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My latest Madison Project

Discussion in 'CB Radio Modifications' started by loosecannon, Jan 8, 2018.

  1. loosecannon

    loosecannon Sr. Member

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    Hi all,

    Well, after completing the analog madison project, and spending a lot of time enjoying it; i began to get the bug to do a digital clock madison project.

    Since my last project involved modding pretty much every section of the radio, including bypassing the audio sections pretty much completely; i decided it would be neat to have a Madison that was essentially stock as far as the audio and RF sections are concerned.

    the only mods to the radio besides the addition of the freq. counter are that i added schottky diodes to the noise blanker section (i always do this), I made the AMC variable (they are not variable in stock form of a madison), and i upped a couple values of the electrolytic caps when i re-capped the radio for improved power supply filtering.

    I started with one of these chinese frequency counters that are available for about 10 bucks on ebay:

    20180107_144816.jpg


    It's size is pretty much perfect for the two screw holes that are left behind when you remove the digital clock module.



    You just need to make a couple of small metal brackets that will provide a hole on either side of the actual three digit LED banks. the two holes in those barrel nuts are 3/4" apart, so if you have some small metal blanks, just drill three holes for each one, with the holes being 3/8" on center.

    The barrel nuts that come with the counter boards are two long, and need to be replaced with barrel nuts that are half their lengths. this will push the actual LED displays further forward in the radio providing a better look.

    sorry i don't have pics with the faceplate off, i got too excited to see it completed and screwed the faceplate on LOL. I will remove it and take a few pics to add in to this thread.

    You need to use metal to make your brackets, and here's why:

    The multiplexing noise these counters create is pretty severe, and you can hear it in your receive all the time.
    By tying the PC board ground to the chassis ground at every point in the radio where i could, adding a shield to the back of the counter board, and filtering the DC in to the board with a 3300uF cap (seen on the back of the shield), i was able to knock this noise down to where it's barely audible, and can't be heard behind normal empty channel static.

    here is a pic of the back:
    20180107_144702.jpg

    In that pic you can see the shield, the electrolytic, and the wires that i ran to one of the tatile switches on the front, so i can turn the counter off if i want.

    since the barrel nuts on the counter board are connected to its PC board ground plane, and it is mounted using metal parts, there is no actual ground wire going to the counter board.

    that black wire you see coming off of the power plug on the board is just going to the electrolytic cap.
    I believe this had a great effect in lowering the noise.

    OK, here is a pic of the finished product:
    20180107_144528.jpg

    yes, i left the stock bulbs in the meter lights for a more vintage look. Here is a pic using a flash:

    20180107_144543.jpg

    Now for the caveat, since there will always be at least one when doing a project like this.

    If you choose to do this to your madison, you are going to find that even though the counter board fits pretty much perfectly into place, the actual display window in the faceplate isn't wide enough, and will cover the last half of the "hundreds" digit. (the zero on the right).

    You will have to carefully tape off the top and bottom of the magenta window on the back of the faceplate, and use a solvent to remove some of the black 'paint' on the right side. about 1/4" should do it.

    Be sure to use a solvent like mineral spirits that won't fade the magenta window material that is under the black paint. thank goodness they used a large enough piece of magenta film at the factory!

    The radio and counter work flawlessly! and it is a real joy to operate. I have to say that the sound of a JFET modded silver eagle D104 with a stock madison set right at 100% modulation sounds really good and this is probably going to be my main radio for this year.

    The only other thing i am planning on doing to this radio is to add a Channel King board, once i can get back in touch with the creator of those boards.

    I can't wait to use all those cool silver tactile switches on the front of the radio for all the functions of the channel king boards.


    aaaaand one more pic for good measure!

    20180103_201622.jpg

    this was a fun build, but it's not as simple as just slapping the thing in there.
    it definitely takes some finesse and a little custom work.

    hope you all enjoy!
    LC
     

  2. 309hellinois

    309hellinois Supporting Member

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    Looks great! I've been looking for one myself and wouldn't have much use for a clock anyway.
     
  3. Riverman71

    Riverman71 Sr. Member

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    Outstanding.
     
  4. StrangeBrew

    StrangeBrew Sr. Member

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    Nice!(y)


    If I find a Madison on Craigslist can I send it to you?:whistle:
     
  5. loosecannon

    loosecannon Sr. Member

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    Actually, yes.

    I would be willing to do an install of one of these for forum members, since it doesn't involve hacking the radio up, or drilling any holes in it, and the radio could be put back to stock if someone wanted to.

    It's not gonna be cheap though! LOL

    this ain't like installing an echo board or putting a swing mod in a radio!
    LC
     
    Shadetree Mechanic likes this.
  6. sonoma

    sonoma Sr. Member

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    Hey LC that looks good. does it track SSB on freq or does it have the off set in SSB mode? can you PM me the link to what part you used. would like to take a look at it.
     
  7. loosecannon

    loosecannon Sr. Member

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    #7 loosecannon, Jan 8, 2018
    Last edited: Jan 8, 2018
    tecnicoloco likes this.
  8. sonoma

    sonoma Sr. Member

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    thanks for the link.I have been going through cbtricks where Sue did a lot of postings over there. I am saving all the pages that she did postings on. some thing like 89 pages of her postings. I read some of what she had posted and only save it if there is any thing worth while. lots of good info there that could be lost if the site goes all the way down.
     
    tecnicoloco likes this.
  9. Low_Boy

    Low_Boy Well-Known Member

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    loosecannon... Very nice job.
     
  10. LeapFrog

    LeapFrog Sr. Member

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    Looks excellent LC, I'm glad more people are finding a use for the frequency counter modules.

