Hello John, Technology is changing this concept. I was recently "re-educated" on this topic after returning from a ham radio hiatus. Like you, I grew up on the principle you mentioned in your message, the transmit dial frequency is the Mark frequency.
This statement is no longer true or false! The answer to what your dial is displaying is... "it depends"! In the old days, you would log and spot a RTTY station using the dial frequency. This was because FSK was generated by switching a small capacitance in and out of parallel with the main VFO capacitor. The Drake equipment (T4X, TR4, and RV4) had a solder tab sticking out the side of the VFO "can" for this connection. Your dial frequency WAS your Mark frequency and you shifted 850 Hz or 170 Hz lower when the external capacitance was switched into the circuit. Today, the modern transceiver dial frequency may indicate the suppressed carrier frequency, the Space frequency, the Mark frequency, or whatever you want (in some cases). There doesn't seem to be any consistency among the manufacturers, and in some cases within the same manufacturer. For a particular transceiver, you may be able to determine what the dial frequency is from reading the operations manual, but sometimes not! You can determine what a transceiver is doing by dialing in 28.100 MHz and transmit in RTTY. Using an external frequency counter or receiver, you can then find your FSK Mark carrier. It may be the same as the dial or not. It's a crap-shoot! Here are some examples why the newer technology has become a quagmire... My Kenwood TS-450 transceiver dial frequency IS the Mark frequency. This is described on Page 38 in the operations manual. The dial displays the Mark frequency, independent of the shift width or polarity. Likewise, the Ten Tec Orion II displays the Mark frequency when operating in FSK mode. But there are a variety of other systems... My Kenwood TS-950S (and TS-950SDX) transceiver dial frequency displays the SPACE frequency. This is described on Page 32 (Page 36) in the operations manual. It shows the Space frequency independent of the shift width or polarity. The dial frequency will be off by 170 Hz, hardly noticeable by most operators. I also have an Icom 756 Pro III. The operations manual is vague regarding the relationship between dial frequency and Mark frequency in this transceiver. I can't find a specific statement in the book, but from experience it appears the dial frequency is the suppressed carrier frequency. The Yaesu FT-920 throws yet another layer of configuration possibilities. This transceiver allows you to program the dial frequency to display Mark, Space, or the Center frequency! See Page 56 in the FT-920 manual which describes Menu Item U-45. Likewise, the FT-1000MP provides menu 6-3 which allows the user to set the transceiver displayed frequency to their choice. The default setting is to display the Mark frequency. See Page 54 of the operations manual. With the introduction of computer soundcards being used to generate RTTY tones, transceivers without FSK capabilities can now be used for digital communications. In this case, the dial frequency is the suppressed carrier frequency. The transceiver has no clue what tones are being broadcast through its audio chain! The contesting (N1MM) and logging (DXKeeper) software I use in my station have provisions to adjust to any method of FSK or AFSK frequency logging. Once you know what your specific transceiver dial is telling you, you can adjust these software so it logs and spots the exact Mark frequency. Welcome to the digital revolution! 73 de Bob - KØRC in MN ----- Original Message ----- From: John Becker To: [email protected] Sent: Thursday, May 17, 2007 8:14 AM Subject: Re: [digitalradio] VFO Dial Frequency, Audio Frequency, Centre Frequency At 01:36 AM 5/17/2007, you wrote: >It has been long usual to define the frequency of an RTTY signal as the >RF frequency of the mark tone. And so on. Really ? In my 37 years I have always seen it given as dial frequency. Reason: RTTY has fixed tones - never changes. Therefore if you give the dial frequency there is no math to be done just tune and go. You will be right on.
