RTTY Signals using SmartSDR 2.4.9

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OK Guys (and Ladies), my reports of success from yesterday may have been not quite accurate!

After my second ever RTTY QSO using a real TTY I got an email from the the other station that said the following:
"One observation.  When you reply to my transmission, you are about 52 hz high.  My tones may be off, or your tones may be off..  The net effect is I retune up the band, and we gradually creep up in frequency."

At least I know why every time I went back to RX with him I had to move up the band a little to copy him clearly.

So I sent a query to the ham that was my first QSO and he replied this morning with this:
"Now that you mention it, I did see that our common frequency was off.  Check into the subject with the Flex community, I think that there is an easy solution."

 As a newbie I really have no idea of what, if anything, I should be doing to resolve this issue, so I'm turning to the group.

Any ideas gratefully accepted!

Steve G./N4TTY

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Steve - N4TTY

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  • Perplexed

Posted 3 months ago

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Don Cunningham

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Steve,
Are you set with Mark 2125 Space 2295  Shift 170 ?  Some RTTY software programs use different and it doesn't work for me.
73,
Don, WB5HAK
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Steve - N4TTY

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Don, the only software involved is SmartSDR as the radio is interfaced directly to a HAL ST-6 and from there to the Teletype M28 KSR. No other software in the picture.

SmartSDR's defaults for RTTY mode are 2125 for the mark tone with a shift of 170.  The RIT and XIT default to 0 (zero), so on my next test, after I transmit the first time as the other station comes back to me I'm going to try changing my RIT by around 50Hz to see if that can be used as a temporary fix until i find the real culprit.

I'm thinking it could be a problem in the ST-6, but knowing so little about their inner workings I'm staying away from that and trying this fix, if it works, for the time being.

Maybe I'll be ready by Jan 1.

And maybe you and I can try a test QSO of both of our setups before Jan 1.  Probably after Christmas day now!

Steve G./N4TTY
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Don Cunningham

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Okay, I understand that you receive by sending audio from the Flex to the ST-6 to the KSR.  When you transmit, do you type on the keyboard, then an AK-1 in the ST-6 that sends tones back to the Flex??  It would be EASY for the AK-1 to be off only 52 cycles (sorry I'm old and it isn't hz to me, HI).  The AK-1 is set by tuning the toroids, and most of the ST-6 builders didn't get that close, OR the capacitors across the toroids have shifted in value that much.
Don
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Don Cunningham

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Oh, and also, use your XIT and adjust it down 50, not RIT.  Dumb question since I'm new to the Flex community, do you get the messages you send "echoed" to you on the email or is there something I need to set to get what I send??  I never see my replies until I go to the community page.
Don
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Steve - N4TTY

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You have the sequence correct Don. When I put my TX/RX switch to TX, which also mutes the audio in to the ST-6, I can begin typing on the keyboard and the AFSK is sent from the ST-^ to the FLEX for transmission.  When I finish typing I put the switch back to the RX position.   And not being real knowledgeable about the ST-6, is the "AK-1" just the proper nomenclature for the AFSK board in the ST-6?  My guess is that is the case without grabbing my documentation on the ST-6 and looking it up.

I was going to change the XIT until my first contact suggested I not do that, but instead use RIT.  Now you might ask why I was listening to him and my answer is he has become my Elmer in this endeavor and knows so much more about RTTY than I.  But now that you have suggested what I originally thought would be the first thing to try, I'm going back to the XIT change.  At least at first.

And your explanation of the tuning of the toroids makes a lot of sense and would explain the real problem.  Seems as you have quite a bit of knowledge of the ST-6.

So you have now become my second Elmer in this endeavor!

And I don't get my replies to previous replies (like this one) either.  The only one I see is the original and any further replies from others.

Thanks for the continuing education.

Steve G./N4TTY
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Don Cunningham

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Yes, the AK-1 is the HAL nomenclature for the AFSK board.  It COULD be an XTK-1, which is crystal controlled, but I've seen very few of those in my time.  Either will produce AFSK, the crystal controlled one is just more stable.  If your "elmer" is Russ, WA3FRP, then do as he suggests.  We WILL set up a QSO on 20M when I get back from Christmas visits.  I'll contact you Wednesday or Thursday upon my return.  If we determine that it is your AK-!, I can help adjust that, or just adjust one of mine "right on the money" and exchange with you.  Glad to do that, but we need to find a "fix" to help short term.
Don
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Don Cunningham

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By the way, let's take this off the community before they get tired of seeing these posts, HI.  My email is wb5hak at arrl.net
Don
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Steve - N4TTY

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Was just going to suggest that myself.  Great minds!!  But some of this has been instructive if someone else that might have this issue stumbles across this thread.

And my email is my call at arrl.net as well.

Bye everyone and Merry Christmas or Happy Holidays,

Steve G./N4TTY SK
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Dudley - WA5QPZ, Elmer

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Steve,

Could be the internal filters are not tuned properly,  I had built one of these years ago,   but first make sure that your radio is on frequency,  be sure to follow the procedure to calibrate the radio to WWV,  if you are off frequency the shift will be off,  I would set the TX frequency and use the RIT on the calling station to find the difference off,  but calibrate the radio first then see is still off.   You can check you shift between the two frequencies by turning of the "Frequency Guides "   (right click the mouse with the cursor in the panadapter of SmartSDR .  

MMTTY is much easier..  

73
Dudley
WA5QPZ
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Steve - N4TTY

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Guess I don't see how MMTTY is easier as that puts more software in the equation.

I'm not trying to use any software except SmartSDR.  Trying to use a real Teletype connected to the radio via a TU.  Not trying a "Glass TTY!"

I have not calibrated the radio to WWV.  Is that procedure in the SmartSDR Manual?  Guess I should RTFM!

Steve G./N4TTY
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Steve - N4TTY

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And Dudley, I have a GPSDO in my FLEX 6700.  Have I been misinformed about the function of the GPSDO.  Doesn't it function to keep the radio accurately tuned?  If not, then what is it's added functionality all about?
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Dudley - WA5QPZ, Elmer

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Be sure the GPSDO is operational..   You should have a solid blue light at the lower right of SmartSDR  and you can not run the frequency calibration .   
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Steve - N4TTY

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GPSDO is fully operational!  So I guess that alleviates the calibration question. I'm going to stick with the suggested RIT/XIT fine tuning for the moment.

Steve G./N4TTY
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k3Tim

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You could transmit (QRP--) into a dummy load, set the 6700 receiver to an open antenna port (xver?) and set to full duplex. Then transmit with the ASFK (via slice A) and read the mark frequency in slice B. The mark frequency is added to the carrier (VFO) frequency. It seems to me if the AFSK is 52 cycles low, than XIT should be adjusted to compensate.

I think it's great you are trying the old mechanical TTYs and the ST6 in operation. I believe I used an ST3 to start RTTY. It had two LC filters for M/S tones and some op-amps for gain but forget the slicer portion. Graduated to a LM565 PLL based unit that would lock onto the received station despite drift. It also would decode well if the 170 shift was off. FSK made xmt a piece of cake.

G/L  - k3Tim/7
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W7NGA

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I'm an electronics engineer. I value accuracy and precision. However ... I also remember the era of the Model 28 mechanical teletype machine and 52 hertz accuracy was a pipe-dream and about the shift in frequency if someone sneezed near the old Viking Valiant, Ranger, or Heathkit DX-100. We'd be thrilled to have even 520 hertz (or greater) stability. Get a counter, adjust those ST-6 tones if you so desire. Or ... consider yourself close enough, call CQ, and light up the airwaves. Have fun! I'll be listening.