It depends... If you want the normal range/performance of a PWS helical, but with 75 metres of coax, you should calculate the loss in the cable and make up that loss with an amplifier just after the antenna.
If you only need the range of a standard omni antenne, but actually have a directional antenna, you can include the "gain" in the antenna in the calculation.
Another thing to remember is to watch out with wideband rf amps on directional antennas. It is quite easy to overload it with stronf RF signals like UHF Motorolas etc. So keep the antennas some metres away from any RF transmitter/ TX antenna. Whenever possible use bandpass filtering before amplifiers. Sennheiser AD-12, Sennheiser AB-1036, the new Sennheiser antennas for the 9000 series, Lectro UFM50 etc.
Thank you for answering the question.
I figured that was the way it works but wanted to confirm.