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 for 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.
1532291 RBN spots between 2026-10-17 00:00 and 23:59 UTC. 382360 spots (25.0%) were from reference skimmers (*). Average spot flow was 1064 per minute from 232 active CW skimmers. 650430 spots from 230 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 +0.9 82 1.000000874 5Z4GO +0.5 450 1.000000454 9M2CNC +0.1 138 1.000000103 AA0O +3.4 75 1.000003421 AA4PA -0.5 3253 0.999999510 AC0C-1* -0.0 4704 0.999999974 AC0VW -0.7 1677 0.999999287 AK6RI-1* +0.1 758 1.000000077 BD7JNA +0.2 151 1.000000220 BD8CS* +0.1 1632 1.000000066 BG2TFW +0.0 131 1.000000039 BG4GOV +0.4 48 1.000000372 BG7IEJ +0.0 17 1.000000000 BH4RRG +7.0 12 1.000006987 BH4XDZ -0.3 338 0.999999740 CT1EYQ -0.6 5341 0.999999360 DC8YZ +0.4 4334 1.000000391 DE1LON* +0.0 2668 1.000000023 DF7GB* +0.1 5811 1.000000075 DG1ELE* +0.1 5230 1.000000109 DK0TE* -0.1 5919 0.999999888 DK9IP* -0.0 4685 0.999999988 DK9IP-1* -0.1 5528 0.999999895 DL0AO +0.4 1214 1.000000392 DL0LA* +0.2 1186 1.000000157 DL0TRZ -14.7 200 0.999985309 DL1HWS -2.8 2835 0.999997204 DL1HWS-3 +1.7 3763 1.000001721 DL3OBQ -7.6 36 0.999992433 DL5RCN +14.6 61 1.000014576 DL5RMH +3.9 943 1.000003863 DL7ZF +0.0 46 1.000000000 DL8LAS +0.2 7507 1.000000190 DL8LAS-1 +0.2 4454 1.000000203 DL8LAS-3 -0.4 3962 0.999999617 DL8TG* -0.1 5492 0.999999927 DL9GTB* +0.0 422 1.000000022 DM5GG +1.0 3641 1.000000953 DM7EE +0.7 3345 1.000000660 DO4DXA* +0.1 6820 1.000000109 DR4W -3.9 4349 0.999996119 EA1DAV* +0.0 5245 1.000000022 EA1URA -1.9 608 0.999998074 EA2CW* -0.0 759 0.999999956 EA2RCF-4 +0.4 4185 1.000000438 EA4RKC +0.3 1427 1.000000265 EA5WU* +0.0 3267 1.000000004 EI4HQ* -0.1 6126 0.999999882 ES2RR* -0.0 7693 0.999999959 EY8ZE* +0.2 1955 1.000000173 F4BPO +1.5 417 1.000001485 F4GOU -0.2 5102 0.999999772 F5AHD +2.7 1219 1.000002713 F6KGL +0.3 5816 1.000000273 G0KTN +0.3 5598 1.000000312 G0TMX -0.6 1950 0.999999367 G3AKX +0.2 8354 1.000000205 G3YPP -0.1 568 0.999999857 G4IRN +0.6 2315 1.000000565 G4ZFE* -0.1 4988 0.999999900 GI4DOH -0.2 6171 0.999999779 