[RTTY] Frequency skew

[Shoppa, Tim]

Here's my little Monday morning quarterbacking on Skimmer performance this past weekend. I was wondering if maybe my VFO or frequency math (when doing AFSK) was out of whack, because skimmer spots were most often 200-400Hz low. Pretty soon I got in the habit of just clicking about 300Hz or so above any skimmer spot and most often found this to handle the skew, but I also began to notice that not all skimmers were offset by the same amount, sometimes clicking 400Hz high was a bit better. Manually entered spots, while they had more callsign busts than the skimmer busts, seemed to have less of a systematic offset in frequency. So I also thought to myself, how can I check what other guys and the skimmer thought my frequency was?

I looked at the peak of my most prolific run in the contest, 3589.9/3590.0kc in the 03:55 to 04:28 timeframe the first night (hint, my station is most effective on 80M, wow is 80M a joy). Many of these QSO's are already confirmed in LOTW (hint, RTTY contesting has extremely high confirmation rates in LOTW). If they are confirmed in LOTW, I can often see the frequency of the other guys VFO too (not all ADIF's have to contain this frequency but for computer-connected rigs it will be very common). Here's my QSO's, with my VFO dial and the other guy's VFO dial where I know it. You can see I slide up about 100Hz in this run to minimize close-in QRM.

N3QE S57UX 2014-02-09 03:55:58 80M RTTY 3.58991 his VFO 3.58982
N3QE W5EW 2014-02-09 03:57:11 80M RTTY 3.58991 his VFO 3.5899
N3QE AB4SF 2014-02-09 03:57:36 80M RTTY 3.58991 his VFO 3.58989
N3QE KS4L 2014-02-09 03:59:37 80M RTTY 3.58991 his VFO 3.5899
N3QE N0EKM 2014-02-09 04:00:14 80M RTTY 3.58991 his VFO 3.5899
N3QE LZ2ZG 2014-02-09 04:01:04 80M RTTY 3.58991 his VFO 3.58983
N3QE VE6SQ 2014-02-09 04:02:48 80M RTTY 3.58991 his VFO 3.58988
N3QE K8MU 2014-02-09 04:03:30 80M RTTY 3.58991 his VFO 3.58988
N3QE AA0AW 2014-02-09 04:04:30 80M RTTY 3.58991 his VFO 3.59105
N3QE KD2A 2014-02-09 04:06:00 80M RTTY 3.58991 his VFO 3.58988
N3QE N3PPH 2014-02-09 04:06:22 80M RTTY 3.58991 his VFO 3.5887
N3QE N2QT 2014-02-09 04:13:29 80M RTTY 3.58991 his VFO 3.58989
N3QE VE3KI 2014-02-09 04:14:07 80M RTTY 3.58991 his VFO 3.58988
N3QE WB2SXY 2014-02-09 04:16:27 80M RTTY 3.58991 his VFO 3.58838
N3QE W4EE 2014-02-09 04:17:10 80M RTTY 3.58991 his VFO 3.58892
N3QE EA2KU 2014-02-09 04:20:20 80M RTTY 3.59000 his VFO 3.590
N3QE KA9MOM 2014-02-09 04:27:21 80M RTTY 3.59000 his VFO 3.58999
N3QE K6UFO 2014-02-09 04:28:35 80M RTTY 3.59000 his VFO 3.590
N3QE KN3A 2014-02-09 04:28:55 80M RTTY 3.59000 his VFO 3.58997

If you look at "my VFO" vs "his VFO" where both are known, maybe my VFO reads like 30Hz high. There's obviously some with random offsets of up to a kc or more out there.

Now look at the RCKSkimmer spots in this same timeframe (fetched from downloads at reversebeacon.net<http://reversebeacon.net/>):

20140209.csv:DL9GTB,DL,EU,3589.7,80m,N3QE,K,NA,CQ,17,2014-02-09 03:47:05,45,RTTY
20140209.csv:WZ7I,K,NA,3589.5,80m,N3QE,K,NA,CQ,26,2014-02-09 03:49:05,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.7,80m,N3QE,K,NA,CQ,25,2014-02-09 03:49:53,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,22,2014-02-09 03:54:10,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,22,2014-02-09 03:59:24,45,RTTY
20140209.csv:N2QT,K,NA,3589.8,80m,N3QE,K,NA,CQ,20,2014-02-09 04:03:50,45,RTTY
20140209.csv:WZ7I,K,NA,3589.6,80m,N3QE,K,NA,CQ,25,2014-02-09 04:04:15,45,RTTY
20140209.csv:DL9GTB,DL,EU,3589.8,80m,N3QE,K,NA,CQ,23,2014-02-09 04:10:32,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.8,80m,N3QE,K,NA,CQ,27,2014-02-09 04:12:38,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.9,80m,N3QE,K,NA,CQ,26,2014-02-09 04:19:23,45,RTTY
20140209.csv:N2QT,K,NA,3589.9,80m,N3QE,K,NA,CQ,27,2014-02-09 04:24:05,45,RTTY
20140209.csv:WZ7I,K,NA,3589.7,80m,N3QE,K,NA,CQ,22,2014-02-09 04:25:05,45,RTTY
20140209.csv:KB9AMG,K,NA,3589.9,80m,N3QE,K,NA,CQ,26,2014-02-09 04:26:18,45,RTTY
20140209.csv:HA6M,HA,EU,3593.7,80m,N3QE,K,NA,CQ,12,2014-02-09 04:28:47,45,RTTY

Note that several skimmers are systematically low by 100-200Hz and one by closer to 300-400Hz. That last one is way out in left field. The systematics seemed to change from band to band.

None of this means that the skimmers are broken. It just means that we have to apply a little observation when using them to increase our band awareness.

Tim N3QE