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.
500218 RBN spots between 2026-03-11 00:00 and 23:59 UTC. 107398 spots (21.5%) were from reference skimmers (*). Average spot flow was 347 per minute from 222 active CW skimmers. 222917 spots from 215 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 ------------------------------------- 3D2AG -0.0 220 0.999999957 5Z4GO +0.0 8 1.000000000 AA0O +1.3 1023 1.000001347 AC0C-1* +0.1 1688 1.000000064 AK6RI-1 -0.0 528 0.999999990 BA4OP -0.0 161 1.000000000 BA6KC +0.0 19 1.000000000 BD7JNA +0.1 71 1.000000067 BD8CS -0.1 48 0.999999926 BG0AJO/0 +0.0 15 1.000000000 BG2TFW +0.1 86 1.000000083 BH4RRG +0.0 27 1.000000000 BH4XDZ -0.2 89 0.999999827 BI4MPH +0.1 109 1.000000131 BI7JMD -12.1 25 0.999987874 CT1EYQ -1.2 1340 0.999998756 DC8YZ* +0.1 1517 1.000000058 DD5XX -0.6 1734 0.999999380 DE1LON -0.3 1631 0.999999707 DE2SAX +0.6 137 1.000000624 DF7GB* -0.1 2102 0.999999927 DK0TE -0.3 1971 0.999999744 DK3WW +0.2 2651 1.000000249 DK9IP -10.9 1495 0.999989081 DK9IP-1* +0.1 1935 1.000000073 DL0LA* -0.1 865 0.999999945 DL1HWS +0.7 2243 1.000000724 DL1HWS-3 +1.8 1212 1.000001789 DL1HWS-4 +0.6 257 1.000000618 DL3OBQ -0.4 13 0.999999634 DL5RCN +13.6 68 1.000013576 DL8LAS* +0.1 3193 1.000000091 DL8LAS-1 -0.3 3109 0.999999735 DL8TG* -0.1 738 0.999999928 DM5GG +0.9 2272 1.000000881 DP5G +1.6 1673 1.000001628 DR4W -2.0 1933 0.999997952 DR5M* +0.1 953 1.000000141 E28AC -0.2 31 0.999999770 EA1DAV -0.2 44 0.999999775 EA1URA +1.6 1441 1.000001646 EA2CW -1.1 173 0.999998898 EA2RCF-4 -0.6 1464 0.999999437 EA5WU* +0.0 2109 1.000000021 EA8/DF4UE -0.1 2947 0.999999853 ES2RR* +0.0 2146 1.000000002 ES5PC* +0.0 2704 1.000000001 EY8ZE -0.7 39 0.999999268 F1EYG -2.1 4204 0.999997934 F4BPO* +0.0 1076 1.000000010 F4GOU +0.2 1749 1.000000249 F4VVG -0.0 178 0.999999971 F5AHD +0.5 274 1.000000484 F5VLY -2.8 445 0.999997217 F6IIT -0.6 73 0.999999414 F8DGY -10.4 886 0.999989629 G0KTN +0.3 2014 1.000000306 G1VWC +2.0 55 1.000001951 G4IRN +0.3 2383 1.000000290 G4ZFE +0.4 1923 1.000000376 GI4DOH +0.2 1620 1.000000249 GX0FRE* +0.3 690 1.000000260 HA1VHF -0.3 2261 0.999999668 HA5PP +1.8 32 1.000001780 HA6PX* -0.0 2224 0.999999974 HA8TKS* +0.1 1140 1.000000092 HA8TKS-2 +0.0 139 1.000000040 HB9AFZ +0.3 419 1.000000313 HB9BXE +0.5 1431 1.000000520 HB9DCO -0.4 1494 0.999999642 HB9GVO +0.2 356 1.000000240 HG0Y +7.4 532 1.000007408 HG8A +0.9 2329 1.000000868 IK3STG +4.0 870 1.000003991 IK4VET +1.3 2451 1.000001302 IQ9RG* +0.1 2152 1.000000109 IW9GDC -1.1 1587 0.999998907 IZ8EYP* -0.0 1262 0.999999980 JA1CCA -0.7 10 0.999999289 JH7CSU1 +1.8 125 1.000001814 JI1HFJ +0.8 29 1.000000765 JJ2VLY -1.6 68 0.999998371 JK1QLQ +0.0 5 1.000000000 JN1ILK -0.7 431 0.999999323 K1RA +1.1 2139 1.000001062 K1RA-4* +0.2 1544 1.000000220 K2PO/7 +0.5 971 1.000000479 K3PA-1 +0.5 1818 1.000000463 K3PA-2 +0.7 92 1.000000703 K4PP +0.4 1273 1.000000399 K5EM +2.3 783 1.000002304 K5TR +5.4 1722 1.000005353 K6FOD +0.0 6 1.000000000 K7CO -0.5 871 0.999999463 K7EK +1.7 368 1.000001670 K9IMM* +0.1 1428 1.000000115 K9LC +0.9 1726 1.000000894 K9QC +1.3 392 1.000001285 KC4YVA +1.0 1068 1.000001000 KD2OGR +0.4 974 1.000000389 KD7EFG +0.6 662 1.000000570 KH6LC -0.5 46 0.999999534 KL2R -0.2 21 0.999999810 KM3T-2 +0.2 1410 1.000000232 KM3T-3 +0.2 2310 1.000000236 KM3T-5* -0.1 1273 0.999999916 KO4BHX +0.4 2048 1.000000409 KP3CW -0.8 243 0.999999234 KV4TT +0.3 1512 1.000000282 KW7MM +0.8 1224 1.000000796 KW7MM-2 +1.9 1089 1.000001923 KW7MM-3 -0.1 342 0.999999867 LA6TPA -0.2 464 0.999999753 LB9KJ -0.9 908 0.999999068 LU8XW +1.2 28 1.000001216 LY3G +0.1 111 1.000000122 LZ3CB +0.1 169 1.000000075 LZ4UX* -0.1 1710 0.999999863 LZ5DI +4.1 1984 1.000004131 LZ7AA +0.5 1767 1.000000540 M1GEO +4.0 1245 1.000003978 M9SJM +6.0 1967 1.000006047 MM0ZBH +0.2 2514 1.000000176 MM9PSY +0.2 2391 1.000000181 N2CR +0.8 1098 1.000000790 N2YCH +1.1 1631 1.000001076 N6TV +1.2 847 1.000001173 N7TUG -0.7 163 0.999999300 N8DXE +0.8 257 1.000000773 N9CO* +0.1 748 1.000000098 ND7K* +0.2 1385 1.000000213 NG7M* +0.2 786 1.000000196 NN3RP +0.1 202 1.000000139 NU4F* +0.1 1210 1.000000053 OE6ADD* -0.0 1233 0.999999956 OE9GHV* +0.1 2420 1.000000073 OH4KA +1.0 472 1.000000997 OH8KA -3.5 437 0.999996464 OK1FCJ* +0.1 446 1.000000147 OK1HRA -4.0 2093 0.999995977 ON6ZQ -0.3 1782 0.999999682 OZ1AAB* -0.5 679 0.999999513 OZ1BZS +0.5 323 1.000000524 PA5KT-4 +0.1 151 1.000000094 PA8MM* -0.0 1503 0.999999990 PE5TT +0.3 1653 1.000000258 PI4CC* -0.1 2634 0.999999940 PY2KNK +4.9 121 1.000004920 RK3TD +0.7 1421 1.000000681 RK3TD-2 +0.6 1244 1.000000628 RL3A +2.5 381 1.000002483 RN4WA +0.9 105 1.000000905 RU9CZD* +0.1 2011 1.000000116 S50U +0.2 1407 1.000000169 S53A -2.7 3015 0.999997341 S53WW -1.1 2261 0.999998885 S54L* +0.0 2137 1.000000012 SE5E* -0.0 2692 0.999999970 SM0TCZ +0.3 73 1.000000277 SM1HEV +0.1 