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Very High SWR
- Thread starter Speedy78
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rfradioconsult
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Start by giving a discription of what your install looks like and any steps you have done so far, also what basic test equipment you have at your disposal.
radioman2001
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How much forward vs how much reflected, a wrong frequency antenna will vary the reflected by how much away from the frequency you are transmitting on and frequency multiples, a shorted or open coax or antenna will be around 40-50% reflected. Water in the coax can be no reflected, or reflected that varies as you move the coax around or day to day.
I have the radio into a dosy tr-100 then into a monkey made anntenna. The anntenna was originally on the toolbox in the bed of my truck but I was told this wasn't a good mounting point. I built a rack that's attached to the bed that puts the anntenna base a few inches above the roof directly over the gap between the cab and bed. I've also tried adjusting the length of it but there isn't much to play with. I'm getting all my swr readings from the meter which also has wattage and modulation messurments. Oh and the radio is a cobra 19 ultra III.
Speedy
Speedy
rfradioconsult
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You just described exactly what your problem is. CB (or any lowband) antennas needs a good groundplane to work against. A groundplane is different from a ground wire to the body. Put the antenna back on the tool box or bite the bullet and drill a hole and mount the antenna in the center of the roof.
Speedy, check the SWR on 1, 19 and 40 making sure to reset the SWR meter at each channel. CB Radio Magazine has a video you can watch just to be absolutely certain that you are using the meter correctly. Not that you aren't, but in case there is any question.
Also, make absolute certain that the coax center conductor goes to the mast of the antenna and the shield of the coax to ground. It is critical that the shield goes to the mount (ground), which is connected to the rack that you built, the bed, the cab etc. and that the mast is isolated from ground. You want the antenna (hot) to see the entire truck as a ground plane, so it all needs to be bonded together.
Also, make absolute certain that the coax center conductor goes to the mast of the antenna and the shield of the coax to ground. It is critical that the shield goes to the mount (ground), which is connected to the rack that you built, the bed, the cab etc. and that the mast is isolated from ground. You want the antenna (hot) to see the entire truck as a ground plane, so it all needs to be bonded together.
I have the mount separated from the bracket by plastic washers and then a plastic sleeve in the hole. The rack is grounded to the bed where it is bolted in and then there is a ground strap from the bed to the cab. The swr changes slightly on the different channels but still remains in the 3s. I'd perfer not to drill a hole in the roof and I got similar readings on the tool box that's why I relocated it.
KC4RAF
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Speedy, you need an external
SWR meter. That will give you readings you can go by. Then as Ohio said, trim or lengthen. And hope the antenna hasn't already been shortened .
SWR meter. That will give you readings you can go by. Then as Ohio said, trim or lengthen. And hope the antenna hasn't already been shortened .
I would start by checking the connectors if the reflected power is that high. Make sure that the connectors are not shorted. THEN worry about tuning the antenna. Get your hands on a seperate SWR meter, the ones in the radio are not too accurate. Any CB shops in your area that you could have check it for you?
I would get rid of that junk antenna and then get a cheap mag mount antenna and put it in the middle of the roof.
Buy a better SWR meter and check it again.
If the SWR is high - then you have the antenna too close to some object that is resonating on a nearby frequency or your ground plane is too small or your antenna is too short.
I would suggest that you add 3 inches at a time to the top of the antenna until the SWR comes down.
If it stays the same - then the antenna is junk!
Center the SWR for the frequency you desire to use the most.
It does no good to tune the antenna to channel 40 if you spend all your time on channel 19
Buy a better SWR meter and check it again.
If the SWR is high - then you have the antenna too close to some object that is resonating on a nearby frequency or your ground plane is too small or your antenna is too short.
I would suggest that you add 3 inches at a time to the top of the antenna until the SWR comes down.
If it stays the same - then the antenna is junk!
Center the SWR for the frequency you desire to use the most.
It does no good to tune the antenna to channel 40 if you spend all your time on channel 19
Adding/removing cable length is a placebo when it comes to antenna installs and SWR. The more cable you have, the more loss you'll have (depending on the mis-match, could be quite large). You'll also see a decrease in SWR, since your rig has an output impedance of 50 Ohms, and the cable has a 50 Ohm impedance (Hopefully)... The longer the cable run, the more place to lose power (Coax is relatively lossy, unless it's LMR400 or something), so your SWR will approach 1:1 (As an aside, you can accomplish the same thing, in less space, with a dummy load).
Your antenna is either not tuned correctly, or there is another issue here. What kind of cable are you running to the antenna? And, do you have access to an antenna analyzer? If you have any ham buddies, they will probably have an MFJ-269, which will show you where your current system is resonant.
I still say the stinger is too long and needs trimmed.
wyomingmedic
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You need to do some trouble shooting with known equipment.
Remove your coax and check it for continuity and shorts, with a volt meter. Completely remove the coax and the problem. Maybe even get another piece of coax and try it. If that does not work, move on.
Make sure the antenna is assembled correctly. Some folks can put together the mounts wrong, or can have a screw missing.
Sadly, I don't think the above items are your problems. If you had a dead short or an open somewhere, the SWR would be much higher. Monkeymade aren't exactly the cream of the crop in antennas. They are fairly poorly designed and overpriced. They are built to look fancy for the CB crowd, but not really perform.
You need to know what the SWR is on channels 1, 20, and 40. If the SWR is better on channel 1 than 40, it means the antenna is too long. If it is better on 40, then the antenna is too short. What would be better is to find an actual antenna analyzer and see what is really going on. You may find a good SWR outside of the CB band. You may not.
If you cannot find a good SWR, and it is not the coax or antenna assembly, it is probably the mounting location. Welding a tab onto a headache rack is NOT a groundplane. There is a huge difference between a groundplane and a DC ground. You may not be able to get a better SWR because of you mounting location. You can buy a cheap magmount that will hold you antenna WHILE PARKED. Set the magmount onto your roof and see what the SWR is. If it is better, then your mounting location is the problem.
Whatever you do, don't go cutting the whip until you have a good picture of what is going on. Also, no need to add length to the whip. Get a SOUND understanding of what you are doing before you permanently alter your investment. Measure twice and cut once, so to speak.
WM
Remove your coax and check it for continuity and shorts, with a volt meter. Completely remove the coax and the problem. Maybe even get another piece of coax and try it. If that does not work, move on.
Make sure the antenna is assembled correctly. Some folks can put together the mounts wrong, or can have a screw missing.
Sadly, I don't think the above items are your problems. If you had a dead short or an open somewhere, the SWR would be much higher. Monkeymade aren't exactly the cream of the crop in antennas. They are fairly poorly designed and overpriced. They are built to look fancy for the CB crowd, but not really perform.
You need to know what the SWR is on channels 1, 20, and 40. If the SWR is better on channel 1 than 40, it means the antenna is too long. If it is better on 40, then the antenna is too short. What would be better is to find an actual antenna analyzer and see what is really going on. You may find a good SWR outside of the CB band. You may not.
If you cannot find a good SWR, and it is not the coax or antenna assembly, it is probably the mounting location. Welding a tab onto a headache rack is NOT a groundplane. There is a huge difference between a groundplane and a DC ground. You may not be able to get a better SWR because of you mounting location. You can buy a cheap magmount that will hold you antenna WHILE PARKED. Set the magmount onto your roof and see what the SWR is. If it is better, then your mounting location is the problem.
Whatever you do, don't go cutting the whip until you have a good picture of what is going on. Also, no need to add length to the whip. Get a SOUND understanding of what you are doing before you permanently alter your investment. Measure twice and cut once, so to speak.
WM
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