I can attest to the AM broadcast guys doing it for years. Even the FCC mentions positive peak modulation in excess of 100% in their broadcast regulations. We have been running positive peak modulation of 120% since before I started in 1983.
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OVER 130% MODULATION!!!
- Thread starter space cowboy
- Start date
I can attest to the AM broadcast guys doing it for years. Even the FCC mentions positive peak modulation in excess of 100% in their broadcast regulations. We have been running positive peak modulation of 120% since before I started in 1983.
And the best part is... it WILL sound good. It has to be done correctly, but it WILL sound good. 
~Cheers~
~Cheers~
Yup.....loud is the word. Negative mod is what cuts the carrier off and causes distortion and splatter. Positive modulation determines loudness. You should see and feel 20Hz at 200% positive mod. I had modulator issues with a transmitter hitting bass notes one time. That was a good test for it. LOL
Shockwave, I've never seen a scope inperson only in pictures. Are you saying if the peaks in picture two were flat at the top the modulation would be over modulated? are those peaks showing an over modulation of the audio signal or would the peaks on the scope be flat at the top ?
"Asymmetrical Modulation" Is not straight forward basic modulation. The enhanced peaks come from increasing the rf power output on the positive going peaks. Yes the negative peaks are suppressed, but if you modulate a standard CB radio your positive peak will be limited. My S45HP schematics show the RF power being adjusted by the modulator circuits.
I was just looking at the scope pics you posted here on the R228 mod for a 148/ 8719 madison mod. you stated you put a 1.2K ohm resister and a 1UF cap at position R228. did you put them in series to get the effect you did or was the 2 items parraleled?
I have a tr296F I am thinking about trying this mod on and just want to clarify the part positions before I mess with it.
Thanks
Sonoma
I have a tr296F I am thinking about trying this mod on and just want to clarify the part positions before I mess with it.
Thanks
Sonoma
The 1.2k ohm resistor replaces the 560 ohm resistor at R228, so remove the 560 ohm and install the 1.2k ohm in its place. The 1uf capacitor goes from pin 9 of the audio IC to the junction of R228/D63/R194.
~Cheers~
~Cheers~
Remember too to lower the dead key to 2w, and make sure you have a stout AM Regulator in there.
Update:
I have since upgraded the AM pass regulator to a TIP41C per Sonoma. The TIP41C is a very stout transistor and is the best replacement for the 2SC1419 (some radios use the 2SD1135). Running my asymmetrical modulation/NPC mod combined with this AM pass regulator results in the pass regulator barely even getting warm with heavy modulation/ragchewing on AM.
If anyone plans on doing my Asymmetrical/NPC modulation mod, I recommend using the TIP41C instead of the 2SC1061 or the NTE-152.
~Cheers~
I have since upgraded the AM pass regulator to a TIP41C per Sonoma. The TIP41C is a very stout transistor and is the best replacement for the 2SC1419 (some radios use the 2SD1135). Running my asymmetrical modulation/NPC mod combined with this AM pass regulator results in the pass regulator barely even getting warm with heavy modulation/ragchewing on AM.
If anyone plans on doing my Asymmetrical/NPC modulation mod, I recommend using the TIP41C instead of the 2SC1061 or the NTE-152.
~Cheers~
Whats up loosecannon?
I know these postings are older, but is there something on the scopes wave fourm that's letting you know the Madison's modulating over 100% or is there another piece of equipment out of picture that's letting you know the percentage?
If not what exactly about the wave forum on the second scope picture is letting you know what percentage of modulation is being achieved?
I know these postings are older, but is there something on the scopes wave fourm that's letting you know the Madison's modulating over 100% or is there another piece of equipment out of picture that's letting you know the percentage?
If not what exactly about the wave forum on the second scope picture is letting you know what percentage of modulation is being achieved?
Here's a picture to illustrate what CK is referring to. Granted, this is a little extreme, as the positive peaks are in excess of 150%. However, the negative peaks are around 100% with no clipping or unusual waveform. It IS possible to achieve over 100% modulation.
This first pic is a carrier of 2 watts, no modulation.
The 2nd pic is the carrier modulated.
This was done on a President Madison with the MB8719 SSB chassis. No modulation limiters were removed, and I maintained full adjustability of the AMC circuit. This is a form of asymmetrical modulation.
(Edited in carrier pic, thanks CK!)
~Cheers~
my Raido has the " The illudium Q-36 explosive space modulator! " The Best but it is olny available by M.T.M,,,,,,,
Man, gotta say that I really like this thread. It taught me a lot, and I really appreciate that. It destroyed some myths I've collected, and in that process I've learned more and found new questions to be answered. Thanks!
Xit13: is it possible to use a 2SB754 or 2SB817 instead of the NTE152 with your mod?
Or are those parts well beyond any possible benefit/use for these Uniden radios?
Xit13: is it possible to use a 2SB754 or 2SB817 instead of the NTE152 with your mod?
Or are those parts well beyond any possible benefit/use for these Uniden radios?
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