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29 receive

Discussion in 'General CB Services Discussion' started by Van Lifeson, Jan 13, 2020.

  1. Van Lifeson

    Van Lifeson Member

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    OK, I have two cobra 29 LTD‘s .
    One is from Taiwan and the other is from the Philippines. My Taiwan radio when receiving, sits at zero. The Philippines model sits at about three. When people talk, I get the same signal. The problem here is that, people who give me about 3 pounds I have a hard time hearing them because I’m getting 3 pounds of static where as the other radio is quiet and sits at 0 pounds . Does the radio need an alignment for the meter to sit at zero even though people give me the same signals on both radios?


     
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  2. 543_Dallas

    543_Dallas Sr. Member

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    I've had new ones like that out of the box. I'd give it a RX alignment and recalibrate the meter afterwards. If it's nice radio I'd replace the electrolytics first. At least look at them closely and make sure none are starting to swell.
     
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  3. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I would be more concerned about the S-3 radio - it sounds like a tuning issue, of where the radios own Internal signals are adding to the noise and may help explain the S-3 NOISY reading versus flat on the floor - not getting the weeds wet.

    Both radios to receive the SAME in performance is possible - it is a simple tuning issue to compensate for the differences.

    I'm working on a solution for you...BRB
     
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  4. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    In light of your symptoms between the two radios...

    Check the Noisy Receiver - that one may have been tuned incorrectly - sounds like you are getting part of the IF carrier...

    See below...

    A simple re-tune.
    StartingPoint.jpg

    The above is for a Cobra 29 later revisions - your radio will differ but the conceptuals have not changed.

    So be aware - but this should help you.

    Just Remember that VR 1 set the GAIN in the IF stage - too high - you'll get distorted and noisy receive.

    The three coils above as separate inset are the ones I'd focus on for proper alignment...
     
  5. nomadradio

    nomadradio Analog Retentive

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    Turning VR1 as high as it will go is what we came to call "truck stop super receive". Raises the noise level, and reduces the radio's ability to cope with a strong signal, and keep the audio clear.

    Simply setting it to between 2/3 and 3/4 of full bore is usually close enough.

    Alignment is a big wild card. Radios routinely leave the factory with at least one tuning slug set away from its peak position.

    The S-meter has its own adjustment trimmer pot, so what it reads is not a reliable guide by itself. Not until you set it with a calibrated-strength signal.

    Two radios that show a different meter reading for the same noise level is not so unusual. Changes in production from one factory to the next can affect this part of what the radio does without causing a performance problem.

    Basic guide for "is my receiver sensitive enough" is mostly about the noise level. Can't hear anything weaker than the noise.

    If the S-meter reads zero with the antenna unplugged, plug the antenna back in. If the meter comes up at all, you won't hear much difference making the radio more sensitive than that.

    And if the meter doesn't read zero with the antenna unplugged, that's a different kind of problem.

    73
     
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  6. 357magnum

    357magnum Sr. Member

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    Thanks guys for this info ! (y) I had a 29 lying around in the shack someone gave me , a Newbie ! He plugged it in & tried to talk w/ NO Antenna !:whistle: I gave it to a Ham friend to tinker with as he wanted & 11m radio in his car . This one had No receive @ first but would put out almost 6w on my Dosy :)LOL:) but 3 " honest " watts on his Bird . Receive has come back intermittent but No modulation . I apologize for Hijacking the thread but I have been giving him this info just in case it helps . 73 & God Bless , Leo
     
  7. Van Lifeson

    Van Lifeson Member

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    Thanks all! I’ll see ignorance I can tweak it.
     
  8. Van Lifeson

    Van Lifeson Member

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    Lol. Auto correct! I’ll see if I can tweak it!
    Maybe auto correct knows I can be as ignorant as anyone.
     
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    If you can, listen and tune for best loudness and volume of receive.

