Signal loss from unhooked second CB coax cable on co-phase coax….

[corneileous]

Hey guys, I have an older Peterbilt daycab semi truck that actually came from the factory with a co-phase coax and after digging into the upper part of the cubby area a little bit further, I found out that the two coax cables that come from the antenna mounts on the top of the mirrors have those BNC type connectors, kind of like what you would find for the antenna connection on a scanner that plugs into a Y cable which is what plugs into the back of the CB. I found out that by unhooking the coax that goes to the passenger side antenna gives me a little bit better SWR but now I’m curious if my SWR could be even better if I was to remove that Y cable that doesn’t have anything connected to that one end and get me the same thing but just basically an adapter cable that goes from the BNC type connector to whatever the connector is called that goes to the back of the CB because wouldn’t I have significant signal loss coming out of that one end that doesn’t have anything connected to it?

 

[merlin]

You won't have any significant loss or SWR change just disconnecting one of the cables at the 'Y' connector.
The main change will be directional gain from antenna toward the truck mass.
Tuning a cophase setup that is how you select on or the other antenna and with an SWR bridge, tune each antenna in turn for best SWR.
If the separation distance is correct, there should be no change in SWR, just your directional characteristicts go from front to back.
Cheers

 

[prcguy]

The Y cable is a simple power divider made with critical lengths of 75 ohm coax that provides close to a 50 ohm match on all ports when all ports are terminated with 50 ohms. In other words when the CB and two tuned antennas are connected it does what it’s supposed to do. If you disconnect one side of the Y cable you will have loss and the VSWR will be affected in a bad way.

If you only want to run one antenna get a separate piece of 50 ohm coax and use that.

 

[corneileous]

You won't have any significant loss or SWR change just disconnecting one of the cables at the 'Y' connector.
The main change will be directional gain from antenna toward the truck mass.
Tuning a cophase setup that is how you select on or the other antenna and with an SWR bridge, tune each antenna in turn for best SWR.
If the separation distance is correct, there should be no change in SWR, just your directional characteristicts go from front to back.
Cheers

From what I’ve read, I kinda knew I wouldn’t have any change in signal or SWR and that my directional gain would change if I went with a single antenna from a co-phase dual antenna setup but what I was actually asking though, due to how this cophase cable was made, would I have signal loss or a false change in SWR from basically an open-ended cable coming from the CB that’s no longer connected to anything….

The Y cable I’m talking about has two coax cables that are joined together as one that’s soldered into the PL259 connector and then there's a female BNC connector soldered on each end of those two cables along with the coax cables that come from each antenna with a male BNC soldered to those.

 

[corneileous]

The Y cable is a simple power divider made with critical lengths of 75 ohm coax that provides close to a 50 ohm match on all ports when all ports are terminated with 50 ohms. In other words when the CB and two tuned antennas are connected it does what it’s supposed to do. If you disconnect one side of the Y cable you will have loss and the VSWR will be affected in a bad way.

If you only want to run one antenna get a separate piece of 50 ohm coax and use that.

the proper adapter connector that goes from BNS to PL259 not work?

 

[slowmover]

The avatar pic I use was the connector I needed to run new coax in a Pete I was in a few years ago in order to connect to the antenna mount from the backside (cab interior).

UHF to mini-UHF

 

[slowmover]

The Y cable is a simple power divider made with critical lengths of 75 ohm coax that provides close to a 50 ohm match on all ports when all ports are terminated with 50 ohms. In other words when the CB and two tuned antennas are connected it does what it’s supposed to do. If you disconnect one side of the Y cable you will have loss and the VSWR will be affected in a bad way.

If you only want to run one antenna get a separate piece of 50 ohm coax and use that.

I’m impressed by the Driver Extreme RG-213U equivalent coax I picked up awhile back (versus standard truckstop fare).

— A better-than-FME termination of their design.

