--- In digitalradio@yahoogroups.com, "Gmail - Kevin, Natalia, Stacey & Rochelle" <spar...@...> wrote:
> > DM780 through the sound card to Kenwood TS-480S/AT, in the data socket. > When I start DM780 and look at the screen, waterfall I see the data mode, in this case PSK31 on 14.081.5, but the radio is showing 14.080. > I remember when I first was using PSK31 I could see other stations within the window of the waterfall, they could of been on 14.082.5 or 14.080.6 and that I was able to leave the radio freq alone and just click on the other station and then make a contact. > What I was interested in, is, should I have moved the radio freq. to pull the station onto the 1.5Khz above the. (Don't know if I explained that correctly) Unfamiliar as I am with the TS-480, when you are using the data mode I guess it is choosing a particular bandpass filter, and probably setting the transceiver to lower sideband as well. That bandpass filter might be narrow, like 500 Hz. So what you see on the waterfall is 500 Hz of spectrum that is centered maybe 1.5 KHz below the dial frequency. Or maybe not. It is more usual in the digital modes to always use USB, and to use SSB mode so you get the filter that is about 2.8 Khz wide. Then if the transceiver dial is set to 14.080 you will see on the waterfall frequencies above that by the amount indicated on the waterfall frequency scale: maybe 500 to 2500 Hz, meaning actual frequencies of 14.080500 to 14.08300 And you point and click with the mouse to choose a PSK signal in that range. One problem then is that if you are trying to copy a weaker signal and a very strong signal comes on nearby the strong signal will cause the receiver AGC to cut down the gain of the receiver, so that the weaker signal is cut down also to where you can barely see it. Hence you would rather have a narrower filter, such as the one you use for data mode, to separate the signal you are trying to copy from the nearby strong signal. And you could tune the main tuning so as to push the strong signal off the edge of the filter, one side or the other, while keeping the desired signal in the passband. > > Also there is heaps mentioned about NO ALC, I have set my TS-480S/AT to the requirements for digital mode, and even dropped the input down further. > I was still getting some ALC when in TX. No-body said I was producing a bad signal so I don't know if I was TXing right. > Should I set the radio up as stated and then drop back the audio out from the soundcard? There are two potential problems with transmit audio level. One is that there might be an amplifier ahead of the gain control in the radio - this is very typical if you are going in through the mike connector rather than through the back panel connector. If you overdrive this amplifier it creates distortion products, and since it is ahead of the gain control knob there is nothing you can do with that knob to eliminated the distortion. The remedy is to cut down the sound card output from the computer, either with the computer volume control or with an attenuator between the computer output and the radio input. The other problem is that PSK requires no ALC. Many other digital modes such as RTTY and MFSK do not have this problem as they transmit only one tone at a time; but PSK is effectively a two-tone signal. This one you can control using the gain control on the radio, just turn it down until the ALC goes to zero. Also you want to be sure that any speech processor is turned off, as this distorts the waveform too. Jim W6JVE
