Skimmer frequency accuracy
To be a good RBN citizen a skimmer should have a frequency accuracy of 2ppm or better.
VERY IMPORTANT: To use the data below to improve the accuracy of your skimmer, multiply the current value of FreqCalibration in your skimmer software’s settings file with the suggested adjustment factor listed below.
The location of the settings files are:
CW Skimmer Server: %appdata%\Afreet\Products\SkimSrv\SkimSrv.ini
CW Skimmer: %appdata%\Afreet\Products\CwSkimmer\CwSkimmer.ini
The data listed below is based on yesterday’s RBN data, 00:00 to 23:59 UTC. This means that when making adjustments, changes in calibration will typically not have full impact on the listed data until the second day after the change.
The deviation estimates are based on spots on all active bands (40m and higher) from the respective skimmer. If different hardware is used for the different bands, the deviation number may thus not represent the actual deviation for a particular band. It is a good practice to run a separate instance of RBN Aggregator with a unique SSID for each hardware, (SM7IUN-1, SM7IUN-2, etc.)
A link to the software used to produce the tables can be found at the bottom of this page. It runs as a cron job in an Ubuntu container on my Synology server and uploads to this WordPress website shortly after midnight UTC daily.
The deviation estimation is done in two steps. The first step uses a small number of highly accurate skimmers (called “anchors” in the code, typically GPSDO-controlled skimmers) as reference. The whole estimation process is then repeated one more time but using both the anchors as well as all skimmers determined to be the “good” as reference. The “good” skimmers are those with less than 0.15ppm average deviation from the anchors, producing more than 100 qualifying spots (the qualification criteria of spots are outlined below.)
Repeating the analysis with this this extended set of skimmers as frequency references drastically increases the geographical coverage of the analysis thereby increasing the number of qualifying spots which means a much more reliable deviation estimates for all skimmers. The skimmers used as reference skimmers in the second stage (i.e. both anchors and “good”) are marked with an asterisk in the table below.
When looking at the numbers, keep in mind that the deviations estimated by the algorithm are 100 to 1000 times smaller than the 100Hz resolution of RBN frequency data. The input data is thus extremely “noisy” which inevitably leads to statistical variations. This is also the reason for not including spots under a certain frequency. Doing so would skew the statistics and cause underestimation of the frequency error.
Due to propagation characteristics, operator behavior (e.g. small QSY), and just statistical variations due to the 100Hz rounding, some skimmers selected as reference skimmers in the first stage may have more than 0.2ppm deviation in the second stage. This is not an error.
If you do not see your skimmer in the list below in spite of it successfully feeding spots to RBN the most likely reason is that it is off in frequency. The analytics discards all spots from skimmers having more than 0.5kHz frequency error.
if you want to implement an automated calibration of your skimmer you can access the skew data in machine-readable CSV format here https://sm7iun.se/rbnskew.csv
An skimmer calibration automation based on Windows PowerShell can be found here. It scrapes the calibration adjustment from this page and can be configured to update two CW Skimmer Server instances, two RTTY Skimmer Servers, and one CWSL_DIGI instance.
