This is an often encountered problem. "What frequency is my signal when I am using [insert mode here]?" is the subject of at least one license exam question in US Amateur Radio tests.
In the US, government agencies and the military specify frequency by the center of emission. For example, in military 3581 would for LSB voice (nominally of 3 KHz BW) require a carrier (dial) setting) of 3582.5 KHz. Digital modes, especially sound card modes,should be addressed in a similar manner, and with some of care. A dial setting of 3580 KHz, with operation in USB mode, would require a waterfall operating frequency of 1,000 Hz. There are reasons to use a lower carrier frequency and a higher waterfall; 3588 and a 2,000 Hz waterfall choice would reduce any radiation of harmonics of the audio input. Overdriving an audio stage does not produce an ALC reading, but it can add significant harmonics to the signal actually transmitted. Keeping audio sent to a rig to the lowest practical level consistent with SNR (where the noise is hum, hiss and the like) we reduce harmonics, but it's worth keeping an eye out for. If you want your net on 3581, you'll need to specify as above; 3580 USB 1 KHz waterfall, or 3589 USB 2 KHz waterfall both produce a PSK signal at 3581 KHz. Regards, Cortland KA5S > [Original Message] > From: Kent VE4KEH <pb232...@mts.net> > To: <digitalradio@yahoogroups.com> > Date: 12/30/2008 10:29:17 AM > Subject: [digitalradio] Specification of Frequency for Net Announcement > > Our ARES group is having difficulty specifying an operating frequency for a PSK31 net. Is there any website which explains the relationship between the actual signal frequency, the transceiver frequency, the audio (waterfall) frequency, USB and LSB for digital operation?
