[GreenKeys] The things I worry about.

[Ralph Mowery]

When running the sound card (audio input) to a ssb transceiver  there are 3 
ways the frequency has been described in the past.  The first is the acutal 
MARK frequency as read by a frequency counter or such .  The second and not 
very common is to split the mark and space frequencies, that is the 
frequency that is in the middle of the two tones.  The more perferred way is 
to use the dial frequency of the transceiver, but only if using the MARK 
frequency of 2125 Hz as fed into the transceiver while operating in the 
Lower Sideband  mode.  If using USB or some other tone for the Mark, then 
you have to recalculate the 'dial' frequency.  If using the 3 rd method, you 
set your audio input for a 2125 Hz mark frequency, transceiver to  lower 
sideband, and the Space tone to be higher by whatever shift you want to use.

While not too common now there used to be the esepression LSMFT from the old 
Lucky Strike cigarette commercials.  Low space means fine teletype.  The 
space frequency was ( and should still be)  actually lower than the mark 
frequency on the low bands.

Someone discovered that you could feed audio tones into a SSB transmitter 
and if only one pure sine wave tone was sent, you could not tell if it was 
actually audio or just a carrier (not counting the 30 or 40 db of the other 
sideband and carrier was surpressed).   By using LSB the Mark tone comes out 
of the transmitter higher in frequency than the space tone. If using USB, 
then the space tone is higher in frequency.   By using LSB the same 
demodulator/modulator could be used for VHF FM and AM rtty as was used on 
the lower bands.


If someone is using the 200 Hz shift, the Mark stays the same at 2125, but 
the Space is shifted up 30 Hz.  This means that when tuning in , you shift 
your receiver up 15 Hz to center the tones.  This will then throw off your 
transceiver by 15 Hz if you are using 170 Hz shift.  The beter way would be 
to tune in the Mark tone and use the RIT of the transceiver for best 
demodulating of the 200 Hz shift.

With a  SSB transceiver, any tone pair could be used that is around 170 Hz 
apart.  However you want them to be high enough so the 2 nd harmonic of the 
lowest tone is over 2500 Hz or so if possiable.  That lets the side band 
filters filter out more if there is any distortion of the wave form.  YOu do 
not want the highest tone (normally Space) to be over about 2200 Hz as this 
starts to filter out the Space tone and it will be weaker than the Mark 
tone.   For the ones using the 850 Hz shift as the old military gear, you 
need to adjust to lower tone pairs.  I forgot what the pairing is, but there 
was a 'standard' called the LOW tonee where the Mark was somewhere between 
1000 and 2000 Hz.

I am not sure what tones the PK-232 actually uses, so you will have to 
calculate where to call the frequency.



----- Original Message ----- 
From: "Jeffrey D Angus" <jdangus at att.net>
To: <greenkeys at mailman.qth.net>
Sent: Monday, September 14, 2015 1:37 AM
Subject: [GreenKeys] The things I worry about.


> Running RTTY.
> Assuming 170 Hz shift, and 2125 Hz mark tone.
> What frequency do you tell people you're at?
> If your receiver is in lower sideband mode and your marking frequency is
> 7097.875 KHz, do you tell people you're transmitting on 7100 KHz. That
> would be where the suppressed carrier isn't if you're running SSB AFSK.
> Do you tell them you're transmitting at 7097.875 KHz because that's
> where the mark tone is. Or do you tell them you're at 7097.790 KHz
> because that's the mid point between your mark and space frequencies,
> especially if you're running true FSK and there isn't a suppressed 
> carrier?
>
> What do you tell them if you're using an AEA PK-232 and you're too lazy
> to change the default RTTY shift from 200 to 170 Hz?
> Which tone is 30 Hz off frequency, or are both tones 15 Hz off frequency.
>
>