Question about signal loss from excess connectors and adapters on a AM/FM car stereo antenna coax….

[corneileous]

I hope this is the right part of the forum to ask this but anyway, what I have is a 2017 Freightliner Cascadia and for those that don’t know anything about how the factory antenna wiring on these trucks works, what they did was, there’s like a 4 foot antenna mounted to each side of the cab towards the back of the cab behind the doors and then they ran a coax from each antenna mount to a spot right behind the speedometer and the tachometer behind the steering wheel into one single male PL-259 connector that threads onto the input side of a multiplexer….

…..on the other side of that multiplexer, there are two female BNC antenna jacks where one output goes up to the headliner where the spot is for the CB and the other female BNC antenna jack on the multiplexer is what goes directly to the antenna input for the AM/FM radio and the whole thought behind all this is, is so that you can have just two antennas that you can use to pick up your radio stations and be able to use your CB……

Well, being that their factory antenna mounts- due to the crazy way they designed them, doesn’t even let you properly ground the antenna mount itself(not the part the antenna threads into) and the coax to the chassis ground through the sheet metal cab, this is another hurdle(besides the multiplexer) that also keeps you from being able to achieve anywhere even remotely close to a good SWR. Not to mention the fact that if it wasn’t for the multiplexer being bad enough, you don’t even have the ability to properly tune each antenna individually because like I said before, both antenna cables are soldered into one PL-259 connector. And then to top it all off, they didn’t even use one continuous string of coax to get from the factory antenna mounts to the multiplexer.

They ran the cable down to the floor from the top of the cab and then ran it underneath the door threshold and right there behind each kick panel where the cable comes up to go into the dash, there’s also another connector right there which, if memory serves me correctly, it’s whatever the proper name is for basically a mini PL 259 connector. And also not to mention, where the coax comes from the multiplexer to go up to where the CB goes, they ran that cable behind the plastic A-pillar cover and basically right in the middle of the A-pillar, there’s, I believe, a BNC connection there as well….lol.

So as you can see, the way they added this in here, if you was to use the factory set up for your CB, your range would probably only be less than 100 feet.

Well, after running my own coax straight to my CB from a modified CB antenna mount that you can get at any truckstop that’s actually bolted to the part of the factory antenna amount that’s bolted to the side of the cab, I got all that straightened out and since I’m now basically only using the passenger side antenna as only my stereo antenna, I’m wondering if I could actually increase that reception if I was to completely remove the multiplexer and just crimp a female BNC connector to that cable and then just take the cable coming from the stereo and connecting it directly to that if that would actually help anything or if I could get by with just cutting the factory coax that used to come from the driver side CB antenna, tape it up real good and then just put a female PL 259 to female BNC and just hook the stereo antenna cable straight to it that way.

Sorry for the long post but I just felt the need to explain exactly how this is so that you guys know what I’m not dealing with.

 

[chief21]

Wow. If I had to deal with that situation, I would probably rip it all out and start from scratch. In the long run, that might be easier.

 

[corneileous]

Wow. If I had to deal with that situation, I would probably rip it all out and start from scratch. In the long run, that might be easier.

Generally that’s the idea if you want better CB performance in these trucks just despite Freightliner “trying” to help you out with a factory-installed plug and play setup. They even give you a convenient place to mount your CB up in the upper console.

There’s a big rectangle area on the driver side that’s held in with two screws that has a single-DIN sized opening in the middle of it with a cover plate so if you’re hooking up a CB, you just pull those two screws, pop that whole piece out and then remove that snap-in cover plate and then they give you a metal bracket that’s attacked to the backside of that you attach to the sides of your radio. That part, they did good on…lol.

But I don’t know, being that I trimmed the passenger side antenna down to about 14” long or so and put the cap back on the top of it to keep it from hitting so many tree limbs, I’m not sure if that might be why it seems as though I really didn’t gain any more AM/FM reception just despite only completely removing the multiplexer and using an adapter to go from the PL 259 connectors to BNC.

Think it would help to go through the time and trouble of only cutting the cable that comes from the passenger antenna and crimping a female BNC to it to go straight into the stereo?

 

[mmckenna]

I’m wondering if I could actually increase that reception if I was to completely remove the multiplexer and just crimp a female BNC connector to that cable and then just take the cable coming from the stereo and connecting it directly to that if that would actually help anything or if I could get by with just cutting the factory coax that used to come from the driver side CB antenna, tape it up real good and then just put a female PL 259 to female BNC and just hook the stereo antenna cable straight to it that way.

The diplexer would handle splitting out the signal between the AM/FM broadcast bands from the CB. These devices usually have a minimal amount of insertion loss, like maybe 0.2-0.3dB. That's pretty small and hard to notice.

But if you are not now, and never going to use it for CB, then removing it might make a very small amount of difference.

