--- On Fri, 2/19/10, James French <w8...@wideopenwest.com> wrote:
> From: James French <w8...@wideopenwest.com>
> Subject: [digitalradio] RTTY and mode selection on radios
> To: digitalradio@yahoogroups.com
> Date: Friday, February 19, 2010, 3:58 PM
> Wondering if someone can point me to
> a link or some literature explaining
> about why there is a FSK mode on the HF radios like the
> Icom ic-746pro,
> Kenwood TS0940sat, and Ten-tec Paragon (585)? Is there a
> reason for this?
>
> I am asking this because I have listened to some RTTY using
> either USB or LSB
> dependent on what band I am on and could copy it with any
> software programs I
> have but then switched to the FSKmode on the radios and
> loose the signal
> completely.
>
> Is this mode just for the older ancient RTTY eqiupment to
> interface with the
> radio?
>
> I haven't tried to send any RTTY yet but planning to be on
> the air next
> weekend for the NAQP RTTY contest from the Red Cross
> station in Ann Arbor,MI.
>
>
> James W8ISS
>
>
RTTY should not be referred to as afsk even if audio is fed into a ssb radio.
What comes out of the transmitter is the same if true FSK or AFSK is used.
Whoever started that wording should be shot. It is AFSK if AM or FM is used.
For the ham bands rtty should be received and transmitted in the LSB mode on
all bands if ssb is used. YOu can set the tones up in reverse and use usb,
but it is not recommended. When you switch from lsb to the rtty mode, most
receivers will shift up or down 2125 hz if you have it set up correctly. That
is what the mark tone should be. Actually any two tones can be fed into a ssb
transmitter as long as they are 170 hz apart. The lowest tone should be around
1500 hz or so as the second harmonic of it will be out of the pass band of the
filter. The station on the other end will not know the differance, just your
dial frequency will not match his.
RTTY was origionally sent on the low bands by shifting the frequency of the
transmitter lower in frequency when the space was sent. When ssb transceivers
came into use it was found that if you put a pure sine wave into the microphone
input you generated just a single output frequency. If that audio tone was
changed a small ammout the frequency of the output would change the same
ammount. If usb is used the frequency would shift up and if lsb was used the
frequency would shift down. LSB is used to keep everything the same weather
the shift was the actual carrier or if audio tones are used.
You have to have a good understanding of how a single frequency fed into a ssb
transceiver will change the output frequency to understand rtty.
