i realize this could be a quite silly question..my IC910H sends Vcc thru coax to a remote preamplifier.Once on the mast,how can i get Vcc out from remote cable to feed into a UHF preamplifier which has a Vcc supply separated from RF?
The biggest challenge in making a separate wideband bias tee is to have low insertion loss over a wide frequency range, and apart from the physical construction, making an RF choke that is effective over a wide band is the key. Usually that is done by having two or three chokes in series, each working over a more limited frequency range.
In your case, you may be able to integrate the bias tee in the preamp. Since it is then a single band device, the RF choke becomes somewhat simpler, and a single choke wound on a ferrite bead should be easy. Don't overdo the choke, too many turns brings self resonance down, and the choke is less effective than you might think.
The capacitor needs a generous rating to cope with spikes from relays if they are not quenched effectively.
You will find circuits in lots of preamp circuits. If you build the bias tee into the preamp, a good idea is to use a pair of diodes to isolate the coax fed DC and an external DC feed terminal on the box (which can be handy).
Commercial bias tees for UHF can be very expensive, hard to justify considering the parts cost.