This documentation is courtesy of Frank Ghigo. With the slower az slew rate due to cold weather, the size of the "keyhole" becomes bigger. This can be a problem when doing AutoPeaks at the lower frequencies, where the scan rate is high. The angular scan rate (Rang) is the azimuth rate (Raz) times cosine of the elevation. So given a desired scan rate and a maximum allowed azimuth rate, the maximum allowed elevation is El(max) = arccos( (Rang/Raz) I have made a table, below, giving the default scan rates used for AutoPeak for the various receivers, and the corresponding elevation limits for the max az rates for the cold and warm conditions. The AutoPeak rate is in arcmin/minutes. You can see that with the L-band receiver, the keyhole is down to 74 degrees for the cold Az rate limit. Receiver Rate El(warm) El(cold) ('/min) (deg) (deg) Rcvr_342 360 80.00 68.43 Rcvr_450 360 80.00 68.43 Rcvr_600 360 80.00 68.43 Rcvr_800 320 81.08 70.83 Rcvr_1070 260 82.69 74.36 Rcvr1_2 260 82.69 74.36 Rcvr2_3 180 84.82 78.98 Rcvr4_8 80 87.48 84.66 Rcvr8_10 40 88.54 86.91 Rcvr12_18 38 88.59 87.02 RcvrArray18_26 18 89.12 88.15 Rcvr26_40 20 89.07 88.03 Rcvr40_52 12 89.28 88.48 Rcvr68_92 6 89.44 88.82 Mustang 12 89.28 88.48 El(warm) = max elevation for warm weather azimuth slew rate (36 deg/min) El(cold) = max elevation for cold rate (17 deg/min)