Shure Mike Model #444 ??? / Freq scheme SSB

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Why do you want to attenuate your audio as that is what you want to pass. Your reasoning makes no sense.
 
Space Varmint said:
How much audio do you think I need? You guys amaze me. So I am supposed to transmit the full fidelity of a symphony orchestra though 2 KHz? I'm in stiches...lol.
Click to expand...

We're all in stiches at yet another complicated badly designed circuit

As suggested, you don't need the transistor - a better opamp (correctly wired) would be good, but also add a proper speech bandwidth filter. A double opamp, and no transistor, would make it all perform so much better.

To pickout one particular useless component, what's the capacitor from the inverting input to chassis for? - think carefully before you answer, assuming you do? - I notice you've just ignored any previous questions completely.
 


Easy, that one got rid of the rest of the local broadcast station.
 
You people really read far too much into a simple speech amp. As long as you push the PTT button and it picks up everything around you. It works. I have plenty of more serious concerns in processing this signal.
 
Broadcast AM radio has a bandwidth of about 4kHz and it sounds pretty bad.
A telephone has a bandwidth of 3kHz and it sounds worse.

Your radio does not have a bandwidth of 2kHz, it sounds like 200Hz.
No highs and no lows. Just a quack sound and narrow-band noise.

Your many wrong value coupling capacitors and very distorted audio circuits have ruined the clarity of speech.

The frequency of your BFO seems to wander all over the place.
 

You guys are a hoot. What is the frequency response of the mic? Call it a compensation network. Actually I won't know what the final design will even look like until I have had a chance to listen to it.

Actually the .1uf coupling cap was very deliberately done. I do not want any clipping but as always, if someone gets too close to the mike it will clip. So the attenuator (.1uf) gives me the level I desire. If I were to use a series resistor then we are looking a band pass filter. Without a resistor the frequency response will be much broader.

I suppose I can give a listen when I have my double sideband out. But that will not be the final frequency. I will have to mix it again after the Xtal filter to obtain true SSB.
 
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Nigel Goodwin said:
No, it does nothing, it's on a virtual earth point.
Click to expand...

I think the cap on the non inverting pin lowers VG noise which would couple to the output. Imagine a changing VG, __~~__~~___
I am thinking the cap gives a VG more like ______

Thoughts?
 
Mikebits said:
I think the cap on the non inverting pin lowers VG noise which would couple to the output. Imagine a changing VG, __~~__~~___
I am thinking the cap gives a VG more like ______

Thoughts?
Click to expand...

Because it's a virtual ground point there's no signal there for it to do anything to - try sticking a scope on that point

The capacitor is completely pointless, and just another random placing of an inappropriate component - presumably he was attempting to create a low pass filter with the input resistor?, but the (lowest quality possible) opamp prevents that.
 

I have to disagree here. It may be virtual ground, but a ground, virtual as it may be, that has noise will be coupled onto the output. The cap will keep the virtual ground clean from noise that would otherwise be amplified.

Everything is relative to the VG.
 
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Consider this. If VG moves a microvolt, the output will follow. Now if the microvolt change occured periodically then the output of the amp would follow. this would equate to noise.
 
Mikebits said:
I think the cap on the non inverting pin lowers VG noise which would couple to the output. Imagine a changing VG, __~~__~~___
I am thinking the cap gives a VG more like ______

Thoughts?
Click to expand...

Oh, that's what the hell that was. That is too slick! Mike you got a way about you dude. I'll go back & take a look. It is to a bare minimum almost ziltch. But that is funny

So Mike knows transmitters too.

I'm gonna run this by you, and tell me what you think.

Got some 4MHz Xtals.

So 10Kz audio minus 4.010MHz = 4MHz LSB (Lower Sideband). Run that through the Xtal filter then mix onto, 40 meters.

So I got a BFO about ready to do USB $ LSB but mostly concerned with LSB for now. Got to keep him very stable but will use VFO for now.

So after the Xtal filter of 4MHz, an 11MHz oscillator mixed with the 4MHz LSB filtered through a 7MHz (40 Meters) band pass filter to output.

Remember, this is low budget which is what I want, but do intend it to be a high quality output signal.

You opinion Mikey????
 

Did you read my post about the local AM broadcast? Once again, I live within a mile of a broadcast station who signal is so predominant that I can touch my frequency counter to the ground of anything or several other points including my own skin and read 750KHz. I can watch the modulation of Shawn Hanity on my scope probe touching it anywhere, and that guy is a dope! Got to get rid of him....lol. That's what that capacitor is for.....Gee Wiz! How many times do I have to say it? It's cheaper than chokes.
 

By Golly! How did you find that? Wish I had gotten it earlier. Notice though, the spec sheet, isn't really clear on the PTT connection. I mean on the 8 pin connector. I think the center pin is a general common for the PTT MOM switch. Seems to work anyway.

I looked at the ham guy's coupling caps and considered them but let's see what this sounds like first. But that is a neat article isn't it? Very ingenious.
 
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It's in the wrong place - that's no place to fit a capacitor - how did you come to place it there, blind chance?.

No one ever mentioned chokes, did they?.
 
I think the lousy old 741 opamp has no gain at 750kHz so the nearby radio station causes the VG input to be a fairly high impedance so the 750kHz is not attenuated without a capacitor to ground.

EDIT: Three cheers for wideband audio.
 
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