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
297047 RBN spots between 2025-05-28 00:00 and 23:59 UTC. 59786 spots (20.1%) were from reference skimmers (*). Average spot flow was 206 per minute from 205 active CW skimmers. 128168 spots from 197 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 49 1.000000000 3V9A -1.6 746 0.999998371 5Z4GO +0.8 9 1.000000791 7N4XCV +0.0 8 1.000000000 AA0O +0.4 458 1.000000380 AC0C-1* -0.0 664 0.999999957 BA4OP -0.2 158 0.999999819 BA6KC +0.0 60 1.000000000 BD7JNA +0.0 6 1.000000000 BG0AJO +6.3 9 1.000006328 BG0AJO/0 +0.0 16 1.000000000 BG2TFW +0.0 13 1.000000000 BG4WOM -0.1 61 0.999999883 BH4RRG +0.0 16 1.000000000 BH4XDZ +0.0 20 1.000000000 BI4MPH-1 -1.0 5 0.999999049 BY4XRA +0.0 31 1.000000000 CT1EYQ +0.2 893 1.000000179 DD5XX +0.9 1281 1.000000895 DE1LON +0.8 950 1.000000752 DF2CK +1.3 2677 1.000001279 DF7GB* -0.0 1597 0.999999974 DK0TE +1.2 1578 1.000001211 DK3WW +0.2 1827 1.000000250 DK8NE +0.2 38 1.000000210 DK9IP* -0.0 917 0.999999954 DK9IP-1* +0.1 1038 1.000000116 DL1HWS +0.3 1643 1.000000290 DL1HWS-3 +0.7 875 1.000000666 DL1HWS-4 +0.1 128 1.000000112 DL8TG* -0.0 1552 0.999999973 DL9GTB +0.4 1130 1.000000360 DM5GG +0.4 1703 1.000000416 DM6EE* +0.1 1351 1.000000062 DO4DXA* -0.1 813 0.999999900 DO4ZT -0.0 321 0.999999991 DR4W -2.3 1427 0.999997703 DR5X +0.8 36 1.000000792 E28AC -0.3 95 0.999999700 EA2CW +0.2 1289 1.000000231 EA2RCF-4 +0.7 687 1.000000708 EA5RQ +0.1 63 1.000000113 EA5WU* -0.0 1546 0.999999972 ES2RR* -0.1 1441 0.999999897 ES5PC* -0.0 1898 0.999999999 F4GOU +4.8 1691 1.000004804 F4VVG +0.2 623 1.000000240 G0KTN +0.4 1252 1.000000428 G3YPP +0.3 102 1.000000348 G4IRN +0.7 1631 1.000000743 G4ZFE +0.5 1477 1.000000510 GI4DOH-2* +0.1 909 1.000000101 HA1VHF +0.5 1888 1.000000526 HA6PX* +0.1 1756 1.000000094 HA8TKS +0.3 901 1.000000328 HB9BXE* -0.1 1468 0.999999937 HB9DCO -0.3 1166 0.999999677 HB9GVO +0.7 39 1.000000731 HG0Y +7.5 20 1.000007485 HG8A +0.6 1674 1.000000565 IK3STG +1.8 1311 1.000001753 IK4VET +4.0 2138 1.000003998 IK7YTT* +0.1 1584 1.000000070 IQ9RG* -0.0 1845 0.999999994 IW9GDC +8.5 490 1.000008495 JH7CSU1 +2.3 57 1.000002273 JI1HFJ +0.4 13 1.000000366 JJ2VLY +15.3 82 1.000015311 JK1QLQ +0.0 6 1.000000000 JN1ILK +0.2 217 1.000000212 K1RA -0.3 882 0.999999749 K2PO/7 +0.6 563 1.000000641 K3PA-1 -0.2 594 0.999999842 K4PP +0.6 465 1.000000564 K5EM +2.1 339 1.000002136 K5TR +0.9 505 1.000000885 K6FOD -0.2 253 0.999999784 K7CO +0.7 402 1.000000686 K7EK -1.4 203 0.999998561 K9IMM -0.7 691 0.999999252 K9LC +0.5 794 1.000000472 KC4YVA +6.1 191 1.000006067 KD2OGR +0.4 400 1.000000433 KD7EFG +0.2 238 1.000000240 KH6LC +0.3 26 1.000000274 KM3T-2 +0.6 640 1.000000600 KM3T-3* -0.0 972 0.999999950 KM3T-5* -0.2 620 0.999999824 KP2RUM -9.6 334 0.999990435 KP3CW +0.1 502 1.000000142 KV4TT +0.1 936 1.000000141 KW7MM -0.1 436 0.999999935 LA6TPA -0.4 165 0.999999576 LA7GIA +0.0 26 1.000000000 LB9KJ -0.2 230 0.999999763 LU6KK +0.0 9 1.000000000 LU8XW +0.0 7 1.000000000 LZ3CB* -0.0 1056 0.999999985 LZ4AE +1.0 1542 1.000001012 LZ4UX* -0.2 1093 0.999999835 LZ5DI +1.0 1710 1.000000997 LZ7AA +0.6 920 1.000000634 MM0GPZ +0.2 1929 1.000000196 MM0ZBH -0.4 1353 0.999999554 N2CR -0.2 338 0.999999786 N2QT -0.3 574 0.999999694 N6TV +1.1 345 1.000001102 N7OR +0.1 113 1.000000105 N9CO +0.0 553 1.000000000 ND7K -0.4 420 0.999999620 NG7M +0.1 341 1.000000114 NN3RP +0.1 217 1.000000131 NT6Q -2.3 440 0.999997690 NU4F +0.1 568 1.000000131 OE6ADD +0.2 1846 1.000000208 OE9GHV +0.1 559 1.000000147 OH4KA* -0.3 194 0.999999721 OH6BG +0.1 1288 1.000000134 OH8KA -6.6 100 0.999993373 OK1FCJ* +0.1 1610 1.000000059 OK1HRA -4.2 1666 0.999995835 ON6ZQ -0.1 1235 0.999999851 OZ1AAB +0.4 237 1.000000421 OZ1BZS +0.3 195 1.000000280 OZ4ADX* -0.1 190 0.999999925 PA0MBO +1.6 18 1.000001581 PE5TT +0.5 1153 1.000000515 PI4CC* -0.0 1785 0.999999956 PY2KJ +2.1 62 1.000002052 PY2KNK +2.4 79 1.000002365 PY2PE +1.3 15 1.000001268 R1LB -0.0 264 0.999999990 R4NCU -0.8 319 0.999999240 R6YY -0.1 183 0.999999916 R9IR +0.6 62 