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Re: [RTTY] RTTY Digest, Vol 27, Issue 25

To: rtty@contesting.com
Subject: Re: [RTTY] RTTY Digest, Vol 27, Issue 25
From: Bob Unger <robert4461@yahoo.com>
Date: Sat, 19 Mar 2005 10:28:46 -0800 (PST)
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Today's Topics:

1. Contest Dinner at Visalia, April 15, 2005 (Jeff Stai WK6I)
2. Re: 24 bit sound card (Kok Chen)
3. 24 bit sound card (Brad Wilcox)
4. Re: 24 bit sound card (Kok Chen)
5. bloody beginner Question (Sven - DD1LI -)
6. Re: bloody beginner Question (Scott Nichols)
7. Gotta love this one (Don Hill AA5AU)
8. Need a friendly PC to ST-8000 RTTY Program



----------------------------------------------------------------------

Message: 1
Date: Fri, 18 Mar 2005 09:49:35 -0800
From: Jeff Stai WK6I 
Subject: [RTTY] Contest Dinner at Visalia, April 15, 2005
To: nccc@contesting.com, sccc@contesting.com, Mldxcc@contesting.com,
rtty@contesting.com, "CQ Contest" 
Message-ID: <6.1.2.0.2.20050318094728.07645c68@pop3.twistedoak.com>
Content-Type: text/plain; charset="us-ascii"


Reservation are now being accepted for the 7th Annual Contest Dinner at the 
International DX Convention in Visalia, CA.

The dinner will be held Friday, April 15, 2005, with serving starting at 7:30pm.

The speaker will be Veijo Kontas, OH6KN with a presentation of his monster 
contest station (one 42m tower, three 60m towers and one 105m tower plus many 
antennas) built in Oulu, Finland.

Cost is $25 per person (in addition to the convention registration fee) PAID IN 
CASH AT THE DOOR!

Reservations are required, so please reserve your seat at the dinner and make 
your menu selection at:

http://www.twistedoak.com/wk6i/contestdinner.html

see you there! - 73 - Jeff, WK6I & Steve, K6AW


--
Jeff Stai jds@twistedoak.com
Twisted Oak Winery http://www.twistedoak.com/
Rocketry Org. of CA http://www.rocstock.org/
Amateur Radio WK6I 




------------------------------

Message: 2
Date: Fri, 18 Mar 2005 09:54:40 -0800
From: Kok Chen 
Subject: Re: [RTTY] 24 bit sound card
To: RTTY Reflector 
Cc: David Hachadorian 
Message-ID: 
Content-Type: text/plain; charset=US-ASCII; format=flowed

On Mar 18, 2005, at 6:32 AM, David Hachadorian wrote:
> Is there any advantage to using a 24 bit sound card when
> demodulating rtty with MMTTY?

I'll bet that you will find that there are various opinions on this. 
Here are my 2 cents.

Warning, this is long. If you don't want to read through all of it, 
the gist is that IMHO, it depends on whether you use narrow IF filters 
or wide IF filters. If there is there is no interfering signal in the 
passband, then a 16-bit converter is ample if you are willing to ride 
the audio/RF gain. If you have the possibility of two signals in the 
same passband or you are using "wide passband RTTY", then the analysis 
becomes more complex. It also depends on whether your operating 
system's audio library can support anything more than 16 bits -- the 
MacOS X's audio framework is floating point, for example.

First consider a 16 bit converter. The maximum numerical range is of 
the order of 96 dB assuming that 1) the A/D converter is linear to 1 
out of 1 bits, 2) there is some noise dithering and 3) the noise floor 
of the stages that precede the is low enough to support the 96 dB.

However, this numerical range is not quite the same in some sense as 
the dynamic range. Let us say there are two signals in the audio 
passband. If the loud signal is 96 dB louder than the weaker signal, 
the weaker signal is itself a 1 bit (square wave) signal. There is 
something in the Radar Astronomy world called the Van Vleck theorem (I 
think it is also called the "arc-sine rule" in Probabililty theory, but 
it has been a long time sine I cracked open a volume of feller or 
Papoulis, so don;t hold me to this). What the theorem says is that you 
can recover the spectrum of a hard clipped signal perfectly, if it is 
in a strong Gaussian noise environment, but at a loss of 2.19 dB of 
SNR.

At the threshold of FSK detection, 2 dB of SNR change (for the case 
where there is no QSB, just noise) is huge, and can be a difference of 
practically printing everything (one or two bad prints per line) to 
printing lots of garbage (one out of 4 characters are bad). Take a 
look at the plots in textbooks and the AWGN plots that Alex VE3NEA had 
posted a month or two back on this reflector. So, 2 dB lowered SNR is 
a "bad thing" for us RTTY folks.

