This is the "secondary zip code" that works to attain channels not in a specific database. For example: WB/S has METV broadcast on 38.2 RF31, not in D* database. By running Memphis TN (37501) as a secondary zip it will give you 38.2 METV with the correct guide. Since Memphis carries METV on 30.2 RF31, the .2 RF31 matches. It will put WLMT as 38.2 in your DVR with the Memphis guide (METV) for that channel. That is, if your antenna receive's 38.2. There might be other stations in the WB/S area that you can get, but I would have to check. You have to match either the channel number, in this case 38.2. Or you can match the subchannel number with the RF, in this case .2 RF31. Then you look for another zip code that has a 38.2 or a .2 RF31 channel in D* database. In this case Memphis and Greensboro NC match and they both carry METV. You look for a match that carries the same station as your local channel so the guides match. Because you get the guide from the channel of the city you use the secondary zip for, in this case Memphis. The explanation for the channel 43 addition is this: your antenna probably picks up channel 43 on an irregular basis. When the Genie rebooted your antenna just happen to have a strong enough signal for that channel for the AM21 to pick it up. When you tried it on the other AM21s the signal was not being picked up, and since the AM21 only puts channels in the DVR that are being picked up at the time of the scan it wouldn't put 43 in the DVR.