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Uniden PC-122, ATTN: Handy Andy

Discussion in 'CB Radio Modifications' started by ExitThirteen, Nov 9, 2018.

  1. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Hiya folks,

    Just snagged a PC-122 Taiwan made recently for 50 bucks.



    Went to Handy Andy's site on these radios (He has a HUGE write-up of mods for this radio, he's the GURU of the 122) and performed some of the mods, but I'm curious, are there any updates or new mods on this board these days? Any new info I should look into? Thank you in advance!

    Andy, I hope things are well with you these days, and I appreciate all that you do for us here on the WWDX forums. :)


    ~Cheers~
     

  2. Handy Andy

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

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    Wish I could update the site, but there was a brief "attack" which I requested my pages get locked down - so they wouldn't get hacked remotely.

    So now, the sites changed (at least I can't access thru my own FTP) and I am no longer able to update the my pages - so I'm kinda stuck...
     
  3. Handy Andy

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

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    I was working and updating as I could about the PC-122 on the Forum back at CB Tricks but...that side is - well - simple messaging - something got corrupted so - the stuff is out there - just not here.
     
  4. sonoma

    sonoma Sr. Member

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    Andy, I was able to pull up all your postings all the way back to 2010, a total of 731 postings you did. all the pictures you put up there are still there.. a lot of info there and was thinking about copying all of it . you did the 452 power mic and there is a lot of info on it.
    there is over 120 pictures that you posted there also.there is a lot more but got tired of counting. just thought I would let you know if you wanted to log them to some thing you currently have.
    the next few days I am going to figure out the best way to save all of them. maybe put them on a DVD for future use.
     
    PA770 likes this.
  5. Handy Andy

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

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    Hey, careful there! There may be movie rights involved!

    LOL!

    (...Always nice to see your life pass you by like you're sitting up on jacks...)

    SIGH...

    (...only 731? There were a LOT more than that BEFORE the site was getting "scanned" by people stealing from Bennie and the Site members - and they sold their "catch" on eBay...Bennie used to post his findings every now and then to remind us...)

    Maybe I'll just exit now and be done with this...
     
    #5 Handy Andy, Nov 9, 2018
    Last edited: Nov 9, 2018
  6. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    But... I need info, Andy! I think I'm gonna cry! :(


    Seriously tho, any new info you may have on the PC-122 would be most welcome. Thanks! :)(y)


    ~Cheers~
     
  7. Handy Andy

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

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    Well, you can always look at Low-Boy's threads - that's an on-going process...

    Else if you have a need to talk- lets' talk! I'm open for something...
     
    ExitThirteen likes this.
  8. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    My biggest issue with it (and it's not really an issue, just an annoyance) is that LSB does not sound quite as clear as USB. The LSB is flat/bassy sounding, almost muffled, even when the TX oscillator IF can is properly adjusted. USB is robust, crisp, and clear. The radio just had a fresh re-cap of all electrolytic capacitors of proper values. Everything else on the radio works as it should. Any ideas?


    ~Cheers~
     
  9. Handy Andy

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

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    Tall order, is this is the only one that sounds like this?

    Have you owned other PC-122 / TRC - 453/465/485 and any other single conversion radios like this?

    There are minor variances amongst the parts in the chain, but I do find parts that don't always equal the schematic.

    Take a look at the AN612.

    SubtleDifferences.jpg
    This is where TX side audio is mixed in - not the RX side, but knowing this area helps you understand how the DE-conversion process works for the RX side of things.

    It's not just a simple tonal filter fix, because it's how the RF and IF are applied and where they meet, is what is deciphered and amplified...

    Like this example - I had to use the more common single conversion sections that use TP 5 as a baseline but you can see the more subtle differences in the application of IF as far as power level and strength to what is available to decode from the RF stream arriving from the IF's RX section.

    SubtleDifferencesRX.jpg

    Now, go into your radio and look for these parts above, you may or may not see the actual values listed above - so this is part of the problem we see a lot of times in the quality of RX performance and the overall flat tonal quality one side has over the other and why...

    SubtlePC122TP5.jpg

    I hope the above advice can help you get started.

    The reason for the differences - is really due to the IF and Clarifier IF zero beat and then the strength of both signals as they arrive to be used for the conversion.

    It's not even an answer but to answer your question requires a basic starting point.

    We can fiddle with part values, and even adjust IF - there is the problem - because both need to be adjusted to obtain an equal balance of tuning and frequency response. That actually goes back to the AN612 and how the Audio from Pin 1 arrives and how much is Pin 3 is used to "center" the audio into the passband. Once we see how that mixer works we can find ways to fix your problem.

    And we haven't even touched on the Crystal filter and its needs yet...

