplify the VHF signal at all? I though guitar amps couldn't amplify RF above the medium wave band and that is why the super heterodyne reciever was invented to allow VHF air traffic control and military communications in WWII? Or does that have to do with Armstrong was playing around with tubes and today we have transistors so super heterodyne reciever is no longer needed because transistors can amplify more RF than tubes? I don't think cell phones use super heterodyne reciever, or else your cell phone would be a WWII radio backpack. I think cell phones use the Phase Locked Loop Homodyne Reciever using transistor amplification because now IF is no longer needed with transistor amplification, at least that is what Wikipedia said I think, if I am interpretting the Wikipedia article on Homodyne Receiver correctly and if I am interpreting the Wikipedia article on Phase Locked Loop correctly and assuming that these Wikpedia articles are even correct which is unlikely since anyone can edit Wikipedia.
     
    Last edited: Feb 11, 2013
  9. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    My guitar amp won't amplify vhf, for many reasons.
    However it could appear to amplify a radio signal, quite possibly even a vhf signal.

    Why this could happen:
    Sometimes corrosion in a solder joint (especially copper corrosion) can produce a rectifier, which would detect a radio signal, meaning that the rf part of the signal would remain as high-frequency ac, while for difficult, complex reasons a copy of the audio signal would enter the audio amplifier.

    Sometimes children making a 2-wire telephone find that their telephone detects the local radio station. This is due to oxidation in a twisted-together joint between copper wires.
     
  10. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    then I recind my last statement when I said all but the last bit was ok and change it to that whole paragraph was not good and even your changed statement you made above in the quote is quite misleading ;)

    Even back in the tube days ... well before transistors ... tubes were working well
    into the microwave bands. And even these days tubes are still often used in the VHF to microwave bands as they can produce much higher power as an amplifier than transistors can :)
    I have tubes at home here that work happily on 10 GHz

    As a side note .... Please use the correct designations ... for kHz, not KHZ
    its only when you get to MHz GHz THz that they become capitals :)


    Dave
     
  11. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    you are not quite understanding the process that is occurring in the guitar amp ( or other piece of audio gear)
    The radio signal is being received by long wire leads ... to mics, guitars etc, its coming into the amplifier and then is getting rectified by the first diode or transistor it encounters
    That rectified signal is now just an audio signal which will be happily amplified by the rest of the amplifier and sent out to the speaker(s)

    Dave
     
    Last edited: Feb 12, 2013
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    To the OP. Are you imagining that the sound from your guitar amp would be transmitted? No it wouldn't; for that, you need a device called a modulator, which generates a radio-frequency signal that is modulated by the sound from the guitar amp. Modulated means varied in some way - either by frequency (FM) or amplitude (AM).

    The sound from your guitar amp is in the audio frequency range - around 20 Hz (hertz) to 20 kHz (kilohertz; 1 kHz = 1000 Hz). Frequencies in this range do not travel through the air; they need wires.

    The FM radio broadcast band is from roughly 88~108 MHz (megahertz; 1 MHz = 1,000,000 Hz). These frequencies travel through the air as electromagnetic waves and can be received and demodulated by radio receivers.

    http://en.wikipedia.org/wiki/Electromagnetic_spectrum
     
  13. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    So since transistors and tubes are directional, does that mean that a crystal is not longer needed in a radio receiver circuit if the circuit has transistors and tubes in it?

    So you are saying that my guitar amp is not amplifying the RF at all and only amplifing the AF that was rectified out of the RF in the first transistor?

    How does any radio receiver amplify RF if transistors and tubes have rectifying properties?

    So is the signal generated by my guitar pickups when I strum a string is it a sine wave that alternates from positive to negative, and when it passes through the first transistor it is rectifyed into the sine squared function which is sinusoidal but has no change of sign?

    By sine squared function, I mean this:
    [​IMG]

    Would a speaker still work if the audio signal was not rectified before being sent to the speaker?
     
  14. Harald Kapp

    Harald Kapp Moderator Moderator

    11,517
    2,652
    Nov 17, 2011
    Your audio signal should not be rectified at all. If it is, then something's wrong with your amplifier.

    What's happening when you hear a radio station via your guitar amplifier is that the radio signal gets demodulated at the input of the guitar amp. The input of the amplifier, being "operated" far outside it's designed range of operation (frequency range, as others have explained before) works like an envelope detector. After demodulation the remaining audio signal is amplified as usual. Your speakers see an AC signal with (ideally) no DC content.

