It's very unlikely to work for you.
Rather than try using two antennas together, I suggest that you take an educated guess at which indoor antenna is best for your location and try it.
If you add your zip code and a close by address (don't post your actual address!) and discribe where the antenna is located, someone will probably give you an opinion.
If you want to do it yourself:
A grainy picture sounds like you just aren't getting a strong enough signal. Find out if the local stations are all UHF (analog channel 14-69) or if you also have VHF-low (analog 2-6) or VHF-high (analog 7-13).
If you are trying to receive digital stations you have to look up the real (also called "actual" or "RF") frequency; the channel numbers like "7.1" do not correspond to the actual frequency. (All digital channels (DTV & HDTV) are not in the UHF band, dispite what "Biker Rob" thinks.)
Use the first link below to find these plus the direction & distance to the transmitters.
Read the antenna reviews at the second link.
For a mixture of VHF & UHF, a Winegard SS-3000 Sharp Shooter Indoor HDTV/DTV Antenna is a good choice. If they are all UHF, perhaps a Channel Master CM 4220 Two-Bay HDTV / UHF Antenna with a Channel Master TV Antenna Preamplifier Model 7777. (If you don't like the looks of it you can always put it in a cardboard box and wrap it in (non-metallic) wraping paper.)
Keep in mind that with any antenna, you may have to play around with it's location and orientation.
If you have an attic, you might consider putting a small "outside" antenna in it.