The Yaesu ATAS-120A is a reasonably good screwdriver antenna designed to mate with several of their HF radios. I enjoy being able to hit the tune button on the FT-897D 70cm-40m with nothing between the radio and the antenna but a duplexer and a length of coax. The efficiency of shortened vertical ground mounted antennas is largely dependent on the radial field under them. With that in mind, I made two sets of radials to play with. I have both a 16 and 32 radial set in 16ft lengths depending on how much copper I’m willing to lug around. The 16ft radial figure was ballparked as it is greater than a 1/10λ on the lowest operating frequency like the ARRL Antenna Handbook recommends and is close enough to a 1/4λ on 20m which makes it nearly an 1/8λ on 40m. It’s also a nice round number here in the US so I went with it. I honestly don’t really think it would make a measurable difference (within reason) to have made them all 16.4042ft (5m) long. The optimum quantity and length of radials is a little disputed but I came to the number by reading this white paper by N6LF and determining what the best bang for my buck was.
Additionally, I drilled and tapped a fender washer to attach male quick disconnect blade tabs to. I am currently discussing making a run of these radial plates with a buddy of mine that owns a machine shop. I may sell this as a kit in the future using the McMaster-Carr list below. Unless you know how to machine stainless, don’t just go out and buy the stainless washer thinking it’s a better solution. You without a doubt will be sorry you did. You’ve been warned!
DIY Radial Plate Shopping List:
- Cablexperts UG-3634 (SO-239 4″ Female Barrel)
- LP UHF-15-DGN (90° SO-239 → PL-259)
- Seamless Steel Spacer (5/8″ x 7/8″ x 1-1/2″)
- Metric Fender Washers (M16) (What I could find ~5/16″ ID at Ace )
- Blade Tab w/ #8 Mounting Hole (Also sold as Noble #747D at Orvac)
- 10-12 Female Quick Disconnect (fits 4 x 14AWG conductors)
- 14-16 Female Quick Disconnect (fits 2 x 14AWG conductors)
- #8 6/32 x 3/16″ Screws (sorry lost the bag)
- #8 Toothed Lock Washers (sorry lost the bag)
- UL1007 300V 16GA Stranded Black 1000′
- Proline Telescoping Boom Microphone Stand (for tripod base)
McMaster-Carr Radial Plate Parts List: