[Elecraft] K2 Problem in NAQP

[Richard Ferch]

I suspect that at least part of the discrepancy is due to the following 
fact: The frequency on the radio's display and the frequency actually 
being transmitted on in RTTY are not always the same, depending on the 
radio and the mode it is being used in.

K3: In FSK D and AFSK A modes, the K3's dial displays the actual Mark 
frequency of an RTTY signal (provided you tune the signal to match the 
PITCH setting in these modes, i.e. so the Mark audio tone is 2125 Hz 
when the PITCH is set to 2125). However, in DATA A, the K3 displays the 
suppressed carrier (or BFO) frequency. Since DATA A is upper sideband, 
in DATA A the actual transmitted Mark frequency would be 2.295 kHz above 
the displayed frequency, assuming MMTTY is using the default 2125/2295 
tone pair (reversed because of the sideband choice). The same is true in 
USB mode. On the other hand, in DATA A-REV and LSB, the actual 
transmitted Mark frequency would be 2.125 kHz below the displayed frequency.

K2: This I am not sure of, but my first guess would be that the K2's 
display in RTTY mode is the suppressed carrier frequency (like the K3 in 
LSB mode).

FT-950: The frequency displayed will probably depend on the mode being 
used. If the FT-950 was in FSK (RTTY-LSB) mode, then I believe it would 
display the actual transmitted mark frequency. On the other hand, if it 
was in AFSK (PKT-LSB or PKT-USB) mode, it would likely display the 
suppressed carrier frequency, unless the radio's packet frequency 
display offset has been changed from the default (0).

Most RTTY software these days has the capability to perform the 
arithmetic (suppressed carrier plus or minus audio mark tone) so that it 
automatically logs the correct transmitted Mark frequency. In MMTTY, if 
you are using the "Radio command" feature, you can set the frequency 
offset to OFF (e.g. for FSK), LSB, or USB to have the program perform 
the required frequency adjustment in the log.

The offset you observed was somewhat different from the expected 2.125 
or 2.295 kHz. A couple of possibilities spring to mind. Perhaps the 
frequency calibration is off on one of the radios, or perhaps one of you 
was not using the default audio tones (for example, if you fine-tuned by 
clicking in the MMTTY waterfall).

The best way I can think of to sort this out is to set MMTTY to its HAM 
defaults and turn AFC off, then tune the radio to an RTTY signal on an 
accurately known frequency (e.g. W1AW bulletins) and observe the radio's 
dial reading versus the published frequency.

73,
Rich VE3KI


W0EM wrote:
> in the process we found
> that on both bands his radio (FT-950) is receiving and transmitting 2.69 Khz
> below my frequency.  My K2 and K3 transmit and receive to each other on the
> same frequency.  We tried changing various settings in his and my radio's
> and in N1MM and MMTTY at his location and mine with no change.
>
> It sure would be wonderful if someone could shed some light on this latest
> head scratcher.