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What I hadn´t realized is that up til now I have been using strong TPs with a high SR to aim. My pansat 2700 which I use for aiming has quite a bit of a delay scanning low SRs.
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If you see delays locking low SR signals, it could be due to poor signal level, but it could also suggest that the LO freq in your LNBF is off. This will make the frequencies that the receiver sees off a bit, and the receiver will have to search around a bit to find the signals. I've seen one lnbf that would drift to about 5 MHz off freq when the temperature got cold, and when that happened, I would then have problems locking transponders that had SRs lower than around 4000. With some receivers I couldn't lock them at all, with other receivers I could lock them but there would be a delay. Some receivers would take as long as several minutes to find the transponders.
Most lnbfs however shouldn't be off by that much. Most should be within 2 MHz, and you really shouldn't have problems or lengthy delays on the NBC mux unless your LNBF is way off.
You might just experiment on a low SR transponder on another sat that you CAN pick up, and try varying the transponder or LO freq by a couple units and see if it will lock quicker. With some PC card receivers, you can get an accurate reading of how far off freq your lnbf actually is, but with an STB, you may just have to experiment a bit to figure out what offset works best. Once you find out how far off your lnbf is, you can change the transponder freq that you're using to search for the sat by that amount, and it should lock quicker making it easier to locate the sat. If the lnbf is always off by that amount, you can change the LO freq to compensate, but if it's a temperature related drift, then you're better off just living with the delays once you locate the sat.
Higher quality LNBs won't drift much at all, like a few tenths of a MHz, but the cheap consumer lnbfs will typically drift over 1 MHz even at normal temperatures, and will drift a bit over 2 MHz during very cold or very hot weather. Since the NBC mux is approximately 7 MHz wide, there really shouldn't be an issue with this mux with most receivers, unless you have a defective lnbf. I had an lnb once that suddenly became off freq by 20 MHz. I had a receiver that allowed me to adjust the LO freq by this amount, and I lived with it for quite a while before finally replacing it.
Different receivers seem greatly different with respect to how they are affected by being off frequency. I have a few receivers, like the TT3200 PCI receiver, and my Fortec Ultra and Fortec Mercury, that can be off by 20 MHz, and will often search around and eventually find a transponder, provided that I have the proper SR keyed in, and provided that there isn't another similar SR signal nearby that it finds first. For example, I could tune in a 4080 H transponder, switch the polarity to V, and after a short delay, a 4060V transponder would pop in, while still tuned to 4080. However other receivers, like my Fortec Lifetime, Coolsat 8100, Diamond 9000, Genpix, and Azbox need to be much closer in freq, or they won't find the transponders. Like within a few MHz. My Twinhan 1020a, however, needs to be right on. Usually within 1 MHz, maybe 2 at the most, or it will not lock. With some receivers, like my my Broadlogic 1030, or with my 4200 DCII receiver, I can go to a diagnostic screen which shows the freq offset it's using. On the 4200, you can watch it search for low SR transponders by moving the LO offset around. The 4200 takes a LONG time, on the order of several minutes, to establish the proper offset, but the Broadlogic generally establishes the offset rather quickly, on the order of 10s of seconds, depending upon how far off the frequency drift is.