    You did say that you aligned the radio - so the best option I can give you is to look over the above sections of TP 5 the slices of the conversion sections from those radios. It can give you a clue as to what and how much resistor and capacitor values can be applied..

    IF you like the sound of one side, then you may need to "tweak" the IF of the PLL side to obtain the Zero Beat adjust and reentering needed to force the Audio from that particular sideband, into a better tonal peak response.

    Yes, I did say, adjust the PLL's IF side up or down in frequency, then readjust that corresponding coil for that mode to help offset - if you are not comfortable with that - that is ok - we may wind up needing to look for a part that has drifted off in values as age has taken some toll of the parts. On the Clarifier side...That deals with the audio side and with subtle changes in the 10.69MHz section for that particular mode, you can raise or lower he passband at the crystal filter for the tonal peaking curve that passes thru.

    Let me know how you're copying this so I can continue...
     
  10. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Hiya Andy, thanks so much for the response back, and I'll try to answer your questions in order!

    1) Is this the only radio that sounds like this?

    Yessir, the PC-122 is the only one that sounds like this. My other two radios sound great.

    2) Have you owned other PC-122/TRC-453/465 and/or other single conversion radios like this?

    Yes, I currently have a President P300 (Cobra 146GTL board), the PC-122 (Non XL) and a TRC-453.

    3) You mention adjusting the PLL's IF side, I have done this to try to change the tone, and re-balance, but it still sounds like my modulation is muffled, almost "overdriven". But only on LSB. USB is fine.

    Hope this answers your questions, I'll look into any components that do not match when I get home from work this evening. Is there any specific radio I should match components to? For instance, Is the TRC-453 better than the PC-122? Maybe the PC-122XL is better? Let me know.

    As always, I really appreciate your help! (y):)

    ~Cheers~
     
  11. Handy Andy

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

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    Ok, thanks for getting back with me on this...

    Since this is specific - that helps.

    In my repairs, I've found 4 different places that each one interacts with each other and can generate pretty much the same symptoms - two deal with the PLL side of IF and the other two deal with Audio Side.

    So to keep it short and sweet - you are given a spot or two to work with and use various values, but still there are reasons otherwise for the offset problems.

    (Disclaimer : Graphics used from CB Tricks and featured radios from their respective companies)

    The IF from PLL and Clarifier sides of a Cobra 146 ... SubtleCobra146GTLsm.jpg

    PC 122XLand Pro 810e ... But notice the changes to values C96, C97 and C98 used between the two...

    SubtlePro81eIF.jpg

    You can't really tell the differences between the Pro810e and the PC-122 XL - because both radios used that same chassis - but look harder at the Oscillator parts values used.

    SubtlePC122XLIF.jpg

    Then an oldie but a goodie - TRC-453...note also its' use of cap values in the Clarifier section...

    SubtleTRC453IFsm.jpg

    Why the difference, they are subtle changes in the tuning ranging from foil pad thickness onto the coil winds and their position of coil winds in the core of the can. Even the oscillators themselves use various cap values to achieve a level of drive or needed signal quality.

    So in each of the above, you can make changes to one mode to change the tuning and where the cores' inductance lands for your passband for audio. I do this to help the operator find "center slot" easier and in some cases for a larger level of clarifier Zero beat - as in once a heterodyne meets the audio signal coming in off of the IF the PLL uses for conversion - the slide itself tends to resonate and offer a better bandwidth where the receiver hears the audio with more fidelity for a greater length of slide allowing the "roundtable" to occur and the operator doesn't need to chase after all of them to listen in.
    XtalCF1resistor.jpg

    But why the above? Well it also comes from how the IF the PLL uses - passes the images thru the Crystal Filter and it's number of poles (Xtal elements) and their exactness to resonate a narrow range and only pass a specific range of frequencies. (Photos courtesy of Low_Boy)
    XtalCF1.jpg

    The above is a 4 pole unit, and note the use of 4 crystals and series of caps to pare down, narrow and sharpen the bandpass of whatever was being sent into it - note too - the 10.4MHz - that's the "center" peak of the filters' passband.

    The "colors" in the peak represent the offset tonal effects of the center IF carrier injection - Grey vertical line - while the pink is the noise and signal EMBEDDED in the image received. Red to Blue signifies the tonal range - Red Bass onto treble high-tones in blue - with most voice range in yellow for speech.

    So, if all things are equal - why the tonal change?

    Several things come into play, one being the TOLERANCE of the Xtals used. Not all crystals can be made to EXACTLY the same resonate frequency - so with the above in mind, you now have an issue of 4 times the poles and their own resonance affecting the signal. This increases the BANDWIDTH the filter unit now has, plus any overtone shift in frequency passage - lower or higher than expected. That means even the IF carrier is going to mix in with the audio signal generating a carrier and an artifact during the conversion process.

