[RTTY] FSK and ft-1000mp

[Kok Chen]

On Mar 11, 2005, at 5:11 AM, tgstewart at pepco.com wrote:
> It's been a while since I've messed with PSK, but what's the 
> convention on that mode?

What we know as BPSK31 and BPSK63 (the double rate BPSK31) are really 
encoded as a differential phase shift.  I.e., it is changes in phase 
(by 180 degrees) that encodes a bit and not the absolute phase itself.

As such, you can use either USB, LSB or anything you like.

That said, the most often seen behavior on the Cluster is to use USB 
with zero offset (i.e, using the USB "voice" mode with the VFO dial 
showing the suppressed carrier frequency).

You will typically see spots on the PacketCluster like

14071 + 1040.

What that means is that the VFO dial is at 14071 kHz, and the tone of 
the audio PSK is at 1040 Hz (a little confusing because of mixed 
units).  Thus, the actual PSK carrier on the RF spectrum is at 14071 
kHz + 1040 Hz or 14072.040 kHz.

Most often, PSK is operated today using the "Digipan mode" that Skip 
KH6TY introduced and changed PSK31 forever.  Skip also was the one who 
introduced PSK63 by double clocking the A/D converter.  What you see 
with Digipan is a "waterfall" of the spectrum with the frequency scale 
showing the audio frequency from 0 to 3 kHz or something like that -- 
and therefore the preference for USB.

With LSB, if you hear a tone, the actual RF carrier of the PSK will of 
course be at a negative offset from the dial, i.e., if your VFO dial is 
at 14071 kHz and the audio PSK tone is at 1040 Hz, then you would spot 
it at

14071 - 1040 or 14071 - 1.040.

I.e., the higher the audio PSK carrier is, the lower on the RF spectrum 
the signal an be found at.

The use of any other VFO offset than zero is rather confusing, to the 
point that for my own homebrew software, I have added settings where I 
can set what my receiver's VFO mode and offset are, and the program 
generates a waterfall with a that is "corrected" to match.  With LSB, 
the waterfall spectrum runs backwards, with negative numbers showing on 
the waterfall scale.  If, in addition there is a VFO dial offset on the 
rig, the waterfall scale shows both positive and negative numbers.

BTW Ty, Ian G3SEK had pointed out that the FT-1000MP series is true 
FSK.  I have confirmed Ian's findings and had traced the FSK keying 
signal of my older (not Mark V) 1000MP right to the DSS chip of the 
rig.  The FT-990/1000/1000D series are however "keyed FSK" -- there is 
an internal AFSK generator, and even a small pot on one of the boards 
of those older rigs for adjusting the maximum AFSK level.  So, the 
current understanding for the Yaesu line is

FT-990/1000/1000D  -  Keyed FSK
FT-1000MP  -  True FSK
FT-1000MP Mark V  -  Most likely True FSK
FT-920  -  Don't know.
FT-9000dx  - rich people don't need to read schematics :-).

73
Chen, W7AY