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Discussion Starter · #1 ·
I debated putting this in the newb area, just so I don't get flamed, but what the heck ... here it goes :D

I was just putting in my cb radio and everything was going well until of course I tested for the SWR. I was just reading that doing it in between buildings probably isn't the best idea, nor is testing SWR in your garage a great idea either, however, I was curious what's the "ideal" place to test SWR within the city. Say a wal-mart parking lot? I need to get the SWR down, it's at about 3.5 right now .... o.0

Also, I bought a cheap CB. I know I know .... I want to make sure I'm going to use it before I get a nice one ... and I figure if I break(read:fry) it, at least it was cheap ...

I bought a Cobra 19 Ultra III from walmart to give you an idea of the one I bought.

It's got a S/RF Meter on the top, and I was curious,the greater the the number on the meter the better? I'm assuming so but I wanted to double check, given the lower number for the SWR the better. Thoughts? A quick search via google yielded a ton of answers, however none addressed that one in particular(probably because it's an easy/obvious answer).

Regarding the SWR, if it is "off" and "unacceptable", it is receiving or transmitting that will end up frying the transmitter? I only ask because 99% of the time I'd just be listening ...

Last but not least, does a tennis ball ontop of the antenna decrease, increase performance any?

thanks in advance :)
 

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The parking lot is a very good place...make sure you're not near any vehicles or light poles when you tune-r-up. Oh, and close all your doors as well!

Mike
 

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First off, if you have an SWR meter built into the radio, set the 'CAL' switch ('calibrate'), key the mic, then turn the SWR adjustment knob until the needle hits the calibration mark (typically on the right side of the scale).

Switch it from 'CAL' to 'SWR' (or whatever the manual states is the SWR measurement setting).

Key the mic for a second or two on channel 1, and note the reading. Ideally, you should have the lowest reading possible. Chances are, you'll probably have anywhere from 1.5 to 2.0 on channel 1, which ain't too bad. Change channels to 19, take another reading, then on to channel 40. You should get progressively lower SWR's as you move up the channel range.

Remember, the goal is to get the lowest SWR reading as possible. So, go back to channel 1. If the SWR's read something like 3, then you can adjust your antenna up or down to tweak the reflected signal (lower your SWR's). If your antenna is a fiberglass Firestik, then under the rubber cap at the top of the antenna is a threaded screw. Turn that a few times in or out of the antenna, and measure SWR's again. If you have a whip-type antenna, then a set screw on the base coil will allow you to raise or lower the whip.

Do these tests in the Wal-mart parking lot, if you like. The goal is not to have immediate obstruction around the antenna while testing (immediate being any metal or permanent structures within 100 ft or so). And, check your SWR's with the doors closed.

Finally, do not put anything on your antenna. It will look goofy, and won't help your signal get out... :)
 

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Discussion Starter · #4 ·
First off, if you have an SWR meter built into the radio, set the 'CAL' switch ('calibrate'), key the mic, then turn the SWR adjustment knob until the needle hits the calibration mark (typically on the right side of the scale).

Switch it from 'CAL' to 'SWR' (or whatever the manual states is the SWR measurement setting).

Key the mic for a second or two on channel 1, and note the reading. Ideally, you should have the lowest reading possible. Chances are, you'll probably have anywhere from 1.5 to 2.0 on channel 1, which ain't too bad. Change channels to 19, take another reading, then on to channel 40. You should get progressively lower SWR's as you move up the channel range.

Remember, the goal is to get the lowest SWR reading as possible. So, go back to channel 1. If the SWR's read something like 3, then you can adjust your antenna up or down to tweak the reflected signal (lower your SWR's). If your antenna is a fiberglass Firestik, then under the rubber cap at the top of the antenna is a threaded screw. Turn that a few times in or out of the antenna, and measure SWR's again. If you have a whip-type antenna, then a set screw on the base coil will allow you to raise or lower the whip.

Do these tests in the Wal-mart parking lot, if you like. The goal is not to have immediate obstruction around the antenna while testing (immediate being any metal or permanent structures within 100 ft or so). And, check your SWR's with the doors closed.

Finally, do not put anything on your antenna. It will look goofy, and won't help your signal get out... :)
Awesome advice! I'm going to give it a shot once I get the chance. Thanks for the input!
 

