[RTTY] Frequency accuracy of WZ7I skimmer

[Don Hill AA5AU]

For those wishing to download 2Tone but do not have a Yahoo account can download several versions from rttycontesting.com:

http://rttycontesting.com/downloads/downloads.html

Thanks to David, G3YYD, to allow me to host 2Tone.

73, Don AA5AU

-----Original Message-----
From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Robert Chudek - K0RC
Sent: Friday, January 10, 2014 3:39 PM
To: rtty at contesting.com
Subject: Re: [RTTY] Frequency accuracy of WZ7I skimmer

Wes, you said /

"This week I used both RCKskimmer and MMTTY to monitor the W1AW bulletin Baudot transmissions on 80, 40, and 20 meters. The
frequencies reported by RCKskimmer were well within 100hz of the published frequency, Using LSB fed to MMTTY and observing the
crossed ellipse display, the VFO dial frequency was quite close to the 2125hz difference from the published Mark frequency one would
have predicted."/

My eye caught your statement "observing the crossed ellipse display...". That method of tuning a RTTY signal is VERY suspect to
error. A better method is to turn on the*FIR*  decoder in MMTTY. Now you will get a nice, crisp "+" plus sign. But even this is an
inferior method when compared to using the new(er)*2Tone*  decoder by David, G3YYD.

David has implemented an excellent bandscope tool that allows you to exactly zero beat a received signal. It has a pair of
stationary vertical lines which represent 2125/2295. A second pair of vertical lines represent the current tones you are receiving.
The objective is to tune your received until one set of lines overlay the other. You can visually see how far off your received
tones are. In addition, if the signal is not exactly zero beat, the status bar tells you how many Hz off frequency from 2125/2295
you are tuned.

The 2Tone program is not a standalone program like MMTTY. It requires N1MM or other software that implements 2Tone as another RTTY
decode engine. If you have not played with this software, I highly recommend downloading it and experience its superior tuning /
zero-beating capability.

The current verions is 13.12a.zip and you can download the 2Tone file here:

http://groups.yahoo.com/group/N1MMLogger-Digital/files/G3YYD/


73 de Bob - KØRC in MN

------------------------------------------------------------------------
On 1/10/2014 9:35 AM, Wes Cosand wrote:
> Hi Folk:
>
> I have received several emails suggesting that the spots from the WZ7I 
> RTTY skimmer may be significantly off.  While it is not my aspiration 
> to be a fiduciary frequency reference, I want to be accurate enough 
> for the reported signal to fall within your RTTY passband filters.  
> That is not the case for some users.
>
> During RTTY Roundup I used QS1R units for 40, 20, and 15 meters.  Each 
> of the QS1R SDR units send RF to 16 instances of HDSDR.  Each instance 
> of HDSDR is calibrated using the built in exalted carrier single 
> sideband calibration facility against WWV.  Audio then goes from HDSDR 
> to RCKskimmer.  Some users suggested that RCKskimmer must be 
> introducing some systematic frequency error since spots from all 
> RCKskimmer spotter stations seemed off.
>
> This week I used both RCKskimmer and MMTTY to monitor the W1AW 
> bulletin Baudot transmissions on 80, 40, and 20 meters.  The 
> frequencies reported by RCKskimmer were well within 100hz of the 
> published frequency, Using LSB fed to MMTTY and observing the crossed 
> ellipse display, the VFO dial frequency was quite close to the 2125hz 
> difference from the published Mark frequency one would have predicted.
>
> During Roundup I was using a 25 year old Ten Tec on 10 and 80 meters 
> so there is greater opportunity for inaccuracy on these bands.  Also 
> RCKskimmer generates a low number of spurious spots by some mechanism 
> I do not understand but they are usually out of band.  For any given 
> 2.4 khz band segment there is some low but significant probability of 
> making an error when I type the reference frequency into RCKskimmer or 
> into HDSDR while setting up the receivers.
>
> The W1AW digital bulletins are transmitted at 6 and 9 PM EST during 
> weekday evenings.  The frequencies can be found at 
> http://www.arrl.org/w1aw-operating-schedule
>
> If anyone has suggestions for how the skimmer spots can be improved I 
> would certainly welcome an email.  I am aware of the issue of spots 
> that are generated by stations in S&P mode.  Hopefully we can improve 
> our skimming tools over the next few months but I, at least, am having fun with the
> present software.  Hope some of you are as well.   ... chuckle....
>
> Wes, WZ7I
> _______________________________________________
> RTTY mailing list
> RTTY at contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
>

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