Before anyone asks, I am not a DIRECTV employee. I just do a lot of reading from sites like SBCA's Educational Programs Website. Now, it does not matter where you put the diplexer on the cable. It is an invalid configuration and will only cause problems with the satellite and OTA reception. DIRECTV has always stated, from the first deployment of the H20, that diplexers are no longer compatible with the DIRECTV system and need to be removed. The reason the myth exists is because DIRECTV was not using the B Band until the recent launch of the HD national feeds. Because the B Band was not used it did not cause interference with the OTA signals. Now that the B Band is live this is no longer the case. Lets explain this a little further… OTA signals are in the 30 MHz - 862 MHz range (depending on which station you are watching). DIRECTV’s A band is in the 1650MHz - 2150 MHz range. As you can see, the ranges are completely separate and there is no overlap. This is the reason why the Diplexer was able to combine the 2 signals onto one cable and then separate them successfully. Now DIRECTV’s B Band is 250 MHz - 750 MHz. That’s right, the B Band is COMPLETELY overlapped by the OTA signals. Think of Monty Python’s giant foot descending from the heavens and squashing something. Now the H20 / HR20 cannot see the 250 MHz - 750 MHz range without a SWM, that is what the B Band converter is for. To up-convert the signal to a range the receiver can see. If you have OTA stations using this range it will up-convert them as well. So lets see what happens, if you have the Diplexer before the BBC on the cable the Diplexer separates the 30 MHz - 862 MHz range, taking the B Band with it. Result, no new HD national feeds and the B Band interferes with the OTA reception. If you have the BBC before the Diplexer everything in the 250 MHz – 750 MHz range gets up-converted to the 1650MHz - 2150 MHz range and you just lost any OTA stations that were broadcasting in that range. Not only that, but the OTA signals are now mixed into the satellite signals and will cause interference on the HD national feeds. Of course, if you have a SWM the SWM up-converts the signal at the multiswitch and this is not a problem. Remember, a SWM installation does not require a B Band converter and all this is handled internally. Now some people MAY LUCK OUT and none of their OTA stations are using the 250 MHz - 750 MHz range. But this is a crapshoot and depends on their market and what range their local stations are using to transmit the OTA signals. The best thing to do, and the best way to play it safe is to run the dedicated line until the SWM becomes widely available.