OVER 130% MODULATION!!!

[loosecannon]

Nice Work Xit13!

this looks very cool, and you've provided the scope pics for all the naysayers!

im guessing that you connected the .22uF cap and the 22uH coil to the same points that the 10uF electrolytic connects to?

which side was the coil on? not really sure that it matters, but thought i would ask since im going to be trying this once my madison is up and running again.
(yes im doing major upgrades to the radio i already upgraded LOL)

this time im setting it up for external modulation using a PNP modulator circuit, and line level out for the receive audio. i will still use it with a normal mic sometimes so this mod will be cool for that.
im also putting heatsinks all over the place so that i can keep it keyed for long periods of time. maybe i'll start a radio show! :w00t:
the loosecannon radio hour has a nice ring to it!
LC

 

[ExitThirteen]

LC,

On my Madison, they go to the same places that I had pointed out in a previous post. I soldered the capacitor to pin 9 of the audio IC, soldered the choke inline with the capacitor, then soldered the other end of the choke to the junction of D63/R194/R228.


I just installed this in my Madison, and I get just about about 140% positive peaks and 100% negative peaks after I did a slight tweak of the AMC to get it right on the scope. Here's a couple pics of the results below.

First pic is a 2W deadkey on the scope.

Second pic shows the radio modulated. Shows 140% positive and 100% negative with nothing pinched or cutoff. Now I know what you're thinking, "Why does the waveform look so weird?" Reason for that is because I modified the mic audio circuit to increase the frequency response curve. I tried to get it matched as close as I could between the low and high response, but it looks like I'm off just a touch on the high end. The studio mic shows it about perfect tho, which is why I'm not going to mess with it. I used a stock mic for this particular test.

Enjoy.


~Cheers~

 

[johnny9]

i thought my old tram d201 had the best modulation

great thread i feel im learning a lot no doubt..are those old bird meters better than any of the newer stuff they sell" just curious so if i buy one" ?
and man if i could learn to use a occiliscope id be a hi tech redneck

you called it a bird 43a,but it says bird 10a,,must be the amps? trying to learn lol..

 

[Captain Kilowatt]

BTW - I use the same scope . . .

I just realized that I do as well. Didn't realize that until I was just in the shack moving things around and picked it up and thought it looked familiar. Tektronix 465 100MHz. Works nice.

 

[space cowboy]

well this thread turned out better than I thought it would. lots of interesting info.
did you go on air with it ExitThirteen? or listen to it yourself? how did it sound?
I've got a Tektronix 465 too,.

 

[ExitThirteen]

I did get it on the air, and reports I got back were very positive, most of the locals said it sounds like a radio announcer's voice with a little extra punch on the audio. I'm going to do a little more experimenting on the Madison, but in all reality, it's really close to where I want it to be. I have a buddy of mine who's general class ham, and he's pretty picky about how the audio should sound, and he liked the audio quality of the radio, so I feel if I can impress him, it's worth something.

Keep in mind that I use a Shure SM-58 studio mic, so it's going to have a different sound than a D104, a hand mic, or a Turner. It kind of has its own unique sound to it.


~Cheers~

 

[Robb]

I did get it on the air, and reports I got back were very positive, most of the locals said it sounds like a radio announcer's voice with a little extra punch on the audio. I'm going to do a little more experimenting on the Madison, but in all reality, it's really close to where I want it to be. I have a buddy of mine who's general class ham, and he's pretty picky about how the audio should sound, and he liked the audio quality of the radio, so I feel if I can impress him, it's worth something.

Keep in mind that I use a Shure SM-58 studio mic, so it's going to have a different sound than a D104, a hand mic, or a Turner. It kind of has its own unique sound to it.


~Cheers~

Impressive.
Cool beans, dude!


*EDIT*
Did you use 'Goldfingers' audio TX/RX cap changes for the audio too?
Did that to my Uniden Grant, and still am impressed with it.

 

[ExitThirteen]

I only used part of the Goldfinger's mods. Only changed 2 caps in the TX audio, none in the RX audio.


Also did some more experimenting, and I believe I have it the best I can possibly get. So let me get some pics and I'll post them shortly.


~Cheers~

 

[ExitThirteen]

Ok, here's the latest test results from my experimentation.

First pic is the radio with a 2W deadkey on the scope.

Second pic shows the radio at full modulation. On this test, I removed the choke that I had installed with the .22uf non-polarized cap from the previous mod, and I installed JUST the non-polarized cap. Also, I added a second .22uf non-polarized cap in parallel with the first one for a total of .44uf. I changed R228 from a 560 ohm to a 1.2K ohm resistor, and then readjusted the AMC accordingly. This is what I got.

Interesting to note that when I removed the choke, the waveform went back to normal when using the 1khz tone, but what was more impressive is the positive peaks, they now show 180%! Negative is still at 100% with no clipping or pinched off waveform.

This time, I used the studio mic for this test. I called up my neighbor friend of mine and asked him if he could give me a radio check on AM and SSB. His response on AM was, "Best that radio's ever sounded, and it sounded great before." He told me SSB sounded like it always did, great audio, with no changes. SSB output remained unchanged @ 17W.

I'm going to do more "on the air" radio checks and see what other people think, but my neighbor loved the audio, and he's been following me on my journey with this whole experiment, so he knows what to listen for.

Right now, the changes I have currently done to get this far, is change R228 from 560 ohms to 1.2K ohms, and put (2) .22uf non-polarized mica dipped capacitors in parallel between pin 9 of the audio IC and the junction of D63/R194/R228.

Hope you folks enjoyed the experiment as much as I did.


~Cheers~

 

[GnG8d]

Can you do some 2 tone or audio tests?

 

[Robb]

Looks like ~180% modulation by what the O'scope shows.
Nice!

 

[johnny9]

very nice! wish you would have wired my mic lol.

 

[loosecannon]

very cool Xit13.

i will be trying this soon. how did you determine the new value of R228? just curious why you doubled it instead of just raising it 20% or so.

your results speak for themselves, i just like to know the work involved.


im thinking that this DEFINITELY needs to be tried on a bone stock (with an alignment) old style 148 or something. with scope pics of course.

LC

 

[ExitThirteen]

LC, I experimented with different values of R228, but it doesn't start showing any significant results until about 1K ohms. If you just change the value of R228 alone, it shows a small amount of compression on the negative peaks, which allowed me to "open up" the AMC a little further before I would start to see any clipping. I figure if I left R228 at 1.2K, and then did the capacitor mod, this would allow me to open up the AMC a little more and gain more on the positive peaks, while retaining good compression on the negative peaks, AND still allow the AMC circuit to do its job.

(Edit) What I really need to do, is to see how this performs using a mic that most people would probably use, which is most likely the venerable Astatic D104. I would probably be safe in saying that the D104 is probably the most common desk mic that's used on bases. I know that not everyone uses one, just saying that it's probably more common. But I should see how a D104 would perform with this mod. Might look into that next week when I get time.

359, I tried to do a two tone test, but I'm using an old B&K 1040 Servicemaster for a two tone output, and it needs some help. I guess I could do a short video on the phone and post that doing some normal modulation (talking).


~Cheers~

 

[Robb]

So, a .47uf silver-dipped mica cap will do the same thing so that only one cap can be used too - I suppose.