In article ,
AB7RU wrote:

As part of the transmitter alignment on my Icom751a, I need an Audio
frequency generator supplying tones at 1.3, 1.9 khz at 3mV - is there
software out there that will do this? I have found some audio
generator software but haven't seen where you can set the mV level
any help is appreciated! thanks, Mike AB7RU

There's no universal way to do this, since PC sound cards don't have
consistent output levels. Full-scale-digital output signals are often
at 1- or 2-volts peak-to-peak on the line-level output jacks, but
they're often at different levels depending on the PC's sound chip,
amplifiers, whether there's a headphone amp involved, etc.

In one case I encountered (my Dell Latitude CPxj) turning the PCM-out
control all the way up to full scale resulted in horrible digital
clipping of the signal, *before* the sound interface's master volume
control. I had to turn the PCM output level down to about 30% to get
a clean sinewave output.

The best I can suggest is that you generate the tone that you need
using the PC software you have, feed the line- or headphone-level
output from the PC sound card to an analog volume control (a 1k or 10k
audio-taper pot is probably a good choice), and use a reasonably well
calibrated oscilloscope or DVM to measure the resulting voltage and
trim it to 3 millivolts (P-P or RMS, depending on what the calibration
procedure asks for).

I'd recommend using a 'scope, to confirm that you're actually getting
a clean signal.

It's best to measure the actual signal level "in circuit", with the
PC/generator and the attenuator driving the rig's transmitter. If you
measure first and then attach to the rig, the rig's input impedance
may shift the level enough to perturb your calibration procedure.

--
Dave Platt AE6EO
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