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.
241988 RBN spots between 2025-08-19 00:00 and 23:59 UTC. 77029 spots (31.8%) were from reference skimmers (*). Average spot flow was 168 per minute from 185 active CW skimmers. 123533 spots from 179 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 +0.4 86 1.000000415 5Z4GO +0.8 6 1.000000793 9M2CNC +0.3 108 1.000000286 AA0O +0.7 355 1.000000665 AC0C-1* -0.0 1036 0.999999954 BA4OP +0.6 29 1.000000574 BA6KC +0.1 66 1.000000144 BD4UNT +0.0 30 1.000000000 BG0AJO +0.5 39 1.000000488 BG0AJO/0 +0.0 23 1.000000000 BG2TFW +0.0 15 1.000000000 BH4RRG +0.0 9 1.000000000 BH4XDZ -0.7 20 0.999999286 BI4UYX +1.0 5 1.000000952 CT1EYQ* -0.1 883 0.999999936 CX6VM +1.0 233 1.000000995 DD5XX +0.7 1439 1.000000744 DE1LON +1.4 1162 1.000001429 DF2CK* -0.0 2923 0.999999981 DF7GB* -0.1 1399 0.999999927 DK0TE +0.2 1277 1.000000191 DK3WW* -0.1 1865 0.999999945 DK9IP +0.2 733 1.000000206 DK9IP-1 +0.1 950 1.000000106 DL0LA* +0.1 520 1.000000062 DL0PF +10.7 2184 1.000010650 DL1HWS +0.5 1486 1.000000507 DL1HWS-3 +0.7 881 1.000000715 DL1HWS-4 +1.0 212 1.000001000 DL5RCN +13.3 651 1.000013290 DL8LAS +1.5 1134 1.000001496 DL8TG* +0.0 1180 1.000000006 DM5GG +0.6 1745 1.000000593 DM6EE* -0.0 1532 0.999999963 DO4DXA* -0.0 1670 0.999999957 DR4W -0.8 1602 0.999999203 E28AC -1.4 27 0.999998590 EA2CW* +0.0 1049 1.000000029 EA2RCF-4 +0.3 706 1.000000332 EA5WU -0.0 249 0.999999971 EA7/VE3NZ* -0.1 494 0.999999913 ES2RR -0.0 1489 0.999999995 ES5PC* +0.0 1852 1.000000030 F4GOU +7.7 1337 1.000007696 F4VVG* +0.1 535 1.000000062 G0KTN +0.4 941 1.000000374 G3YPP +0.6 75 1.000000599 G4IRN +0.3 312 1.000000315 G4ZFE +0.8 1439 1.000000780 GI4DOH-3* +0.0 1005 1.000000034 GX0FRE +0.0 8 1.000000000 HA1VHF +0.5 1197 1.000000521 HA6PX* +0.0 1548 1.000000013 HA8TKS +0.1 780 1.000000142 HA8TKS-2 -0.1 90 0.999999890 HB9BXE* +0.2 1295 1.000000190 HB9DCO* -0.1 1169 0.999999855 HG8A +2.6 1377 1.000002648 IK7YTT* +0.1 1443 1.000000068 IT9GSF* +0.1 1055 1.000000061 IW9GDC -0.1 565 0.999999896 JH7CSU1 +2.0 42 1.000001982 JI1HFJ -0.7 20 0.999999287 JJ2VLY +1.4 71 1.000001427 