The concern is the phasing harness. Those two different lengths of coax coming from each side of the truck to the common UHF connector play a role in the CB side. Not sure how it impacts AM/FM broadcast. Even with one of the antenna removed. I don't know the answer to that.

As for the cable harnesses, sounds like it was designed that way for ease of installation as the truck goes down the assembly line. No, not ideal, but good coax connectors can induce a bit of loss, but if done right, probably not a huge deal. Unless you were doing AM/FM broadcast DX'ing, you may not notice a difference.

Not sure you'd see a big improvement by ripping and replacing. I think if it was me, I'd cut the two pieces of coax where they meet the UHF connector at the diplexer. Take the one from the side of the truck opposite the CB antenna and crimp on a new connector and run that up to the AM/FM radio and see how it goes.

 

[mmckenna]

But I don’t know, being that I trimmed the passenger side antenna down to about 14” long or so and put the cap back on the top of it to keep it from hitting so many tree limbs, I’m not sure if that might be why it seems as though I really didn’t gain any more AM/FM reception just despite only completely removing the multiplexer and using an adapter to go from the PL 259 connectors to BNC.

Yeah, that would do it. Antenna length is part of the equation and randomly cutting it isn't helping. I'd find a AM/FM broadcast antenna designed with a 3/8 x 24 base, if that's what it's got, and replace it.

Think it would help to go through the time and trouble of only cutting the cable that comes from the passenger antenna and crimping a female BNC to it to go straight into the stereo?

Maybe.

 

[corneileous]

The diplexer would handle splitting out the signal between the AM/FM broadcast bands from the CB. These devices usually have a minimal amount of insertion loss, like maybe 0.2-0.3dB. That's pretty small and hard to notice.

Hmm. Well, I guess maybe all the other flaws they did was primarily what makes it not ideal.

When I get home, I’ll have to post a picture of what’s inside that multiplexer. Kinda odd looking and not what I would’ve expected.

But if you are not now, and never going to use it for CB, then removing it might make a very small amount of difference.

I did. Figured it was gonna make a difference but due to the other things they did and how I did my CB, it’s just extra junk…lol.

The concern is the phasing harness. Those two different lengths of coax coming from each side of the truck to the common UHF connector play a role in the CB side. Not sure how it impacts AM/FM broadcast. Even with one of the antenna removed. I don't know the answer to that.

Oh yeah. Forgot about the different lengths of coax but the fact that you can’t even isolate and tune one antenna at a time is, I’m sure a big thing.

But yeah, I don’t either. I could still receive good but since there’s not many radio stations and because I play music off my iPhone more than anything, I’ve just never paid attention to it.

As for the cable harnesses, sounds like it was designed that way for ease of installation as the truck goes down the assembly line. No, not ideal, but good coax connectors can induce a bit of loss, but if done right, probably not a huge deal. Unless you were doing AM/FM broadcast DX'ing, you may not notice a difference.

Yeah, at least they tried…lol. Surprisingly enough, it does work for some.

Not sure you'd see a big improvement by ripping and replacing. I think if it was me, I'd cut the two pieces of coax where they meet the UHF connector at the diplexer. Take the one from the side of the truck opposite the CB antenna and crimp on a new connector and run that up to the AM/FM radio and see how it goes.

Yeah, that’s probably what I’m gonna do being that I now have the tools to do it from when I did up my home scanner antenna.

 

[corneileous]

Yeah, that would do it. Antenna length is part of the equation and randomly cutting it isn't helping. I'd find a AM/FM broadcast antenna designed with a 3/8 x 24 base, if that's what it's got, and replace it.

Yeah I figured on a receive-only AM/FM stereo antenna that it wouldn’t matter but then again, I didn’t take into consideration that even through they are just radio stations, they’re still the same thing as any other specific frequency that requires different antenna lengths kinda like the one antenna I have for my portable scanner that depending on what frequencies you’re scanning, the antenna is made to where you can extend it in certain ways.

 

[slowmover]

The antenna is molded into the cab over the windshield.

I’d run a separate CB antenna. Just leave factory harness alone.

6’ Skipshooter off drivers side mirror mount.

.

 

[corneileous]

View attachment 182787

The antenna is molded into the cab over the windshield.

I’d run a separate CB antenna. Just leave factory harness alone.

6’ Skipshooter off drivers side mirror mount.

.

This is a 2017 with external antennas on each side of the cab…..

And I’ve already dealt with my CB- this is asking about improving my AM/FM stereo reception.

 

[slowmover]

This is a 2017 with external antennas on each side of the cab…..

And I’ve already dealt with my CB- this is asking about improving my AM/FM stereo reception.

If it has multiplexer, then it applies. Starboard antenna for AM-FM, all new set-up (on new mount) on Port for CB.

New RG-6 thru hole into interior and across headliner to A-pillar then down is a maybe.

There’s no guarantee anything will “improve” AM/FM RX.