I had done some work many eons ago to extend van Vleck to the multi-bit 
case (playing with joint Gaussian distributions and integrations 
thereof) and showed that the SNR ratio loss can be made "negligible" 
when you are up at the 4 bit region instead of the 1 bit (hard clipped) 
region. In practice, we don't have Gaussian noise on the ham bands, 
and no one uses the arc sine transform to receiver spectra, so we will 
do worse that "2.19 dB" of SNR loss.

So, the 96 dB numerical range of a perfect 16 bit converter now reduces 
to 72 dB of usable dynamic range if you need 4 bits to represent the 
weaker signal.

Is 72 dB enough?

First, the 72 dB is for ideal additive Gaussian noise and if you also 
apply the corrective transformations. My guess is that in practice, 
you are playing more in the area of 60 dB to 70 dB.

Now lets consider two cases: 1) you are using a 250 Hz filter and 2) 
you are using a 2500 Hz filter ahead of the A/D converter.

With a 250 Hz filter, unless another signal straddles the desired 
signal, you are working with a single signal case. I cannot imagine, 
in this case that you need more than 30 or 40 dB of dynamic range, as 
long as there is no QSB which your rig's AGC has not taken care of, and 
the band conditions don't change over time. Afterall, under the single 
signal case, even a hard clipped (some people call it limitered or "FM" 
demodulation of RTTY) signal prints pretty well, although both RITTY 
and cocoaModem use linear matched filters and work better when there is 
no limiter or hard clipping whatsoever.

Furthermore, band conditions could change so you might have to ride the 
gain of your transceiver so that the A/D converter "sees" a signal that 
neither clips it nor less than 4 to 6 bits in magnitude -- this is 
where more bits help. Modems such as the ST-8000 (85 dB dynamic 
range) and the Timewave DSP-599zx have built in AGC. Notice that 
good 24 bit converters have between 95 to 105 dB weighted noise floors, 
and they can basically give you better dynamic range than modems of the 
past which had to use AGC! AGC has its own problems -- you may have 
noticed that with AGC engaged in a modem, you might miss the first 
couple of characters when a very loud CQ'ing station starts up in a 
contest.

If you are willing to install a pot before the A/D converter (or have a 
mechanism to adjust the attenuation in the A/D converter) and have a 
way to constantly monitor the signal to make sure the signal is large 
enough but not saturating the A/D converter, then a 16 bit converter, 
with the operator manually riding the gain is plenty good enough, IMHO 
in the single signal case.

However, the problem is different if you do any "wide passband RTTY," 
i.e., watching an entire 2 to 3 kHz, or more passband). In this case, 
you just about always have more than two signals in the passband. 
Under a DX pileup condition (where you can see both DX and the pile) or 
under contest conditions, the "60 dB to 70 dB" worth of dynamic range 
is not good enough for a wide passband. That is assuming that the 
rig's front end dynamic range is good at least to the 70-80 dB region 
in the first place.

My crazy prediction is this: RTTY will eventually move to use wide 
passband and perhaps also the point and click waterfall tuning as 
practiced today in PSK31. There are simply too many advantages with 
wide passband operation (for a DX station picking a signal from the 
pile, for a non-DX station fining where in the pile to call, for 
multiple decoding streams in a contest when you are doing S&P, etc etc.

To use wide passband RTTY, you will need A/D converters that have 
better dynamic range than the rig's front end or the A/D converter will 
be limiting the overall dynamic range of your station.

Personally, I use a M-Audio Transit (24-bit) as my A/D converter, into 
a homebrew software modem that does make use of 24 bits of numerical 
range. Your mileage may vary.

And be careful... not all "24-bit" converters perform the same, just as 
not all "16-bit" converters perform the same. Look for actual dynamic 
range, including noise floor contributions, and not just count the 
bits.

73
Chen, W7AY



------------------------------

Message: 3
Date: Fri, 18 Mar 2005 11:43:29 -0700
From: Brad Wilcox 
Subject: [RTTY] 24 bit sound card
To: RTTY Refector 
Message-ID: 
Content-Type: text/plain; charset=ISO-8859-1

Dave,

I just upgraded my computer and found a Creative SBLive 24 Bit card on
sale for under $20.00. I thoughtI would be smart and install the
extra soundcard to
have for digital HF, and the one on the motherboard for my son's games, etc.

The sound card on the motherboard (Asus A7N8X-E DX)passed the sound
check program 7f, but the Creativecard did not.

Nevertheless, I did use it in the NA Sprint last week and it seemed
fine with no compatibility problems with the motherboard card, and
that's the only thing I was
concerned about.

Brad - KJ7NO

>Is anyone using a 24 bit card that passes all the Writelog tests 
>for functionality?

