biasing

Discussion in 'Wireless & RF Design' started by hardrock, Jan 1, 2014.

  1. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    i have a 10 meter radio mobile. i have a loud popping when the
    mic is keyed in the external speaker. its very annoying. the
    schematics shows the audio ic amp being switched off when transmiting.
    when it should be biased off. poor design. its there a simple fix
    to stop this pop noise when keying up? thanks
     
  2. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    schematics need to be posted...........
     
  3. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
  4. radiohead

    Active Member

    May 28, 2009
    474
    31
    It sounds like there might be an issue with the switching within the radio. Make sure your antenna has a good ground. Make sure your radio has a good ground as well. Another possible solution is to put a low value .001uF to .1uF capacitor in series with the speaker positive. And/or wrap a few turns of the speaker positive wire around a ferrite bead. The bead should choke out most stray RF the speaker wire may be picking up.
     
  5. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    Can you hear the popping using the internal speaker?
    If not,is the external speaker a passive one,or does it have a built in amplifier?
    If it is only happening with the external speaker,perhaps it is an RF pickup problem.

    You could probably use a relay to disable the speaker when the PTT operates.
    I d suggest you ask on QRZ.com as well,but a word of caution--many Hams don't like the "Ranger" series of radios & may give you a hard time!
    Most of them are ready to help,however,after they have had their say.:D
     
  6. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    Can you hear the popping using the internal speaker? yes
    If not,is the external speaker a passive one,or does it have a built in amplifier?
    If it is only happening with the external speaker,perhaps it is an RF pickup problem.

    You could probably use a relay to disable the speaker when the PTT operates.
    I d suggest you ask on QRZ.com as well,but a word of caution--many Hams don't like the "Ranger" series of radios & may give you a hard time!
    Most of them are ready to help,however,after they have had their say.:D
    [​IMG]
     
  7. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    True. the switching transistors switch the audio ic amp a 5 watt monolithic audio amp off when keying the mic. this is where the pop
    comes from. it should have been biased off.

    i tried a tried a 4.7 uf cap across the speaker terminals. i did not help.
    my thought on a resistor in series with the + line. would lower the pop
    at the same time when having to turn the volume up more because of
    the resistance the pop is still gonna be there???
     
  8. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    OK,you've discovered one thing-----the external speaker is nothing to do with the problem.

    The other posters are mainly thinking about RF getting back into your speaker amp in the instant that the Transmit function is keyed.

    You can prove this isn't the problem by disabling the Transmit function---no RF,no feedback.

    I haven't dived into the equivalent circuits from other Radios,but from memory,they switch the amplifier off in the same way,so maybe you have a real fault,not a design problem.

    I haven't seen a lot of comments on the 'Net about this problem as would seem likely if they all did it.

    Are you a Ham?----if not,transmitting,with this Radio is probably illegal in your country in any case!
     
  9. #12

    Expert

    Nov 30, 2010
    16,330
    6,818
  10. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    #12 likes this.
  11. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    "10 meter mobile radios" are frequently used illegaly as cb radios, and modified with some weird mods. some are in the speaker circuit, to give strange chirps when the mic is first presssed, and some to provide "talk back" or listening to your own voice on transmit. look for any signs of modifications, spliced wires, or signs of soldering in the audio output stage.
     
  12. #12

    Expert

    Nov 30, 2010
    16,330
    6,818
    Are you referring to the Lawyer? or the guy that seemed to object to finding legal advice on so many RF threads?
     
  13. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
     
  14. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    There is nothing illegal about the radio. All i need to know is there a way to stop the pop on transmit. I came to this site
    to get information for a fix, is there anyone that might have a solution ? Thanks
     
  15. BR-549

    Well-Known Member

    Sep 22, 2013
    2,004
    394
    What does the talk back switch do?
     
  16. BR-549

    Well-Known Member

    Sep 22, 2013
    2,004
    394
    Is that like side tone?
     
  17. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    Thanks, the talkback switch enables you to hear yourself in the speaker when on. I have 3 of these radios 2 of them have no talkback switch. The weird thing is when talkback is enabled the pop goes away. The problem is i dont want to hear talkback .
    The pop is annoying. It is caused by the audio ic being switched of or muted . It should have been biased off. pin 3 of the ic
    which is 5.8 watts ta 72222 is the muting pin would a cap to ground off pin 3 help ?
     
  18. BR-549

    Well-Known Member

    Sep 22, 2013
    2,004
    394
    I'm going to assume that you just acquired unit and do not know it's history. I did a search on startpage.com for "popping sound when keying ranger radio". There are many examples of talk back circuit mods. Unfortunately, these radio's can be abused in many ways. Also, look for mic mods.
     
  19. hardrock

    Thread Starter Member

    Nov 16, 2012
    30
    1
    I think there is no fix...... thanks for the reply.
     
  20. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    exceept for a few newer radios, the audip output ic is used for both recieve and transmit. you never said the model of the radio, if its an electronic switched radio or relay switched. if electronic switched, the recieve audio quits when the mic is unplugged, on the electronic switched radios, the spacing or timing of the contacts in the mic can cause the pop, usually because of trying to stay in recieve when switching to transmit and visa versa.
     
Loading...