680 1.000000083 SM7IUN* +0.1 1606 1.000000119 SP5GQ +0.2 1156 1.000000181 SQ5J +7.7 791 1.000007722 SV1CDN +0.7 46 1.000000698 SZ1A -2.4 1448 0.999997582 TF3Y +0.6 17 1.000000582 TI7W +1.7 1478 1.000001711 UA4M +4.2 166 1.000004243 UT5R +0.6 293 1.000000569 UY2RA* -0.1 763 0.999999899 V51YJ +0.0 5 1.000000000 VE4DRK -9.9 41 0.999990145 VE6JY +3.8 1289 1.000003837 VE6WZ* +0.1 954 1.000000073 VE6WZ-3 -1.1 535 0.999998884 VE7CC +1.4 720 1.000001374 VK2GEL +1.1 47 1.000001062 VK2RH +0.0 18 1.000000000 VK6ANC +0.4 170 1.000000378 VR2FUN-77 +0.4 473 1.000000436 VU2CPL -0.3 33 0.999999748 VU2OY +0.4 143 1.000000424 VU2TUM +3.5 99 1.000003491 W1NT-2 +0.2 1830 1.000000173 W1NT-6 +0.1 2468 1.000000147 W2AXR +0.4 12 1.000000397 W2NNN +0.6 163 1.000000636 W3DAN +1.4 41 1.000001389 W3LPL -0.2 835 0.999999780 W3OA +0.3 1539 1.000000308 W3RGA -0.3 1147 0.999999709 W4KAZ -0.3 1204 0.999999730 W5ZN +0.9 189 1.000000887 W6YX -0.0 1322 1.000000000 W8WTS -0.4 943 0.999999552 W8WWV -1.4 1344 0.999998599 WA7LNW +0.5 1501 1.000000505 WB6BEE -0.1 320 0.999999928 WC2L* +0.1 1323 1.000000112 WC8GOP -5.5 84 0.999994546 WE9V* -1.1 1703 0.999998914 WF8Z-2 -3.9 239 0.999996064 WS2C +7.3 1183 1.000007285 WS3W -0.3 88 0.999999676 WT9U +0.5 796 1.000000454 WV4P +0.6 1192 1.000000620 WX7V/5 +1.0 153 1.000000978 WZ7I +0.2 2179 1.000000206 YO2CK* -0.0 1973 0.999999996 YO2KAR +0.2 1840 1.000000233 ZF1A* +0.0 2678 1.000000014 ZF9CW +1.2 1785 1.000001245 ZL3X -0.4 412 0.999999620 ZL4YL +3.8 608 1.000003822 ZS1NN -4.1 28 0.999995898 Last updated 2026-03-12 00:15:46 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 0311 0310 0309 0308 0307 0306 0305 0304 0303 0302 --------------------------------------------------------------------- 3D2AG -0.0 +0.1 +0.2 -0.2 +0.3 +0.3 +0.2 +0.0 +0.0 5Z4GO +0.0 +0.3 +0.6 +0.6 +0.2 +0.0 +0.3 +0.1 +0.2 AA0O +1.3 +0.8 +1.2 +0.9 +1.0 +1.3 +1.0 +1.3 +1.2 +0.9 AC0C-1 +0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 AK6RI-1 -0.0 +0.0 +0.1 -0.1 +0.1 -0.0 +0.0 -0.1 +0.1 +0.0 BA4OP -0.0 -0.0 -0.6 +0.1 -0.1 -0.1 -0.1 -0.5 -0.3 -0.3 BA6KC +0.0 -0.1 +0.7 +0.2 +0.1 -0.1 -0.1 -0.2 -0.1 +0.0 BD7JNA +0.1 +0.0 +0.2 +0.3 +0.1 -0.2 -0.0 -0.1 +0.0 +0.1 BD8CS -0.1 +0.1 +0.1 +0.1 +0.1 -0.0 +0.0 +0.1 +0.0 +0.1 BG0AJO/0 +0.0 +0.4 +0.8 +0.6 +0.6 +0.8 +0.5 +0.6 +0.1 +0.0 BG2TFW +0.1 +0.0 -0.1 -0.1 -0.0 -0.0 -0.1 +0.2 +0.2 +0.0 BH4HKZ +0.0 +0.0 -0.1 -0.4 +0.0 BH4RRG +0.0 +0.0 +0.6 +0.6 +0.6 +0.3 +0.3 +0.5 +0.1 +0.3 BH4XDZ -0.2 +0.0 -0.2 +0.1 -0.5 +0.2 +0.0 -0.2 -0.2 +0.0 BI4MPH +0.1 +0.0 -0.4 +1.0 +0.1 +0.5 BI4UYX +0.0 -0.5 -0.1 BI7JMD -12.1 -10.5 -10.7 -12.7 -9.7 +11.1 +11.6 +13.2 CN3A +12.8 +12.8 CT1EYQ -1.2 -2.0 -1.6 -1.3 -1.7 -1.4 -1.3 -1.1 -1.2 -1.4 CX6VM +6.1 +5.5 +4.8 DC8YZ +0.1 +0.0 -0.0 -0.1 -0.1 -0.1 -0.2 +0.0 +0.0 +0.0 DD5XX -0.6 -0.4 -0.5 -0.5 -0.8 -0.8 -1.1 -0.6 -1.1 -0.8 DE1LON -0.3 -0.2 -0.3 -0.3 -0.4 -0.3 -0.4 -0.6 -0.3 -0.3 DE2SAX +0.6 +0.4 +0.7 +0.3 +0.7 +0.8 +0.6 +0.9 +0.8 +0.9 DF1VB +0.0 -0.1 +0.0 -0.1 -0.0 -0.1 DF2CK +0.6 +0.7 +0.6 DF7GB -0.1 +0.0 +0.1 +0.1 -0.0 +0.1 +0.1 +0.0 +0.0 -0.0 DK0KK -3.2 -3.0 -2.6 -3.3 -2.9 -3.4 -2.7 -3.0 -3.2 DK0TE -0.3 -0.1 -0.3 -0.0 -0.2 -0.3 -0.4 -0.5 -0.4 -0.6 DK3WW +0.2 +0.0 +0.1 +0.0 +0.1 +0.0 +0.1 -0.0 +0.1 -0.0 DK9IP-1 +0.1 -0.1 -0.1 -0.1 -0.1 -0.0 -0.0 -0.1 -0.1 +0.0 DK9IP -10.9 -11.1 -11.5 -11.1 -9.4 -11.2 -11.0 -11.1 -10.7 -11.5 DL0LA -0.1 -0.1 +0.1 +0.1 -0.0 -0.0 +0.1 -0.1 -0.1 +0.0 DL1HWS +0.7 +0.5 +0.8 +0.5 +0.3 +0.8 +0.7 +0.7 +0.8 +0.7 DL1HWS-3 +1.8 +2.0 +2.0 +1.2 +1.8 +1.9 +2.0 DL1HWS-4 +0.6 +0.8 +0.7 -0.0 +0.8 +0.6 +0.5 DL3OBQ -0.4 -0.2 -0.2 +2.3 +3.6 +4.1 +14.0 +14.4 +13.0 DL4CF +0.2 DL5RCN +13.6 +13.4 +13.2 +12.3 DL8LAS +0.1 +0.0 +0.1 +0.0 +0.1 +0.1 -0.0 +0.1 +0.1 +0.0 DL8LAS-1 -0.3 -0.3 -0.2 -0.2 -0.3 -0.2 -0.3 -0.3 -0.3 -0.2 DL8TG -0.1 -0.0 -0.0 +0.0 -0.0 -0.1 -0.2 -0.2 -0.1 -0.1 DM5GG +0.9 +1.0 +0.9 +0.9 +0.9 +0.9 +1.0 +0.9 +1.0 +0.9 DO4DXA +0.5 -0.1 +0.0 +0.0 DP5G +1.6 +1.9 +2.2 +1.8 +2.7 +2.3 +2.4 +2.4 +2.4 +2.3 DR4W -2.0 -1.7 -1.9 -1.3 -2.7 -1.9 -2.1 -2.3 -2.8 -2.5 DR5M +0.1 +0.1 -0.2 -0.2 -0.0 -0.1 E28AC -0.2 -0.4 -0.9 -0.6 -2.1 -2.8 -3.2 -2.6 -3.1 -3.2 EA1DAV -0.2 +0.1 +0.0 +0.0 +0.0 +0.0 +0.0 -0.0 -0.0 EA1URA +1.6 +2.0 +0.9 +1.7 +1.1 +0.9 +1.0 +2.4 +2.6 +2.5 EA2CW -1.1 -1.0 -0.3 -0.2 -0.6 -1.2 -0.9 -0.8 -0.5 -1.1 EA2RCF-4 -0.6 -0.5 -0.5 -0.4 -0.5 -0.4 -0.4 -0.5 -0.4 -0.6 EA5WU +0.0 +0.0 -0.0 -0.0 -0.1 +0.0 -0.0 -0.0 -0.0 -0.0 EA8/DF4UE -0.1 -0.1 -0.1 -0.2 -0.2 -0.2 -0.3 -0.2 -0.3 -0.3 EA/VE3NZ -1.6 -0.3 -1.7 ES2RR +0.0 -0.1 -0.1 -0.1 -0.1 -0.0 -0.0 +0.0 ES5PC +0.0 -0.1 -0.0 +0.0 +0.0 +0.0 +0.0 -0.0 -0.0 -0.0 EY8ZE -0.7 -1.4 -1.1 -0.9 -0.2 -0.2 -0.3 -0.4 -0.2 -0.2 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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 OE9GHV WB6BEE Last updated 2026-03-12 00:15:56 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.