That's a distinct possibility depending on what you want to hear.
A discone really isn't very efficient below 100 Mhz or so (it will work, just not well) so if you want to hear things below that, a better antenna is called for. You already know about some antennas for CB and 10 meter ham...
Let's start by saying there's no one perfect antenna - physically impossible to make something with a flat response across such a range like the 7100 hears. So what to do?
Consider that this is not a scanner - it's a receiver that happens to scan (albeit very slowly). Most folks that I know that have the R7xxx series use them as fixed receivers, monitoring a single channel (or sets of channels, if they can stand the slow scan rate). It's an excellent receiver for milcom purposes - satellites, too (although if you do get heavy into satellites, there are very specialized antennas for that). A discone will serve you well in the milcom world, although it may fall short for satellite monitoring (it will work, just not optimally).
It will also hear the various conventional public service stuff, civil aircraft, hams (not just on 10 meters - we have many other bands that may be active, but this is very regional in nature - some areas may have little or no activity simply because there's no interest there), FM broadcast (although why you would use this radio for that...), maritime and probably a lot more I didn't mention.
Time, I think, to make some decisions as to what you want to hear - that will play a big role in the kind of antenna(s) you will need to make that happen, assuming that there is such activity in your area. Get familiar with your state's forum, and any scanning email group(s) for your area. Our
wiki collaboration area can help you with that. Get familiar with your county's database entries.
Answer a simple question, so locals can help guide you -
where are you (county/state is fine)? That will help determine what activity is in your area...then go make like a gopher and dig...Mike
