Need some experienced opinions on my issue. Installed a firestick2 so I could tune the antenna to my radio. Problem is, I have high SWR (2.9+) and can not get it to come down. Switched to a brand new coax to compare and ecmxavt same readings. Used a multi meter and confirmed I had a good base ground with an open circuit on the antenna itself. Tried two meters as well to make sure it was working correctly. Question is, it’s a fleet tractor, so the factory mounts are behind the ferring with only 4-8” stick past it. Will the ferring and trailer interfere with the antenna and cause the high SWR readings?
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Antenna location causing high SWR
- Thread starter Daffypuck
- Start date
Anything closer than 2 wavelengths affect SWR
Absolutely. I drive semis here in the UK and we close couple our trailers with usually no more than 3ft from the back of the cab to the headboard of the trailer. DAF and Volvo put the factory CB antenna mounts on the back of the cab and you have all hell on trying to tune them if you're pulling a curtainside, box trailer or containers. OK if you've a flatbed, a tipper or a tanker but not any tall trailers.
Let me get this straight...
BEHIND the Faring?
Ok, Pick one and we'll work with it...
Side, behind - or you NEED a mount?
This one is for a type called "outback" ...
Since you're in a Fleet - you go where your Dispatcher tells you to go... - type of Fleet...
Then mounting a new one is out of the question...
So when you're looking at how the antenna can even work, the best logical one is to think about the age of the fleet and the cab itself - more than likely it is not a viable working "well and good" one.
By your problems with what you have, you should not have an extremely hard time trying to get a LOW SWR because the antenna like Firestik - if you bought one at the Truck Stop - would easily slap on and work - this might be something bigger - INTERNALLY...
Is this a refurb? That instead of using RG 59 coax (75Ω ohm stuff) in a Co-phased harness - they used RG 58 (50Ω ohm) instead?
Can't always tell on the sleeve, jacket - it's printing
I don't know what you're up against except by experience - you're getting ground but are you grounded - where? At the Radio or at the antenna?
Might need a little more info to help steer you...
Pics go a long way...
BEHIND the Faring?
Ok, Pick one and we'll work with it...
Side, behind - or you NEED a mount?
This one is for a type called "outback" ...
Since you're in a Fleet - you go where your Dispatcher tells you to go... - type of Fleet...
Then mounting a new one is out of the question...
So when you're looking at how the antenna can even work, the best logical one is to think about the age of the fleet and the cab itself - more than likely it is not a viable working "well and good" one.
By your problems with what you have, you should not have an extremely hard time trying to get a LOW SWR because the antenna like Firestik - if you bought one at the Truck Stop - would easily slap on and work - this might be something bigger - INTERNALLY...
Is this a refurb? That instead of using RG 59 coax (75Ω ohm stuff) in a Co-phased harness - they used RG 58 (50Ω ohm) instead?
Can't always tell on the sleeve, jacket - it's printing
- BUT a good clue is to try tuning for ONE antenna on ONE mount use only one
- - does the SWR go lower?
- - then you KNOW you have issues
- - we'll just have to sort this all out.
I don't know what you're up against except by experience - you're getting ground but are you grounded - where? At the Radio or at the antenna?
Might need a little more info to help steer you...
Pics go a long way...
Welcome to the forum Daffy,
You want to make very certain that your mount (shield side of coax) is very well grounded.
Www.k0bg.com is a great source of info for mobile installs.
In my time on the road I never tried antennas behind the bunk. Can't imagine a scenario where that's a good mounting location. Always found a way to get a firestik mounted on a mirror or at least side of the cab.
Transmitting antennas don't work ( or tune) that well with vertical sheet metal a couple or three inches away. My suggestion is find or fab a way to mirror mount. There's always a way.
Best of luck and 73
You want to make very certain that your mount (shield side of coax) is very well grounded.
Www.k0bg.com is a great source of info for mobile installs.
In my time on the road I never tried antennas behind the bunk. Can't imagine a scenario where that's a good mounting location. Always found a way to get a firestik mounted on a mirror or at least side of the cab.
Transmitting antennas don't work ( or tune) that well with vertical sheet metal a couple or three inches away. My suggestion is find or fab a way to mirror mount. There's always a way.
Best of luck and 73
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Sorry for taking so long to get back, im still trying a few more things to lower the SWR. I’m going to try and mount in the mirror and also I’m going to try and angle the firestik2 behind the ferring/cowling and get it away a bit. I was wondering, can the power ground in the cab affect SWR? When I turn the air in high, I can hear it through the radio if squelched down enough.
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Sigh, why does those darn fleets have to put antennas in places they KNOW they won't work...?
