Choosing the Right Coax

1. Choosing the Right Coax by Marty Woll N6VI ARES-Los Angeles Amateur Radio . . . when all else fails

2. Coaxial cables vary in: size and weight loss characteristics durability and weather resistance flexibility and ease of handling impedance and velocity factor connector requirements Amateur Radio . . . when all else fails

3. General observations about coax: Most ham gear is designed for 50 ohms loss goes down as diameter goes up loss goes up as frequency goes up larger coax can handle more power more flexible means somewhat lossier better coax improves both TX and RX Amateur Radio . . . when all else fails

4. How are coax losses measured? The decibel (dB) is a comparative measure. Typical spec is dB/100 ft. at xx MHz. dB = 10 log [P2 / P1] +3 dB =~ x2 +10 dB = x10 -3 dB =~ x1/2 -10 dB = x1/10 Amateur Radio . . . when all else fails

5. Some actual numbers: RG-58/U on 80m: 0.62 dB/100’ 13% loss on 10m: 2.35 dB/100’ 42% loss on 2m: 5.52 dB/100’ 72% loss on 70 cm: 10.82 dB/100’ 92% loss ! ! ! RG-58/U is a bad choice for long VHF+ runs Amateur Radio . . . when all else fails

6. Some actual numbers: RG-8/U on 80m: 0.28 dB/100’ 6% loss on 10m: 1.00 dB/100’ 21% loss on 2m: 2.40 dB/100’ 42% loss on 70 cm: 4.78 dB/100’ 66% loss RG-8/U is a bit better for long VHF+ runs Amateur Radio . . . when all else fails

7. Some actual numbers: LMR-400 on 80m: 0.25 dB/100’ 5% loss on 10m: 0.70 dB/100’ 15% loss on 2m: 1.50 dB/100’ 29% loss on 70 cm: 2.90 dB/100’ 49% loss LMR-400 is a low-loss, RG-8-sized cable (but solid-cond. center makes it a bit stiffer) Amateur Radio . . . when all else fails

8. Some actual numbers: LDF4-50 on 80m: 0.12 dB/100’ 3% loss on 10m: 0.35 dB/100’ 08% loss on 2m: 0.80 dB/100’ 17% loss on 70 cm: 1.42 dB/100’ 28% loss Andrew LDF4-50 is a “semi-rigid” cable, sometimes referred to as “Heliax”. Amateur Radio . . . when all else fails

9. Some actual numbers: LDF5-50 on 80m: 0.07 dB/100’ <2% loss on 10m: 0.19 dB/100’ 04% loss on 2m: 0.44 dB/100’ 10% loss on 70 cm: 0.79 dB/100’ 17% loss Andrew LDF5-50 is commonly used in commercial VHF and UHF installations. Amateur Radio . . . when all else fails

10. On 80m, coax is not so critical RG-58/U 0.62 dB/100’ 13% loss RG-8/U 0.28 dB/100’ 06% loss LMR-400 0.25 dB/100’ 05% loss LDF4-50 0.12 dB/100’ 03% loss LDF5-50 0.07 dB/100’ <2% loss Not much benefit to big, expensive coax Amateur Radio . . . when all else fails

11. On 70 cm, coax is everything! RG-58/U 10.82 dB/100’ 92% loss RG-8/U 4.78 dB/100’ 66% loss LMR-400 2.90 dB/100’ 49% loss LDF4-50 1.42 dB/100’ 28% loss LDF5-50 0.79 dB/100’ 17% loss Nice return on your coax investment! Amateur Radio . . . when all else fails

12. Why not use Heliax all the time? It does have great performance, but . . . it won’t roll up under your car seat it makes a lousy rotator loop it will pull the HT right out of your hand it costs more (but there are surplus deals) connectors cost more (but more deals) Amateur Radio . . . when all else fails

13. Suggested way to choose coax: -Whatever the size, get good quality Use low-loss for long, fixed runs Use short, flexible jumpers at the ends Weatherproof the joints in fixed installations Use proprietary connectors if called for Read manufacturer’s instructions & data Amateur Radio . . . when all else fails

14. Coax connector types: PL-259 ”UHF connector” is a misnomer non-constant impedance raises SWR not inherently weatherproof lossy at VHF and UHF frequencies reasonably durable in the field right vs wrong way to install on the cable ubiquitous on commercial ham gear Amateur Radio . . . when all else fails

15. Coax connector types: Type N Military grade- and for a reason good past 10,000 MHz (10 GHz) constant 50-ohm impedance weatherproof (but tape them up anyway) installs with hand tools – minimal soldering Amateur Radio . . . when all else fails

16. Coax connector types: BNC & TNC similar to Type N but for smaller cable BNC uses bayonet and spring to join TNC uses threaded shell – very rugged available in mil-clamp and crimp types BNC’s fit many handheld radios single-hole patch panels and feed-throughs Amateur Radio . . . when all else fails

17. Coax connector types: SMA good well into microwave region very small and lightweight uses threaded shell and coax center solders onto miniature hardline (UT-141) harder to install – need special tools used on some mini-ht’s (e.g., VX-2R) not designed for frequent mate / unmate Amateur Radio . . . when all else fails

18. A tip for your “Go-Kit”: Keep various adapters between connector series, such as UHF-BNC) on hand Amateur Radio . . . when all else fails

19. Thank you! Amateur Radio . . . when all else fails