JN1ILK +0.3 209 1.000000341 K1RA +0.3 861 1.000000280 K2PO/7 +0.7 407 1.000000738 K3PA-1* +0.0 907 1.000000033 K3PA-2 +0.0 11 1.000000000 K4PP* +0.0 528 1.000000017 K5EM +2.9 206 1.000002886 K5TR -3.1 630 0.999996908 K6FOD -0.1 159 0.999999911 K7CO +0.9 367 1.000000947 K7EK +0.5 172 1.000000493 K7RUT -0.5 13 0.999999452 K9IMM +0.0 442 1.000000041 K9LC +0.5 774 1.000000513 KD2OGR +0.2 496 1.000000212 KD7EFG +0.5 296 1.000000536 KH6LC +0.3 85 1.000000335 KM3T-2* +0.1 652 1.000000106 KM3T-3* -0.1 477 0.999999858 KM3T-5* +0.0 633 1.000000014 KO7SS +1.1 194 1.000001063 KP2RUM +0.1 261 1.000000105 KP3CW -0.3 401 0.999999672 KV4TT* +0.1 872 1.000000107 KW7MM +0.1 627 1.000000084 KW7MM/7 +0.0 559 1.000000009 LA6TPA -0.9 493 0.999999114 LA7GIA -0.1 306 0.999999950 LB9KJ -0.2 374 0.999999844 LU8XW +2.1 19 1.000002124 LZ3CB* -0.0 721 0.999999967 LZ4AE +0.1 1304 1.000000140 LZ4UX* +0.1 1000 1.000000064 LZ5DI +2.2 1640 1.000002229 LZ7AA +0.8 941 1.000000840 MM0ZBH* -0.0 1919 0.999999952 N2CR -0.0 275 0.999999966 N2YCH* +0.1 1144 1.000000100 N6TV +0.7 336 1.000000693 N7TUG -0.1 70 0.999999921 N9CO +0.4 444 1.000000396 ND7K -0.3 441 0.999999730 NG7M -0.1 376 0.999999929 NT6Q +5.5 93 1.000005529 NU4F* +0.2 541 1.000000246 OE9GHV* +0.2 475 1.000000214 OH4KA +0.9 225 1.000000875 OH6BG +0.2 1794 1.000000226 OH8KA +5.2 33 1.000005185 OK1FCJ* +0.1 1997 1.000000095 OK1HRA -4.4 1567 0.999995604 OK2ZAW +11.6 623 1.000011617 ON6ZQ +0.5 1193 1.000000512 OZ1AAB +0.2 548 1.000000218 OZ1BZS +0.4 276 1.000000422 OZ4ADX +0.2 140 1.000000204 PA5KT-14 -0.8 1776 0.999999241 PA8MM +0.2 738 1.000000214 PE5TT +1.0 936 1.000000998 PI4CC +0.2 1671 1.000000209 PY2KNK +2.2 233 1.000002158 PY2PE -2.4 96 0.999997632 R4NCU -0.7 68 0.999999266 RK3TD +0.1 123 1.000000058 RK3TD-2 +0.4 587 1.000000403 RN4WA +1.7 712 1.000001724 RU9CZD +0.1 477 1.000000051 S50U +0.2 952 1.000000181 S53A +0.7 2215 1.000000681 S53F +3.0 804 1.000003047 S54L +0.6 1662 1.000000636 SE5E* +0.1 1853 1.000000063 SM0TCZ -0.2 41 0.999999767 SM1HEV* -0.2 633 0.999999848 SM7IUN* +0.0 1124 1.000000029 SP5GQ +5.4 331 1.000005353 SZ1A -1.3 1286 