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Are You Frequency Confused With RTTY?

Do not contact (N4ZOU) on February 7, 2004
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Are you frequency confused with RTTY?

So you're on 40 meters after dark talking to someone in RTTY mode and the band is beginning to get long and you ask the other person your talking to if he would like to try 80 meters to continue the chat. The answer is yes and you tell him to try 3605.00 and he agrees so off you go. When you get there and call him you get no answer so you move up and down and finally find him on 3607.13! You think to yourself, I know my frequency readout can't be that for off! So you ask the other fellow what he is reading on his dial and he tells you it's exactly 3605.00! So whose frequency readout is way off? The strange answer is neither one! When you operate on a FSK mode like RTTY, Amtor, Pactor, and Packet you can end up with three different frequencies reading on your radio according to how you generate your Mark and Space tones. RTTY or DATA mode where you're using FSK to key the transceiver to send the Mark and Space tones, LSB, and USB where the proper tones are generated by a terminal unit, TNC, or sound card into the microphone connector in the transceiver.

Years ago the standard was set to use the frequency of the Mark tone. Also about this time the use of LSB mode for AFSK generated Mark and Space tones was also set as a standard on all amateur bands so everyone could copy the tones generated with the Mark frequency as the low tone and Space as the high tone. This was done to keep things simple. This was also before digital frequency displays and a number of transceivers with the analog display would have three marks under the dial. This was done to show the offset used between the different modes. Today we now have nice digital frequency displays that automatically shift between the different modes except when generating AFSK tones. Modern transceivers will display the Mark frequency when in RTTY or DATA mode so there's no confusion about what frequency you're on. The confusion starts when you're in LSB or USB mode and just dial up the frequency without calculating the proper frequency offset or posting a frequency without telling anyone if it's the Mark frequency, LSB frequency, or USB frequency. Also most modern transceivers will automatically select USB mode on 20 meters and up and LSB on 40 meters and down adding to the confusion. A good example would be that everything works fine on 20 through 10 meters after you get it setup but when you drop to 40 or 80 meters and call CQ you get no answers. Why? You never noticed that the radio switched from USB mode to LSB mode and now your tones are upside down with the Space tone low and the Mark tone high and all that prints on the other stations screen is garbage. If you were lucky an old timer would call and tell you that your tones are upside down. Of note here is that there is nothing wrong with sending AFSK tones with the transceiver as no one on the other side will be able to tell the difference in the signal. You just need to remember to setup properly and always calculate the frequency offset when talking about what frequency your own using the Mark frequency standard.

So how do you calculate the Mark frequency? Easy! If you use LSB to generate your tones just add 2.13 to the display frequency. If you use USB then Subtract 2.28 from the display frequency. It's easy to do and eliminates frequency confusion.

Member Comments:
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Are You Frequency Confused With RTTY?  
by N6AJR on February 7, 2004 Mail this to a friend!
mmtty has a REV button that fixes this problem and I still forget it untill the garbage starts running across the screen.. push the button..ohhhhhhhhhh there it is now :)
 
Are You Frequency Confused With RTTY?  
by N4QA on February 7, 2004 Mail this to a friend!
RTTY is a great QRP mode.
MMTTY is my favorite RTTY app.
Presently operating QRP RTTY using two FB rigs(modified) from Small Wonder Labs:

Rock-Mite-20
DSW-20

Both using FSK RTTY as opposed to AFSK...
It's easy...except for the poor receiving op :0)

http://www.n4qa.com

http://www.qsl.net/n4qa/
 
Are You Frequency Confused With RTTY?  
by W5GNB on February 7, 2004 Mail this to a friend!
The STANDARD operating proceedure for RTTY and other "digital" modes has been long established as LSB on ALL bands forever since I can remember. This came about from the old days when you had to add a capicator to your VFO and manually "KEY" the shift frequency (tones) for RTTY with the old teletype equipment. As a matter of physics of the setup, the shift was Down in frequency.

As long as everyone checks thier equipment prior to going on the air, there should be no problem with what the article has described.

I have been running RTTY for many years and all the old timers from the mechanical days seem to have no problems even with the newer equipment and software based systems.
 
RE: Are You Frequency Confused With RTTY?  
by N4ZOU on February 7, 2004 Mail this to a friend!
You are correct in that RTTY is a good QRP mode! I worked W0EB just the other day using a small wonders lab 20 meter transceiver and MMTTY. He was 100 percent copy with an honest S-7 signal! That 3 watts was doing a great job. You could buuld a Hamcomm or Volksrtty modem and run Terman93 (AN93) software and get RTTY and ARQ AMtor and Pactor 1 modes also and run it on an old 386 or higher Laptop computer, no sound card required!
 
RE: Are You Frequency Confused With RTTY?  
by K4JSR on February 7, 2004 Mail this to a friend!
Is all this to say, "Caveat Amtor"?
:-D
K4JSR
 
RE: Are You Frequency Confused With RTTY?  
by KE4MOB on February 7, 2004 Mail this to a friend!
Truth in advertising: It's 2.295 and 2.125.

I would say 2.13 is a good approximation to use...but I don't know about 2.28. At best, it's a 150 hz error.
 
RE: Are You Frequency Confused With RTTY?  
by KA4KOE on February 7, 2004 Mail this to a friend!
Yes, I am frequently confused. What else is new?
 
RE: Are You Frequency Confused With RTTY?  
by WA4MJF on February 7, 2004 Mail this to a friend!
Easiest is just specify the mark
frequency or the center frequency.

If mark, just key transmitter and
look at freq counter. If center,
do first sentence and then move down
half the distance of the shift (425 for
850, 85 for 170, etc).

Used to do that in Army MARS all the
time when on a freq I did not have a
crystal for.

73 de Ronnie
 
Are You Frequency Confused With RTTY?  
by ON4MGY on February 8, 2004 Mail this to a friend!
TNX for this help topic on the right frequency for RTTY.
All I needed.

73

ON4MGY Nic
 
Are You Frequency Confused With RTTY?  
by KC7GNM on February 16, 2004 Mail this to a friend!
Now if you can just keep the RTTY contesters away from the packet radio freqs on 20m all would be fine. Most RTTY folks don't seem to listen to the freq before they transmit. Everytime there is an RTTY contest they jump right on top of 14.105mhz and start calling CQ. I don't know if the packet signals are messing up their QSO's but they sure are tearing up packet. Yesterday I tried to do HF packet and couldn't because of the idiots on RTTY not listening and letting packet have a little breathing room.

73 de Greg
KC7GNM
 
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