GX0FRE* -0.1 4435 0.999999882 HA1VHF* +0.2 5614 1.000000188 HA5PP +2.6 125 1.000002620 HA8TKS* +0.1 3185 1.000000138 HB9BXE +0.3 4754 1.000000263 HB9DCO -0.2 5063 0.999999843 HB9EMP* -0.0 3766 0.999999999 HB9GVO +0.6 289 1.000000608 HB9YC +0.6 1717 1.000000630 HG8A -1.4 6572 0.999998587 HS0ZGZ +1.5 438 1.000001518 IK3STG +3.2 3096 1.000003237 IK7YTT* -0.0 4594 0.999999972 IT9GSF* -0.0 7856 0.999999967 IW9GDC* -0.2 4065 0.999999847 IZ2CPS +0.0 7 1.000000000 JA1CCA -1.3 420 0.999998737 JE2YCR +0.5 114 1.000000459 JH7CSU1 +1.8 447 1.000001827 JH8YOH-1 +0.3 87 1.000000328 JI1HFJ -2.3 184 0.999997656 JK1QLQ +0.7 35 1.000000690 K1HTV-4 +0.0 2199 1.000000006 K1RA-4 -0.5 4215 0.999999503 K2PO/7 -0.2 1270 0.999999822 K3FEF* +0.1 6113 1.000000076 K3GMQ* -0.0 1601 0.999999995 K3PA-1 +0.9 3939 1.000000925 K3PA-2 +0.0 29 1.000000000 K4EVT +4.6 997 1.000004649 K4PP +0.4 2105 1.000000439 K5EM +5.3 387 1.000005291 K5KHK* +0.1 1918 1.000000119 K5TR +0.5 2874 1.000000467 K6FOD* -0.0 576 0.999999991 K7CO* +0.3 731 1.000000299 K7EK -1.0 747 0.999999028 K9IMM* -0.0 4080 0.999999962 K9LC -0.2 3357 0.999999764 KC2DAC +0.2 1802 1.000000164 KC4YVA +2.0 2442 1.000002003 KD2OGR +0.5 939 1.000000528 KD7EFG +0.5 1767 1.000000538 KG6NFJ +0.3 1177 1.000000328 KH6LC -0.0 148 0.999999952 KK4FL +0.2 2643 1.000000159 KM3T-2 +0.7 4701 1.000000719 KM3T-3 +0.2 5922 1.000000229 KM3T-5* -0.0 4691 0.999999976 KM7W -0.4 203 0.999999650 KR4IXC +0.2 1576 1.000000202 LA6TPA -1.2 1512 0.999998802 LB9KJ +0.4 4072 1.000000383 LB9KJ-1 +4.4 1344 1.000004385 LU8XW +2.8 114 1.000002785 LZ2HQ -5.9 5571 0.999994131 LZ3CB* -0.0 5031 0.999999977 LZ4AE +0.9 10384 1.000000857 LZ4UX* +0.1 5790 1.000000053 LZ5DI +2.1 5408 1.000002070 LZ7AA +0.8 5478 1.000000758 M9PCX* +0.0 2475 1.000000044 M9PSY-2* -0.0 6460 0.999999969 MM0ZBH -1.2 9135 0.999998813 MM9PSY* -0.0 7536 0.999999988 N2CR +0.3 1525 1.000000336 N2EPE* -0.0 4351 0.999999983 N2YCH +0.1 2053 1.000000136 N4HAC -0.1 373 0.999999949 N6TV* +0.0 1034 1.000000031 N7OR +0.3 1384 1.000000283 N7TUG +2.5 92 1.000002549 N7VVX -0.0 340 0.999999993 N8DXE +2.0 1821 1.000002001 ND7K -0.9 2502 0.999999081 NG7M* -0.1 1531 0.999999897 NN3RP -1.0 170 0.999998953 OE6ADD +0.4 5256 1.000000446 OE8TED* -0.0 4667 0.999999959 OE9GHV* -0.0 7111 0.999999956 OH4KA +2.8 2082 1.000002828 OH6BG +0.2 5032 1.000000205 OK1FCJ +0.9 6980 1.000000879 OK1HRA -3.5 4013 0.999996476 OK2RZ +14.7 4132 1.000014731 OK4YL +14.7 4915 1.000014750 OK4ZW -3.7 211 0.999996288 OM5ALL +0.7 1997 1.000000656 ON6URE* -0.1 932 0.999999948 ON6ZQ +0.3 1788 1.000000268 OZ1AAB -0.9 2723 0.999999100 OZ1BZS +0.8 1444 1.000000795 PA0MBO +0.4 602 1.000000441 PA3GRM +0.2 1496 1.000000194 PA5KT-4* -0.1 2845 0.999999896 PD2RPS* -0.0 9615 0.999999989 PE5TT +1.2 5456 1.000001203 PI4CC +3.7 2325 1.000003702 PT2FHC* -0.1 759 0.999999929 PY2KNK +5.7 456 1.000005730 R4NCU -0.3 1097 0.999999675 RK3TD +0.4 4427 1.000000360 RK3TD-2 +1.1 4379 1.000001080 RN4WA +1.4 4359 1.000001356 RU9CZD* +0.1 5905 1.000000127 S50ARX -0.3 5702 0.999999701 S50U +0.2 1000 1.000000212 S53A +1.2 9268 1.000001193 S53WW -0.6 6778 0.999999363 S54L* +0.1 6690 1.000000056 S58W* +0.1 1947 1.000000055 SE5E* -0.0 6884 0.999999991 SK6AW* +0.0 3898 1.000000005 SM0TCZ +1.5 386 1.000001451 SM1HEV -0.3 5097 0.999999714 SM7IUN* -0.0 5053 0.999999957 SP5GQ* +0.0 1829 1.000000050 SQ5J +8.6 2597 1.000008643 SV1CDN +0.4 1466 1.000000418 SZ1A -0.3 6271 0.999999747 TF3Y +2.0 6081 1.000002015 TI7W +3.3 3377 1.000003252 UR4RXX -0.2 280 0.999999761 UT5R -0.2 2035 0.999999836 UY2RA -2.0 900 0.999998025 V51YJ +2.0 589 1.000002008 VE3EID +0.5 5815 1.000000548 VE4DRK +4.6 881 1.000004589 VE6AO -1.4 949 0.999998632 VE6JY +0.9 1333 1.000000869 VE6WZ -1.0 4104 0.999999027 VE6WZ-3 +16.2 237 1.000016182 VK2GEL -0.4 79 0.999999639 VK2RH +0.5 169 1.000000464 VK3RASA +0.2 291 1.000000199 VK6ANC* +0.2 378 1.000000170 VU24DX-1 +0.3 139 1.000000251 VU2CPL-88 +0.4 69 1.000000449 VU2OY +0.8 60 1.000000831 VU2OY-9 +11.9 25 1.000011938 VU2PTT -0.1 59 0.999999932 VU2TUM +1.3 954 1.000001260 W1NT-2* -0.1 5510 0.999999947 W1NT-6* -0.0 6996 0.999999978 W2MV +0.4 1053 1.000000365 W2NAF +2.2 1523 1.000002222 W2NNN +3.4 5445 1.000003442 W3DAN +1.9 1754 1.000001858 W3OA +0.2 