Thanks for the clarification Ray.
I was responding to Jim's question about how to tell the difference between an FSK transmitter and a SSB transmitter using AFSK to modulate it; using his terms. I related how switching a capacitor into and out of the L C of a VFO-multiplier-amplifier transmitter was Frequency Shift Keying. Using a SSB transmitter with Audio Frequency Shift Keying tones into the audio input creates a pseudo-FSK signal. If the carrier suppression of the SSB transmitter is not adequate, you can hear (and see using the wonderful SDR-1000 panadapter) the third frequency (carrier). If the opposite sideband suppression is not adequate, you will also see the mirror-image of the audio tone. This is a way that you can tell if the transmitter is pseudo-FSK using AFSK tones. Then there's the issue of distortion by over-modulating the SSB transmitter with too much mic gain. AFSK originally referred to using a shifting audio tone into an AM or FM transmitter, used on VHF because it is not legal on HF. The advantage was that you didn't need high stability or accurate tuning to decode the RTTY signal, as you were not using a BFO. Mike - AA8K Ray Andrews wrote: > > Mike, > > You wrote: AFSK is not legal on HF. > You are only partly correct. Part 97 does not use or define the term > AFSK, only RTTY & data. If you refer to AFSK as feeding audio tones > into a SSB transmitter, then it would be either emission type J2B (RTTY) > or J2D (data) both of which are legal on HF. Refer to 97.3(c)2 > & 97.3(c)7 for the definition of data & RTTY emissions respectively. > These paragraphs specifically include emission type J2D for data and > emission type J2B for RTTY. The table in 97.305(c) specifies that RTTY > & data emissions are authorized on all HF bands. However, if you are > referring to AFSK as modulating an AM or FM transmitter, then it would > be emission type A2B, A2D, F2B, F2D, G2B, or G2D. These emission types > are not included in the definition in 97.3 for data or RTTY emissions > and are therefore not legal on HF. > > The FCC recognizes that using a properly adjusted SSB transmitter to > generate a pseudo-FSK signal (as you call it) is indistinguishable from > a "true" FSK signal generated by shifting the carrier frequency and > therefore allows J2B & J2D emissions to be used wherever F2 emissions > are authorized. > > 73, Ray, K9DUR > > _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