    I use my ears to help align these radios...so the tuning is really more for Audio reproduction than S-meter signal strength...Your ears are the best tool you've been supplied to work with...

    Sure you can focus on S-meter Units and dB stuff, but the receiver is audio - not a visual show like TV is...

    It's why I recommended to look at these "IF coils" those larger slug core cans are the IF section - one takes in the 10.7 IF extracted by the 10.240 DIFFERENCE leaving you 455kHz. It then is strongly (Read: Really Really amplified) and then sent - coupled thru the coil into the Detector section of those Glass diodes just to the right of the Rightmost Can in the inset.

    Note the location of VR1 - if you have a simple fine tip marker - make a sight mark so you can return it back to that position as a starting point if you "tune the receive" the wrong way. Do the same for those Core Slugs - so you can find home position if you screw up. They take several turns so remember to Mind your P's and Q's when it comes to realigning a receive.

    Here's a graphical guide to help you with the IF...
    StartingPointStep2.jpg


    Here's a bigger picture of the mess you'll be working with...
    StartingPointStep3.jpg

    Hope these hints help...
     
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  10. Van Lifeson

    Van Lifeson Member

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    That’s awesome! Thanks Andy.
    It’s funny, I have been talking on radios for 40 years, got my degree in electronics 30 years ago and I never really have messsed with cb’s. ( probably because I never had any problems with them ) but all the radios I have now, are getting old like me. Although, I still have the very first radio I ever bought brand new. A cobra 87 GTL and that one still performs flawlessly .
     
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  11. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Just like Richard Simmons promoted taking care of yourself because no one else can - pretty much sums up the passion I have for CB radio by the conversations I've had using them. Take care of your radio and someday it will help take care of you.

    Good luck, have fun!

    Thx!

    ... You know you're a CB'er when...
    ... Elvis shows up and wants to talk on your radio...
     
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  12. Van Lifeson

    Van Lifeson Member

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    One question Andy, in what order do you adjust? Vr1 first then the cans or vice versa?
     
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  13. nomadradio

    nomadradio Analog Retentive

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    Setting VR1 about 2/3 of the way up from minimum should do, before or after.

    Remember that the weaker your test signal is, the sharper the peak you'll see on the tuning slugs when they're turned.

    73
     
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  14. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Great information guys, this should be pinned.
     
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  15. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    As Nomad pointed out -

    It's best to Turn down VR1 - so as you tune thru the cans for IF - you can see the peaking.

    Eventually you'll have to then go back to Step 3 Graphic and have it help you tune thru the ENTIRE RX set of coils - but to obtain the most equal of results - turn down VR1 and tune - Adjust VR 1 a little more - Tune - and so on, until you obtain about as much "gain" in receive as you can, then leave VR 1 in that setting for the moment and then tweak the coils starting at the BACK two cans shown in that Step 3 Graphic.

    The issue is to equalize the receive peaking - to make it as broadbanded as possible for the channels 1 - 40.

    It would also help in tuning to adjust VR1 (adjust as you see fit) to obtain less noise and focus more on the audio quality and signal - so now you have the last IF stages done - VR1 can help you obtain gain levels to help you retune the PRECEEDING stages to peak them out.

    A little word of caution...I don't want you to break slugs so use the right tools if you can...

    IF you have a ceramic tip tool for slugs - its' the best for this type of tune and radio chassis. At least the interaction of the ceramic tuning tip wont be like what you would have using -- say a Eyeglass Screw tool. The metal tip is nice, but can damage the slugs and also interact to a point that can make it difficult to tune properly for those not accustomed to doing this.
    Proskittool.gif

    The above is old - but they still offer this type of tool. This can really help in RF tuning circuits.

    Note the Size of the tip - 0.4 X 1.2 - simply a sizing - and fits the Cobra/Uniden (or pretty much any radio from that era) slugs.

    Then once completed, you can then "Reset" VR 1 to a POSITION that you SEE FIT to use!
     
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