The choke for 144 MHz Yagis in 50 Ohm design is a bit different from the 28 Ohm version. Read here what Martin, DK7ZB, writes on his website:

The Yagis with an impedance of 50Ohm reach not the highest gain and the best patterns, but they are very uncritical for constructing and very good objects for beginners. I use stretched dipoles with an isolated middle part and a coaxial lambda/4-choke. The choke has 5 windings with RG-174 (for 100Wtts) or RG-188- Teflon (for 200Wtts) on a piece of PVC-tube with 16mm diameter. One end of the choke is connected to the radiator, the other side is connected to a coax-socket which should be grounded to the boom.



There are no currents on the shield of the cable and you can get a very good SWR of 1,0! The Yagis work without any corrections, if you use the given data. You can use this construction instead a 200/50-Ohm folded dipole (easier to tune!) in other descriptions.



Above is a choke with RG-58 coax of good MIL-quality. There are some inferior cables on the market for CB-use with a very thin shield, avoid such products! Use cable with a full-PE insulation, foam cable is very bad for bending it to a choke. This choke has 5 windings on a 20mm-PVC-tube and can handle 200Wtts CW/SSB. With these chokes you have no common mode currents on the outer side of the coax-shield and a symmetrical pattern.