>I am thinking of something along the lines of the Sound Blaster 
>Live 24. My current on-board audio is ok, but I


------------------------------

Message: 4
Date: Fri, 18 Mar 2005 12:11:53 -0800
From: Kok Chen 
Subject: Re: [RTTY] 24 bit sound card
To: rtty@contesting.com
Message-ID: 
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

On Mar 18, 2005, at 10:17 AM, rwmcgwier@comcast.net wrote:
> The dynamic range of the audio coming out of the modern 
> transceiver from
> ANY port, headphone, speaker, line level output, is less than 
> that afforded you
> by an 8 bit audio card.

I will try to find time to record the audio amplitude variations 
across the band in some future contest and also study how many bits 
an RTTY signal (plus noise) needs to be above the LSB of an A/D 
converter for it to be "close enough" to the optimal case.

I will also try to record the strength of the really weak signals 
that come across the Pacific when the 20m band is "dead."

On top of the audio variation, hard clipping a signal before passing 
it through a matched filter is obviously not optimal, so you will 
need a few more bits than just letting a weak signal tickle the least 
significant bit of the A/D. The only analyses I have seen are based 
on the AWGN case, so it is worth looking at more real world cases.

The case of quantized FSK can be readily simulated with the sound 
files from VE3NEA (especially Alex' multipath and selective fading 
files) and are probably worth doing, before going to actual recorded 
signals off the band.

BTW, here is another vote for the SDR-1000.

With the SDR-1000, even good two channel 24 bits A/D converter do not 
have enough I and Q channel balance across the passband to deliver 
the kinds of dynamic range that the SDR-1000 is capable of, but the 
"radio" does have a pulse generator in the front end to give you the 
capability of equalizing the A/D converters. Macintosh users will be 
happy to learn that there will soon be an alternative to using a 
parallel port to control the SDR-1000, which means you can run it on 
any modern Macs. I don't think that it is listed at Flex-Radio's web 
page yet but I have been playing with a USB (as in Universal Serial 
Bus and not upper sideband) adapter from them (you do have to write 
code yourself to download the adapter's firmware -- but it is just 
the standard Anchor chip set).

73
Chen, W7AY



------------------------------

Message: 5
Date: Fri, 18 Mar 2005 21:34:24 +0100
From: Sven - DD1LI - 
   
Subject: [RTTY] bloody beginner Question
To: rtty@contesting.com
Message-ID: <200503182134.24171.dd1li@gmx.de>
Content-Type: text/plain; charset="us-ascii"

I know , I have to google before I ask dumb questions !!!!

But i have a bloody beginner Question :
Where can I find the results of the CQ WW WPX RTTY - Contest ??????
Is there a special side where they are shown ???

CU on BARTG this Weekend !!!

DD1LI
-Sven-

-- 
German Amateur Radio Station
Member of :
DARC M11
IGFiH 80FF



------------------------------

Message: 6
Date: Fri, 18 Mar 2005 17:51:39 -0400
From: Scott Nichols 
Subject: Re: [RTTY] bloody beginner Question
To: dd1li@gmx.de, rtty@contesting.com
Message-ID: <002f01c52c04$aab7f100$6501a8c0@old>
Content-Type: text/plain; charset=iso-8859-1

http://www.rttycontesting.com/results.htm


----- Original Message ----- 
From: "Sven - DD1LI -" 
   
To: 
Sent: Friday, March 18, 2005 4:34 PM
Subject: [RTTY] bloody beginner Question


> I know , I have to google before I ask dumb questions !!!!
> 
> But i have a bloody beginner Question :
> Where can I find the results of the CQ WW WPX RTTY - Contest ??????
> Is there a special side where they are shown ???
> 
> CU on BARTG this Weekend !!!
> 
> DD1LI
> -Sven-
> 
> -- 
> German Amateur Radio Station
> Member of :
> DARC M11
> IGFiH 80FF
> 
> _______________________________________________
> RTTY mailing list
> RTTY@contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty


------------------------------

Message: 7
Date: Sat, 19 Mar 2005 00:07:35 -0600
From: "Don Hill AA5AU" 
Subject: [RTTY] Gotta love this one
To: "'RTTY Mailing List'" 
Message-ID:
<20050319060735.WSAD14689.imf20aec.mail.bellsouth.net@AA5AU>
Content-Type: text/plain; charset="us-ascii"

DX de EA4CRP: 14089.5 EA4CRP RTTY TEST




------------------------------
Message 8
Saturday March 19, 2005

>From Bob Unger, WB3DTG

To:  RTTY Mailing List

Subject:  PC terminal program for RTTY with/using ST-8000

Can anyone steer me to a PC/RTTY program using Serial Interface form the 
computer to TU.  I like the versitility of my old St-8000 and would like to 
keep it running. Any help would be  greatly appreciated.

73 de Bob

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End of RTTY Digest, Vol 27, Issue 25
************************************




73 de Bob in Bethlehem, Pa.    WB3DTG@#CEPA.PA.USA.NOAM
                
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