bjmoose installs CB Cobra 75

OK, there are LOTS of good threads on TW showing CB installations. Netmonkey has a good one here: http://www.tacomaworld.com/forum/2nd-gen-tacomas/134082-my-cb-installation-detail.html

There's not a lot for a guy like me to add. But I noticed that although a lot of folks have done bed mounts antennas attached to the bed rails, toolbox, or other location inside the bed, so far no one has installed a bed mount antenna in combination with a tonneau cover - where I wanted to put it on top of the bedside cover here:



So I'll focus on that part of the installation and skip over some of the other parts like running power wires, which has been well covered in other threads.

Start of with a "ProCom Extra Heavy Duty Stud Mount" JBC930SS. Google it - you'll probably find an ebay seller. I bought from this guy: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270611582691

Now the install - first remove the bed side cover. I did driver side. There are two plastic body clips to remove from inside the bed, then it just pops off by lifting up. It's a little fragile, don't break any of its clips. You may need to loosen your tonneau rails first. I did.



First thought is - hey -we'll use this hole right here to mount the antenna!



But that doesn't work out - the cover has a deep alignment pin that goes in that hole. So we move back a couple inches and remove the center reinforcing that's in the way of the hole we need to cut. Sharp wood chisel works really well for this - and any other plastic trimming you need to do on the truck - much better than an Xacto knife.



Measure, so when we reinstall the cover, we'll know where we want to drill.



Now, reinstall the cover and pop the front half firmly into place in its exact position. We're going to drill a pilot hole through both the bedside cover, and the bedside top itself all at once so the "real" holes will line up exactly. IMPORTANT - this pic shows a centered hole and that DOES NOT work out. You must move outboard about 1/2" from this position for the hole to clear everything it needs!!



Remove the cover again and see the pilot hole



Now drill the antenna mount hole proper. Make sure you're looking at the correct side of the plastic mount insulator when determining the drill bit size. If you use the wrong side, you'll make a hole that's too big.

In this pic - you can see there's some reinforcing steel that's in the way of the mount. The hole must be outboard of here. I had to move it out half an inch from here. But YOU will be forewarned, and won't make that mistake.


Bring the mount into position from underneath. Make sure that you've removed enough paint from the bottom side to make a good ground connection. Removing paint from the top WON'T WORK, as that's the side the insulator sits on!



Tighten into position (I painted mine black first)



Connect up the cable and test continuity. There must be GOOD continuity (low resistance) between the center and the RG-58 center wire. There must be NO continuity (infinite resistance) between the center antenna mount point and the truck ground!!



Test Continuity from the cable housing (outer part of the connector) and ground. You want good continuity here. And, obviously, we want infinite resistance between the RG-58 cable center and housing on the connector. Otherwise, there's a short that must be fixed NOW, not later after the cable is all routed.



Hey Bullwinkle, how did you get up under the bedside to tighten the mount and attach the cable? Well, it's a stretch:



Use a 1&1/8" hole saw to cut through the bedside cover, using the earlier pilot hole as an exact locator, and re-mount the bedside cover.



I ran the coax into the cab through the big access hole where the parking brake cable is routed through, right over the driveshaft:


As I said, lots of folks have described how to run power. So I'm not doing that here. The cobra 75 shows a single plug - I wanted it in the center console next to my external HAM speaker:



Which doesn't leave a bunch of choices for where to mount the Cobra 75 control box. I'm big on adhesive mounting, but this is mounted upside down, right above the shifter. I didn't want any risk of it coming off and interfering with the gearshift lever, so I attached it with four little machine screws, nuts, washers, and lockwashers.



Everything buttoned up. "Communications mode" with the Yaesu in the center, pivoted to face the passenger (the mount pivots any way you want - just flip a lever) and the Cobra 75 one piece mike/unit on passenger side. The 2m mike is on driver side.



And "stealth" mode, with microphones and head unit unplugged and removed:



Typically, I'll have the HAM radio in, and the CB out - I talk on local 2m repeaters during the commute hours. And if I want, I can also simply unscrew the CB antenna - the mount is fairly low profile. But now I've got the CB as well as the HAM for long road trips and trail runs, where folks typically (at least for now) seem to chat on CB, not HAM.

