Another CB radio SWR issue

Jorge Bolivar said:
Ive noticed that when I put the firestik "cap" back on it throws my SWR all over the place. Could this be an indicator that I need a longer antenna such as a 3' instead of this 2'

Not sure. I have a 3’ one and my SWR is around 1.5 and i just have a CB. My GMRS radio is a handheld. Hope @Jerry Bransford is back and can educate us on that part, He is a communication expert.
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Kinda-sorta back, I am recovering from cataract surgery. Yes the vinyl tip cover has a capacitive effect on the antenna which simply means it slightly detunes the antenna by changing its resonant frequency. It's normal.

You get around that issue by slightly detuning the antenna in the direction where when replacing the vinyl cover it moves it back where you want it so the SWR is low or at least lower. It's a trial and error procedure. Detune it with the tuning screw off to the side of the lowest SWR and see if replacing the cover makes the SWR better or worse. If it makes it worse, tune the antenna to the 'other side' of the lowest possible SWR and see if reinstalling the cap moves the SWR lower as it should. Doing this a couple times should give you a good low sub-2 SWR. Yes I hate the effect that vinyl tip cover causes too lol.
 
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Jerry Bransford said:
Kinda-sorta back, I am recovering from cataract surgery. Yes the vinyl tip cover has a capacitive effect on the antenna which simply means it slightly detunes the antenna by changing its resonant frequency. It's normal.

You get around that issue by slightly detuning the antenna in the direction where when replacing the vinyl cover it moves it back where you want it so the SWR is low or at least lower. It's a trial and error procedure. Detune it with the tuning screw off to the side of the lowest SWR and see if replacing the cover makes the SWR better or worse. If it makes it worse, tune the antenna to the 'other side' of the lowest possible SWR and see if reinstalling the cap moves the SWR lower as it should. Doing this a couple times should give you a good low sub-2 SWR. Yes I hate the effect that vinyl tip cover causes too lol.
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Thanks for you input Jerry.
Wish you a prompt recovery!
 
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Jerry Bransford said:
Kinda-sorta back, I am recovering from cataract surgery. Yes the vinyl tip cover has a capacitive effect on the antenna which simply means it slightly detunes the antenna by changing its resonant frequency. It's normal.

You get around that issue by slightly detuning the antenna in the direction where when replacing the vinyl cover it moves it back where you want it so the SWR is low or at least lower. It's a trial and error procedure. Detune it with the tuning screw off to the side of the lowest SWR and see if replacing the cover makes the SWR better or worse. If it makes it worse, tune the antenna to the 'other side' of the lowest possible SWR and see if reinstalling the cap moves the SWR lower as it should. Doing this a couple times should give you a good low sub-2 SWR. Yes I hate the effect that vinyl tip cover causes too lol.
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Thanks for the help as always Jerry! Hope all is well in recovery👍
 
So I tried my buddies 3ft antenna and it fixed my problem. Although Im curious how much more a tuned 4' over a tuned 3' would benefit me. Ive always heard the ham guys saying power isnt everything and how they go far with 1W and a very fine tuned antenna setup
 
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DylanM345 said:
Could my SWR be high due to it being so close to my GMRS antenna?
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You have multiple things going on here. The antennas in close proximity are absolutely causing high SWR. A 2' antenna is very hard to tune to begin with. It will be very narrow banded as well, meaning you can tune it for say, channel 20 but it will be bad on 1 and 40. I like 5' antennas. 4' work. 3' and smaller is difficult. You seeing the change in SWR when you removed one of the antennas is a clue to the problem you are having. Antennas are not invisible to eachother, even if they are on different bands. The system can be designed to work together, but that takes some work. I also noticed your 10' coax length which also pays into tuning your short antenna. There are a lot of coax misconceptions out there and one of these days I'll do a post on it that will clear it all up.

The instructions for the Firestik II antenna tell you you have to install the cap when tuning. Just read the instructions. Jerry correctly answered why.
 