    PLJ-8LED (8 digit)
    PLJ-6LED (6 digit)
     
    #10 LeapFrog, Jan 8, 2018
    Last edited: Jan 9, 2018
  11. nomadradio

    nomadradio Analog Retentive

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    Rock on!

    Nice job. Too bad it can't compensate for changing modes. We just set them for either AM or LSB, whichever the customer prefers.

    Learned to use plexiglass for the mount brackets. Takes care of the chassis ground-loop headache. Still had trouble with "zing" noises in the receiver audio. Fixed this by running the power leads to the big filter capacitor on the main pc board. We splice coax onto the input plug. A 470-ohm resistor goes in line with the center conductor where it taps off the radio's VCO test point. Reduces the risk that the counter's input circuit will reduce the PLL's drive level to the radio. The shield doesn't get grounded directly to the coax ground foil. We put a .001uf disc cap between the input-coax shield and the ground foil alongside the VCO test point. This prevents a DC ground loop from the input coax through the power leads.

    The SanJian PLJ-6LED counter is really handy. Came up with a way to "shrink" it to fit behind smaller front-panel windows. If you didn't catch that post, it's here ->> http://www.worldwidedx.com/threads/tram-d201a-digital-frequency-display-update.223694/

    Great work, looks good!

    73
     
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  12. loosecannon

    loosecannon Sr. Member

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    Thanks to all for the flowers!


    Thank you Nomad for the notes as well!

    That "ZING" noise that you refer to is the exact reason why i tied PC board ground and chassis ground together (which in the case of the Madison, allows you to remove two very long ground wires).
    Before tying them together, i indeed used phenolic for the mounting tabs.
    I found that the noise, even with the shielding, and the large electrolytic (i was up to 15,000uF and still noticing noise reductions with increases in capacitance) was still noticeable in the receive static.

    I added a 100pF cap in series with the center lead of the coax that i also spliced on to the RF input of the counter board. This didn't really do much.

    Honestly, as soon as the chassis of the counter board was connected to the metal chassis of the radio, which now provided the ground return, the noise went down by about 75%, without the big cap!

    Obviously it reduced more when i put the cap in place.

    My observations are that the RF portion of the counter doesn't produce any noise, whether using the two wires provided or changing them out for a length of coax.

    to me, it seemed that all the noise was coming right down the DC line because of the multiplexing.

    I might try the 470 ohm series resistor, just to see its effects. thanks for the tip!

    I never minded the counters showing the offset, but maybe some do.

    I have started making some videos of the radio, but i'm not happy enough with my production skills yet to post them on youtube. LOL

    I will have to do a video on the comparison of how much noise this thing made when i started as opposed to how little it makes now. It's really quite a dramatic change.

    was playing with the radio this morning, and found myself just turning the clarifier back and forth in order to see the counter digits change.
    I don't think i'll ever fully grow up! LOL

    LC
     
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  13. nomadradio

    nomadradio Analog Retentive

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    The best result we have gotten leaves the radio's two ground circuits isolated the way the factory built it. Depending on where the two grounds get joined, we have had ground-loop issues doing this.

    The noise is from the multiplex-switching of the six digits. Only one of them at a time is powered. Flicker fusion makes them all appear lighted at the same time. Every on-off transition of those digits produces a tiny pulse of RF.

    The DC circuit to the power leads goes to the big filter cap. A dropping resistor in the red wire helps, with the 47uf filter cap soldered directly across the solder side of the counter board, under the power socket. A 47 ohm 1/2-Watt resistor should reduce the heat load on the counter board's 5-Volt regulator. It also improves the filtering.

    The disc capacitor goes between the input coax shield and circuit-board ground at the RF tapoff point. The 470 ohm resistor between the radio's test point and the center wire of the input coax serves to prevent the radio's internal drive level from being loaded down by the input coax and the input diodes connected to the counter's signal input.

    Mounting the counter board on plastic brackets is how we kept the counter pc board's ground isolated from the chassis. We have used fiber shoulder washers under the screws on metal brackets, but it's more work than cutting a couple of pieces of plastic.

    There is nearly always more than one way to skin a cat. But this is what trial-and-error produced here, with the least multiplex noise leaking into the radio's audio.

    73
     
  14. loosecannon

    loosecannon Sr. Member

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    Nomad,

    I don't usually tie the grounds together in my, or other peoples' radios, but in this particular case, since it's the change that made the biggest difference in the noise level, i left them tied together while continuing the experimenting, and then just went with it.

    The madison in particular uses two really long skinny black wires to get the ground return around the radio, and it has always bothered me. sure, i will probably never notice a difference in the performance of the radio, but since it is mine, and bugged me, i chose to get rid of them in an attempt to get everything at the same potential.

    When i tied the grounds together, i made sure to do it all over the radio expressly because i was concerned about ground loops.

    the funniest part of this whole thing is that this radio has become my daily driver, and i have had a constant S-7 noise level for the past four months so i would probably not hear the noise from the counter anyway LOL.
    i think i'm just going to move. :D

    i have had a few people express interest in having me do this to their digital clock madisons, but as of yet, no one has liked the idea enough to pay for the custom work LOL.

    now if i can just get ahold of a channel king board from Mark I'll be all set!
    LC
     
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  15. Onelasttime

    Onelasttime Well-Known Member

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    That sounds cool. I have been wanting to play with one of those. I hear they got really hot and they can be really noisy! Looks like you already know about the noise.


    I recently acquired a Mint "could pass for new Cobra 138 XLR". It was used as a base so it looks absolutely 100%. I am thinking about installing a board to broadband the freq. coverage to the full practical limit of the uPD858. So a freq. counter is a must. I am going to use a project box for mine though.
     

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