Discone antennas were designed By the Military because of needing to transmit on many freqs . Two way radio shops use them to receive and transmit to test radios . In ham radio We use them because they are broadband and the SWR Is low . Not much gain but the secret is to get it up high and use good low loss coax like LMR-400 many are made and if you plan on putting it outside get the ones that use the stainless steel parts and solid elements .. Below is a site you can read the reviews of people who have used them . I see someone said just get a Tri band ham ant. That’s ok if you want to use it on ham freqs they are very narrow band with for those freqs a Discone is broadband and better for a scanner depending on what you are trying to hear . The higher the freqs coax loss is a factor I had a 60m ft tower and a discone on top with 80 ft of small RG-58 Coax picked up pretty good until I tried to receive a 800mhz freq 10 miles away it was noisy and only S-1 on a icom R-7000 Receiver .
I opened up a paper clip to about 3 inches and put that in the antenna port and it was 30 on the meter sounded great lesson learned about coax loss …RG-6 Cable type coax it great to it is 75 ohm but that is ok for a scanner Tip do not try and solder a connector on it will melt the foam and short out use a good adapter like Amphenol . The best antenna we can use in Scanning is one that is tuned for the freqs We want to monitor .
Happy Scanning , I Started over 60yrs ago using an old tube type regency tunable radio with a vibrator power supply .. We have come a long way but it’s a Wonderful Hobby First PD calls I heard on an old floor model shortwave radio that was tuned just above the Am Broadcast band . New York , Chicago California …