A note on tuning. It's REALLY important to tune the antenna with an SWR meter. I got one from Radio Shack for about $40. When I first tested it, SWR was so high (off the scale) that I would have thought there was a ground or continuity fault - except that I'd already tested for those before hooking up the SWR meter. So I started playing with the antenna length tuner - and was able to bring the SWR right down.

My preliminary SWR test with the antenna mounted but no wires routed and the radio and SWR meter outside the truck sitting on the ground was really good - 1.1 for channel 20 and 1.4 on channels 1 and 40. But after I routed the cables and mounted the unit in the cab, the best I could get was 1.4 on channel 20 and 2.8 on channels 1 and 40. I have no explanation for the difference. I didn't cut the coax or route it in a loop making a choke.

 

Wow, not even one comment. I guess people are more blasé about CB installs than I thought. Ah well. The important thing is that folks can find the thread via search if they're looking for CB install resources.

 

how did you ground your antenna? I (for some reason) can't understand how this process works so I didn't ground mine. What part of the antenna mount/antenna is the ground supposed to touch? What parts shouldn't it be touching?

 

Usually, it's not much of an issue if you're mounting it to metal bodywork - as long as you make sure enough paint is removed around the mounting surface. So it's possible that without doing anything special, you still got it right.

The mount comes in multiple parts. Part of it is designed to be in direct contact with the metal bodywork to which it is mounted. This is electrically connected with the shielding on the coax, and isolated from the coax center conductor. That's why you can do a continuity test between the coax connector outer conductor and a metal part on the truck chassis.

The mount also typically has a plastic insulating piece so that the part of the mount that attaches to the radiating element of the antenna is electrically isolated from the ground. This is important -- you don't want a short here. And despite the fact that it's called "50 ohm cable" that doesn't mean there should be 50 ohms of resistance - it means there's 50 ohms of IMPEDANCE. The resistance should be infinite.

So, the most important part of the grounding process is to install the mount in the way it was designed to work. Directions are not always clear here - and that's why continuity testing is important - to make sure you got it right.

If you're installing to a toolbox, railing, mirror, etc... then you complete the grounding process by making sure that your mount point is electrically grounded to the body/frame of the truck. A bit of flat braided cable can be useful here.

 

Ok currently I have a ground wire running from my mount to the frame of my truck. I made a custom mount that uses the bed rail to secure it. I figured the bed rail wasn't really much of a ground so I ran the wire. I drilled a hole into the mount itself and attached my wire there and then the other end to the frame. Would this work?

 

Probably. You want to keep the ground runs short (there's a technical reason but I'll get it wrong if I rattle it off of the top of my head) so a long tortured routing isn't good.

Have you measured your SWR? That's the ultimate arbiter of whether you got it right, or not.

 

I had my SWR set by a friend BEFORE I grounded it. I assume, and correct me if I am wrong here, that the SWR would not become worse but only improve by the grounding of my antenna.

 

That's what you'd think - but I don't think that's really a safe assumption.

I had to retune my antenna after I moved it into that cab (as I mentioned above) it doesn't take much to change the electrical length of a ground-plane antenna.

You're probably not WAY WAY off like it was coming out of the box, but it could probably benefit by being re-tuned.

 

i see, alright, well I don't have a SWR meter so I will have to have my buddy tune it for me again.

 

When it was grounded, but after it was tuned, i was transmitting right at about 3 on that little meter on the radio. Now I am transmitting at 4, very close to the red. Idk if that helps at all.

 

I think I've run out of helpful things to say. Good luck with it.

 

Hahahah, yeah I am horrible with electronics. Thanks for all the help though. I am going to reread it again and see if I can't tackle it. I want the best out of my CB.

 

Very nice! Great idea for the antenna placement.

 

Thanks!

 

Not only is that EXACTLY what I wanted to do with a CB antenna install but you gave the EXACT perfect instructions for doing it right! This should be a sticky as it is how EVERYONE with a soft tonneau should do a CB install! I have waited so long for someone to post this, thanks so much!

 

X2

 

Absolutely fantastic pro install! Thank you for emphasizing the groundage

 

+1 Rep

 

Thanks fellas.