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SWR only comes into play when you transmit. So if you never key-up, you wont hurt a thing.
Adding balls (or anything) to the antenna should make the number go up if anything, bad idea...
High SWR for the most part will not come from a stock radio, so I would guess you have to tune the antenna better. Also it could be caused by a poor ground on the antenna (scrape a bit more paint off the Bandi).
What antenna are you using?
IMO, the antenna is more important then the radio. Most radios will work great with a good antenna on them.
My set-up is running at 2.5 across all channels (running at 1000 watts). I could have gotten it less on lower channels, but then my upper channels go up, so I picked the mid point.
Tuning the antenna is a bit of a pain. You got to cal it, then test it, then open door, get out and adjust the antenna. I think it took me 10 adjustments to get mine centered. That was a lot of the in and out, up and downs...
 

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2.5 across all channels (running at 1000 watts).
2.5 at 1kw is bad very very bad. (I'm not going in to legality since it would be the pot calling the kettle black)

You are going to smoke the finals on that non-type accepted liner.

They higher the power output the more critical the match. The more resistance you have will cause the finals to overload and fry.

Do yourself a favor and get that antenna match down or you will have to replace finals often.
 

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2.5 at 1kw is bad very very bad. (I'm not going in to legality since it would be the pot calling the kettle black)

You are going to smoke the finals on that non-type accepted liner.

They higher the power output the more critical the match. The more resistance you have will cause the finals to overload and fry.

Do yourself a favor and get that antenna match down or you will have to replace finals often.
You know, I was just thinking the same thing.

In my experience, with any SWR above ~2, it's cooking time. I've cooked amps into non-existence in a single key-up with conditions like that. If it's actually putting out 1kW (which I'm going to also somewhat dispute -- I think that's your linear's rating, not the true output) you're heading for disaster.
 

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SWR stands for "standing wave ratio". Your transmission comes as waves of current that eminate from your radio and antenna, relative to the grounding plane. This sets up a voltage differential between the antenna and grounding plane, which in turn sets up an electric field. The field is reversing back and forth (alternating at a frequency defined by the "channel" you're transmitting on).

Just like a pipe in an old steam organ, there's a frequency in your antenna that's the sweet spot. At this frequency, your SWR will be lowest. What it means to have a low SWR is that the energy being spent in creating the electric field is dissipating into the environment rather than reverberating back down into the cables and your radio. If it bounces back into the electronics, it creates impedance and heat. That's why it kills your radio. With a higher wattage transmitter, there's a lot more energy to get rid of, but even with a CB and 4 Watts, there's plenty of energy to overheat parts.

Just like with a pipe organ, length matters. Unlike when you run coaxial cable to your various TV sets, you can't just use any old amount of wire for a CB. You have to use multiples (or fractions) of a wavelength. The more precise, the better.

Tuning the antenna is the final length adjustment. Fractions of an inch matter. If you have a screw on the end to tune the length and a plastic cap that goes over it, then you should do an adjustment and replace the cap before you check. If you get it tuned with the cap off, and then you replace the cap, you'll end up with a different reading.

CB transmission follows the inverse square law just like any other emitted energy. The amount of energy at a given distance from a point source is inversely proportional to the square of the distance. If you have a wide open space, that's great, but at 4 Watts, you're not putting out so much power that your antenna will "see" the reverberations off of buildings 20 yards away. If you're in your driveway against your house, with an aluminum camper trailer in the spot next door and powerlines over head, then that would be noticable. I tuned my system with a really accurate SWR meter on my street, in a spot nicely separated from buildings and cars by about 20 yards, and I checked it again when I was in the open desert and it was the same.

If you graph the SWR per channel, you'll find it minimizes at the "sweet spot", or frequency best suited for that particular adjustment of the system. If you adjust it to be best at around channel 19/20 and get an SWR near 1, then you'll have a reasonably low SWR across all 40 channels. I've got 1.something at 20 and it's below 2 on channel 1 and channel 40. If you know that your group always chats on channel 4 and you want to optimize for that channel, then tune your antenna on channel 4. The SWR on channel 1 will be almost as good but it will be much farther out of adjustment on channel 40.

My understanding is that when the SWR is above 3 it starts to put the electronics under a bit more stress than it needs to be.
 

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Discussion Starter · #10 ·
You know, I was just thinking the same thing.

In my experience, with any SWR above ~2, it's cooking time. I've cooked amps into non-existence in a single key-up with conditions like that. If it's actually putting out 1kW (which I'm going to also somewhat dispute -- I think that's your linear's rating, not the true output) you're heading for disaster.
Eeek! Thanks so much for the heads up ....

Now you have me scared! I had to test it out quite a bit, tweaking here and there .... with the swr above 3 o.0

Doh! Good thing I started out cheap.

