SSB Carrier Supression

[Nigel Goodwin]

Ha Ha. I'm still working on the amp. I got a whole 3 watts so far. I'll let you know.

Is that 3W of carrier leakage, or 3W of modulation?

 

[Space Varmint]

Is that 3W of carrier leakage, or 3W of modulation?

Well, change that. It's now 5 watts of clean output. No spurious emissions with even over modulation. If the is no audio in I cannot see any carrier on the scope or pick it up on my receiver.

 

[Space Varmint]

I'm up to ten watts now. I see a little bit of spurious emission probably some power getting into one of the driver stages. Got to work on grounds and shielding.

 

[kchriste]

Originally Posted by Mikebits
What is your criterion for working great? What sort of test equipment have you used to verify your circuit?

My criteria is an attentive well trained ear and eyes. My equipment is cheap as they come. a 40MHz scope and a voltmeter and any signal generator is an oscillator built by muy and homebrew receiver.

Well, change that. It's now 5 watts of clean output. No spurious emissions with even over modulation. If the is no audio in I cannot see any carrier on the scope or pick it up on my receiver.

How do you know this without a spectrum analyzer or equivalent equipment? I'm sure your alien ears cannot hear all the way up to 300Mhz. How can you have "over modulation" of SSB without clipping and how can you have clipping without spurious emissions? Maybe now is the time to add an ALC circuit to the mix.

 

[Space Varmint]

How do you know this without a spectrum analyzer or equivalent equipment? I'm sure your alien ears cannot hear all the way up to 300Mhz. How can you have "over modulation" of SSB without clipping and how can you have clipping without spurious emissions? Maybe now is the time to add an ALC circuit to the mix.

I got the audio gain backed down to where you literally have to scream in the mike to clip.

Without a spectrum analyzer I have to look as the cleanliness of the wave shape.....a well trained eye.

 

[kchriste]

I got the audio gain backed down to where you literally have to scream in the mike to clip.

So you are not over modulating then?

 

[Space Varmint]

Here is one apparently none of you know:

Carrier when completely suppressed in the balanced modulator becomes more of an issue in the filter and ground loops.

Of course I ask many questions of which I never get an answer. But usually one person knows one or two things and think that's all you need to make a radio

 

[xanadunow]

I think - in the correctly wired marriage of a "ballanced modulator + filter" system, there is not much of the carrier to speak about and it is well outside of the filter's passband.

 

[Space Varmint]

I think - in the correctly wired marriage of a "ballanced modulator + filter" system, there is not much of the carrier to speak about and it is well outside of the filter's passband.

OK, give me the DB spec and I will let you know.

 

[Space Varmint]

Dern it! I just got a K3N from West By God VA. He said my signal was jumping around alittle and sort of distorted but he said it was strong which is confusing. I'm showing about 5 watts out if I get right up on the mic. He heard everything I said and repeated it back though.

I figure whats happened, is I was right up on the mic trying to get more power out so I can see a little distortion, the jumping around of frequency could be over loading the modulator causing the oscillator to swing some. I may need to buffer it but I think if I just back off the mic it will be OK. I need more power. I couldn't get much out of this MRF477 running single ended. About 10 watts max.

 

[flat5]

"Scotty, I gotta have more power"

 

[audioguru]

He said my signal was jumping around a little and sort of distorted

Yeah.
The audio circuit for transmitting has the same circuits with extremely high distortion as the circuits in the radio receiver. I think I spotted a filter that cuts off all audio frequencies above 89Hz.

The transmitting frequency might be wandering all over the place like the BFO frequency in the receiver.

Maybe the transmitting audio needs a compressor circuit so that loud speech produces full power without the severe distortion of clipping.

 

[Space Varmint]

I found an inductor with too many turns and reduced it and my power jumped up to about 20 watts but it wants to feedback. Got to find and fix again.

 

[xanadunow]

spec

just google XF9A for your tx and XF9B for your Rx and .. browse some more in the "library"..

 

[xanadunow]

Alternatively,

please look how it is done today; Icom 7700

 

[xanadunow]

Bfo

The 1st IF, is usually quite high - it can very sucessfully be locked at frequencies of 60MHz and over audioguru.

It is the 2nd (or even third) IF where you really shape the performance, and again - if you are stable enough to "lock" the frequency of 60MHz.. would you find yourself wondering about @9MHz, 500kHz.. or even less, if you're required?

This is where your BFO does come in - in CW, and it is very much xtall locked on SSB..

xanadunow

 

[Nigel Goodwin]

This is where your BFO does come in - in CW, and it is very much xtall locked on SSB..

Only if it's designed right!

 

[xanadunow]

Clipping, limiting, e.t.c

When you transmit the audio signal, you are concerned with maintaining the power to "pass the message" in the most efficient manner.

There are only two ways to do it.

You need to employ, both the pass band filter to limit the range of audio frequencies and the compressor to effectively control the level of modulation. Distortions do come in with the compressor - but "pass the message" is the bottom line, hence you do have to live with it and make somwhere the "cut" balancing these two requirements within the compressor.

As it is a serial arrangement, i.e. flter/compressor - do follow each other; would you get caught at - which one of these two would be first in line following the input from the mic?

Regards,
xanadunow

 

[xanadunow]

Right

Right, thanks Nigel

 

[audioguru]

Years ago, I did boardroom tele-conferencing. Customers asked if I could make the speech sound clearer. So I measured the frequency response of a typical telephone line and found the response at 3kHz -10dB to -12dB lower than at lower frequencies.
I complained to Bell who said it was normal. The limit is -15db at 3kHz.

So I built equalizers to boost 3kHz to 3.5kHz +10dB and the customers said it sounded crisp and clear. Every equalizer I demo'd was sold.