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Dino - KX6D said:
You have multiple things going on here. The antennas in close proximity are absolutely causing high SWR. A 2' antenna is very hard to tune to begin with. It will be very narrow banded as well, meaning you can tune it for say, channel 20 but it will be bad on 1 and 40. I like 5' antennas. 4' work. 3' and smaller is difficult. You seeing the change in SWR when you removed one of the antennas is a clue to the problem you are having. Antennas are not invisible to eachother, even if they are on different bands. The system can be designed to work together, but that takes some work. I also noticed your 10' coax length which also pays into tuning your short antenna. There are a lot of coax misconceptions out there and one of these days I'll do a post on it that will clear it all up.

The instructions for the Firestik II antenna tell you you have to install the cap when tuning. Just read the instructions. Jerry correctly answered why.
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Not to argue at all - everybody's situation is different - but I've had the exact opposite situation. 5' firestik has been a PITA, and the best I've been able to get out of it is about 1.8 across the band. A ProComm 2' whip tuned right up - is essentially 1.0 on channel 1, about 1.2 on channel 19, 1.5 or so on 30, and goes up to 1.9 on 40. The old timer at the ham shop where I purchased the 2' ProComm said - truly or not - that it was the only 2 footer that actually works. I'm actually thinking of trying a 4 foot ProComm and dumping the FireStik. Much easier to tune at least, and maybe I'll get better SWR out of a 4 foot ProComm as well - they're cheap enough.
 
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Dino - KX6D said:
You have multiple things going on here. The antennas in close proximity are absolutely causing high SWR. A 2' antenna is very hard to tune to begin with. It will be very narrow banded as well, meaning you can tune it for say, channel 20 but it will be bad on 1 and 40. I like 5' antennas. 4' work. 3' and smaller is difficult. You seeing the change in SWR when you removed one of the antennas is a clue to the problem you are having. Antennas are not invisible to eachother, even if they are on different bands. The system can be designed to work together, but that takes some work. I also noticed your 10' coax length which also pays into tuning your short antenna. There are a lot of coax misconceptions out there and one of these days I'll do a post on it that will clear it all up.

The instructions for the Firestik II antenna tell you you have to install the cap when tuning. Just read the instructions. Jerry correctly answered why.
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Ill be getting a 3ft at moab, and another friend of mine has a 4' that ill try
 
Dino - KX6D said:
Very true. What works in one situation, may not in another. I haven't used ProComm antennas and was talking about the 2' and 3' Firestiks vs the 4' and 5' Firestiks. I'll have to give the ProComm a try.
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Yea - the ProComm is certainly cheap enough - I'll have to see how a 4 footer (they don't make a 5 apparently) does. A friend who knows a hell of a lot more about RF says that tuning SWR is 25% science, and 75% black magic! OTOH, I haven't been able to raise anybody on the 2 footer - but then again its hard to raise anybody around here period. I do know that I can get out pretty well with the 5 foot FireStik - I'd expect far less with the 2 footer.
 
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Zorba said:
Yea - the ProComm is certainly cheap enough - I'll have to see how a 4 footer (they don't make a 5 apparently) does. A friend who knows a hell of a lot more about RF says that tuning SWR is 25% science, and 75% black magic! OTOH, I haven't been able to raise anybody on the 2 footer - but then again its hard to raise anybody around here period. I do know that I can get out pretty well with the 5 foot FireStik - I'd expect far less with the 2 footer.
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They make a 5' and 8'. SWR is not an indication of performance. It just means the feedpoint matches the feedline. As an example, there are antennas on satellites with a 5:1 SWR by design and working just fine. I have no doubt a 5' antenna will work better than a shorter one.
 
Dino - KX6D said:
They make a 5' and 8'. SWR is not an indication of performance. It just means the feedpoint matches the feedline. As an example, there are antennas on satellites with a 5:1 SWR by design and working just fine. I have no doubt a 5' antenna will work better than a shorter one.
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I always thought SWR affects performance though, for example if you have high SWR, doesnt that prevent the unit from transmitting far since the power being reflected could be used to transmit? Or am I mistaken
 
DylanM345 said:
I always thought SWR affects performance though, for example if you have high SWR, doesnt that prevent the unit from transmitting far since the power being reflected could be used to transmit? Or am I mistaken
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It doesn't. SWR stands for Standing Wave Ratio. Without spending way too much time on what standing waves are and how they are caused, I'll just say that its a ratio between the feedpoint of the antenna and the feedline (coax) feeding it.

