[RTTY] Bad AFSK

[Ron Kolarik]

Dick, I have to agree with Joe on this.....they have a problem. I first noticed
it last August and sent along the information to NJ1Q several times. I still
have the screen captures from RTTY, PSK and MFSK on different bands
and the signals are pretty bad. I can send them if you're interested.

Ron K0IDT


----- Original Message ----- 
From: "Dick Kriss" <aa5vu at arrl.net>
To: "RTTY Reflector" <rtty at contesting.com>; "Joe Subich W4TV" <lists at subich.com>
Cc: "Joe Carcia, NJ1Q" <nj1q at arrl.org>
Sent: Tuesday, January 29, 2013 8:48 PM
Subject: Re: [RTTY] Bad AFSK


Joe Subich, W4TV

It was pretty obvious you were talking about a W1AW with the "terrible" AFSK signal. 
There are no W1AW RTTY bulletins on Tuesdays so I listened to the early BPSK-31 
bulletin on 14.095 and on 18.102.5 using a Kenwood TS-590S with a direct USB interface 
to fldigi-3.21.67 on an iMac with OS X 10.8.2. The W1AW signal was on frequency on 
both bands with solid print, clean looking BPSK-31 signals with none of the harmonics 
or birdies you mentioned.

I am aware of the W1AW setup with Icom transmitters and the station manager tries very 
hard to be sure each band dedicated transmitter is correctly adjusted with no ALC 
showing. The Station Manager uses a custom interface hard wired to the digital ports 
on the rear - not via the Mic connector as implied in your message.

I think you owe the Joe Carcia, NJ1Q, the W1AW Station Manager and this reflector a 
retracton for your public comments about the "terrible" W1AW signal and your statement 
"….One simply *can not* run "all sliders to the max" and "all knobs to the right" with 
AFSK."

You may want to check your setup for local interference causing the harmonics and 
birdies you observed. There was no evidence of harmonics or birdies on the early 
29-Jan-2013 PSK-31 bulletin.

Dick AA5VU



> Date: Tue, 29 Jan 2013 10:38:45 -0500
> From: Joe Subich, W4TV <lists at subich.com>
> To: MMTTY at yahoogroups.com, RTTY <rtty at contesting.com>
> Subject: [RTTY] Bad AFSK
> Message-ID: <5107ED05.6010405 at subich.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
> Elecraft have taken the lead on FSK bandwidth - thanks to W7AY, K0SM
> and W0YK among others.  Lets hope other manufacturers follow quickly.
>
> Yesterday evening as I was looking for some RTTY activity to try the
> new Elecraft "narrow FSK filter", I stumbled across another terrible
> AFSK signal.  It just happens to belong to a well known club so I
> won't give the call here but I have contacted the trustee.
>
> However, I've posted a screen capture from my P3 that clearly shows
> what happens when over driving the mic input of an SSB transmitter at:
> http://www.subich.com/BAD_AFSK.jpg (the last spike at about 14.0972
> is a local birdie).
>
> Note this transmitter has not only "second harmonic" energy at
> +1 KHz/340 Hz shift and "fourth harmonic" energy at +2 KHz/680 Hz
> shift, it also shows insufficient opposite sideband suppression (or
> possibly IMD in the PA - it's impossible to tell which).
>
> One simply *can not* run "all sliders to the max" and "all knobs to
> the right" with AFSK.  Any manufacturer or individual who says to
> do so is giving you bad advice.  Again, unless you have the tools
> to make absolutely sure you are generating clean AFSK, *use FSK*,
> the clicks are far less objectionable than 2nd/3rd audio harmonics
> that are suppressed by -18 and -15 dB respectively.  This capture
> was made during a fade - signal levels were generally much higher
> and even the spurious signals were well above -73 dBm (S9+).
>
> 73,
>
>    ... Joe, W4TV


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