Keep the suggestions coming. Hopefully after work today I'll take a peek and see if I can't get it tweaked.

"Thanks again! :bigthumb:
 

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Discussion Starter · #11 ·
SWR stands for "standing wave ratio". Your transmission comes as waves of current that eminate from your radio and antenna, relative to the grounding plane. This sets up a voltage differential between the antenna and grounding plane, which in turn sets up an electric field. The field is reversing back and forth (alternating at a frequency defined by the "channel" you're transmitting on).

Just like a pipe in an old steam organ, there's a frequency in your antenna that's the sweet spot. At this frequency, your SWR will be lowest. What it means to have a low SWR is that the energy being spent in creating the electric field is dissipating into the environment rather than reverberating back down into the cables and your radio. If it bounces back into the electronics, it creates impedance and heat. That's why it kills your radio. With a higher wattage transmitter, there's a lot more energy to get rid of, but even with a CB and 4 Watts, there's plenty of energy to overheat parts.

Just like with a pipe organ, length matters. Unlike when you run coaxial cable to your various TV sets, you can't just use any old amount of wire for a CB. You have to use multiples (or fractions) of a wavelength. The more precise, the better.

Tuning the antenna is the final length adjustment. Fractions of an inch matter. If you have a screw on the end to tune the length and a plastic cap that goes over it, then you should do an adjustment and replace the cap before you check. If you get it tuned with the cap off, and then you replace the cap, you'll end up with a different reading.

CB transmission follows the inverse square law just like any other emitted energy. The amount of energy at a given distance from a point source is inversely proportional to the square of the distance. If you have a wide open space, that's great, but at 4 Watts, you're not putting out so much power that your antenna will "see" the reverberations off of buildings 20 yards away. If you're in your driveway against your house, with an aluminum camper trailer in the spot next door and powerlines over head, then that would be noticable. I tuned my system with a really accurate SWR meter on my street, in a spot nicely separated from buildings and cars by about 20 yards, and I checked it again when I was in the open desert and it was the same.

If you graph the SWR per channel, you'll find it minimizes at the "sweet spot", or frequency best suited for that particular adjustment of the system. If you adjust it to be best at around channel 19/20 and get an SWR near 1, then you'll have a reasonably low SWR across all 40 channels. I've got 1.something at 20 and it's below 2 on channel 1 and channel 40. If you know that your group always chats on channel 4 and you want to optimize for that channel, then tune your antenna on channel 4. The SWR on channel 1 will be almost as good but it will be much farther out of adjustment on channel 40.

My understanding is that when the SWR is above 3 it starts to put the electronics under a bit more stress than it needs to be.
Very informative. Thanks bellydoc :)
 

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First off, if you have an SWR meter built into the radio, set the 'CAL' switch ('calibrate'), key the mic, then turn the SWR adjustment knob until the needle hits the calibration mark (typically on the right side of the scale).

Switch it from 'CAL' to 'SWR' (or whatever the manual states is the SWR measurement setting).

Key the mic for a second or two on channel 1, and note the reading. Ideally, you should have the lowest reading possible. Chances are, you'll probably have anywhere from 1.5 to 2.0 on channel 1, which ain't too bad. Change channels to 19, take another reading, then on to channel 40. You should get progressively lower SWR's as you move up the channel range.

Remember, the goal is to get the lowest SWR reading as possible. So, go back to channel 1. If the SWR's read something like 3, then you can adjust your antenna up or down to tweak the reflected signal (lower your SWR's). If your antenna is a fiberglass Firestik, then under the rubber cap at the top of the antenna is a threaded screw. Turn that a few times in or out of the antenna, and measure SWR's again. If you have a whip-type antenna, then a set screw on the base coil will allow you to raise or lower the whip.

Do these tests in the Wal-mart parking lot, if you like. The goal is not to have immediate obstruction around the antenna while testing (immediate being any metal or permanent structures within 100 ft or so). And, check your SWR's with the doors closed.

Finally, do not put anything on your antenna. It will look goofy, and won't help your signal get out... :)
All good advice...also, if you could, buy a stand-alone SWR meter to do all of your testing, don't rely solely on built-in meters, they have there limitations.

Mike
 

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SWR stands for "standing wave ratio". Your transmission comes as waves of current that eminate from your radio and antenna, relative to the grounding plane. This sets up a voltage differential between the antenna and grounding plane, which in turn sets up an electric field. The field is reversing back and forth (alternating at a frequency defined by the "channel" you're transmitting on).