273312 RBN spots between 2025-07-09 00:00 and 23:59 UTC. 69688 spots (25.5%) were from reference skimmers (*). Average spot flow was 190 per minute from 189 active CW skimmers. 130412 spots from 174 skimmers qualified for analysis by meeting the following criteria: * Mode of spot is CW. * Also spotted by a reference skimmer within 1000 spots. * Also spotted by a reference skimmer within 10s. * SNR is 3dB or higher. * Frequency is 7000kHz or higher. * Frequency deviation from reference skimmer is 0.5kHz or less. * At least 5 spots from same skimmer in data set. Skimmer [ppm] Spots Adjustment ------------------------------------- 3B8GL +0.0 17 1.000000000 3D2AG +0.6 83 1.000000601 5Z/VE3NZ -0.8 64 0.999999182 5Z4GO +0.8 27 1.000000792 7N4XCV +0.2 30 1.000000159 AA0O +0.7 547 1.000000747 AC0C-1* -0.0 1635 0.999999983 BA4OP +0.0 14 1.000000000 BA6KC +0.2 149 1.000000191 BG0AJO +0.3 27 1.000000264 BG0AJO/0 +0.0 9 1.000000000 BG2TFW +0.7 137 1.000000676 BH4RRG +0.0 33 1.000000000 BH4XDZ +0.0 31 1.000000000 BI4MPH-1 +0.0 28 1.000000000 CT1EYQ +0.2 1136 1.000000214 CX6VM +0.3 305 1.000000273 DE1LON +1.4 1338 1.000001367 DF2CK +0.3 962 1.000000257 DF4UE/1 -9.0 959 0.999990955 DF7GB* -0.0 1418 0.999999953 DK0TE -0.7 737 0.999999274 DK3UA +0.0 17 1.000000000 DK3WW* -0.1 1791 0.999999949 DK9IP* +0.1 899 1.000000106 DK9IP-1* -0.0 1404 0.999999959 DL0PF +7.2 1626 1.000007179 DL1HWS +0.6 2104 1.000000626 DL8LAS +1.4 20 1.000001422 DL8TG* -0.0 1872 0.999999970 DM5GG +0.6 1852 1.000000598 DO4DXA -0.0 892 0.999999956 DR4W -2.3 2238 0.999997668 E28AC -3.9 86 0.999996113 EA2CW* -0.1 1280 0.999999858 EA2RCF-4 +0.3 757 1.000000266 ES5PC* +0.0 2003 1.000000006 F4GOU +8.1 1498 1.000008118 F4VVG* +0.0 849 1.000000021 F6IIT -0.5 1160 0.999999531 F6KGL +0.2 282 1.000000194 G0KTN +0.5 1371 1.000000452 G3YPP +0.6 140 1.000000645 G4IRN +0.2 2208 1.000000154 G4ZFE +1.0 1904 1.000000990 GI4DOH-2 +0.3 1340 1.000000344 GX0FRE +0.3 1014 1.000000258 HA1VHF +0.6 1811 1.000000581 HA5PP +3.6 249 1.000003633 HA6PX* -0.0 1743 0.999999984 HA8TKS +0.4 1072 1.000000435 HB9BXE* +0.0 1510 1.000000041 HG8A +1.7 1629 1.000001653 IK3STG +1.1 1272 1.000001115 IK7YTT* +0.1 2639 1.000000108 IW9GDC +8.5 718 1.000008482 JH7CSU1 +1.0 118 1.000000966 JI1HFJ -0.6 15 0.999999365 JJ2VLY +1.0 167 1.000000972 JN1ILK +0.0 484 1.000000031 K2PO/7 +0.6 371 1.000000563 K3PA-1* +0.0 1306 1.000000005 K4PP +0.1 657 1.000000052 K5EM +2.4 489 1.000002390 K5TR +0.8 744 1.000000807 K6FOD -0.0 662 0.999999982 K7CO +0.7 66 1.000000732 K7EK +0.0 138 1.000000001 K7RUT -0.1 184 0.999999935 K9IMM -0.0 906 0.999999968 K9LC +0.7 1066 1.000000708 KD2OGR +0.4 33 1.000000432 KD7EFG +0.4 372 1.000000434 KH6LC +0.2 72 1.000000165 KM3T-2* +0.2 644 1.000000228 KM3T-3 -0.3 1581 0.999999732 KM3T-5 +0.1 607 1.000000121 KO7SS +1.0 225 1.000000980 KP2RUM +0.2 669 1.000000235 KP3CW +0.2 481 1.000000168 KV4TT* +0.0 1050 1.000000015 KW7MM* -0.1 895 0.999999925 KW7MM/7 -0.1 646 0.999999914 LA6TPA +0.3 473 1.000000337 LU8XW +0.0 5 1.000000000 LZ3CB* +0.0 1191 1.000000002 LZ4AE -0.8 1134 