I'm sorry, I forgot to add the broadband requirement.
Big picture:
My main interest is RF, so I want a "system" to cover the whole spectrum. MF to SHF. Of course, that's impossible. So for low bands, I have a random/long wire stretched across my property at very low height. It's basically invisible. Usefulness of that antenna cuts off at around 50Mhz. So I need another that covers from there and up to about 2GHz. It does not necessary need to be one signle antenna. But I have been using a discone. So, no, it's not 137Mhz or near there but the whole spectrum.
Further, since it is an attic, there are other structures. Rotating is not possible and not necessary. Omni-directional is desired. Gain expectation is NONE. 0dBi or 0dBd is just fine.
Thanks again.
By the way, since this is for receive only, active antenna would be great too.