I’ve looked into it from long ago. Haven’t found any avenue for non-West Coast mirror trucks.

You could try this one (it’s meant to go on hood or ahead of cab), but since you are in the habit of whacking tree branches, then . . . .?

The curb mirror mount has same height problem. Doesn’t bond well.

— The factory mounts (side of cab) have a bond strap to the truck metal.

International used to build a 3/8-24 mount into flat cowling just ahead of windshield.

 

[slowmover]

FLAF5K - ProComm Back Of Cab AM/FM Antenna Kit For Freightliner Cascadia

FLAF5K - ProComm Back Of Cab AM/FM Antenna Kit For Freightliner Cascadia

www.wearecb.com

Back of cab for AM/FM/WX.

If it’s your truck?
And you’re not pulling a van.

I’d use this DRX antenna to retain WX (and quality is far higher).

.

 

[corneileous]

If it has multiplexer, then it applies. Starboard antenna for AM-FM, all new set-up (on new mount) on Port for CB.

New RG-6 thru hole into interior and across headliner to A-pillar then down is a maybe.

There’s no guarantee anything will “improve” AM/FM RX.

I’ve looked into it from long ago. Haven’t found any avenue for non-West Coast mirror trucks.

You could try this one (it’s meant to go on hood or ahead of cab), but since you are in the habit of whacking tree branches, then . . . .?

The curb mirror mount has same height problem. Doesn’t bond well.

— The factory mounts (side of cab) have a bond strap to the truck metal.

International used to build a 3/8-24 mount into flat cowling just ahead of windshield.

Well, it had… a multiplexer. I took it out being that it’s no longer needed but…. Even if it was still there, the CB end is irrelevant because I’ve already dealt with that and this is strictly about improving AM/FM reception for my stereo… Lol.

But I don’t know… I really don’t listen to the AM/FM a whole lot due to playing the majority of my music from my phone directly into my radio so I was just curious if the stuff I talked about above would make a difference or not.

 

[corneileous]

FLAF5K - ProComm Back Of Cab AM/FM Antenna Kit For Freightliner Cascadia

FLAF5K - ProComm Back Of Cab AM/FM Antenna Kit For Freightliner Cascadia

www.wearecb.com

Back of cab for AM/FM/WX.

If it’s your truck?
And you’re not pulling a van.

I’d use this DRX antenna to retain WX (and quality is far higher).

.

It’s not my truck and no, I’m not pulling a van. Just pulling a 40 foot end dump that’s really no higher than the truck and I don’t even have a sleeper.

Don’t need to retain whether due to the fact that I got rid of the cheesy factory radio that was in his truck.

I like that the DRX antenna, though. I might have to look into one of those to replace my 3 foot fire stick I use for my CB.

 

[slowmover]

Well, it had… a multiplexer. I took it out being that it’s no longer needed but…. Even if it was still there, the CB end is irrelevant because I’ve already dealt with that and this is strictly about improving AM/FM reception for my stereo… Lol.

But I don’t know… I really don’t listen to the AM/FM a whole lot due to playing the majority of my music from my phone directly into my radio so I was just curious if the stuff I talked about above would make a difference or not.

What others have done is as I’ve described. The most common approach. Extra work short of an all new system may not work, and even all new may not be much better.

My first post, which you misread: separate CB, and leave the rest alone.


.
.

 

[corneileous]

What others have done is as I’ve described. The most common approach. Extra work short of an all new system may not work, and even all new may not be much better.

My first post, which you misread: separate CB, and leave the rest alone.


.
.

I didn’t misread your first post. It was all about telling me how to deal with my CB and that’s not even what the conversation is about. My CB situation has long been dealt with. I modified the driver side cab mount so that everything is grounded how it’s supposed to be and I ran a 9 foot coax from the new mount to the CB.

This is all about improving the radio reception on my trucks stereo.

 

[slowmover]

New CB setup to separate it from the AM/FM.

THATS the improvement of what’s possible with a dedicated AM/FM antenna (inspect system).

 

[corneileous]

New CB setup to separate it from the AM/FM.

THATS the improvement of what’s possible.

And again, I’ve already done that… Lol.

This is purely about improving the AM/FM radio station reception if it’s even possible but for whatever it’s worth, I think I’ve already answered my question because removing the multiplexer completely and then adapting Freightliner’s poor antenna co-phase cable directly to the BNC connector that goes directly to my AM/FM radio didn’t really improve reception like I had hoped but of course, as per one of the other members who responded, that could possibly be because I trimmed the passenger side antenna, which is only for my AM/FM radio reception.

In other words, being that I took that 4 foot antenna and trimmed it down to about 18 inches to make it less susceptible to getting broken off from a tree limb, it probably doesn’t really matter what else I do at this point other than getting a regular complete replacement AM/FM antenna kit from like O’Reillys or something and putting it on the passenger side antenna amount and running that directly to my radio, but then again, is it even worth it?