picking coax gauge size.

[Cody Dixson]

I've been enlightened and turned onto some different coax. The gage size of recommend 50ohm coax is 15 awg but when looking for 75ohm the closest I can find is 20 awg

I'm wanting to pair my bearcat 980ssb with a 2x4 and phase a pair of skip shooters any thoughts

 

[Slowmover]

Someone else can tackle the specifics of your questions. RG58 is the norm after RG59 legs,

BELLS or BOBS CB for ARIES Co-phase Harness is how I “upgrade”. This rig is BELDEN RG8 + (2-ea) RG59 legs + AMPHENOL connectors. Typical 18’ legs.

Get some UV-resistant 1/4” split-loom cover for it (50’ roll) and same type zip-ties.

FWIW, Skipshooter is a better quality antenna. I make gifts of Firestik antennas I’ve gotten stuck buying. They’re not “bad”, just not quite as good as Skipshooter

If this is for that FL tractor, I’ve used WILSON 305-702
antenna mounts with good success on West Coast mirror arms. Many years of use on & off. I run them with the bolt-head faced forward to make clean-up easier. (Bolt-thread forward becomes a bug cemetery and corrosion is worse).

Some crocus cloth on mount-arms after polishing off any corrosion. Then a thin film of JET LUBE SS-30. I use a level before I make the final torque-down sequence.

Whatever mount or coax used, will want some self-fusing tape (Rescue Tape) to waterproof the outside connections after the lightest bit of SS-30 inside barrel. A couple of layers of Scotch 88 over that. (A razor blade will split it open to remove later).

How do you plan to bring the coax from body to mirror arm? Is the factory hole large enough for a PL-259? Otherwise Wilson makes a Mini-8 harness with FME-ends (screw-on 259’s). OEM body grommet still available?

— Getting access to — and RF Bonding all mirror arm attach points to body from inside — will be bigger than fussing with custom coax featuring extra connectors, IMO. Bonding across all door hinges. Combine them and run series of short bonds to frame.

 

[secret squirrel]

Bobs CB makes his own Co-Phase harnesses in house. I second everything Slow Mover said about Skip Shooter quality. The only reason to use a Firestik is no Skip Shooter on hand. Nothing wrong with the Firestik, just Skip Shooter comes ahead in quality. Then you have people with too much time on their hands on one day and try different types of nails in the end of the Skip Shooter to see if that had an effect.

 

[Slowmover]

Bobs CB makes his own Co-Phase harnesses in house. I second everything Slow Mover said about Skip Shooter quality. The only reason to use a Firestik is no Skip Shooter on hand. Nothing wrong with the Firestik, just Skip Shooter comes ahead in quality. Then you have people with too much time on their hands on one day and try different types of nails in the end of the Skip Shooter to see if that had an effect.

That’s funny. Brass vs stainless vs galvanized.

 

[Cody Dixson]

My main question I guess would be what's the threshold for mixing gauges if my 50ohm section is 15 gauge can I get away with 20 gauge on my 75ohm legs? I understand people make them and sell them but they don't come with the coax I would like.
@Slowmover @secret squirrel

 

[Slowmover]

My main question I guess would be what's the threshold for mixing gauges if my 50ohm section is 15 gauge can I get away with 20 gauge on my 75ohm legs? I understand people make them and sell them but they don't come with the coax I would like.
@Slowmover @secret squirrel

I haven’t seen “gauge-size” used as a parameter in distinguishing coax types one from another. Maybe it’s a reference to outer diameter?

A factory (or shop) built phase harness makes simple something that isn’t improved, IMO, by using two legs of (normally) RG59 to a T-connector and (normally) RG58 to the radio.

For mobile CB — for the most part — flexibility means more than XHD shielding (large diameter).

$35-$65 is the usual range of online cophase harness purchase price.

Custom-cut and terminated coax jumpers plus connector and adaptors could easily exceed that and not be better.

Don’t know how else to answer.

.

 

[Cody Dixson]

The center conductor is what I'm referring to @Slowmover. I've got the required 75ohms and 50ohm sections picked out im just wondering if im running an amplifier would this cause an issue in resistance so normal rg 58 has a center conductor diameter of 1/.64 which would be close to 28 gauge. And rg 59 is 20 gauge. Maybe im confusing myself lol I just want to make sure I don't run into resistance issues where they combine if ive got a mismatch thats far off

 

[freecell]

Cody Dixson posted:

"but when looking for 75ohm the closest I can find is 20 awg"

TMS LMR-400-75
https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-400-75.pdf

problem? you won't be able to stuff two pieces of this into a single pl-259.

rg-59/59b will handle 870W @ 30 mhz.. you don't need a "t" connector.


reposted from april 4, 2007.

what is required to match two 50 ohm loads to a single 50 ohm source is a harness composed of two sections, each consisting of a 1/4 section of line. (1/4 wave transformer) a 1/2 wave line mirrors impedance and a 1/4 wave line inverts impedance. in the case of dual antennas we want to invert the impedances presented by the loads to match them to the source transmitter. with polyethylene line at .66% VF the length of a 1/4 wave line at cb frequencies is approximately 6' and ANY ODD MULTIPLE.

246 / 27.205 X .66% VF = 5.968' or 5' 11.6"

so the lengths required for a 1/4 wave transformer based on VF and the frequency in question would be: 6', 18' 30' etc. for polyethylene @ .66% VF

using foam line @ .78% VF the length is approximately 7' OR ANY ODD MULTIPLE.
246 / 27.205 X .78% VF = 7.053' or 7' 0.6"

so the lengths required for a 1/4 wave transformer based on VF and the frequency in question would be 7'. 21' 35' etc. for foam @ .78% VF

since there is no feedline impedance that is close to that value and since we are matching two 50 ohm loads in parallel, (which equals 25 ohms) then two 70 - 75 ohm lines in parallel provides the necessary impedance transformation.

1/4 Matching Section = sqrt ( Z1 * Z2)
sqrt ( 25 * 50 )
sqrt (1250)
35.35 ohms

there is no such thing as "co-phased" antennas. that term is a "madison avenue," manufacturer generated advertising catch phrase. an identical pair of antennas configured in the above manner constitutes what is correctly referred to as a "phased antenna array." a phasing harness is an impedance transformer.

https://www.worldwidedx.com/threads/dual-coax-with-single-102.26351/page-2#post-86020