Not at you @Daffypuck - this situation comes up more than you think.
Any specialty "brand" truck gets similar "where do I put this - thing" and is what you the driver, have to suffer with.
As said earlier, yes, your trailer and the cowl/fairing braces - all the stuff amalgamated in that area are tearing up your SWR.
You did a good job of using metal - the problem is - you have more metal that surrounds the antenna
in the mounting area - interfering with your ability to even put out any sort of signal
Another I see is the "impactor resistor" that tubing
- is not the best because it's pretty close to the load...
but I do understand why you did it - to keep the shrink wrap from splitting open,,,
This antenna has to move out, relocated into open air alongside or nearer to the front nose of the truck if you're going to have much of a chance to "Get out" -SWR will be an issue. It's hard to tame in these setups - many just run a radio to monitor and if they need to key up - the shop puts in a resistor across the mount - - about 150 ohms 2W so a simple CB can be heard - not from far away - but we've had "specific instruction" from the owners of the cab's like this - these kids drive - on how to do this.
There's a two edged sword in this, the driver is limited to what the shops' supply and their constraints of location and even antenna type to use - because of the Branding the owners have - they don't want to spoil, ruin or otherwise drill into the artwork and graphics of their "style" ..
IF you did this on your own - you're doing better than most...
Got any other drivers from the line able to help you solve this? (A basic flexibility problem of they won't let you)
As in what did the company finally let them do? - we can't go very far with what we're seeing here...
Not at you @Daffypuck - this situation comes up more than you think.
Any specialty "brand" truck gets similar "where do I put this - thing" and is what you the driver, have to suffer with.
As said earlier, yes, your trailer and the cowl/fairing braces - all the stuff amalgamated in that area are tearing up your SWR.
You did a good job of using metal - the problem is - you have more metal that surrounds the antenna
in the mounting area - interfering with your ability to even put out any sort of signal
Another I see is the "impactor resistor" that tubing
- is not the best because it's pretty close to the load...
but I do understand why you did it - to keep the shrink wrap from splitting open,,,
There's a two edged sword in this, the driver is limited to what the shops' supply and their constraints of location and even antenna type to use - because of the Branding the owners have - they don't want to spoil, ruin or otherwise drill into the artwork and graphics of their "style" ..
IF you did this on your own - you're doing better than most...
Got any other drivers from the line able to help you solve this? (A basic flexibility problem of they won't let you)
As in what did the company finally let them do? - we can't go very far with what we're seeing here...
I have had success in the the past mounting this type of antenna when it will be next to or obstructed by metal. The loading coil is elevated up from the base on the antenna. I understand that you are looking for solutions with your current antenna. In that location, you may only be able to achieve a safe operating range of SWR with the Firstick 2 that you have. Once you are in a safe operating range and not to beat up the finals in your radio your may be pleased with the TX/RX of your radio, for the application you are using the radio.. You do not need to have a perfect SWR match, or ever below 1.5, for every application. Try to get it below 2.0. You may be pleased with the results.
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Thanks for all yalls advice. I have to work a little each day to get everything squared away, so a day or few may go by before I come back with results/issues. One thing that is confusing me is last week I tested the ground with a multi meter and all was good. I tested again yesterday and now the coax shield is still showing a good ground, but the antenna top part is also showing grounded as well. How is that possible? I have the nylon washer mounted on top to prevent contact with the top part of the mount to the truck.
Is the antenna connected to the radio when you're using an ohm meter?
Thats why I asked about how is this thing grounded?
Looking in the photos, the PL-259/SO-239 on the mount may be causing this now.
The "center 3/8-24" threaded stud - you can use the Nylon on the top, but if the whacking continues - the SWR will skyrocket because of the torque the antenna places on the mount can make it shift...
A better look
If you are ok to continue using the Mirror mount bracket - you can just used a different stud to SO-239 adapter
I guess I would continue to use the mount - just improve the stud to SO-239 adapter to a beefier one like the workman above...
Looking in the photos, the PL-259/SO-239 on the mount may be causing this now.
The "center 3/8-24" threaded stud - you can use the Nylon on the top, but if the whacking continues - the SWR will skyrocket because of the torque the antenna places on the mount can make it shift...
A better look
If you are ok to continue using the Mirror mount bracket - you can just used a different stud to SO-239 adapter
I guess I would continue to use the mount - just improve the stud to SO-239 adapter to a beefier one like the workman above...
Attachments
Maybe you have some water in the coax. That connector and bracket have surface rust so it’s possible water got in through the threads.
If no water has damaged the coax I would wrap that connector with temflex and 3M Super 88 tape.
If no water has damaged the coax I would wrap that connector with temflex and 3M Super 88 tape.