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

[Space Varmint]

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.

Hey guru? If your still around, can you give me a quick estimate on the output impedance. I'm getting ready to wind the transformers for the ballanced modulator.

 

[flat5]

The "HW8 Double Sideband Mod" page

His photographs are professional too.

 

[Space Varmint]

The "HW8 Double Sideband Mod" page

His photographs are professional too.

You like that flat? I was looking for contact info. I wanted to compliment his page.

 

[audioguru]

Hey guru? If your still around, can you give me a quick estimate on the output impedance. I'm getting ready to wind the transformers for the ballanced modulator.

The output impedance of an opamp is its output resistance (50 ohms) divided by its internal gain. Its internal gain is about 1000 at 1kHz with an external gain of one, or 100 with an external gain of 10. So its output impedance is 0.05 ohms to 0.5 ohms at 1kHz.

Its output impedance is less at lower frequencies and is higher at higher frequencies.

 

[Space Varmint]

The output impedance of an opamp is its output resistance (50 ohms) divided by its internal gain. Its internal gain is about 1000 at 1kHz with an external gain of one, or 100 with an external gain of 10. So its output impedance is 0.05 ohms to 0.5 ohms at 1kHz.

Its output impedance is less at lower frequencies and is higher at higher frequencies.

Wow! That is low. Thanks man. That's one for the note book.

 

[Space Varmint]

OK got my double sideband. It has excellent carrier suppression. At least twice "full quite" or 120 db down. The rest can be done through the crystal filter or an attenuator before the post mixer amp. I need to shape that carrier wave a little. Looks like excessive loading even though I'm bringing it out through a Darlington. I tried to match the impedances as closely as possible. That's two specs by guru, the 2nd being the low audio impedance. Looks he was right on.

The transformers are Amidon FT-37-43's.

 

[JimB]

At least twice "full quite" or 120 db down.

That is a large amount of carrier suppression, can you explain how you measured it?
Also, what is "full quite", and if it is "full" how can you have twice as much of it.?

The rest can be done through the crystal filter or an attenuator before the post mixer amp.

The rest of what?
OK the crystal filter will remove the unwanted sideband and contribute maybe 10dB or so to carrier supression, but what is "the rest" ?
"or an attenuator" ? what are you expecting an attenuator to do for you? improve the carrier suppression? please explain how it will do that.

JimB

 

[Nigel Goodwin]

That is a large amount of carrier suppression, can you explain how you measured it?

Using simple home made transformers, and (presumably) unmatched diodes - quite remarkable

 

[Space Varmint]

That is a large amount of carrier suppression, can you explain how you measured it?
Also, what is "full quite", and if it is "full" how can you have twice as much of it.?


The rest of what?
OK the crystal filter will remove the unwanted sideband and contribute maybe 10dB or so to carrier supression, but what is "the rest" ?
"or an attenuator" ? what are you expecting an attenuator to do for you? improve the carrier suppression? please explain how it will do that.

JimB

Yeah Nigel, your supposed to match them, but really not necessary.

How did I know the suppression? Estimated for now. Read voltage peak to peak levels. Seen it enough times.

"Full quiet" is 60 db down. It might be kind of a slang radio term. But it is still used fairly often like in PLL when talking about the level of the first phase sidebands. They should be atleast 60 db down.

Yes an attenuator can add to suppression. After the mixer (post mixer) the signal is created with two signals, by attenuating unwanted components from one, it is possible to eliminate them from the composite result.

Yeah that is allot of suppression. That's a good circuit. Thought I would share that with you. I've used them before.

 

[JimB]

Yeah Nigel, your supposed to match them, but really not necessary.

How did I know the suppression? Estimated for now. Read voltage peak to peak levels. Seen it enough times.

"Full quiet" is 60 db down. It might be kind of a slang radio term. But it is still used fairly often like in PLL when talking about the level of the first phase sidebands. They should be atleast 60 db down.

Yes an attenuator can add to suppression. After the mixer (post mixer) the signal is created with two signals, by attenuating unwanted components from one, it is possible to eliminate them from the composite result.

Yeah that is allot of suppression. That's a good circuit. Thought I would share that with you. I've used them before.

Well, what can I say!
I am in awe of your grasp of the art of radio engineering, I salute you.
You will be entered into the electro-tech-online hall of fame along with such lumiaries as mstecha and walters.

JimB

 

[Space Varmint]

Well, what can I say!
I am in awe of your grasp of the art of radio engineering, I salute you.
You will be entered into the electro-tech-online hall of fame along with such lumiaries as mstecha and walters.

JimB

Do they have one? Will they send me a plack or trophy or something? Tell them I'd rather have the cash.

 

[ecerfoglio]

At least the audio amp has its supply decoupled

 

[Space Varmint]

Right now I have another concern. The dern balanced modulator is loading the piss out of my carrier signal. I picked up harmonics and crap. Got to shape it up before I tackle that filter.

 

[Mikebits]

Yeah Nigel, your supposed to match them, but really not necessary.

If the diodes and baluns are not matched then it is hardly a balanced modulator is it? Your output will be unpredicatble.

Your best option is to purchase a off-the shelf mixer/modulator.

 

[Space Varmint]

I had the change that amp. So not sure if I have the same suppression but ready for filter. Here's a pic of the DSB. The mic was a little close to the speaker.

https://www.mediafire.com/file/zkzymkt5zr5/Dbl_SB.MOV

 

[Space Varmint]

If the diodes and baluns are not matched then it is hardly a balanced modulator is it? Your output will be unpredicatble.

Your best option is to purchase a off-the shelf mixer/modulator.

Ask yourself what is balanced? There is no control gate so we couldn't be talking about hfe as in Push-Pull amplifiers. I believe it is the diode internal capacitance, thus notice how I worked them.

 

[Mikebits]

Ask yourself what is balanced? There is no control gate so we couldn't be talking about hfe as in Push-Pull amplifiers. I believe it is the diode internal capacitance, thus notice how I worked them.

The diodes have to be matched so they turn on and off at the same time, without this symmetry your output will be full of spurious signals. The in out impedance must also be matched. Without this you have an unbalanced modulator/spur generator.

Most RF designers use off the shelf mixer/modulators as they understand the pitfalls of building their own. They leave it to the experts.

 

[Space Varmint]

Did you look at my sample? That's just the double sideband. Wait until I get it to single.

I know what the envelopes should look like. I don't ever put out spurious anything.

What ya do is pause it. Catch it where there is allot of modulation but where it is not clipping. Like I said, the mic was too close to the speaker. You will see near perfect symmetry and no spurious signals. I do know what you are talking about and have had this one do that. It has to do with the bias threshold of carrier/modulation.

 

[Space Varmint]

Here's a couple of DSB samples:

**broken link removed**

This looks like a two tone test:

**broken link removed**

 

[Mikebits]

Hardly looks like a two tone test. Also looks very clipped.
**broken link removed**