If you are looking for a broadband scanner antenna, you may be lured towards the direction of the discone antenna. Discones have unique features that make good scanner antennas, but are they the right choice for your setup? Would a J-Pole better suit your purposes?
A discone antenna is a form of bi-conical antenna with spoke radiating both outward and downward in a circular pattern. The antenna is vertically polarized and extremely widebanded (meaning it will receive, and transmit, on a wide range of frequencies). The frequency range that a discone covers is dependent on the length of the individual spokes. The longer the spokes, the greater the frequency range. Some military discone antennas can have wire spokes tens of feet long to cover HF, VHF, and UHF frequencies.
But the features that make discones attractive also have their downsides. Applying the phrase ‘you can’t get something for nothing’ the broad-band aspect of the discone comes at a trade-off of gain. Most discones are at unity gain and will perform no better than a 1/4 wave ground-plane antenna. Also, most discones sold for the ham radio and scanner market tend to have shorter spokes and are much more fragile than the commercial and military models. While this makes the antennas more affordable, with the shorter spokes you give up frequency range. Outside the VHF high and UHF bands, you may not get any better reception than a J-Pole antenna would provide.
The J-Pole as a scanner antenna focuses it’s frequency range on a smaller part of the spectrum. Tuned to the 150-160 MHz public safety band, it will excel on these frequencies, but will also easily receive signals along the entire 136-174 MHz VHF High band. J-Pole scanner antennas are solidly constructed out of copper tubing for unmatched ruggedness and reliability. They also have a much lower noise floor and about 3db of gain. You will often pick up the weaker signals overlooked by a discone with the J-Pole antenna.
Selecting the proper antenna for your situation can be a tough choice. If you need to monitor a wide variety of VHF and UHF frequencies, and you are relative close to the signal source or repeater site, then the discone may be the answer to you. But if you scanning pleasure concentrates activities on the 136-174MHz VHF range, then I would recommend the J-Pole Land Mobile and Scanner Antenna. You’ll hear more stations at greater distances than what a comparable discone could provide.