142 1.000000201 W4KAZ -0.7 2363 0.999999338 W5ZN +2.8 2910 1.000002774 W6YX +0.9 1992 1.000000866 W8WTS +0.4 2363 1.000000355 W8WWV -2.0 3277 0.999998026 WA7LNW -0.0 446 0.999999952 WB6BEE* -0.0 4628 0.999999995 WC2L* +0.1 2635 1.000000112 WE9V -0.1 4231 0.999999877 WS2C +9.2 1708 1.000009204 WT9U +0.3 1967 1.000000261 WX7V/5 +0.7 534 1.000000733 WZ7I +1.1 5359 1.000001150 YO2CK* +0.1 4866 1.000000064 YO2KAR +0.2 4679 1.000000185 YO5LD-U +3.4 4752 1.000003394 ZF1A -1.5 612 0.999998487 ZL2KS +0.5 637 1.000000481 ZL4YL +0.6 264 1.000000562 ZS1NN -4.4 586 0.999995615 Last updated 2026-10-18 00:17:16 UTC
The following skimmers had an estimated skew exceeding 3ppm yesterday
AA0O BH4RRG DL0TRZ DL3OBQ DL5RCN DL5RMH DR4W IK3STG K4EVT K5EM LB9KJ LZ2HQ OK1HRA OK2RZ OK4YL OK4ZW PI4CC PY2KNK SQ5J TI7W VE4DRK VE6WZ VU2OY W2NNN WS2C YO5LD-U ZS1NN
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 1017 1016 1015 1014 1013 1012 1011 1010 1009 1008 --------------------------------------------------------------------- 3B8GL +0.9 +0.2 +1.0 +0.8 +0.4 +0.0 +2.6 +0.0 +4.0 5Z4GO +0.5 +0.3 +0.3 +0.8 +0.6 +0.0 +0.4 +0.4 +0.3 +0.6 9M2CNC +0.1 +0.0 +0.0 -0.2 +0.3 +0.0 +0.2 +0.2 +0.0 +0.4 AA0O +3.4 +3.2 +2.6 +3.0 +2.8 +2.9 +2.5 +3.3 +2.4 +2.4 AA4PA -0.5 -0.2 -0.0 +0.2 +0.3 +0.2 +0.3 +0.3 +0.1 +0.4 AC0C-1 -0.0 -0.0 -0.1 -0.0 -0.0 -0.0 -0.1 +0.1 -0.0 -0.1 AC0VW -0.7 -0.6 -12.1 -8.6 -0.4 -0.5 AK6RI-1 +0.1 -0.4 -0.0 +0.1 -0.1 -0.1 +0.2 +0.0 -0.1 -0.3 BA4OP -2.0 -0.0 +0.0 -0.2 +0.0 +0.0 -0.1 -0.1 +0.2 BD4UNT +0.2 +0.2 +0.3 +0.2 +0.3 +0.3 -0.1 -0.1 BD7JNA +0.2 +0.0 +0.0 +0.0 +0.4 +0.0 +0.0 +0.0 +0.0 -0.3 BD8CS +0.1 -0.1 -0.1 -0.1 -0.0 +0.1 +0.1 -0.0 -0.1 -0.0 BG2TFW +0.0 +0.1 -0.5 +0.0 +0.1 +0.0 +0.1 +0.1 +0.0 -0.4 BG4GOV +0.4 +0.0 +0.2 +0.6 +0.4 +0.4 BG7IEJ +0.0 -0.1 +0.0 -0.3 -0.3 +0.0 -0.4 -0.2 -0.2 -0.2 BH4RRG +7.0 -7.8 BH4XDZ -0.3 +0.0 -0.0 +0.2 -0.1 -0.5 +0.0 +0.1 CT1EYQ -0.6 -0.4 -0.5 -0.3 -0.4 -0.6 -0.7 -0.5 -0.2 -0.3 CX6VM +3.6 +4.7 +4.3 +4.1 +4.4 +4.9 +4.8 DB0GIE-11 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.0 +0.1 DC8YZ +0.4 +0.4 +0.1 +0.4 +0.1 +0.3 +0.2 +0.2 +0.1 +0.2 DD5XX +0.0 +0.5 +0.2 +0.3 +0.3 +0.3 +0.1 +0.7 DE1LON +0.0 -0.0 +0.1 +0.1 +0.0 +0.0 +0.1 +0.0 +0.1 +0.1 DF7GB +0.1 -0.0 +0.0 -0.0 -0.0 +0.1 +0.1 -0.1 -0.0 -0.0 DG1ELE +0.1 +0.0 +0.0 DK0TE -0.1 +0.0 +0.0 +0.0 -0.3 -0.1 -0.2 -0.1 +0.0 +0.1 DK3WW +0.0 +0.1 +0.1 -0.0 DK9IP -0.0 -0.0 -0.1 +0.0 -0.0 -0.0 +0.0 +0.1 -0.0 -0.0 DK9IP-1 -0.1 -0.1 +0.0 +0.0 +0.0 -0.1 -0.0 +0.1 +0.0 +0.0 DL0AO +0.4 +0.1 +0.2 +0.1 DL0LA +0.2 -0.1 +0.1 +0.2 +0.0 -0.0 +0.2 -0.1 +0.1 +0.2 DL0TRZ -14.7 -12.2 -13.5 -12.2 -14.6 -14.7 -14.9 -16.2 -15.3 -15.1 DL1HWS -2.8 -1.9 -1.5 -1.5 -1.5 -2.1 -1.9 -1.5 +0.1 +0.6 DL1HWS-3 +1.7 +1.1 +1.0 +1.1 +1.0 +1.0 +0.9 +1.0 +0.8 +0.9 DL1HWS-4 +1.1 +1.3 DL3OBQ -7.6 -7.1 -7.4 -7.3 DL5RCN +14.6 +13.8 +12.9 +13.7 +13.8 DL5RMH +3.9 DL7ZF +0.0 +0.0 +0.2 +0.0 +0.0 +0.0 +0.0 +0.0 +0.0 +0.0 DL8LAS +0.2 +0.1 +0.1 +0.1 +0.1 +0.2 -0.1 -0.1 -0.0 +0.3 DL8LAS-1 +0.2 +0.0 +0.0 +0.0 -0.1 -0.1 -0.3 -0.2 -0.2 +0.0 DL8LAS-3 -0.4 -0.4 -0.4 -0.3 -0.4 -0.3 -0.2 -0.2 DL8TG -0.1 -0.1 -0.1 -0.0 -0.0 -0.1 -0.1 -0.1 -0.1 DL9GTB +0.0 +0.0 -0.1 -0.0 -0.1 -0.0 +0.1 +0.1 +0.1 -0.1 DM5GG +1.0 +0.7 +0.8 +0.9 +0.8 +1.5 +1.0 +1.5 +1.0 +1.4 DM6EE +0.0 +0.1 -0.1 -0.1 -0.0 -0.1 DM7EE +0.7 +0.0 DO4DXA +0.1 +0.0 +0.1 +0.1 +0.0 +0.1 +0.1 +0.1 +0.0 +0.1 DR4W -3.9 -3.8 -3.6 -3.7 -5.4 -5.0 -5.0 -4.7 -4.5 -2.6 E28AC +0.0 +2.8 +0.0 +0.8 +0.5 +1.4 EA1DAV +0.0 +0.0 +0.0 +0.0 -0.0 -0.1 -0.0 -0.1 -0.1 EA1URA -1.9 -0.5 -0.3 +0.2 -0.5 +0.1 -0.3 -0.8 -1.8 EA2CW -0.0 +0.2 +0.1 +0.1 +0.1 -0.1 -0.1 -0.1 +0.0 -0.8 EA2RCF-4 +0.4 +0.3 +0.4 +0.3 +0.2 +0.3 +0.2 +0.2 +0.2 +0.3 EA4RKC +0.3 +0.1 +0.2 +0.2 +0.2 +0.0 +0.1 EA5WU +0.0 -0.1 -0.0 +0.1 +0.0 -0.0 +0.0 +0.0 -0.1 +0.1 EI4HQ -0.1 -0.0 +0.0 +0.0 +0.0 +0.0 +0.0 -0.0 +0.0 +0.0 ES2RR -0.0 -0.1 +0.0 -0.0 +0.0 -0.1 -0.0 -0.0 -0.0 +0.0 ES5PC -0.1 -0.0 -0.0 +0.1 -0.0 -0.1 -0.0 -0.0 EY8ZE +0.2 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-4.2 -3.8 -4.3 -4.4 -4.9 Last updated 2026-10-18 00:17:47 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 ES2RR KM3T-5 LZ3CB LZ4UX MM9PSY OE9GHV WB6BEE Last updated 2026-10-18 00:17:47 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.