0.999999226 LZ4UX* -0.0 829 0.999999978 LZ5DI +2.3 1516 1.000002270 LZ7AA +0.7 1114 1.000000747 MM0GPZ +0.3 1477 1.000000265 MM0ZBH* -0.0 813 0.999999954 N2CR +0.3 366 1.000000331 N2YCH -2.9 952 0.999997107 N6TV +0.9 356 1.000000912 N7TUG -0.8 47 0.999999241 N9CO -0.2 827 0.999999750 ND7K -0.2 835 0.999999803 NG7M +0.1 441 1.000000075 NT6Q -0.2 696 0.999999787 NU4F -0.1 726 0.999999908 OE9GHV* +0.1 590 1.000000080 OH4KA +0.3 314 1.000000301 OH6BG +0.2 1961 1.000000185 OH8KA +3.4 331 1.000003360 OK1FCJ* +0.1 2146 1.000000065 OK1HRA -4.6 1891 0.999995397 OK4QRO +2.4 1597 1.000002383 ON6ZQ +0.6 1232 1.000000593 OZ1AAB +0.4 268 1.000000372 OZ4ADX +0.1 274 1.000000052 PA5KT -0.2 217 0.999999790 PA8MM +0.4 1110 1.000000421 PE5TT +1.0 1207 1.000001050 PI4CC* +0.0 2304 1.000000049 PR1T -4.3 59 0.999995690 PY2KNK +1.1 252 1.000001089 PY2PE -5.7 65 0.999994277 R4NCU -1.3 39 0.999998721 R6YY -0.1 69 0.999999897 RK3TD +1.2 116 1.000001249 RN4WA +1.7 814 1.000001726 S50U +0.2 708 1.000000200 S53A +0.7 1771 1.000000740 S53F +2.1 1139 1.000002083 S53WW +0.7 900 1.000000677 SE5E +0.4 1698 1.000000403 SM1HEV +0.0 187 1.000000025 SM7IUN* -0.0 958 0.999999985 SQ5J +9.1 167 1.000009083 SV1CDN +4.8 8 1.000004755 SZ1A -1.1 630 0.999998850 TF3Y +1.6 1173 1.000001599 TI7W +0.8 1216 1.000000761 UT5R +5.0 53 1.000005011 UT5R-1 +4.3 149 1.000004313 UY2RA -0.6 842 0.999999392 VE6JY +2.9 1761 1.000002939 VE6WZ +4.1 206 1.000004144 VE7CC +1.1 334 1.000001110 VK2GEL +0.0 46 1.000000000 VK3RASA -1.4 147 0.999998642 VK6ANC -2.2 45 0.999997784 VR2FUN-77 +0.4 481 1.000000400 VU2CPL +3.2 8 1.000003164 VU2PTT -0.2 25 0.999999810 VU2TUM +0.5 88 1.000000459 W1NT-2* -0.0 1422 0.999999993 W1NT-6* -0.1 1623 0.999999929 W2LB +2.9 132 1.000002909 W2MV +0.9 82 1.000000867 W2NNN +13.0 915 1.000012980 W3OA +0.2 1187 1.000000204 W3RGA* +0.1 884 1.000000064 W4KAZ +3.3 26 1.000003283 W6YX +0.4 32 1.000000424 W8WTS +0.4 616 1.000000387 W8WWV -1.5 577 0.999998549 WA7LNW +0.7 1132 1.000000664 WB6BEE -0.3 78 0.999999726 WC2L* +0.1 914 1.000000140 WC8GOP +13.2 40 1.000013243 WE9V +0.1 1055 1.000000102 WS2C +7.9 709 1.000007853 WT9U +5.5 106 1.000005460 WV4P +0.5 729 1.000000479 WX7V/5 +0.6 109 1.000000588 YO2CK +0.3 1273 1.000000316 YO2MAX* -0.1 1722 0.999999911 YO5LD +0.6 541 1.000000609 ZF9CW -0.3 1286 0.999999653 ZL3X -0.6 120 0.999999406 ZL4YL +3.0 50 1.000002994 ZS1NN -4.4 35 0.999995565 Last updated 2025-07-10 00:15:26 UTC
Historical skimmer frequency accuracy
Below you will find historical accuracy data for the past ten days. Do not be concerned over minor daily variations. Since RBN spots only have 100Hz frequency accuracy, the input data is very noisy. Even for a perfectly accurate skimmer, the typical RMS rounding error across all shortwave bands is around 3ppm. This means that for a skimmer with 1000 spots per day the statistical variation is up to 0.2ppm. For skimmers with less than 100 spots per day the statistical variation can be above 2ppm. The content of the table below is based on the historical content of the above table.
