OVER 130% MODULATION!!!

[LeapFrog]

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?

I guess my question is: what part has the most headroom in place of the original?

And no this is not a literal question. I can swap parts out if I want to try and figure it out, I understand wanting to save time and energy before ordering parts.

Thank you gentlemen for contributing to the thread, WWDX & the hobby!

 

[543_Dallas]

I guess my question is: what part has the most headroom in place of the original?

And no this is not a literal question. I can swap parts out if I want to try and figure it out, I understand wanting to save time and energy before ordering parts.

Thank you gentlemen for contributing to the thread, WWDX & the hobby!

Lower the carrier and use a bigger amplifier. Gives you more headroom the honest way.

 

[LeapFrog]

Lower the carrier and use a bigger amplifier. Gives you more headroom the honest way.

I forgot about the "s"-wing word and decided I'd study more on "text-book A.M.", I have a lot to learn.
To me the honest way is with clean modulation, not with flat topping or pinching of the negative peaks. We all know anyone can lower the carrier on a radio like the Cobra 29 LTD (cap/resistor), and see some massive "AAUUDDDIIIOOOO" "Swang" out of it with a cranked VR, but it's not honest in my eyes, even if the microphone gain is turned down enough to "sound good n' loud".

But as long as the needle swings forward and sounds good, 75% of people will be happy with that. I guess "getting louder" means different things to different people, I can see how an under modulated station with more ERP could drown out and cover a "loud n' clipped" radio with less power.

It just seems like cheating to crank that VR and watch the thing go crazy (29 LTD/amp combo) on a watt meter/scope! All with the same PSU, AMP, MIC, etc, etc!!.
And getting the louder audio from the increased modulation alone, is an added bonus that make some "black hat" operators turn a blind eye to the 'scope!

I think the whole line "it swings forward, & sounds good/loud" is a total cop-out and should not be the end of examining how somebody setup/runs an AM station, well I guess some CB'ers care more than others, but I don't know.

I just like to talk on the blasted things, I sure am glad I found WWDX!
(This forum helps many people)

Thank you
-LeapFrog
73

 

[543_Dallas]

I forgot about the "s"-wing word and decided I'd study more on "text-book A.M.", I have a lot to learn.
To me the honest way is with clean modulation, not with flat topping or pinching of the negative peaks. We all know anyone can lower the carrier on a radio like the Cobra 29 LTD (cap/resistor), and see some massive "AAUUDDDIIIOOOO" "Swang" out of it with a cranked VR, but it's not honest in my eyes, even if the microphone gain is turned down enough to "sound good n' loud".

But as long as the needle swings forward and sounds good, 75% of people will be happy with that. I guess "getting louder" means different things to different people, I can see how an under modulated station with more ERP could drown out and cover a "loud n' clipped" radio with less power.

It just seems like cheating to crank that VR and watch the thing go crazy (29 LTD/amp combo) on a watt meter/scope! All with the same PSU, AMP, MIC, etc, etc!!.
And getting the louder audio from the increased modulation alone, is an added bonus that make some "black hat" operators turn a blind eye to the 'scope!

I think the whole line "it swings forward, & sounds good/loud" is a total cop-out and should not be the end of examining how somebody setup/runs an AM station, well I guess some CB'ers care more than others, but I don't know.

I just like to talk on the blasted things, I sure am glad I found WWDX!
(This forum helps many people)

Thank you
-LeapFrog
73

When I said lower the carrier maybe I should have said reduce the output?

You can lower the carrier and not resort to over modulation. The idea is to have enough headroom that the positive peaks and even the occasional overshoots will not flat top. If you cut the carrier back and still run the same pep power you haven't gained any headroom.

When I said bigger amp I didn't necessarily mean for more power but for headroom. Running both the radio and amp at half throttle will usually lower imd substantially.

 

[LeapFrog]

When I said lower the carrier maybe I should have said reduce the output?

You can lower the carrier and not resort to over modulation. The idea is to have enough headroom that the positive peaks and even the occasional overshoots will not flat top. If you cut the carrier back and still run the same pep power you haven't gained any headroom.

When I said bigger amp I didn't necessarily mean for more power but for headroom. Running both the radio and amp at half throttle will usually lower imd substantially.

Agreed 100%, the correct way does not use "super-modulation", I just think it's funny that many stations are setup in a 'hap-hazard quest for swing' and not really done in a more controlled manner, It takes a special operator to be concerned with IMD and to minimize the chance for interference is the NEW proper way to be "loud"! haha.

The Cobra 29 super-modulation crew (clipped limiter crew) knows how to get loud, just not in a real clean way!

Lowering the output, 'de-tuning' the radio is the cleanest way. I like how you explained it 543.

A.M. can be ran so many different ways, I need to go read some books!

 

[543_Dallas]

De tuning isn't usually a good way to lower output. Think of cranking the plate tune knob on an amplifier to reduce output.

With a ssb rig you usually have an am carrier adjustment. Most AM only radios do not. You have to lower the collector voltage to reduce power without improperly tuning the radio.

 

[LeapFrog]

De tuning isn't usually a good way to lower output. Think of cranking the plate tune knob on an amplifier to reduce output.

With a ssb rig you usually have an am carrier adjustment. Most AM only radios do not. You have to lower the collector voltage to reduce power without improperly tuning the radio.

