CB Radios

Topic 16569 | Page 1

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Duane C.'s Comment
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Hello fellow truckers, I am having a CB radio crisis. I am looking for a good radio that gets out pretty good. I currently have a cobra 29 which is ok I guess, but a lot of times I get no response from others or I get walked on. What makes for a pretty strong radio? Is it the radio itself or the antenna? I use a Wilson 3000 antenna. Can anyone help me with some suggestions without breaking my wallet? A lil humor there....... Thanks in advance......

Rick S.'s Comment
member avatar

Assuming you've had the antenna (and wiring) checked out and tuned in - then realize that a stock/unmodified radio is only going to get out so far.

Most of the guys that are walking all over you - probably have modified radios or linear amps running behind the radio to boost their output.

Rick

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Duane C.'s Comment
member avatar

Ok. That must be it. The Linear amps because everything else checks out.

Assuming you've had the antenna (and wiring) checked out and tuned in - then realize that a stock/unmodified radio is only going to get out so far.

Most of the guys that are walking all over you - probably have modified radios or linear amps running behind the radio to boost their output.

Rick

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

John L.'s Comment
member avatar

How did you check your setup?

Just because you calibrate the SWR meter on your radio you cannot be certain that your antenna and feed line are working properly.

I use an MFJ-822 or my Bird 43 with a 50W/2-30MHz slug to measure the forward and reflected power (and then break out my slide rule to calculate the SWR). I also use a shunt on my DC input power line to measure input current. Although input power not an accurate way to measure output power, I does allow me to measure relative power output once I get a baseline input into a known good load. I'll usually establish the baseline by connecting the radio to a dummy load so I know what the maximum ideal input power will be.

I also use a program called 4NEC2 (available as a free download) to model the antenna system. A poorly designed (or tuned) antenna will not perform well, no matter how much power you put into it.

I try to use the best quality feed line that I can afford. RG-59U has very high loses at 11 meters. I never use anything less than RG-8X for mobile stations and LMR-400 for fixed stations.

Finally, don't fall into the trap of thinking that you need a modified radio, export radio, or linear amplifier to be heard by other stations. I've literally worked the world with less than 15 watts of power. I've even had a contact with an operator in Japan while only using 5 watts!

When you say that you get no response from others, do you mean that stations that you can hear do not respond? Or are you calling and hoping to get a response from someone, but you've not heard anyone on the air?

It may simply be that there is no one close enough to hear you. Remember that your CB has limited range - its just the nature of the 11 meter band and your antenna system - except during peak sun spot cycles and occasional tropospheric events that allow long distance contacts (DX or skip).

Find a reputable shop or amateur radio operator to check and test your setup before you start throwing money at the problem.

John, KW4CR

OWI:

Operating While Intoxicated

EPU:

Electric Auxiliary Power Units

Electric APUs have started gaining acceptance. These electric APUs use battery packs instead of the diesel engine on traditional APUs as a source of power. The APU's battery pack is charged when the truck is in motion. When the truck is idle, the stored energy in the battery pack is then used to power an air conditioner, heater, and other devices

John L.'s Comment
member avatar

I forgot to mention:

The reason for measuring forward and reflected power and calculating the standing wave ratio or SWR is to determine if the antenna is the correct length for the frequency. Often you will need to adjust (usually by trimming or shortening) your antenna.

Many people think that reflected power or a high SWR means that you will lose the power output from your radio. This is only partially (and coincidentally) correct. Just because your radio is set for 4 watts of output power does not mean that it will always put out 4 watts. It will only output maximum power when the input impedance of your antenna system exactly matches the output impedance of your radio (50 ohms real or [50 + 0j] ohms). The vertical whip antenna that is most commonly used for CB typically has an input impedance of about 34 ohms with a significant capacitive component. That is also one of the reasons for the loading coils on most antennas.

There are so many factors that can effect the performance and the impedance of your antenna system that you really need to provide more details before anyone can suggest a solution.

Once again, your best bet is to find a reputable CB shop or an amateur radio operator to check, test, and adjust your setup.

John, KW4CR

EPU:

Electric Auxiliary Power Units

Electric APUs have started gaining acceptance. These electric APUs use battery packs instead of the diesel engine on traditional APUs as a source of power. The APU's battery pack is charged when the truck is in motion. When the truck is idle, the stored energy in the battery pack is then used to power an air conditioner, heater, and other devices

Kurt G.'s Comment
member avatar
I've literally worked the world with less than 15 watts of power. I've even had a contact with an operator in Japan while only using 5 watts!

But I'll bet it wasn't 27Mhz AM...

Bulwinkle J. Moose's Comment
member avatar

KW4CR is on target

Are you for sure the rig ( radio) is tuned correctly to your current setup? ( i.e antenna system and the way its mounted on the truck) ? Any thoughts on what you have for SWR readings?

When you roll thru a major city start trying to make some contacts were there are more stations on the air. get off channel 19 and find some locals hopefully base stations not mobiles. Contact some different operators and determine their direction and distance relative to your position to determine your rigs performance. Ask them how you sound. How do they sound? If you can talk and hear someone 5 miles away and in different directions from a mobile setup on a truck that's about the best you can expect without a band opening (skip). Not to say you may not get longer distances. Don't be expecting to talk to someone 25 miles away under normal circumstances.

