[RTTY] RTTY spectrum analysis article

[aflowers at frontiernet.net]

Salvo brings up an interesting point when it comes to generating FSK.  (Incidentally, one of the "narrow" examples on the webpage happens to be a Flex 5000 and with an Alpha 8410 running about 1000W, using MMTTY.)  To my knowledge, the Flex 1500/3000/5000 architecture has no on-off keyed FSK line--if you want to send FSK you can do it with software-defined audio tones and a "virtual audio cable" through the firewire connection.  The interesting thing here is that the "AFSK" is generated in the radio and there is no analog link between the software defining the modulation waveform and the conversion to RF.  The entire "audio" chain from PC to RF is digital, so you won't get RF distortion in the audio and it becomes much harder to "overdrive" the radio, particularly if the Flex/PowerSDR is smart enough prescale the levels (I have no idea if it actually does this).  In some sense it's really "faux-AFSK".
 
I have not been the transceiver market recently, but I decided to look around to see what has changed in the last 5-10 years as far as interfacing for digital modes.  The Flex architecture is not unique in having the potential for this "faux-AFSK" model.  It looks like several radios have built-in "sound cards" that are available by a USB connection.  In principle this should be essentially the same thing as the Flex flex is doing--no analog audio line to the radio.  I have no idea what the interface is like, what the quality is, or to what extent you can mess it up, but a bit of internet searching and browsing through manuals indicates that this is something that people really haven't looked into very much, even in the world of PSK31 and other digimodes.  Perhaps its just so common that nobody mentions it?  The higher-end Icoms even have S/PDIF in and out.  Not only can you not "overdrive" the S/PDIF input on the radio (I don't what is
 downstream in the radio that you could still mess up, however), but the RF isolation on a 3-ft TOSLINK cable is supurb below 300 THz :-)
 
This is of course in addition to radios that provide filters and prescalers for (legacy?) analog audio inputs.  The K3 and some others already have features like this specifically for AFSK-RTTY.  In any event, line-level inputs are pretty much standard on every radio in the last 10 or 15 years.  (Why anyone would use a microphone input when there is a line-level alternative is crazy to me, but it doesn't help that the manufacturers are currently endorsing this in their manuals).  I guess my realization is that "AFSK", as we tend to call it, has the potential to be much safer than it used to be five or ten years ago, at least with some of the more recent inovations.  That said, I'm sure there are definately still some wrong things one can do.
 
Anyway, these just some thoughts that Salvo triggered.  Is anyone out there using SPDIF or the radio's internal soundcards for RTTY or other digital modes?  I'd be interested in your experiences, be they good, bad, or ugly.
 
Regards,
 
Andy K0SM/2
 
 
 
 
 

________________________________
 From: "rtty-request at contesting.com" <rtty-request at contesting.com>
To: rtty at contesting.com 
Sent: Saturday, January 12, 2013 12:00 PM
Subject: RTTY Digest, Vol 121, Issue 37
 
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Message: 1
Date: Fri, 11 Jan 2013 22:19:10 +0100
From: iw1ayd - Salvatore Irato 
To: rtty at contesting.com
Subject: Re: [RTTY] RTTY spectrum analysis article
Message-ID: <50F081CE.8040103 at googlemail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

As Bill wrote and I perfectly agree: clever!
I would also like to somewhat rephrase Bill, trowing in my short 
experience: clever and effective notes, FB, TU!
As usual, IMHO, a picture make much more clever than a tons of words.

I already made my tests with my FLEX 3000. Having my feedback on various 
scenarios, like FLEX to ICOM and ICOM to FLEX.
The best TX configuration I find out is the FLEX in TX with the MMTTY 
tightened TX BPF, 512 tap and a FLEX TX filter of 400 Hz  (no more than 
500 Hz).
I would test 2Tone, but not for now. By now I use it like a II RX 
windows together with MMTTY FIR having great results at any time.

Empirically I could say: WOW! It's easy to get rid of those large M/S 
with the proper AFSK tones configuration and also they could becomes 
more better than those FSK generated tones!
Remember that MMTTY is somewhat aged even if well maintained.

Then I switched back using 7600 for contesting, when not at home, not 
too easy to check Pout and ALC for peoples not acquainted to it. 
Contesting means M/S or M/2 for me, some 2 or more operators have to 
share the same setups. Two at least of each of those, operators and 
setups. But after even after tens of minutes of steady RUN with a good 
rate somebody get into my <500Hz filters. So, my signals aren't quite 
offending statistically speaking.
They don't get the same noise I get from theirs signals or they wouldn't 
come so near to me. I know that there are several other facts about, but 
just to summarize this may sound.

At home my FLEX run this way, TX BPF & tight TX filter,  since then, 
almost 2 years ago.
So, to who was telling here about ... there aren't transceivers that 
could do the right job even transmitting FSK ... may I answer: no sir 
there are already those radio, such as FLEX and, maybe, others SDR TXing 
boxes with.
Still taking care that I whistle inside my SDR, but in the right way.

BTW one of the fact is that each of the brands that work for ours market 
doesn't find so appealing to have great features like variable and tight 
TX filters.
For brands that made DSP tone generation in the TX MF this add on would 
be quite just a matter of some and several line of code to be added. 
Some lines for the filtering and several lines to give us the control 
about all the parameters on the menu: set and forget or use external CAT 
cmds with some more lines of code. Bat you know the marketing versus 
engineering is anytime a win win by the first group. I already read 
something like that here, so ...
Anyway there is a well known radio brand  that had make newest BF 
filters worse than the oldest and kindly refuse to add useful CAT commands .

Hope my poor English and my short experience could be sounding here.

         73 de iw1ayd, Salvo


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