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Advice on antenna setup.

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adam8622

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Jan 22, 2017
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Hello,

Need some advice on setting up my cb on new pickup. I currently have it set up on my F150 (galaxy 979 w/wilson 1000). Radio is tuned and works great! Upgrading my truck to an 2017 F350 CC long bed. The new pickup has a glass roof covering about the whole roof, so magnetic mount would not work. I basically have the antenna down to two possible ways to mount. My overall goal is as much range as possible, within reason, but dont want the antenna be 14ft in the air.

I have a 979 with two firestiks on my International 9200i and it works great! I was leaning towards putting two 5ft firestiks mounted on the toolbox on the bed. The biggest problem is even mounted on the far sides on box, they will still be quite close together (about 6.5ft). Now, I do pull a camper a few times a year from PA down to FL. Current camper is 11ft high but will be upgrading to a 5th wheel in a couple years that will be close to 13'6.

The other option I had was using a 102" whip mounted in the middle of the truck on the front of my bed by leaving a few inch gap between the toolbox and front of the bed. Now the F350 is a 4x4 and very high compared to my F150. I understand this way would most likely give me the best range but it will be VERY high above the truck. Maybe even cutting the antenna down a little bit giving me about 11ft-11.5ft overall high of antenna off the ground is an idea, pro or cons?

Do you think the 2 5' firestiks on the toolbox or 102" whip mounted middle on truck on front of bed will work better for how my configuration? Another thing to consider is the cab and bed on the new F 350's are all aluminum, will this make a difference in either of the two ways I would like to mount the antenna?

Thanks!
 

mmckenna

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102" whip if properly installed should work well.

The two co-phased whips only 6.5 feet apart will create a funky radiation pattern. I've heard many recommendations for people who really want both antennas for looks to hook up one and not the other. They work well on your big truck because they have the right amount of separation.

If it was me, I'd put an NMO mount at the rear of the cab and use a Larsen NMO-27. I used those for years back when I was active on CB, and they are great performers. A permanently installed antenna on the top of the cab will work very well.

Aluminum won't matter, it's still conductive. Fire engines and ambulances have been using aluminum bodies for a long time.
 

lmrtek

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Feb 11, 2009
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533
you need 9 ft spacing on dual antennas and the 9 ft whip is way too high.

all that's needed is a base loaded antenna like a k40 on the roof to get the job done
 

adam8622

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Jan 22, 2017
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Have an update, not a good one though. Finally got everything set up in the truck and have a swr close to 3 on ch 1 & 40. Thinking it has something to do with my mount set up. I tried a fiberglass antenna off my tractor trailer and get the same swr reading. Ideas on what to try?
 

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mmckenna

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Looks like a number of things.

1. Hard to tell how the mount is set up, but I don't see an insulator between the antenna mount and the bracket. That would suggest you have a direct short to ground. If you have a multimeter and know how to use it, disconnect the coax from your radio and check for continuity between the center pin and vehicle ground. If there is continuity, you've got to fix that first. If there isn't, also check by removing just the coax from the base of the antenna. Check for continuity between the center pin of the antenna jack on the mount and the mount itself.

2. 1/4 wave on CB is around 108 inches. With all that extra fold over hardware, it's likely too long. With that fold over adapter, looks like you've added a few extra inches. If you need to keep that, you'll have to trim the antenna.

3. Mounting an antenna directly behind the cab like that can cause issues since a fair portion of the antenna is so close to grounded body steel/aluminum. That'll detune the antenna.

As for the mount, that looks awful close to the window. I know the cabs are on semi-flexible mounts and the bed is bolted directly to the frame. Off road, speed bumps, or even a particularly rough road may cause contact between the mount and the rear glass. I'd strongly suggest moving it farther away, maybe even moving it to the back side of the tool box.

First step, though. Check for a direct short to ground from the center pin to the mount and between the center pin and vehicle body. I think that is likely the primary issue. The rest of them will need to be addressed one at a time.
Your mount also needs to be well grounded to the vehicle body. I'm not confident it's getting that. A clamp type bracket like that can create issues if it's just touching paint/bed liner and not actually making a good connection to the body.
 

adam8622

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Jan 22, 2017
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Ok. In regards to the insulator, the top of the SO239 there is on. The insulator is between the SO239(top of it) and the bottom part of the mount. Do I need to add one? Or is it in the wrong place? I will check the multimeter tomorrow. After I shot these pictures, I moved the mount as far to the drivers side as possible. The SWR went from 3 on ch1/40 to 2.5 on ch1/40. If there is continuity, how would I go about fixing that? A ground?

In regards to length, I dont mind trimming the antenna, crazy high as is lol. Should I measure from the mount up to 102" and cut the rest off?


I figured this was the best place to mount the antenna. As of now I would like to try and get it as best I can before I think about mounting else where.

