choosing the right coax by marty woll n6vi ares-los angeles amateur radio... when all else fails
TRANSCRIPT
Choosing the Right Coax
by Marty Woll N6VI
ARES-Los Angeles
Amateur Radio . . . when all else fails
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
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
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
Some actual numbers: RG-58/Uon 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
Some actual numbers: RG-8/Uon 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
Some actual numbers: LMR-400on 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
Some actual numbers: LDF4-50on 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
Some actual numbers: LDF5-50on 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
On 80m, coax is not so criticalRG-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
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
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
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
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
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
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
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
A tip for your “Go-Kit”: Keep various adapters between connector series, such as UHF-BNC) on hand
Amateur Radio . . . when all else fails
Thank you!
Amateur Radio . . . when all else fails