Just like a pipe in an old steam organ, there's a frequency in your antenna that's the sweet spot. At this frequency, your SWR will be lowest. What it means to have a low SWR is that the energy being spent in creating the electric field is dissipating into the environment rather than reverberating back down into the cables and your radio. If it bounces back into the electronics, it creates impedance and heat. That's why it kills your radio. With a higher wattage transmitter, there's a lot more energy to get rid of, but even with a CB and 4 Watts, there's plenty of energy to overheat parts.

Just like with a pipe organ, length matters. Unlike when you run coaxial cable to your various TV sets, you can't just use any old amount of wire for a CB. You have to use multiples (or fractions) of a wavelength. The more precise, the better.

Tuning the antenna is the final length adjustment. Fractions of an inch matter. If you have a screw on the end to tune the length and a plastic cap that goes over it, then you should do an adjustment and replace the cap before you check. If you get it tuned with the cap off, and then you replace the cap, you'll end up with a different reading.

CB transmission follows the inverse square law just like any other emitted energy. The amount of energy at a given distance from a point source is inversely proportional to the square of the distance. If you have a wide open space, that's great, but at 4 Watts, you're not putting out so much power that your antenna will "see" the reverberations off of buildings 20 yards away. If you're in your driveway against your house, with an aluminum camper trailer in the spot next door and powerlines over head, then that would be noticable. I tuned my system with a really accurate SWR meter on my street, in a spot nicely separated from buildings and cars by about 20 yards, and I checked it again when I was in the open desert and it was the same.

If you graph the SWR per channel, you'll find it minimizes at the "sweet spot", or frequency best suited for that particular adjustment of the system. If you adjust it to be best at around channel 19/20 and get an SWR near 1, then you'll have a reasonably low SWR across all 40 channels. I've got 1.something at 20 and it's below 2 on channel 1 and channel 40. If you know that your group always chats on channel 4 and you want to optimize for that channel, then tune your antenna on channel 4. The SWR on channel 1 will be almost as good but it will be much farther out of adjustment on channel 40.

My understanding is that when the SWR is above 3 it starts to put the electronics under a bit more stress than it needs to be.
Excellent in-depth explanation on how to tune. Kudos BellyDoc! :bigthumb:


Eeek! Thanks so much for the heads up ....

Now you have me scared! I had to test it out quite a bit, tweaking here and there .... with the swr above 3 o.0

Doh! Good thing I started out cheap.

Keep the suggestions coming. Hopefully after work today I'll take a peek and see if I can't get it tweaked.

"Thanks again! :bigthumb:
Definitely take a look!

I run 1/10th that power and I use a good ole' 102" SS whip. SWR sits pretty much flat around 1 across the band. Even back with I wasn't running much power and used a 4' K40 fiberglass, the SWR was about 1.2 maximum. Definitely an essential to a situation where you use a linear...

One more thing -- with a setup like that, buy a decent SWR/combo meter that's good up to 2K watts. That will be a worthwhile investment with a nice rig like that.


All good advice...also, if you could, buy a stand-alone SWR meter to do all of your testing, don't rely solely on built-in meters, they have there limitations.

Mike
I agree! Like I mentioned above there... Definitely a good investment for such a nice setup. I think it's good to have one if you're into CB's on any level beyond the occasional trail chat (such as if you regularly communicate on the highways).

:cheers:
 

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Discussion Starter · #18 ·
hehe ...

Well somebody told me by putting a ball on the top of an antenna would so something to the signal ... I fell for it, hook line and sinker :) Like the alt + f4 routine :)

Anyways, I've since cut another hole in it, and slid it further down the antenna so it doesn't go smacking into my FJ. :)
 

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One of the best tools you can get yourself is one of these.



It is a MFJ-259B SWR analyzer, sure it's a little coin but you will be dead on. This was the best investment I have ever made in my radio tool quiver.
 

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One of the best tools you can get yourself is one of these.



It is a MFJ-259B SWR analyzer, sure it's a little coin but you will be dead on. This was the best investment I have ever made in my radio tool quiver.
Well, that's an insanely nice piece of equipment, BUT... I can't say that's necessary for the average user!

Radioshack has a $49.99 one that's more than ample for the average user.

I use one of these Dosy meters, they're some of the best for the money.

This PDC-1
is actually not a bad meter either at $15.

I own all three, they're all decent meters. I don't care much for the PDC-1 anymore, but that's mostly because I've been spoiled by the better ones.
 
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