Skimmer 0709 0708 0707 0706 0705 0704 0703 0702 0701 0630 --------------------------------------------------------------------- 3B8GL +0.0 3D2AG +0.6 +0.2 +0.5 +0.1 +0.8 +0.5 +0.9 5Z4GO +0.8 +0.6 +0.5 -0.1 +0.6 +1.2 -0.1 +0.8 +0.0 +0.0 5Z/VE3NZ -0.8 7N4XCV +0.2 +0.8 +0.4 +0.0 +0.3 +0.2 +0.5 +0.1 -0.1 +0.8 AA0O +0.7 +0.6 +0.7 +0.4 +0.9 +0.7 +0.9 +0.7 +0.7 +0.7 AC0C-1 -0.0 +0.0 +0.0 -0.1 -0.0 +0.0 -0.1 -0.1 +0.1 -0.1 BA4OP +0.0 -0.1 -0.4 -0.1 -0.2 -0.1 +0.1 -0.2 BA6KC +0.2 +0.2 +0.0 +0.2 +0.0 -0.1 +0.1 +0.1 +0.0 +0.1 BD7JNA +0.0 +0.8 BG0AJO/0 +0.0 +0.0 +0.0 -0.2 -0.4 -0.2 +0.3 +0.0 +0.0 +0.0 BG0AJO +0.3 +0.4 +1.3 +0.2 +0.4 +0.3 +0.2 +0.5 +0.3 +0.3 BG2TFW +0.7 +0.5 +1.1 +0.1 +0.4 +0.2 +0.4 +0.4 +0.4 +0.7 BG4WOM -0.6 +0.0 +0.3 +0.1 -0.0 +0.0 BH4HKZ +0.0 +0.0 +0.0 +0.0 BH4RRG +0.0 +0.3 +0.5 +1.9 +0.0 +0.0 +1.2 +0.2 +0.7 BH4XDZ +0.0 +0.0 +0.0 +0.6 +0.2 +0.1 -0.1 +0.2 +0.6 -0.1 BI4MPH-1 +0.0 +0.0 -0.8 +0.2 CT1EYQ +0.2 +0.1 +0.1 +0.1 +0.2 +0.1 +0.2 +0.2 +0.5 +0.5 CX6VM +0.3 +0.4 +0.2 +0.0 +0.3 -0.2 -0.3 -0.3 -0.4 -0.1 DE1LON +1.4 +1.1 +1.2 +1.7 +2.2 +1.9 +2.2 +2.8 +1.9 +2.0 DF2CK +0.3 +1.3 +1.4 +1.6 +1.3 +1.6 +1.8 +1.2 +1.4 +1.4 DF4UE -10.0 -10.0 DF4UE/1 -9.0 -9.4 -9.3 DF7GB -0.0 +0.0 +0.0 +0.0 +0.0 +0.0 -0.0 -0.0 +0.0 -0.0 DJ3AK +2.2 DK0TE -0.7 +0.1 +0.1 +1.6 +1.8 +1.4 +1.4 +0.8 +0.7 +1.8 DK3UA +0.0 +0.1 -0.3 -0.3 +0.0 -0.2 +0.1 +0.2 DK3WW -0.1 -0.2 -0.3 -0.2 -0.2 -0.3 -0.1 -0.1 -0.2 -0.1 DK8NE +0.2 -0.1 +0.0 -0.0 DK9IP +0.1 +0.0 +0.1 +0.2 +0.2 +0.1 +0.1 +0.2 +0.2 +0.5 DK9IP-1 -0.0 +0.0 +0.1 +0.0 +0.2 +0.1 +0.0 +0.2 +0.2 +0.2 DL0PF +7.2 +7.4 +9.0 +7.1 +13.4 +12.1 +11.8 +11.6 +11.8 DL1HWS +0.6 +0.4 +0.5 +0.7 +0.8 +0.5 +0.5 +0.4 +0.5 +0.5 DL1HWS-3 +0.6 +0.6 +0.5 +0.5 DL1HWS-4 +0.1 +0.3 +0.3 +0.6 DL5RCN +9.7 +13.6 +14.1 +14.4 DL5RMH +0.0 +0.2 DL8LAS +1.4 +0.7 +1.4 +1.6 +1.5 +1.5 +2.0 +2.2 +1.7 +1.4 DL8TG -0.0 -0.1 -0.2 -0.0 -0.1 +0.0 -0.0 -0.1 +0.1 +0.0 DM5GG +0.6 +0.6 +0.7 +0.9 +0.9 +0.5 +0.5 +0.4 +0.6 +0.8 DM6EE -0.1 +0.1 +0.1 +0.1 +0.0 +0.1 +0.1 -0.0 DO4DXA -0.0 -0.1 -0.0 +0.0 +0.0 +0.0 -0.0 -0.1 +0.1 -0.1 DR4W -2.3 -1.9 -0.7 -1.3 -1.1 -0.9 -0.5 -0.5 -1.0 -0.1 E28AC -3.9 -4.2 -2.9 -3.7 -3.2 -4.0 -3.1 -2.9 -3.2 EA2CW -0.1 -0.3 -0.3 -0.0 +0.1 -0.1 -0.1 +0.0 +0.2 +0.5 EA2RCF-4 +0.3 +0.3 +0.3 +0.3 +0.4 +0.3 +0.5 +0.5 +0.5 +0.5 EA5RQ/A +0.5 -0.0 +0.0 EA5WU -0.0 -0.0 -0.0 +0.0 +0.0 +0.0 +0.1 +0.0 +0.1 ES2RR -0.0 -0.1 +0.0 -0.0 -0.1 -0.0 -0.0 -0.1 +0.0 ES5PC +0.0 -0.1 -0.1 -0.0 +0.1 +0.0 -0.0 +0.0 +0.0 +0.0 EU1ST +4.0 F4GOU +8.1 +8.4 +8.4 +8.7 +8.9 +9.0 +9.1 +9.1 +9.1 +9.6 F4VVG +0.0 -0.1 -0.0 +0.0 -0.1 -0.1 -0.1 -0.3 -0.3 F6IIT -0.5 -0.5 -0.4 -0.3 -0.2 -0.1 -0.0 +0.2 +0.0 +0.0 F6KGL +0.2 +0.1 +0.2 +0.1 +0.1 G0KTN +0.5 +0.5 +0.5 +0.5 +0.5 +0.4 +0.5 +0.5 +0.4 +0.6 G3YPP +0.6 -0.3 +0.1 +0.2 +0.2 +0.5 +0.2 +0.9 +0.0 +0.1 G4IRN +0.2 +0.2 +0.3 +0.4 +0.4 +0.2 +0.3 +0.3 +0.3 +0.2 G4ZFE +1.0 +0.8 +0.8 +0.9 +1.1 +0.7 +0.8 +1.2 +1.1 +1.3 GE0FRE +2.4 +1.4 GI4DOH-2 +0.3 +0.1 +0.1 +0.3 +0.3 GX0FRE +0.3 +0.0 +0.0 +0.2 +0.3 +0.1 +0.1 +0.1 +0.1 +0.2 HA1VHF +0.6 +0.7 +0.8 +1.2 +1.3 +0.9 +1.2 +1.0 +1.0 +1.1 HA5PP +3.6 -0.1 -0.5 HA6PX -0.0 -0.0 -0.0 -0.2 -0.1 +0.0 +0.0 +0.1 +0.1 +0.1 HA8TKS +0.4 +0.2 +0.5 +0.4 +0.4 +0.3 +0.3 +0.3 +0.3 +0.4 HB9BXE +0.0 +0.1 +0.1 +0.2 +0.3 +0.3 +0.2 +0.3 +0.3 +0.4 HB9DCO -0.2 -0.1 -0.3 +0.1 +0.0 +0.2 +0.2 +0.1 +0.1 HG0Y +7.9 HG8A +1.7 +2.8 +3.2 +3.3 +3.3 +3.1 +3.2 +3.1 +2.5 +3.1 IK3STG +1.1 +0.7 +0.7 +0.9 +0.8 +0.7 +1.2 +0.6 +0.6 +0.8 IK4VET +4.6 +3.6 +3.6 IK7YTT +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.2 IQ9RG +0.0 +0.1 +0.1 +0.1 +0.0 IW9GDC +8.5 +8.4 +8.8 +8.7 +8.8 +8.7 +8.6 +8.4 +8.6 +8.8 J68HZ +18.4 JG1DLY +0.0 -1.5 -0.4 JH7CSU1 +1.0 +1.6 +0.9 +1.4 +1.4 +1.5 +1.7 +1.3 +1.9 +1.2 JI1HFJ -0.6 +0.0 +0.4 +0.4 +0.6 -0.6 -0.1 +1.4 +0.7 JJ2VLY +1.0 +1.8 +1.4 +1.5 +1.7 +1.4 +2.6 +1.3 +1.8 +1.3 JK1QLQ +0.0 +0.0 +0.4 +0.0 +0.0 JN1ILK +0.0 +0.1 -0.3 +0.1 +0.1 +0.1 +0.1 +0.2 K1RA +1.3 +1.3 +0.7 +0.9 +0.8 +0.9 +0.9 +1.2 +1.0 K2PO/7 +0.6 +0.4 +0.7 +0.5 +0.7 +0.6 +0.7 +0.9 +0.9 +0.7 K3PA-1 +0.0 -0.0 +0.1 -0.0 +0.1 -0.0 -0.0 -0.1 +0.0 +0.0 K3PA-2 -0.2 -0.1 -0.3 -1.2 K4PP +0.1 +0.2 +0.1 +0.0 +0.2 -0.0 -0.1 +0.2 +0.6 +0.2 K5EM +2.4 +3.2 +3.2 +3.8 +4.0 +3.4 +3.7 +3.3 +3.6 +3.9 K5TR +0.8 -4.8 -4.9 -4.9 -3.6 -3.9 -4.7 -3.7 -4.5 -3.6 K6FOD -0.0 -0.1 +0.1 +0.1 +0.1 -0.1 +0.0 -0.0 +0.1 +0.0 K7CO +0.7 +1.1 +0.5 +1.3 +1.1 +1.2 +1.0 +1.2 +1.4 +1.1 K7EK +0.0 -1.5 -0.9 -0.5 +0.4 +0.6 -1.4 +0.2 -0.7 -0.6 K7RUT -0.1 K9IMM -0.0 -0.1 -0.0 -0.2 -0.4 -0.4 -0.3 -0.6 -0.7 -0.9 K9LC +0.7 +0.7 +0.6 +0.3 +0.7 +0.7 +0.6 +0.8 +1.0 +0.5 KC4YVA +3.1 +4.5 +3.9 +4.7 +4.6 +4.5 KD2OGR +0.4 +1.0 +0.2 +0.0 +0.4 +0.2 +0.1 +0.4 +0.3 +0.3 KD7EFG +0.4 +0.1 +0.3 -0.2 +0.3 +0.4 +0.4 +0.3 +0.4 +0.4 KH6LC +0.2 +0.6 +0.4 +0.2 +0.3 +0.3 +0.0 -0.0 +0.4 +0.0 KM3T-2 +0.2 +0.0 +0.1 +0.0 +0.2 +0.1 +0.3 +0.2 +0.2 +0.1 KM3T-3 -0.3 -0.2 -0.2 -0.1 -0.1 -0.2 -0.3 -0.3 -0.3 -0.2 KM3T-5 +0.1 +0.1 +0.1 -0.1 +0.0 -0.1 -0.0 -0.1 +0.2 -0.0 KM4SII +0.5 +1.4 KO7SS +1.0 +0.7 +0.7 +0.6 +1.6 +1.1 +0.7 +1.1 +1.1 +0.9 KP2RUM +0.2 -0.2 -0.3 +0.2 +0.4 +0.0 -0.1 -0.1 +0.1 +0.2 KP3CW 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UTC
Anchor skimmers
The below skimmers use external frequency references and are confirmed to have continuous, high accuracy. Their accuracy is also confirmed against each other on a daily basis.
DF7GB KM3T-5 LZ3CB LZ4UX OE9GHV WB6BEE Last updated 2025-07-10 00:15:32 UTC
It is the owners of these skimmers who make this web page possible. Thank you.
To get good geographic coverage and a good size dataset, a two-step method is used for the analysis shown above. Since the second step also relies on spots from skimmers with slightly lower accuracy the displayed error for the anchor skimmers may not always be 0.0, even though they are perfectly accurate.
Software
The software powering this page can be found on github.