Thanks for the tip about the mount being close to window. I plan on adding some rubber between where the mount and glass is. The mount was really REALLY hard to get in place due to these new trucks having such small gaps between cab & bed.

There is a ground screw on the mount. Im sure I can find a nice ground off the frame some where and ground the mount.


__________________
 

mmckenna

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Ok. In regards to the insulator, the top of the SO239 there is on. The insulator is between the SO239(top of it) and the bottom part of the mount. Do I need to add one? Or is it in the wrong place? I will check the multimeter tomorrow. After I shot these pictures, I moved the mount as far to the drivers side as possible. The SWR went from 3 on ch1/40 to 2.5 on ch1/40. If there is continuity, how would I go about fixing that? A ground?
I don't know, I've never seen a mount quite like that.
The threaded part of the antenna base, spring, fold over mount, etc. should not have contact with the mount in any way. Usually there is a set of nylon (or similar material) insulators that keep the center pin of the coax mount all the way to the place where the antenna/spring screw in isolated. It looks like that's missing.

Moving the antenna could mean a number of things. Could be when you moved it and tightened it back down it made ground contact between the base and the vehicle body. Trouble is that sort of connection is going to be flakey at best. Corrosion, movement, etc will impact that.

Still, it's going to do better farther away from the cab. If you went through all the work and expense to make this function right, keeping in in a less than ideal location is going to negate that work. Where I've seen installs like this work is when they are away from the cab. I've even seen people have good results mounting the base at the back of the bed.

Antenna location is very important and often gets overlooked. Your at a disadvantage having it so close to the cab.


In regards to length, I dont mind trimming the antenna, crazy high as is lol. Should I measure from the mount up to 102" and cut the rest off?
No, too easy to cut it too short. Actual length is going to be closer to 108", and that will vary from install to install. Little things will impact the exact length needed.
The right way to do it is to get everything fixed, then shoot the SWR. By looking at where the SWR is better/worse you can get an idea if the antenna needs to be longer or shorter. Once you do that, you start by cutting off a 1/4 inch or so and see if SWR improves or not. If it does, then you keep making small incremental cuts until the SWR is acceptable. Remember, once you cut it too short, you'll have a hard time making that longer.


I figured this was the best place to mount the antenna. As of now I would like to try and get it as best I can before I think about mounting else where.
That location is going to work against you. If you are OK with that limitation on system performance, then that's up to you. If you look at police cars, fire trucks, ambulances, etc. you'll see they almost always mount on the roof or trunk. That's because it works best. Anything else is going to be a compromise. But, I understand, you do what you can with what you've got and what your budget allows. If you are happy with it, that's what matters.

Thanks for the tip about the mount being close to window. I plan on adding some rubber between where the mount and glass is. The mount was really REALLY hard to get in place due to these new trucks having such small gaps between cab & bed.
Rear windows are expensive, tinted with defroster is going to add to that. I'd really encourage you to move it to the back of the tool box if you can.

There is a ground screw on the mount. Im sure I can find a nice ground off the frame some where and ground the mount.
It needs to be grounded, looks like the manufacturer thought of that. The ground needs to be short, so you really want to keep the ground lead as short as possible. Running a long wire all the way down to the frame may not work as well as running one to the body. After all, you are trying to connect to a ground plane. The vehicle body is the ground plane. Relying on the mechanical connection between the truck frame and the truck body may not work as well as it could.
Again, attaching the mount to the rear of the tool box, actually bolted, not clamped, will address some of this. Making sure that the tool box is well grounded is important, too.
Also, RF ground and DC grounds are different things.
 

adam8622

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Jan 22, 2017
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Ok. A lot of people raved about the Breedlove mounts, which is the maker of the mount that I have. So I need an insulator on the top of the mount also at the bottom of the fold over part. I will add that. At that point there is no part of the antenna touching the mount directly.

I know the antenna mount is not grounded due to the front side of the bed is painted and the other side has Line X. I will look into adding a ground to the mount. In regards to placement of the mount, Id like to see how this works out before I move it. After these improvements I will see how it works and go from there.

Noted about cutting the antenna. Mounting on the roof is a no go. The entire roof is glass (double moon/sun roof). I would be happy with a 1.5 or 1.8 SWR at this point lol. Funny on the last truck I just threw everything together and bam, 1.1. Same thing with my tractor trailer, looking back now, I was lucky those installs worked so well with no effort.

The thing that worries me about mounting on the toolbox is it is a cheap tool box. Id worry it would break. Also its a low profile box, not many options on the sides of box. I did have to leave about 4 inches at the back of the box, towards the front of the bed to give room to the current mount. If I exhaust my options with how it is now, I may be able to rig this mount up to attach to the back end of the box towards the front of the bed.

The ground makes more sense now, thanks for explaining that. Looks like I have my work cut out for me.
 
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