The usual scanner/ham discone are designed for low SWR from 100MHz to 1000MHz. But as prcguy and others pointed out, at higher frequencies the directional loob tilts up in the sky and a discone that actually are made to cover 800Mhz have almost 10dB more gain at the horizon. But there's nothing that says that you cannot modify a standard discone to cover that frequency band. The military needs good working antennas and use small discones to cover upper UHF and those are made to last for decades and to almost survive a nuclear explosion, which makes them expensive and totally unneccesary for private use.
There's no noticable difference in performance between different discones if they have 8 or more legs, it's just metal in the air that receives the radiosignal and directly couples it to a coax, no mysteri or hokus pokus there with coils or transformers. I would say that a discone works well in a 1:3 range, 100MHz-300MHz. But why have good reception of the FM broadcast band that often overloads our scanners. Cut all elements down 20% to cover 120MHz-350Mhz and then take another discone, the smaller ones are cheaper, and cut the elements down to 1/3 of the original 100Mhz discones elements lenght. You then have one good 120MHz-350MHz discone and another good 350MHz-900MHz discone.
If you go to Mini-Circuits website and check into their lowpass and highpass filters you find both ready made inline filters with BNC connectors at about $40 each and SMD solder ones for $6 each and GPIOLabs website have circuit boards with connectors for those SMD components, two for $15. Low pass and high pass filters connects together using a standard T connector.
Mini-Circuits
Mini-Circuits
/Ubbe
