I recently came across an article from RF Venue which had some excellent information regarding passive vs. active antenna setups. This information is critical to understand as a location sound mixer, and a synopsis along with a link to the original article is below.
An active antenna is one with an integrated amplifier built in to the unit, and a passive antenna is one which has no amplifier. As the article below describes, it really is that simple. For the location sound mixer, it is very rare to require an active antenna setup unless the cable run between the antennas and the receiver is longer than 50 feet. Using active antennas on a cable run of less than 50 feet may cause you to overload the receiver and reek havoc on your system.
In regards specifically to the RF Venue Diversity fin, it is important to note that the Diversity Fin LPDA already has a gain of 5dB, and the integrated Dipole antenna in the unit also has a gain of 1.8dB. This means that any gain lost in a cable run of less than 50 feet should be more than made up for by the antenna itself without the requirement for any boost beyond that.
Systems like the Zaxcom Mic Plexer 2 add another 6dB gain, which should compensate for any loss through connectors, wiring of the receiver system, cable runs to the antennas and even allow the transmitters to be brought down to 50mW for the average job. In practical use this is wildly dependent on location, building type, location of your cart, etc. but the concept remains: Don't add too much gain!
Full article at this link: Understanding the Difference Between Active & Passive Antennas
Special Thanks To: RF Venue, both for their products and their thoughtful article.