PSK31 audio levels from sound card

[AC0FP]

What is the typical PSK31 audio output level from a sound card? Is this just card dependent or does the software you select cause this to vary?

73,

Frank
:)

[KB1JUF]

I think the level is more rig dependent than anything else. It depends on whether you apply the signal to the rig's mike connector or to any auxiliary connector on the back.

Sound cards typically have 1 volt peak output on line out jack which can be controlled by the microsoft audio contol panel or similar for other operating systems. If you are using a commercially made interface box or a homemade one, they usually have a level control on the front panel as well. If you are going straight from the sound card to the rig, you may need a resistor attenuator in line.

[AC0FP]

I think the level is more rig dependent than anything else. It depends on whether you apply the signal to the rig's mike connector or to any auxiliary connector on the back.

Sound cards typically have 1 volt peak output on line out jack which can be controlled by the microsoft audio contol panel or similar for other operating systems. If you are using a commercially made interface box or a homemade one, they usually have a level control on the front panel as well. If you are going straight from the sound card to the rig, you may need a resistor attenuator in line.

Thanks, I was interested in the sound cards line output. I have isolation transformers between inputs and outputs. I was working on a automatic PTT keying circuit using the line output signal. It looks like with a conventional diode rectifier circuit I would need a minimum of a 1.4 volt peak-peak signal. It looks like I may have to add an additional power source (wall-wart) to my interface box to run whatever circuit I decide on.

73,

Frank
:)

[K7JEM]

Thanks, I was interested in the sound cards line output. I have isolation transformers between inputs and outputs. I was working on a automatic PTT keying circuit using the line output signal. It looks like with a conventional diode rectifier circuit I would need a minimum of a 1.4 volt peak-peak signal. It looks like I may have to add an additional power source (wall-wart) to my interface box to run whatever circuit I decide on.

73,

Frank
:)

I built one using an NPN transistor, a diode, a resistor and 2 caps.

[AC0FP]

I built one using an NPN transistor, a diode, a resistor and 2 caps.

That's the conventional one I built also, to confirm it would take the theoretical 1.4 volts peak-peak to get it to work. I love simple but I still have concerns about that circuit.

I'm now thinking of going with a Opto-isolator for the PTT key.

73,
Frank
:)

[K7JEM]

That's the conventional one I built also, to confirm it would take the theoretical 1.4 volts peak-peak to get it to work. I love simple but I still have concerns about that circuit.

I'm now thinking of going with a Opto-isolator for the PTT key.

73,
Frank
:)

It worked OK with my sound card, turned up almost to the max. Keyed beautifully.

[AC0FP]

It worked OK with my sound card, turned up almost to the max. Keyed beautifully.

The circuit "keyed" (collector/emitter junction went low) just fine at an input level of 1.4 volts p/p. I was concerned about the circuit having to "steal" energy from the sound cards PSK's signal and whether that might cause distortion to the PSK31 signal before it was modulated by my radio!

There are a lot of circuit choices on how to do this one! :eek:

73,

Frank
:)

[K7JEM]

The circuit "keyed" (collector/emitter junction went low) just fine at an input level of 1.4 volts p/p. I was concerned about the circuit having to "steal" energy from the sound cards PSK's signal and whether that might cause distortion to the PSK31 signal before it was modulated by my radio!

There are a lot of circuit choices on how to do this one! :eek:

73,

Frank
:)

Just add a series resistor of about 1K. That will make the input impedance be 1K or greater. That won't load down any sound card.

[AC0FP]

Just add a series resistor of about 1K. That will make the input impedance be 1K or greater. That won't load down any sound card.

I will do some bread boarding. By definition the output impedance of a commercial "line output" is 600 ohms, therefore I would need a 6k to 10k resistor in series with the base of the transistor to feel comfortable. With this circuit you also have a hard ground between your radio and the computer.

I'm shopping for a opto isolator to try but my parts bin came up empty! :o

73,
:)

[K7JEM]

I will do some bread boarding. By definition the output impedance of a commercial "line output" is 600 ohms, therefore I would need a 6k to 10k resistor in series with the base of the transistor to feel comfortable. With this circuit you also have a hard ground between your radio and the computer.

I'm shopping for a opto isolator to try but my parts bin came up empty! :o

73,
:)

You really need to keep the ground potential between the computer and the radio the same, anyway. The computer case is always grounded to the electrical ground, the HR care should be also.

What I did for the audio was a series 10K, then a 1K pot to ground, to set level to radio. That reduces the voltage at the top of the pot to around 140 mV P to P, which is more than enough to run into the mike input. Between the series 10K on the audio side, and the series 1 K on the keying transistor, the impedance seen by the computer is close to 900 ohms, or more.

Joe

[AC0FP]

You really need to keep the ground potential between the computer and the radio the same, anyway. The computer case is always grounded to the electrical ground, the HR care should be also.

What I did for the audio was a series 10K, then a 1K pot to ground, to set level to radio. That reduces the voltage at the top of the pot to around 140 mV P to P, which is more than enough to run into the mike input. Between the series 10K on the audio side, and the series 1 K on the keying transistor, the impedance seen by the computer is close to 900 ohms, or more.

Joe

I indicated I had 600:600 ohm audio transformers for the audio. I'm glad to hear you got by without audio transformers.

My original question as to what is the average output level of a sound card is still unanswered though. Although maybe I should qualify that, since its adjustable, with the qualification of having low distortion at a given output level! :p

73,

Frank