// Create a Custom Antenna // // by dual_parallel // // www.oldskoolphreak.com One day there was some good discussion on the Hackermind message board. People were talking about scanners, and this was good. This intelligent conversation was inspirational. It inspired me to make an antenna. Antennas are good. If you haven't messed around with radio frequency (RF) technology, then you're missing out on a whole world of hacking and phreaking fun. Your cell phone is just an advanced two-way radio. Hams routinely use phone patches on repeaters to make phone calls. Listening to your hot MILF neighbor on her cordless phone is.. oh,uhh... nevermind. Actually, a lot of people in my barrio still use those old school 10/25 channel cordless phones. Granted most phone calls are boring, there is the occasional doozie. And I know the antenna on my scanner (Telescoping Antenna, RadioShack Cat. No. 20-006A) is not optimal for those lower frequencies (around 44 to 47 MHz). I think I've found a candidate. As I walk through my creation of a new antenna, you will be imparted with the basic theory and procedure for creating your own custom antenna, starting with some basics. Transmitting antennas emit electromagnetic waves (the broadcast) that when picked up by a receiving antenna (the scanner), induce a voltage in said antenna that is transformed by the RF equipment into sound. An ideal receiving antenna will be the length of one wavelength of the frequency you want to monitor. So that's the first thing I had to determine. I found canned formulas, like w = 984/f, but that didn't tell me much. Let's start at the beginning... w = c/f, where w = wavelength c = speed of light f = frequency First, I converted the speed of light so I'd get antenna length in feet... c = (186,000 mi/sec)(5280 ft/mi) c = 982,080,000 ft/sec Then I used the lowest frequency for the cordless phones, 43.720 MHz, to catch them all... w = (982,080,000 ft/sec)/(43,720,000 cyc/sec) w = 22.46 ft ~ 22.5 ft That's a little too long for a handheld scanner. I could've made a half-wave dipole, but that was still too much. Quarter- wave might work... 22.5 ft/4 = 5.6 ft ~ 5.5 ft = 66 in Ok, now we're talking (or listening, rather). With an idea of proper antenna length, I headed for the local RadioShack. Sure enough, they had a CB whip that was 64 inches long. Close enough. But I did have to adapt it to a handheld scanner. That meant scouring the antenna section for parts. Here's what I came up with: Mobile CB Antenna Cat. No. 21-988 Mobile CB Antenna Mount Cat. No. 21-961 2-Ft. RG-58 Coax Cable Assembly Cat. No. 278-968 PL-259 to Female BNC RF Adapter Cat. No. 278-120 I put it all together (I'm sure you can figure out how). It all hand tightened nicely. Finally, to test it. The antenna worked well. I heard tones in the target range I never heard before, signals had less static compared to my other antenna, and most importantly, I heard new cordless phone users almost every time I turned on my scanner. This antenna may not be perfect - a quarter-wave should have a ground plane, I didn't account for electrical length and the standing wave ratio (SWR) should be tested. Regardless, it was a fun project and I hope that sharing it with the community spurs some interest in RF.