Several lengths available:

Driver Extreme (DRX-1518) - DRX-1518 Premium Mini Coaxial Cable Assembly with Patented DX259 Connector, M213 Quantum Flex Cable, 18', Black, Coaxial Cable

Driver Extreme (DRX-1518) - DRX-1518 Premium Mini Coaxial Cable Assembly with Patented DX259 Connector, M213 Quantum Flex Cable, 18', Black, Coaxial Cable in Coaxial Cable

www.bobscb.com

Single antenna recommendation. The “best” daycab operators with whom I speak use singles.

If you have the Pete tab on the back, use that (not grab bar). Otherwise, the roof mounts (cover starboard side and run port side).

Measure mount height from ground and get antenna that tops at 14’. Skipshooter brand (buy two, one as spare).

Skipshooter Antennas Home

Welcome to Skipshooter Antennas!

skipshooterantennas.com

The truckstop equivalents aren’t as good. I have at least three pairs in different lengths. (Clear cover color recommended).

SKIPSHOOTER Antenna: Tuning Nail Rust & as Big Truck Default Choice.

SkipShooter® Mobile Antennas Have seen this question come up about rust. The SKIP SHOOTER antenna uses a common nail as the length-adjusting tip (held by an Allen screw). Yes, it will rust. I’ve used a Dremel to polish the nail to a fair shine and used FLITZ to finish. This seems to work well...

forums.radioreference.com

.

 

[slowmover]

IOWA 80 has this cab-back mount I’d prefer to have in order to exert more control over antenna length (longer being better, overall)



You earlier said trailer was cab-height.

Can’t use this with a 13’3” trailer.

Changes from this pic include split-loom conduit over coax and weather-proofing of connector to mount.

.

 

[slowmover]

I’d get out my GR45 if I could run it from that back tab.

5’ antenna that rivals a 7’ Predator 10k.

Lightning Antennas Mobile GR45

The Ultimate Mobile Antenna GR45

www.lightningantennas.com

GoldenRod 45 A+ antenna

With the MFJ analyzer (259b) just putting the GR45 together, with the top hat loops flat out to the sides, with no adjustments, SWR was at 1.5 across from channel 1 to 40... OK, not bad, I think that was what Lightning stated the antenna to be at. But, X=4 to X=9 too and Ohm was 59 to 60...

www.worldwidedx.com

When I spoke with S-E, lo, these many years ago (1997), this antenna was designed to go on the rear cowl of a full-sized car to get up over the roof the last few feet (perfect for my big Chrysler).

Used on the roof of a Jeep XJ from Dallas to Chicago and back numerous times (including IH44/MO a major truck route) I’ve not ever had so many compliments on audio quality (Uniden 76 with dual final mod; Clay Thompson; RK56).

As this was in years just after 9/11, traffic parted lanes for me (ha!).


Point is that the back-tab means further experimentation as time goes on.

.

 

[corneileous]

Well last night, I ordered me a right-angle adapter that goes from the bnc connector to the PL259 connector so I guess we’ll see how that works out.

 

[corneileous]

Well after realizing I had ordered the wrong adapter, I changed my order to the correct one which was a male PL259 to male BNC connector; the one I originally ordered was the same but it had the female BNC connector instead.

Got the right one in and hooked it up but after dong a little googling when it didn't change much, I found out that the coax Peterbilt put in that truck the adapter was for was all wrong anyway because supposedly co-phase coax needs to be RG-59 and single phase coax is RG-58 due to the difference in ohms in the cabling so I ended up running a whole new RG58 coax that worked so much better and even gave me a lot better SWR.

 

[slowmover]

Well after realizing I had ordered the wrong adapter, I changed my order to the correct one which was a male PL259 to male BNC connector; the one I originally ordered was the same but it had the female BNC connector instead.

Got the right one in and hooked it up but after dong a little googling when it didn't change much, I found out that the coax Peterbilt put in that truck the adapter was for was all wrong anyway because supposedly co-phase coax needs to be RG-59 and single phase coax is RG-58 due to the difference in ohms in the cabling so I ended up running a whole new RG58 coax that worked so much better and even gave me a lot better SWR.

Replacing their low quality coax was a good step. Cophase harness or single jumper.