Perhaps the phrase "de-tuning" can mean different thing depending on the angle taken, yes I see what you are saying about an AM carrier adjust on the SSB radios, turning down the carrier and checking the modulation is what I mean, on the AM only high level transformer modulated final rigs the process is much more touchy/tricky/involved and I could see how "de-tuning" carries with it a negative connotation.

Especially when the common belief seems to be: "Set it below two watts & let 'er swing", it's all in how the tune is done!

I once set up a TRC-427 with a TIP31C/TIP120 variable carrier and 1uF cap, the radio would put out a lot less, and sounded good with a little help, barefoot though it was quit, very quit. The guy didn't seem happy because his linear didn't "swing good" I cannot explain to him that he will get good audio and relative clean signal without the swing, he didn't care the high peak numbers and meter swing are all he wanted, who am I to try n' change his outlook..

IMHO It takes much more on a 29 ltd than a 148, to "de-tune" the radio, however that word means to you. I could see a little proto-board and some additional components to change the nature of the radio, as long it all comes out clean in the end... Adding parts or just "tuning" are two different things obviously, some one has a 29 out there with a nice variable carrier adjust and low level modulation scheme modification, a lot more involved than just turning down a 148.

 

[Sonar]

This is Midland's version of the GE Superbase. Exact same board in both radios, the "double-sided" PLL02A SSB chassis. Stay away from these like the plague unless you're just going to buy the radio for AM use only, or to put on the shelf as a collector's item. I've had several of these and the GE Superbase models come across my bench, all with the same issue, SSB problems. Some had no TX/RX, like this one, other has problems with SSB "bouncing frequency" under modulation. They look neat, but unfortunately, their performance is less than spectacular.

~Cheers~

I'm surprised. I've never owned the super base or the mobile version but have heard that both are worth the premium they usually fetch on eBay. One learns something new every day.73

 

[Shadetree Mechanic]

I read this a long time ago before I became a member. Just read it again. Good stuff here.

 

[Captain Kilowatt]

A request was made to reopen this thread and after a lot of cleaning in the spirit of the holiday season I agreed. This is not something that will become the norm. Just too much editing and cleaning to be bothered.

 

[ExitThirteen]

So, final update on the asymmetrical modulation mod:


For the double conversion MB8719 chassis (Cobra 2000, 148, President Madison, President/Uniden Grant):

Change R228 to a 1.5k ohm.
Solder a 1uF, non-polarized capacitor from pin 9 of the audio IC to the junction of R228/D63/R194.
Replace the AM pass regulator with a TIP41C.
Set your deadkey to 1.5~2W.

You'll also need to re-adjust the AMC to set your negative peaks so you aren't clipping. This HAS to be done with a scope.


For the single conversion MB8719 chassis, I have all that info on a previous post on this thread, on page 7. Only difference is instead of using an NTE152 or a 2SC1061 in place of the stock 2SC1419 AM pass regulator, replace instead with a TIP41C.

This mod will net you about 180% (or slightly better) positive peaks. Results will vary slightly depending on radio. Output will range (depending on where you set deadkey) from 10-14W peak output.


Have fun and enjoy.


~Cheers~

 

[Sonar]

So, final update on the asymmetrical modulation mod:


For the double conversion MB8719 chassis (Cobra 2000, 148, President Madison, President/Uniden Grant):

Change R228 to a 1.5k ohm.
Solder a 1uF, non-polarized capacitor from pin 9 of the audio IC to the junction of R228/D63/R194.
Replace the AM pass regulator with a TIP41C.
Set your deadkey to 1.5~2W.

You'll also need to re-adjust the AMC to set your negative peaks so you aren't clipping. This HAS to be done with a scope.


For the single conversion MB8719 chassis, I have all that info on a previous post on this thread, on page 7. Only difference is instead of using an NTE152 or a 2SC1061 in place of the stock 2SC1419 AM pass regulator, replace instead with a TIP41C.

This mod will net you about 180% (or slightly better) positive peaks. Results will vary slightly depending on radio. Output will range (depending on where you set deadkey) from 10-14W peak output.


Have fun and enjoy.


~Cheers~

How does one figure out weather they've got the single or double conversion rig (Madison?) I always thought all Madison's were double. I'd be surprised to find out my Madison was single conversion. It receives so nicely.
I'm going to assume some outboard audio gear (eq, and studio mic) will help ones audio reach the desired "HiFi" effect after the mods are completed?
A most excellent and straightforward modification. Thanks for sharing.

 

[loosecannon]

Sonar,
single conversion means that there is one IF (intermediate frequency. 7.8mhz in this chassis) and double conversion means there is another IF frequency added (455khz in this chassis).
the schematic is the best way to determine whether a certain radio has just the one, or two IF stages. (some older ham rigs of the same vintage as our beloved classic CB radios had triple conversion receivers)
oh, and all 8719 madisons are dual conversion. the upd858 madisons were single.
LC

 

[Sonar]

Sonar,
single conversion means that there is one IF (intermediate frequency. 7.8mhz in this chassis) and double conversion means there is another IF frequency added (455khz in this chassis).
the schematic is the best way to determine whether a certain radio has just the one, or two IF stages. (some older ham rigs of the same vintage as our beloved classic CB radios had triple conversion receivers)
oh, and all 8719 madisons are dual conversion. the upd858 madisons were single.
LC

I knew that! Lol.

 

[LeapFrog]

I knew that! Lol.

I love my 142 GTL even though it's only a single conversion receiver; it sure talks well!