Looks like you have a good radio and antenna setup. Is it mounted to a metal roof? looks like its a ground plane antenna which means 1/2 of of the antenna system is the metal roof it's mounted to. Or is it a wilson designed to be mounted onto a mirror mount? Don't mount a ground plane antenna system to a mirror or bumper. It ain't gonna work right.

Don't fight the mega watt operators running a lot of heat that walk all over you, you will never win. They are knobs and don't have a clue about what it takes to operate a radio correctly. A first class radio operator is courteous doesn't cause a lot of interference were they will mess up someones TV

( the radio and antenna is tuned correctly) and always uses the least amount of power needed to make a contact.

i think one of the best antenna setups for a truck is still the defacto dual mirror mount phased antenna array like the old "twin trucker" which I don't think is made anymore. Other manufactures have something comparable these days from the looks of it.

John L.'s Comment
member avatar

double-quotes-start.png

I've literally worked the world with less than 15 watts of power. I've even had a contact with an operator in Japan while only using 5 watts!

double-quotes-end.png

But I'll bet it wasn't 27Mhz AM...

True.

The Japan contact was 20 meters JT65 (a low power digital mode) at a frequency of 14.076MHz.

I've worked Australia, New Zealand, Hawaii, and Alaska on 10 and 15 meters CW and PSK31 (another low power digital mode) with as little as 15 watts.

Of course one great thing about having an amateur radio license is the ability to use so many different modes and having access to so much more bandwidth. I've worked stations on frequencies from 3-430 MHz.

I've worked all of those locations on phone (voice) using single side band (SSB), but that did require more power (between 50 and 100 watts). But than again I'm on the east coast of Virginia, so right off the bat it takes some doing just to reach the Pacific coast.

One great thing about CB radio is the fact that the band is so narrow. It means that it is easy to work the entire band with an antenna that is resonant anywhere within the band. If you get your SWR low (enough) on any channel, you'll still be low enough on all the rest.

My primary point is this: You can do more with low power and a good antenna system than you can with a poor antenna fed with high power. I have never owned or operated with any kind of amplifier and I rarely operate any of my equipment at full power.

My mobile 2 meter radio is capable of 50 watts maximum output and has three power settings - 10, 25, and 50 watts output. I typically leave it set to low power when I'm running around town and can hit any repeater in the area and work nearly anyone in the area simplex. When needed I increase my power to 25 watts and have never needed to use full power to talk to anyone that I was able to hear. I regularly talk with other operators on the simplex calling frequency who are 15 to 25 miles distance from my location.

Any broadcast engineer or radio amateur will agree that you'll get more bang for your buck if you invest your time and money into your feed line and antenna system rather than in amplifying your power output.

HOS:

Hours Of Service

HOS refers to the logbook hours of service regulations.

DWI:

Driving While Intoxicated

JakeBreak's Comment
member avatar

Since we have the cb gurus here I have a question. I have a stock 29 and I'm using the stock antenna system since I'm not allowed to run my own. My question is my swr is running around 3 and I don't know how to reduce it without buying a reduced that a cb shop was trying to sell me. I didn't have the money or I woulda just bought it but he also was telling me that I could possible reduce it with the antenna. Should I go longer or shorter?

John L.'s Comment
member avatar

my swr is running around 3 and I don't know how to reduce it without buying a reduced that a cb shop was trying to sell me. I didn't have the money or I woulda just bought it but he also was telling me that I could possible reduce it with the antenna. Should I go longer or shorter?

If you have any kind of CB antenna connected to a working radio, you should not be seeing such a high SWR.

First: How are you measuring the SWR? Are you using an external meter or the 29's meter? Have you calibrated the meter? If not, then that is the first thing to do.

Second: If you are still seeing high SWR readings after calibrating the meter then:

1) check your feed line and connectors between the radio and antenna(s). Make sure that the connectors are tight and in good condition. Make sure the cable is not cut, crushed, or otherwise damages (sounds like a pre-trip inspection item, doesn't it?)

2) find someone who can connect a dummy load to your radio with a known good cable. If that checks out, then connect the dummy load to the end of the feed line in the truck. If that checks out then you have a bad antenna (if the SWR reading is still 3) or you'll need to trim the antenna (if the SWR reading was less than 2)

Third: To trim or tune an antenna you'll need to check the SWR at three channels. Check at channel 1, 40, and 20 (19 would be better, but you don't want to key your mike if there are people using channel 19).

The SWR readings (if you check them for every channel and graph them like you did back in high school) will form an upward opening curve - think bowl or saucer - that you want centered at channel 20 (or 19). When channels 1 & 40 have the same SWR reading then you are about as well centered as you can get.

To center the curve: If channel 1 is higher than channel 40 then the antenna is long. If channel 40 is higher than channel 1 then the antenna is short.

The adjustments that you make will be TINY! Don't trim your antenna by more than an 1/8" at a time.

Finally: Although it would be ideal to have a 1.0 SWR reading, be happy with any reading under 1.5. Once you've learned a bit about antenna's, wavelength, and frequency and have built or tuned an antenna or two you can begin to try to achieve lower readings. Until then, you risk trimming to much from your antenna and doing more harm than good.

If you find yourself in the Hampton Roads area, contact me at John @ KW4CR.com and I'll meet you to provide whatever help I can.

John, KW4CR

Pre-trip Inspection:

A pre-trip inspection is a thorough inspection of the truck completed before driving for the first time each day.

Federal and state laws require that drivers inspect their vehicles. Federal and state inspectors also may inspect your vehicles. If they judge a vehicle to be unsafe, they will put it “out of service” until it is repaired.

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