I've finally decided on how our TVs are going to be set up from now on. I thought I'd share how I did it.
In our house, we've got 4 TV receiver type devices. Two of them have DirecTV HR21 DVRs, one is a TV in the guest bedroom with an ATSC tuner, one is an HD HomeRun ATSC decoder on the network for the computers.
We actually have 8 RG6 cable runs in our house, which is a lot given its small size. To the extent possible, it would be nice to give all of these cable runs the same signal, so if we decide to move a receiver around it won't be a problem. It also turns out that splitting the signal that much causes problems for some of the channels. Plus, we only have two cable runs to the living room, which causes a problem for the HR21 (ordinarily) because it has 2 tuners plus the AM21 ATSC tuner (which would require a third cable run for its antenna feed).
Fortunately, all of this can be worked out.
We start at the TV antenna. There are actually going to be two of them - one is a ChannelMaster 4228 UHF antenna. This will capture most of the DTV signals. However, we are going to have a couple of VHF-hi channels post 2/09 - KGO and KNTV. For those, I have an AntennaCraft Y5-7-13 VHF-hi antenna. Both of those feed into a ChannelMaster 7777 mast-mounted amp. The 7777 can take a separate VHF and UHF input and amplify and combine them into one feed into the house. The amplifier is necessary because of all of the losses caused by all of the splitters used to feed all of the drops.
We also have DirecTV. The fix for the living room running out of cables is an SWM-8. The SWM-8 allows a single feed to be split with conventional splitters and drive up to 8 DirecTV tuners. Not only that, but the SWM also has an input to diplex in the terrestrial antenna feed too! The downside of that is that we need to power the pre-amp. So we need to inject power into the antenna line, but after the SWM, which is awkward. Fortunately, there is an RG6 run from the distribution point out back into the garage, where the pre-amp's power supply can live. The only thing left is to figure out how to inject that power into the line after the SWM.
Well, it turns out that you can use an ordinary satellite diplexer to do just that! Just connect the VHF/UHF line to the OTA-in port on the SWM with a short length of RG-6, connect the satellite port to the line coming from the power supply in the garage, and connect the combined port to the lead going to the CM7777. The satellite leg of the diplexer has a DC power-pass on it, and the VHF/UHF side has a DC block. A regular power injector would probably do this job with slightly less loss (since the diplexer has a needless low-pass filter on the VHF/UHF port), but it was handy and worked.
The SWM also has its own power injector. If you use a splitter on the SWM1 port, it needs to have a power-pass port, and that port must be connected to the port in the house to which the SWM's power supply is connected. In our case, however, I just connected one line from the bedroom directly to the SWM-1 port. Inboard of the SWM power supply, I am using a diplexer to break out the VHF/UHF and satellite signals for that receiver.
The SWM-2 port has a 1-4 splitter feeding two lines to the living room and one line each to the guest bedroom and the port for the HDHomeRun (which is actually in the dining room). If we want to upgrade the guest bedroom from standard TV to DirecTV, we simply need to diplex that port.
The only downside to this setup is that we now are only able to use SWM compatible receivers. Turns out that isn't likely to be a problem going forward, since we already have the two HR21s we're probably going to have for the foreseeable future, and if we wanted to add a receiver later, we would probably only be able to get compatible ones new.