0.999998682 TF3Y +1.2 724 1.000001216 TI7W +1.0 841 1.000000960 UA0S +4.3 284 1.000004320 UA4CC +13.8 591 1.000013820 V51YJ +1.3 56 1.000001287 VE3EID -0.8 1262 0.999999163 VE6AO -0.4 163 0.999999621 VE6JY +3.1 450 1.000003086 VE7CC +0.2 176 1.000000247 VK2GEL +0.0 132 1.000000000 VK3RASA -2.2 154 0.999997826 VK6ANC -0.2 63 0.999999837 VU2CPL -0.2 30 0.999999762 VU2TUM +1.3 131 1.000001252 W1NT-2* -0.1 1255 0.999999875 W1NT-6* -0.1 1655 0.999999889 W2LB +0.6 181 1.000000628 W2MV +0.4 69 1.000000412 W2NAF +0.9 969 1.000000938 W3OA +0.2 855 1.000000163 W3RGA* +0.1 1205 1.000000082 W4KAZ +0.0 638 1.000000045 W6YX +0.4 592 1.000000385 W8WTS +0.5 441 1.000000497 W8WWV -1.2 682 0.999998786 WA7LNW +0.1 758 1.000000092 WB6BEE -0.2 374 0.999999849 WC2L* -0.0 735 0.999999985 WE9V -0.1 859 0.999999936 WS2C +7.1 685 1.000007087 WT9U +5.7 407 1.000005718 WV4P -0.0 471 0.999999960 WX7V/5 +1.0 95 1.000001048 WZ7I +0.6 1503 1.000000559 YO2CK -8.8 1298 0.999991160 ZL2KS -6.1 14 0.999993923 ZL4YL +3.1 159 1.000003082 ZS1NN -5.4 40 0.999994573 Last updated 2025-08-20 00:10:23 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 0819 0818 0817 0816 0815 0814 0813 0812 0811 0810 --------------------------------------------------------------------- 3B8GL -0.1 3D2AG +0.4 +0.3 +0.3 +0.4 +0.0 +0.2 -0.2 +0.4 +0.3 +0.1 5Z4GO +0.8 +0.6 +0.2 +0.7 +1.1 +2.8 +1.1 +0.0 +0.0 +0.5 7N4XCV +1.0 +1.0 +0.0 +0.3 9M2CNC +0.3 +0.3 +0.6 +0.8 +0.6 +0.8 +1.2 +0.8 AA0O +0.7 +0.5 +0.7 +0.5 +0.4 +0.5 +0.9 +0.3 +0.7 +0.8 AC0C-1 -0.0 -0.0 -0.1 +0.0 -0.1 -0.0 -0.1 -0.0 -0.1 -0.1 BA4OP +0.6 -0.0 -0.1 -0.1 -0.2 -0.1 +0.2 +0.0 +0.0 +0.0 BA6KC +0.1 -0.3 -0.0 -0.0 -0.1 +0.2 -0.0 +0.0 +0.0 -0.1 BD4UNT +0.0 -0.1 +0.0 -0.0 +0.1 +0.0 -0.3 +0.0 -0.1 BD7JNA +0.1 +0.1 +0.1 -0.1 +0.2 +0.2 -0.0 -0.3 BG0AJO/0 +0.0 +0.2 +0.0 +0.0 +0.3 +0.0 +0.5 +1.0 +0.0 BG0AJO +0.5 +0.9 +0.4 +0.6 +0.4 +1.1 +0.3 +0.0 +0.7 +0.2 BG2TEM -0.5 +0.4 +0.6 +0.4 +0.8 +0.8 +0.0 +0.6 +0.3 BG2TFW +0.0 +0.8 +0.8 +1.1 +0.2 +0.0 +0.0 BG4GOV +0.0 +0.9 +0.4 +0.3 BH4HKZ +0.0 -0.2 -0.7 BH4RRG +0.0 +0.0 +0.5 +0.5 +0.5 -0.7 +0.6 +0.0 +0.0 +0.3 BH4XDZ -0.7 +0.0 +0.1 -0.0 -0.2 +0.3 +0.3 +0.2 +0.0 -0.2 BI4MPH -0.2 -0.0 -0.3 +0.1 BI4MPH-1 +0.2 -0.0 +0.6 +0.0 -0.8 +0.0 +0.1 BI4UYX +1.0 CT1EYQ -0.1 +0.2 +0.2 +0.3 +0.3 +0.5 +0.5 +0.4 +0.3 +0.2 CX6VM +1.0 +0.9 +0.6 +0.0 +0.4 -0.0 +0.4 DD5XX +0.7 +0.5 +0.9 +1.5 +1.1 +1.2 +1.2 +1.0 +0.7 +1.3 DE1LON +1.4 +1.5 +1.6 +2.0 +2.2 +2.1 +2.0 +1.9 +1.9 +2.0 DF2CK -0.0 -0.1 +0.1 +0.2 -0.1 -0.2 -0.0 -0.1 -0.1 +0.1 DF4UE -9.6 DF7GB -0.1 -0.0 -0.1 +0.0 -0.0 +0.1 +0.0 -0.0 -0.0 -0.1 DG6FL +1.0 +0.2 +0.0 +0.4 DK0TE +0.2 +0.3 +1.5 +1.8 +1.4 +1.0 +0.6 +0.5 +0.4 +1.4 DK3WW -0.1 -0.1 -0.0 +0.1 +0.3 +0.1 -0.0 +0.1 +0.2 +0.0 DK8NE +0.4 +2.0 -0.5 +0.2 DK9IP +0.2 +0.0 +0.1 +0.2 +0.3 +0.3 +0.1 +0.0 +0.1 +0.2 DK9IP-1 +0.1 +0.1 +0.1 +0.2 +0.2 +0.1 +0.1 +0.1 -0.0 +0.1 DL0LA +0.1 +0.1 +0.1 +0.2 +0.1 +0.1 +0.2 -0.0 +0.2 -0.0 DL0PF +10.7 +10.5 +10.2 +11.2 +11.1 +10.8 +11.2 +10.3 +11.0 +8.0 DL1AXX -1.5 -0.6 -1.2 -1.7 -0.9 -0.9 -1.0 DL1HWS +0.5 +0.5 +0.7 +0.9 +0.7 +0.7 +0.0 -1.1 -1.5 -1.4 DL1HWS-3 +0.7 +0.6 +0.7 +1.0 +0.6 +0.7 +0.8 +0.8 +0.8 +0.8 DL1HWS-4 +1.0 +0.8 +0.9 +1.1 +0.7 +0.7 +0.5 +0.9 +0.6 +0.6 DL5RCN +13.3 +12.0 DL5RMH +0.1 DL8LAS +1.5 +1.5 +1.8 +1.9 +1.8 +1.7 +1.6 +1.3 +1.3 +2.0 DL8TG +0.0 +0.0 +0.1 -0.0 +0.0 +0.1 -0.0 -0.0 -0.0 -0.1 DM5GG +0.6 +0.6 +0.7 +1.0 +0.8 +0.7 +0.5 +0.7 +0.6 -0.0 DM6EE -0.0 -0.1 -0.0 -0.0 -0.1 +0.0 +0.1 -0.0 +0.2 +0.1 DO4DXA -0.0 +0.0 -0.0 +0.0 +0.0 +0.1 +2.1 -0.0 -0.0 -0.0 DR4W -0.8 -0.9 -1.1 -0.9 -0.5 -0.5 -0.2 -0.6 -0.4 -1.1 E28AC -1.4 -2.3 -4.3 -3.4 -4.4 -3.1 -1.3 -2.0 -5.0 EA1RX +0.0 +0.1 EA1URA +6.9 +7.1 EA2CW +0.0 +0.1 +0.3 +0.4 +0.4 +0.2 +0.2 +0.2 +0.4 +0.3 EA2RCF-4 +0.3 +0.3 +0.7 +0.6 +0.4 +0.5 +0.6 +0.3 +0.4 +0.4 EA5WU -0.0 -0.7 -0.1 -0.2 -0.0 +0.3 -0.2 -0.1 -0.1 -0.1 EA7/VE3NZ -0.1 +0.0 ES2RR -0.0 -0.0 -0.1 -0.0 -0.1 -0.0 +0.1 -0.1 +0.0 -0.0 ES5PC +0.0 -0.0 -0.1 +0.0 -0.0 -0.0 -0.1 -0.0 -0.0 -0.1 ET3AA -11.8 F4GOU +7.7 +7.7 +8.1 +8.3 +8.0 +7.7 +8.4 +8.1 +8.1 +7.6 F4VVG +0.1 +0.8 +0.2 +0.2 +0.3 +0.1 +0.8 +0.0 F6KGL +0.3 +0.3 +0.2 +0.2 +0.2 +0.0 +0.1 +0.2 F8DGY -1.4 -2.3 -2.6 G0KTN +0.4 +0.4 +0.5 +0.6 +0.4 +0.4 +0.4 +0.3 +0.3 +0.5 G0TMX -1.1 -0.3 G3YPP +0.6 +0.4 +0.4 +0.7 +0.7 -0.3 +0.4 +0.7 +0.5 +0.7 G4IRN +0.3 +0.3 +0.2 +0.3 +0.3 +0.3 +0.0 +0.1 -0.0 +0.3 G4ZFE +0.8 +0.8 +1.0 +1.2 +0.9 +1.1 +1.2 +1.1 +0.9 +1.1 GI4DOH-3 +0.0 +0.1 -0.0 +0.0 +0.1 +0.3 +0.6 +0.2 +0.2 +0.1 GX0FRE +0.0 +0.3 +0.4 +0.2 +0.2 +0.2 +0.3 +0.2 +0.1 +0.2 HA1VHF +0.5 +0.8 +1.2 +1.4 +1.2 +1.1 +0.9 +0.9 +1.1 +1.3 HA5PP +3.3 HA6PX +0.0 -0.0 +0.0 -0.0 +0.1 -0.1 -0.0 -0.0 -0.1 -0.1 HA8TKS +0.1 +0.2 +0.3 +0.3 +0.1 +0.2 +0.3 +0.1 +0.3 +0.2 HA8TKS-2 -0.1 +0.0 -0.2 -0.0 +0.1 +0.2 +0.1 -0.1 +0.0 -0.0 HB9BXE +0.2 +0.1 +0.1 +0.5 +0.4 +0.4 +0.5 +0.3 +0.2 +0.3 HB9DCO -0.1 -0.2 +0.3 +0.4 +0.3 +0.4 +0.3 +0.3 +0.2 +0.2 HG8A +2.6 +3.5 +4.0 +4.1 +3.7 +3.3 +3.3 +3.2 +3.4 +3.8 HI3R +0.3 +0.2 +0.0 +0.1 +0.3 IK3STG +0.8 +0.0 +1.0 +0.7 +0.6 +0.8 +0.7 +0.8 +1.2 IK4VET +4.8 +3.5 +4.0 +3.7 +3.5 +3.9 IK7YTT +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.2 +0.2 IT9GSF +0.1 -0.1 +0.1 +0.1 +0.0 -0.0 +0.0 -0.1 -0.0 +0.0 IW9GDC -0.1 -0.3 -0.3 -0.3 +2.3 +8.6 +8.3 +8.9 +8.1 +8.9 JG1DLY -0.7 -0.5 -0.6 -0.9 +0.0 -1.2 -0.5 JH4UTP +0.5 +0.5 +0.2 +0.1 JH7CSU1 +2.0 +1.2 +1.7 +1.9 +1.7 +1.9 +1.8 +1.3 +0.9 +1.5 JI1HFJ -0.7 -2.4 -0.7 +0.6 +0.1 +2.0 +0.2 +0.9 -0.6 JJ2VLY +1.4 +1.1 +2.5 +2.2 +1.8 +1.9 +1.7 +1.9 +1.9 +1.9 JK1QLQ +0.0 -0.1 +0.3 +0.0 +0.0 JN1ILK +0.3 -0.1 +0.8 +0.5 +0.3 +0.5 +0.6 +0.1 +0.1 +0.0 K1RA +0.3 +0.5 +1.4 +1.3 +0.8 +0.9 +1.1 +0.8 +0.6 +1.2 K2PO/7 +0.7 +0.5 +0.6 +0.6 +0.4 +0.5 +1.1 +0.3 +0.5 +0.7 K3PA-1 +0.0 +0.0 +0.1 +0.0 -0.1 +0.1 +0.0 -0.0 +0.0 +0.1 K3PA-2 +0.0 -0.6 -0.7 K4PP +0.0 +0.1 +0.3 +0.3 +0.2 +0.1 +0.2 +0.2 +0.3 +0.2 K5EM +2.9 +2.9 +3.8 +4.2 +5.8 K5TR -3.1 -3.5 -2.7 -2.7 -4.2 -5.0 -4.1 -3.0 -4.5 -6.6 K6FOD -0.1 +0.1 +0.1 +0.1 -0.1 +0.0 -0.3 +0.0 -0.0 +0.1 K7CO +0.9 +0.8 +0.9 +0.6 +1.0 +1.1 +0.6 +0.8 +0.8 +0.7 K7EK +0.5 -0.1 -0.4 +1.1 -0.2 -0.8 +0.9 -0.3 +0.3 -2.2 K7RUT -0.5 -0.4 -0.3 -0.8 K9IMM +0.0 -0.1 -0.0 +0.1 -0.0 -0.1 -0.2 +0.0 -0.1 -0.1 K9LC +0.5 +0.5 +0.7 +0.7 +0.6 +0.8 +0.9 +0.5 +0.9 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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 2025-08-20 00:10:29 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.