OVER 130% MODULATION!!!

[loosecannon]

thanks for the reply Xit13, and the others too! i love when these things get discussed.

i reason i asked about the mod to your madison is precisely because i wanted to know if you did the NPC mod with the cap or if you did something different.

ive done the cap thing before too, and i found the audio to be a bit "mushy".
not distorted, just mushy. LOL

i do appreciate seeing how you did your AMC also! i will be doing mine the exact same way.

anyone ever done Justin Depolis' version using the 1000uF cap (in a different location)?
LC

 

[Shockwave]

When you say "mushy" do you mean it lacked treble or brilliance? That's what I would expect a capacitor with a reactance of 5 ohms at 3000 cycles to do in that location.

 

[Robb]

When you say "mushy" do you mean it lacked treble or brilliance? That's what I would expect a capacitor with a reactance of 5 ohms at 3000 cycles to do in that location.

Since that cap is only in the audio chain, at that point the range should easily exceed 3kcps and go below 5 ohms. Wouldn't the audio IC see that as a dead short @5kcps at that point and fry it? Not sure what you are saying here.

 

[Shockwave]

Almost Rob. The audio bandwidth of that board will not reach 5000 cycles because the high frequency negative feedback loop limits it to around 3000 cycles. That keeps both sidebands in the AM TX bandwidth within 6 KHz. Just running these simple numbers we can see the loading ranges from very little if any around 300 cycles and a near short at 3000.

That why I say the loading device should be a resistive voltage divider whose resistance will not change with the frequency applied. Furthermore, the resistive divider will take the negative loading off the IC and place the AF voltage drop across a resistor.

 

[Robb]

Almost Rob. The audio bandwidth of that board will not reach 5000 cycles because the high frequency negative feedback loop limits it to around 3000 cycles. That keeps both sidebands in the AM TX bandwidth within 6 KHz. Just running these simple numbers we can see the loading ranges from very little if any around 300 cycles and a near short at 3000.

That why I say the loading device should be a resistive voltage divider whose resistance will not change with the frequency applied. Furthermore, the resistive divider will take the negative loading off the IC and place the AF voltage drop across a resistor.

Could you diagram it and show how to implement its use?
That could be a first for the WWRF. . .

 

[loosecannon]

Shockwave, thats exactly what i mean. it also seemed to lack the clarity that would have been provided by less high freq roll off. at least thats how it sounded to me.

after years of trying different audio mods to CB radios, it seems like most of them will increase your PEP, but dont really do anything to add more actual modulation. by that i mean the loud punch that makes the listener have to turn their volume down when you key up.

for example, ive run my DX929 for years with an NPC mod, dual finals, and the "RWOB". the PEP swing was awesome! but since going back to stock (just for fun) and just a good tune up, the audio itself is noticeably louder to my ears.

the way i would describe it is "more present in your ears".

doing this has changed the way i think about audio mods. i still do NPC mods for people because thats what they want, and they sound good when they leave my shop, but for my own radios, im going in a different direction.

i imagine many of us have found this out over the years; im just a late bloomer i guess. LOL
LC

 

[ExitThirteen]

I've been pretty fortunate. I played AM only for about a year or two before I got into SSB. And yeah, I was like most typical CB'ers on AM, everything turned to the right, all limiters out, full tilt boogie. That changed real quick after I got into SSB and discovered that clean and clear is really the only way to go. Now I set all my personal radios to 100% on the scope and call it a day.

I do like experimenting and modding radios tho, never know when a person could stumble onto something good!

However, if there is a way to mod a CB radio so asymmetrical modulation can be produced correctly, I'd be all for that, even tho I seldom talk on AM.


~Cheers~

 

[Robb]

I do like experimenting and modding radios tho, never know when a person could stumble onto something good!

However, if there is a way to mod a CB radio so asymmetrical modulation can be produced correctly, I'd be all for that, even tho I seldom talk on AM.

I agree . . .

 

[w9cll]

I've been pretty fortunate. I played AM only for about a year or two before I got into SSB. And yeah, I was like most typical CB'ers on AM, everything turned to the right, all limiters out, full tilt boogie. That changed real quick after I got into SSB and discovered that clean and clear is really the only way to go. Now I set all my personal radios to 100% on the scope and call it a day.

I was the same way, had a tricked out Cobra 1000gtl till I switched to SSB and never looked back.

 

[dave457]

Phase Rotator

 

[Captain Kilowatt]

Phase Rotator

I'll see your phase rotator and raise you one symetripeak.

 

[ExitThirteen]

ive done the cap thing before too, and i found the audio to be a bit "mushy".
not distorted, just mushy. LOL

Makes sense that it would sound "mushy", since you're "compressing" the negative peaks of your modulation. The "mushy" sounding audio is a byproduct of this.

Great examples of this are Turner +3, +3B, and Super Sidekick mics, and any Magnum radio that uses the CP-1 speech compressors. They all tend to have that muddy, flat, bassy audio, because of the compression. I had this exact problem with my Magnum 257, people did not like the sound of the radio, they kept complaining about "muddy, flat, bassy" audio, on AM and SSB. I discovered that the radio had the CP-1 compressor in it, so I removed the compressor, and with no other changes, the same people told me my audio was much better, night and day difference.

Your observation comes as no surprise.


~Cheers~

 

[Robb]

Makes sense that it would sound "mushy", since you're "compressing" the negative peaks of your modulation. The "mushy" sounding audio is a byproduct of this.

Audio compression uses positive peak compression; not negative peak compression. If too much compression is applied to a limited audio bandwidth (like 3kc's wide), of course it will sound >squished< or 'mushy'. Sure sign of too much compression; but it is the threshold that starts too early that causes that.

IIRC, the AM Limiter is actually a positive peak limiter type of compression, which means that once the gain reaches a certain threshold compression takes place at a 4:1 ratio. I've been trying to find out how to change the upper threshold of limiting by finding out which part to affect in the AM Limiter circuit. Perhaps Shockwave can figure it out.

Some Turner mics have an adjustable compression threshold. Others have it fixed.

 

[Captain Kilowatt]

Normal audio compressors do indeed use positive peak compression. As for the Turner +3B sounding mushy. WHAAA??????? My old +3B always gave me great unsolicited reports. Nice and clear I was always told. Stock radio BTW. No funky modulation or power swing mods.

 

[ExitThirteen]

Interesting, I have learned something new then! I always believed that audio compression compressed both positive and negative peaks and compressing only the negative side could potentially have the same "muddy sound" as compressing the positive side. I stand corrected.


People locally around here don't like the sound of Magnum radios or the Turner mics I mentioned, nobody uses the Turner mics, and if a local gets a Magnum radio, it usually comes across my bench to have the CP-1 compressor circuit yanked out of it. Too many complaints of muddy, flat, bassy audio. It's probably the fact that most of the locals around here run primarily SSB, and since SSB runs a narrower bandwidth than AM, it's probably a bit more noticeable.