[RTTY] [rckskimmer] Frequency accuracy of WZ7I RCKskimmer spots

[Dave Hachadorian]

I just turned on the radio at 1800Z, and saw the following spots from WZ7I-#:

1800Z  W1AW/7 21080.9  My K3/mmtty reports 21081.13

1802Z EA1HNP  14087.5  My K3 reports 14087.66

At 1805Z, WQ1H spotted W1AW/7 at 21081.1, agreeing with my K3.

In the last few minutes WZ7I-# also reports AG3V, WB4GLI, KI0KB, W6SFK, IK2RPE cq’ing on 21080.9.  These are actually stations working W1AW/7.

I guess I don’t understand what’s going on.  W1AW/7 is still there with a good pileup, so here is a chance for others to report some measurements also.

Thanks.

Dave Hachadorian, K6LL
Yuma, AZ


From: Wes Cosand 
Sent: Friday, January 10, 2014 8:32 AM
To: rckskimmer at yahoogroups.com 
Subject: [rckskimmer] Frequency accuracy of WZ7I RCKskimmer spots

  

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
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