1.000000575 RN4WA +1.2 665 1.000001226 RU9CZD +0.2 642 1.000000153 S50U +0.5 398 1.000000465 S53A +0.7 2220 1.000000661 S53F +0.8 155 1.000000771 S53WW +0.3 1729 1.000000347 SE5E +0.5 1853 1.000000451 SM0TCZ -0.2 35 0.999999830 SM1HEV +0.3 295 1.000000251 SM7IUN* -0.1 1031 0.999999904 SQ5J +9.8 1474 1.000009778 SV1CDN -0.6 6 0.999999405 TF3Y +1.2 426 1.000001246 TI7W +0.4 248 1.000000438 UA0S +3.4 365 1.000003442 UA4CC +13.9 609 1.000013919 UT5R +4.4 113 1.000004433 UT5R-1 +2.2 258 1.000002248 UY2RA -1.3 993 0.999998716 V51YJ +0.0 29 1.000000000 VE3EID +0.3 274 1.000000321 VE6JY +3.4 660 1.000003409 VE6WZ +3.9 416 1.000003865 VE7CC +0.9 167 1.000000882 VK2GEL +0.0 92 1.000000000 VK3RASA -0.8 151 0.999999246 VK6ANC -0.2 43 0.999999770 VR2FUN-77 +0.9 598 1.000000879 VU2CPL +4.8 12 1.000004750 VU2PTT +1.6 33 1.000001619 VU2TUM +0.1 67 1.000000131 W1NT-2 +0.1 1121 1.000000131 W1NT-6* +0.2 1185 1.000000166 W2LB +2.5 166 1.000002482 W2MV +0.3 83 1.000000343 W2NAF +1.4 290 1.000001398 W3LPL -0.3 177 0.999999679 W3OA +0.2 778 1.000000182 W3RGA -0.2 741 0.999999795 W3UA* -0.1 814 0.999999941 W4AX +4.1 69 1.000004131 W4KAZ -0.7 738 0.999999299 W6YX +0.3 567 1.000000320 W8WTS -0.3 402 0.999999664 W8WWV -1.2 464 0.999998796 WA7LNW +1.5 614 1.000001464 WB6BEE* -0.2 496 0.999999817 WC2L +0.6 656 1.000000553 WC8GOP +9.2 28 1.000009161 WE9V +1.9 638 1.000001903 WS2C +7.1 438 1.000007054 WS3W -12.2 132 0.999987770 WT9U +5.6 53 1.000005606 WV4P +0.6 427 1.000000633 WX7V/5 +0.3 47 1.000000269 WZ7I +0.5 1368 1.000000474 YO2CK +0.3 1365 1.000000325 YO2MAX +0.2 1075 1.000000237 YO5LD +0.4 1162 1.000000369 ZL3X -0.7 264 0.999999342 ZL4YL +1.2 254 1.000001153 ZS1NN -3.7 24 0.999996300 Last updated 2025-05-29 00:15:29 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 0528 0527 0526 0525 0524 0523 0522 0521 0520 0519 --------------------------------------------------------------------- 3B8GL +0.5 +0.9 +0.2 +0.3 3D2AG +0.0 +0.0 +0.0 +0.4 +0.4 +0.0 +0.1 +0.2 +0.1 +0.3 3V9A -1.6 -1.6 -1.2 -4.4 -5.5 -5.3 -6.4 5Z4GO +0.8 +1.2 +0.6 +0.6 +0.7 -1.1 +0.3 +1.7 +0.0 +0.8 7N4XCV +0.0 +0.6 +0.8 +0.3 +0.5 +0.4 +0.8 +0.0 +0.4 +0.6 AA0O +0.4 +0.5 +0.6 +0.8 +0.7 +0.6 +0.6 +0.8 +0.3 +0.5 AC0C-1 -0.0 +0.1 -0.1 -0.0 -0.0 +0.0 +0.1 +0.1 +0.3 -0.1 BA4OP -0.2 -0.2 -0.2 -0.2 -0.2 -0.3 -0.2 +0.1 -0.7 -0.1 BA6KC +0.0 -0.1 +0.4 -0.0 +0.0 +0.1 +0.1 +0.2 -0.3 +0.1 BD7JNA +0.0 -0.6 +0.5 +0.3 +0.3 +0.1 -7.0 BG0AJO/0 +0.0 -0.5 +0.2 +0.4 -0.1 +0.0 +0.0 +0.1 +0.0 +0.3 BG0AJO +6.3 +0.9 +0.9 +0.4 +0.5 +0.2 +0.5 +0.2 +0.1 +0.4 BG2TFW +0.0 +0.2 +0.4 +3.2 +9.8 +9.7 +9.1 +8.9 +8.9 +10.3 BG4GOV +0.0 +0.4 +0.5 +0.1 +0.0 BG4WOM -0.1 +0.1 +0.4 +0.0 +0.1 +0.0 -0.4 -0.0 +0.0 BH4RRG +0.0 +0.1 +0.2 +0.3 +0.4 +0.2 -0.4 +0.0 +0.2 +0.5 BH4XDZ +0.0 +0.0 +0.1 -0.0 +0.0 -0.2 -0.4 +0.0 +0.0 +0.0 BI4MPH-1 -1.0 +0.0 -0.6 +0.1 +0.1 -0.0 +0.4 +0.0 +0.1 BY4XRA +0.0 +0.0 +0.1 +0.1 +0.2 +0.0 +0.6 +0.1 +0.0 +0.0 CT1EYQ +0.2 -0.2 -0.2 -0.2 -0.1 -0.1 -0.0 +0.0 +0.2 CX6VM +0.6 +1.0 +0.8 +0.2 +0.4 +0.4 +0.1 +0.9 CX7ACH +17.9 +17.6 DD5XX +0.9 +0.9 +0.9 +1.1 +1.0 +0.8 +0.9 +1.0 +1.2 +1.1 DE1LON +0.8 +0.8 +0.8 +0.8 +0.9 +1.3 +1.2 +1.1 +1.2 +1.2 DF2CK +1.3 +1.3 +1.4 +1.6 +1.5 +1.2 +1.3 +1.3 +1.0 +0.9 DF7GB -0.0 -0.0 +0.0 -0.0 -0.0 -0.0 +0.0 -0.0 -0.0 -0.1 DK0TE +1.2 +1.1 +1.1 +1.4 +1.7 +1.1 +1.3 +1.3 +1.3 +1.2 DK3UA +0.0 +0.0 +1.0 +0.7 +0.4 +0.1 -0.1 +0.2 -0.4 DK3WW +0.2 -0.1 -0.1 +0.4 +0.4 -0.1 +0.2 +0.1 +0.1 -0.1 DK8NE +0.2 +0.0 +0.4 -0.0 +1.0 DK9IP -0.0 -0.1 +0.0 +0.0 +0.0 -0.0 +0.0 -0.1 -0.1 +0.0 DK9IP-1 +0.1 -0.0 +0.0 -0.0 -0.0 +0.0 +0.0 -0.1 -0.0 -0.0 DL0PF +8.1 +8.1 +8.5 DL1HWS +0.3 +0.2 +0.2 +0.4 +0.4 +0.3 +0.2 +0.3 +0.2 +0.2 DL1HWS-3 +0.7 +0.7 +0.5 +0.9 +1.0 +0.6 +0.7 +0.6 +0.6 +0.6 DL1HWS-4 +0.1 +0.2 +0.2 +0.2 +0.2 +0.0 +0.1 +0.4 +0.0 +0.1 DL5RCN +2.4 +13.1 +13.2 +13.0 DL5RMH +0.1 -0.2 -0.1 -0.2 DL8LAS +0.1 +0.0 +0.1 +0.3 +0.7 DL8TG -0.0 -0.0 +0.0 -0.0 +0.0 -0.1 -0.1 +0.0 DL9GTB +0.4 +0.2 -0.1 +0.0 +0.2 +0.4 DM5GG +0.4 +0.4 +0.5 +0.7 +0.6 +0.3 +0.4 +0.5 +0.4 +0.4 DM6EE +0.1 +0.0 +0.0 +0.0 +0.1 +0.0 +0.0 +0.1 +0.0 -0.0 DO4DXA -0.1 -0.1 -0.1 -0.0 -0.0 -0.1 -0.2 +0.0 -0.0 -0.0 DO4ZT -0.0 +0.0 -0.1 -0.0 +0.0 -0.0 +0.1 +0.0 -0.1 -0.1 DR4W -2.3 -2.1 -1.2 -2.6 -2.8 -2.9 -1.7 -1.3 -2.2 -2.1 DR5X +0.8 +0.6 +0.8 +1.1 E28AC -0.3 -0.8 -0.8 -0.8 -0.2 -0.2 -0.8 -0.9 -0.4 EA2CW +0.2 +0.1 +0.1 +0.1 +0.1 +0.0 +0.0 -0.0 +0.0 +0.1 EA2RCF-4 +0.7 +0.9 +0.8 +1.1 +1.0 +0.6 +0.8 +0.7 +0.7 +0.7 EA5RQ +0.1 -0.4 +0.1 -0.1 -0.0 -0.1 -0.1 -0.0 EA5RQ/A +0.0 EA5WU -0.0 +0.0 +0.0 -0.0 +0.0 +0.0 +0.0 +0.1 -0.0 +0.0 EA7CJK +14.3 +10.9 ES2RR -0.1 +0.0 -0.1 -0.0 -0.0 -0.0 +0.0 -0.0 -0.0 -0.0 ES5PC -0.0 -0.0 +0.1 -0.0 -0.0 +0.0 +0.0 +0.0 +0.0 -0.0 EU1ST +2.4 +4.9 +4.8 +3.7 +3.1 +2.9 +3.0 +3.1 F4BPO -0.1 -0.2 -0.0 F4GOU +4.8 +5.1 +5.4 +5.7 +5.8 +5.5 +5.4 +5.3 +5.5 +5.7 F4VVG +0.2 +0.1 +0.2 +0.3 +0.3 +0.2 +0.3 +0.1 +0.2 +0.1 F6KGL +0.3 +0.3 +0.2 +0.2 +0.2 +0.2 +0.2 G0KTN +0.4 +0.3 +0.3 +0.5 +0.5 +0.4 +0.4 +0.4 +0.3 +0.3 G3YPP +0.3 -0.0 +0.2 +1.3 +1.3 -0.1 +5.1 +0.0 +0.2 +0.1 G4AON +0.5 G4IRN +0.7 +0.6 +0.7 +0.9 +1.0 +0.7 +0.4 +0.5 +0.6 G4YBU +0.3 +0.2 +0.6 +0.3 +0.4 G4ZFE +0.5 +0.5 +0.6 +0.9 +0.8 +0.4 +0.5 +0.6 +0.6 +0.5 GI4DOH-2 +0.1 +0.1 -0.0 +0.2 +0.3 +0.1 +0.5 -0.1 +0.3 +0.4 GX0FRE +0.8 +0.3 +0.6 +0.6 +0.5 +0.3 +0.4 +0.2 +0.1 HA1VHF +0.5 +0.3 +0.5 +0.5 +0.5 +0.4 +0.5 +0.5 +0.4 +0.3 HA5PP +1.8 -1.4 HA6PX +0.1 -0.0 +0.0 -0.0 -0.0 +0.0 -0.0 +0.0 -0.0 +0.0 HA8TKS +0.3 +0.3 +0.3 +0.4 +0.5 +0.3 +0.3 +0.3 +0.2 +0.2 HB9BXE -0.1 -0.0 +0.1 +0.2 +0.1 +0.1 +0.1 +0.1 +0.1 -0.1 HB9DCO -0.3 -0.4 -0.4 -0.6 -0.5 -0.3 -0.3 -0.3 -0.1 -0.5 HB9GVO +0.7 +1.4 +1.3 +1.3 +0.9 +0.0 HG0Y +7.5 +7.7 +7.8 +8.5 +8.4 +7.5 +7.3 +7.2 HG8A +0.6 +0.3 +0.2 +0.2 +0.3 +0.4 +0.4 +0.3 +0.2 +0.1 IK2LFF +0.5 IK3STG +1.8 +1.9 +1.9 +2.7 +2.7 +1.7 +1.8 +1.9 +1.6 +1.7 IK4VET +4.0 +4.2 +4.0 +4.2 +4.2 +3.8 +4.2 +3.8 IK7YTT 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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 ES2RR KM3T-5 LZ3CB LZ4UX OE9GHV WB6BEE Last updated 2025-05-29 00:15:35 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.