    The rectification should not occur for the signals from your guitar pickup since these are within the operating range the amplifier was designed for.
     
  15. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    Okay, so rectification is a relative term that means what ever you want to be rectified to; it doesn't have to mean rectified from AC to DC and it doesn't have to mean rectified from sine function to sine squared function. I think so, right?

    So you mean if a guitar amp is converting the sine function audio signal to a sine squared function then something is wrong with the guitar amp. Actually my guitar amp does not rectify from sine function to sine squared function, at least according to the waveforms of the audio from the radio waves recorded in Audacity it does alternate between positive and negative.

    So since rectification is a relative term, it would be correct to say an envelope detector performs rectification from RF to the audio envelope of the RF.

    So an envelope detector is simply a passive circuit of a diode or crystal, resistor, and capacitor.

    So the envelope detector equivalent that is allowing me to hear radio waves on my guitar amp is dirt on the cable contacts, the resistors in my guitar for the pots, and the capacitance of the coaxial cable.

    Note that these radio waves are very quite audio in the video link and are mostly over powered by mains hum, so mostly what I hear in my guitar is mains hum and only audio from radio if I listen very closely. I opened the audio file (the same one that is in the video link) in Audacity today and added an 80Hz high pass filter to remove mains hum near 60Hz and that made a huge difference allowing me to hear the words the radio voices are saying rather than only being able to detect the presence of radio voices (when I said earlier that I heard the WBBM station identifier, I lied, what I actually heard was I recognized the radio announcer's voice even though I couldn't hear what he was saying). For example, a snippet of words from the radio announcer's voice that I can now hear are: "[female anouncer]...the internet...today...now...[now male anouncer]...inbound...12 minutes...outbound... 12 minutes..." It appears to be the traffic report by the male anouncer that followed a news report by the female announcer on something that happened on that day on the internet. Wow 12 minutes inbound and outbound on a Chicago expressway. Oh that's right I think it was 3AM when I was recording this so that is why traffic would be so light then.
     
    Last edited: Feb 12, 2013
  16. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    Basically, Yes, this is the function of a detector diode in a radio receiver

    Not quite, just the diode or crystal, not the resistor or capacitor



    again not quite, possible dirty contacts may sometimes produce a diode detector function
    but it will still more likely be a diode junction of a transistor or even an actual diode within the early stages of the amplifier ( probably the pre-amp stage)

    No not the pots, or the capacitance of the cable. The only thing the cable can do is act like an antenna to bring the RF signal into the amplifier


    Dave
     
    Last edited: Feb 12, 2013
  17. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    no, a detector diode of some description is still needed


    rectified/detected, yes maybe the first transistor or some other transistor or diode

    I cant answer that specifically .... its probably not a totally simple process.
    Other than to say it occurs under a certain set of circumstances

    no, its not rectified, its still a complex sine wave full of the harmonics of the string(s) you have strummed

    Dave
     
  18. davenn

    davenn Moderator

    13,836
    1,951
    Sep 5, 2009
    careful Kris .... you're heading down the same path as dietermoreno ;)
    see my earlier post on RF frequencies of various signals

    go back and look at the wiki link you posted and look at the second image down on the right side

    Dave
     
    Last edited: Feb 12, 2013
  19. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    So the Wikipedia article on envelope detector is wrong? Or do you mean that yes resistance and capacitance are needed in addition to the diode or crystal, but usually the internal resistance of the wires and the capacitative reactance of the wires is enough?




    Oh really, then it is impossible to connect your guitar amp to a speaker with a cable without a RF modulator. This is a false statement. So I don't think it is the case that audio frequencies can not be made into electromagnetic waves. Otherwise there would be no such thing as an electric guitar because the electric guitar pickups convert the sound waves on the strings into an alternating sinusoidal wave.

    In addition, if RF near audio frequencies did not exist, then that would mean that 60Hz AC power transmission would be impossible so you would have no power for you computer allowing you to view this web page, unless you lived within half a mile from an Edison power plant and payed an arm and a leg for electric power, which Edison doesn't care that it can only go half a mile he only cares that you are paying him an arm and a leg for electric power.
     
    Last edited: Feb 12, 2013
  20. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Dieter,

    Read Kris's post that you quoted again. He said "Frequecies in this range do not travel through the air". When you connect your amp to your speaker the signal goes through the wires, not through the air. Same with the 60Hz power. Why do you think you have to plug your amp into the wall?

    Bob
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-