    So one mode give you nice sharp tones and clarity, but the other mode is slightly different - almost muddy sound - then that indicates the filter - although sharp - may not be narrow enough to remove any artifacts including it's own IF carrier image generated so the radio can select the signal out of all that noise.

    So therefore - you have some choices to make changes and allow the IF "centering" to be shifted to accommodate the less than ideal tonal bandpass for reception.

    I hope this helps...

    Mostly - due to the artifact, it will require experimentation of your part to find the right balance. They kinda' did the same thing back where the radio was made. At least IMO it's why they have parts like C100 - C102 in the 146 board, onto the C96, C97, C98 mess in others. In my research and repairs, these areas were the most likely to show values not corresponding to the schematic - but to variations in values to accommodate the parts and years these boards were made....
     
    #11 Handy Andy, Nov 10, 2018
    Last edited: Nov 10, 2018
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  12. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Sounds like the best two ways to go about fixing this is to change the crystal filter or change the cap values at C97/C98/C99.

    If this were your radio, what would you go after first? I know it’s a bit of trial and experimentation, but what would your plan of attack be on this particular radio? As always, many thanks for your help! (y)

    ~Cheers~
     
  13. Handy Andy

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

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    The Cap swap - and the tweak of the IF - both sides.

    I have some other options to try as you see fit. They work to a degree, but the region we are talking about is in the TR11 AF amp. That's the amp, that once the conversion or detection is done, takes it all in and sends it to the Squelch amp and then the Volume control - Audio Amp...

    It (this whole affair) also tells you to hold onto the older chassis for their IF cans for the 10.4MHz filter are worth gold for replacing others when it comes to parts you can't get like this anymore.

    Anyhoo...Even I went as far as a cap swap on the audio amp of the TP5 and AM detector - so the "tone" the ex-XYL heard was better for her hearing.

    TRC-453

    SubtleAFAmp.jpg

    Once the conversion is captured, it's up to the AF amp. It just amplifies what is there with a preset gain and tonal pass. Although she liked it for it's simplicity - she had a problem with hearing low flat tones - so the mod was done to "Brighten and lighten" the tone of the entire spectrum. So I've changed C25 as well as C26 to different values - lower ones, to lessen the bassy sounds present in even AM signals when the Clarifier was exactly centered on the carrier of the other operator she wanted to hear.

    Too low, the audio was weak, not enough oomph, or strength in dynamic range as well as fidelity - mostly with the Electrolytic cap C25. C26, if changed, can introduce a "hiss" from the conversion process if you use too low or no values there at all - it is a filter for the output of that AF amp.

    R37 and R39 play a role too - R39 is from the AM detector output. R37 is a bias and gain control for the Base. Other radios of this TP5 conversion style used different values. Use discretion.

    R39 handled the AM detector - in the above, it's a 220K but this value changes like the weather - I've seen 56K to as high as 470K~680K in some of the newer 465 and last of the PC-122XL series - you could tell when they were getting to the bottom of the barrel when it came to finishing out the production runs of the "XL" series - like they used everything even off the floor to finish up and empty the parts bins.

    C27 is a different horse of another color - in the schematic is a 562 (0.0056uf), but in real life - can be as high as a 0.047uF or a 473 disc. - you can play with this value too. This can improve the tone - for if there is too small of a value in there it loses the fidelity and inflections of tone. So you may also want to broaden the response curve here, changing that to any of the larger values that can fit in there, can make the radio more likeable to use. Careful though - this is a single conversion receiver and you will get noise in the receiver - this tight limiting cap and resistor combo is for the selectivity so it's also looks / uses a particular frequency of the converted/detected output to amplify - not many are tolerant of the limiting effects and nearly mono-tone-ish results this radio does to someone's signal.

    The Cobra 146 GTL uses - calls it, as C29 - and it's even larger...take a look...
    SubtleAFAMchanges.jpg

    So tailor it for your needs. Doing the C27 thingy may provide some better relief for those that use an external speaker - the cap swaps to larger values really does bring out the subtler tone inflections - especially on AM signals.
     
    #13 Handy Andy, Nov 10, 2018
    Last edited: Nov 10, 2018
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  14. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    Update:

    I changed out C98, which is tied to L20 (LSB). No change, was still muffled. Decided to change out the crystal filter, that DID give me some improvement, cleaned up the audio a bit. I also changed C25, from a 22uf to a 10uf. That also further cleaned up my audio, the radio sounds nice on LSB as it should, and I only had to adjust USB just a touch on both the sides to match it to LSB for audio tone.

    Many, MANY thanks to you, Handy Andy, for your in-depth knowledge and descriptions. You are more valuable than you'll ever know. Perhaps one day I can be of some help to you in the future. (y):)


    ~Cheers~
     
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  15. Handy Andy

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

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    Just keep your shop going until I can get back on the road to get there!
     

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