The radio is designed with a 50 ohm feedpoint. The coax is also 50 ohms. The antenna can be all over the place based on design and frequency. You want the feedpoints and feedline to "match". This is already done at the radio end so now we need it to match at the antenna end. If it doesn't, the reflected power going back to radio will blow up the final transistor. This is why we match antennas.

I can guarantee you that the performance of the antenna was just fine all the way up to the point the radio let the smoke out.
 
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Dino - KX6D said:
It doesn't. SWR stands for Standing Wave Ratio. Without spending way too much time on what standing waves are and how they are caused, I'll just say that its a ratio between the feedpoint of the antenna and the feedline (coax) feeding it.

The radio is designed with a 50 ohm feedpoint. The coax is also 50 ohms. The antenna can be all over the place based on design and frequency. You want the feedpoints and feedline to "match". This is already done at the radio end so now we need it to match at the antenna end. If it doesn't, the reflected power going back to radio will blow up the final transistor. This is why we match antennas.

I can guarantee you that the performance of the antenna was just fine all the way up to the point the radio let the smoke out.
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Thanks for the clarification. Last (hypothetical)question, If my ground is good, SWR is good, along with my radio being properly functional, then what affects my performance? How does antenna height help the cause(if any) and thank you for taking the time to explain these your being a great help👍
 
SWR is the ratio between watts pushed vs. watts reflected. If your transmitter puts out 4 watts, and 2 of them are reflected back, then you're only putting out 2 watts net. Damn straight SWR is a measure of performance - just not the only measure.
 
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DylanM345 said:
Thanks for the clarification. Last (hypothetical)question, If my ground is good, SWR is good, along with my radio being properly functional, then what affects my performance? How does antenna height help the cause(if any) and thank you for taking the time to explain these your being a great help👍
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The best location for a CB antenna is smack dab in the middle of the roof. Its high and not surrounded by any metal like roll bars and window frames, but its not practical for a Jeep so you do the best you can.
Zorba said:
SWR is the ratio between watts pushed vs. watts reflected. If your transmitter puts out 4 watts, and 2 of them are reflected back, then you're only putting out 2 watts net. Damn straight SWR is a measure of performance - just not the only measure.
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This is 100% incorrect.
 
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Dino - KX6D said:
The best location for a CB antenna is smack dab in the middle of the roof. Its high and not surrounded by any metal like roll bars and window frames, but its not practical for a Jeep so you do the best you can.

This is 100% incorrect.
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So does a higher (taller) antenna work better since the tip is away from something like the hardtop for example? Am still a little confused about big antennas with low power going far
 
Another oddity I observed while playing with my GMRS antenna. I stuck it right in the middle of the hood. As far as SWR goes, it wasn't the best location, somewhat surprisingly. But it *would* be the best location for radio propagation. To reinforce what @Dino - KX6D is saying, SWR is important, but its not the only consideration.
 
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DylanM345 said:
So does a higher (taller) antenna work better since the tip is away from something like the hardtop for example? Am still a little confused about big antennas with low power going far
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Partially. Antennas like to be a sub-multiple of the wave length. CB is a fairly long wavelength, so larger antennas just work better. The famed 108" 1/4 wave whip is the gold standard of practical CB antennae. Dino can probably explain it better than I can...
 
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DylanM345 said:
So does a higher (taller) antenna work better since the tip is away from something like the hardtop for example? Am still a little confused about big antennas with low power going far
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A top loaded antenna like a Firestik moves the current up the antenna. If that part of the antenna is clear of obstacles than more of the signal will get out. So a taller antenna in this case is better. Back in the day when you had a Jeep with a 9' antenna on it they would get out great. I recommend a longer antenna every time over a shorter one. They usually tune in better as well.
 
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