Motor homes are uniquely different simply because for the most part the body and the roof are made of fiberglass the frame system includes vertical rails that run from the front to the rear of the motorhome.

Basically there are two options when it comes to a working antenna system type. You can go with a fire stik no ground antenna system such as the LG-M2 mounted to the upper side of the body of the motor home.You can also go with a conventional grounded type of antenna system by installing a side body mount such as the MK-M2 and drilling the mounting holes in the upper side of the motor home to where the side body mount is attached to the vertical framework. Either antenna type will be a short fiberglass antenna such as the Firestik FS series antennas.

We highly recommend the use of a spring such as the SS3H due to the possibility of striking a tree branch or some other obstacle. The no ground type antenna system does not require setting the SWR. The conventional type or grounded type of antenna system does require tuning the SWR. Another primary difference between the non-grounded and grounded antenna types is the non-grounded type of antenna system can be mounted to any service type and the conventional type of antenna system must be attached to the vertical frame rail for proper grounding.

The thought of running wires from the antenna mount to metal framework is not adequate and will not work so removal of the inside wall panels is required in order to locate the vertical frame rails. We recommend marking and drilling the holes from the inside of the motor home. Mark and measure twice and only then drill. You don’t want to make a mistake concerning this step. If you use a grounded antenna type use 18 feet of RG58 or mini 8 such as Firestik’s K8 coax. We highly suggest 95% shielding and a multi strand center conductor.

There are two distinct types of squeals. An audio feedback and an RF squeal or hum.

An audio feedback (squeal) is caused when the speaker is located to close to the mike and the talkback function is set to loud. The more sensitive the mike the worse the audio feedback. The less distance from the mike to the speaker the worse the squeal.

Audio feedback defined: A phenomenon that occurs when the sound waves produced by speakers interact with an input transducer such as a microphone or phonographic cartridge. If the feedback exceeds a certain amount, any of various undesired effects may occur, such as howling, whistling, motor-boating, or excessive cone movement. Also, the sound heard as a consequence of this. Also known as acoustic feedback, acoustic regeneration, acoustic howl, audio frequency feedback, audio feedback, or howl.

An RF squeal or growl has a much harsher sound as compared to an audio feedback. It is normally caused from the radios own signal re-entering the radio and effecting the mike amp circuit or the transmitter circuit. This phenomenon normally occurs when there is a ground problem at the antenna, radio chassis, or inadequate voltage supply.

The first step is to figure out which type of squeal you have in order to fix The problem.

Turn the mike gain all the way to the right. It should squeal badly when keyed.

Now cup your hand over the mike and key the mike. Does it squeal?

If it does you probably have an RF squeal, if not you probably have an audio squeal.

Do you have the talkback function? This is a function that allows the user to monitor there audio transmission.

If so try turning it down or off. Turning it off should eliminate the squeal if the problem is an audio feedback or squeal. Turn it off and verify the condition by getting a radio check from another radio operator.

To fix an audio squeal: Turn the external speaker around facing away from you. If the speaker has a noise filter switch turn it on. Did this resolve the squeal?

If you still have the squeal try moving the speaker farther away from you. If your talkback has a variable volume control reducing the volume and turning the speaker facing away from you may be the trick. If neither resolves the problem try replacing the mike with either an Astatic 636L or a Turner RK56 noise canceling mike.

The RF squeal can be a bit more complicated.

The RF squeal can be caused from any of the following:

1) Inadequate ground on the antenna or case of the radio.

2) The radios ground wire location or to long of a ground wire. Never connect the ground wire to the battery.

3) High antenna SWR normally caused from lack of ground.

4) Inadequate shielding in the mike cord.


Unfortunately there is no scientific testing that will tell us exactly which option is causing the problem.

The fix involves process of elimination.

To fix an RF squeal:

1) Attach short braided straps from the case of the radio to the dash. The screw must go through the dash material into metal. The strap must be a basket weave type material and must be short. No longer than 18 inches. Two straps are better than one. Coax shielding works well for this application.

2) Check your SWR. Set the SWR and verify the SWR is lower than a 2.0. Move the coax while you are checking the SWR. Does the SWR fluctuate? If the SWR fluctuates read up on troubleshooting antenna system problems in our blog.

3) Wrap the mike cord around your hand about 4 wraps half way down the cord and key the mike. Does it squeal now? If this stopped the squeal purchase a .01 pf 50v ceramic disc capacitor. Cut the legs short, take the mike plug apart and solder the capacitor from the shield pin (bare wire) to the modulation pin (the wire the shield wire wraps around). This will be pin 1 to pin 2 if you have a 4 pin mike plug and a Cobra, Uniden, President, Galaxy, or Midland radio.

4) If the DC ground wire feeding the radio is attached to the battery remove it, cut it short and connect it to a ground close to the radio. A screw can go through plastic dash providing it screws into metal behind the plastic.

 

 

 

Basic troubleshooting procedures require a process of elimination in order to get to the culprit.

Remember easy & cheap 1st, hardest and expensive last.

With the antenna system the possibilities are the coax cable, a stud mount, antenna or antenna’s, the antenna ground, and in some cases the mounting location of the antenna.

Check them out in this order – ground, antenna, stud mount, coax and antenna placement.

Try moving the coax back and fourth, then grab the antenna mounting bracket.

Take caution here; stay away from the antenna and don’t touch it or the top of the stud mount.  If the SWR fluctuates you have a ground problem.

The SWR should be below a 2.5 and not fluctuate more than .1 up or down when moving the coax or grabbing the bracket. In other words 1.9-2.1 of fluctuation is ok. Remember, paint and primer are your enemy.

Pinched or melted coax jacket is not good- replace it. Use an 18 foot long RG58 coax cable for a single antenna system and two 18 foot legs of RG59 for a dual antenna system. Read about coax cable.

Spin the antenna in a circular direction and check the SWR. Look for serious fluctuation or a spike. If it exhibits either replace it and same for the stud mount is screws into. The SWR will fluctuate when the antenna is spinning.
For example: The SWR is a 3.0, you spin the antenna and the SWR fluctuates up to a 4.3. This is normal especially if their is anything close to the antenna such as an exhaust stack, pickup cab, headache rack and so on.
If you experience an off scale spike or fluctuation close to off scale, replace the antenna and the stud mount it screws in to.

Ground is a consideration and tends to be the problem much of the time. For example, the antenna mount must be bolted to clean metal with no paint or primer. The structure the mount is bolted to, must also connect to the chassis and make an electrical connection.

A good example of this is a tool box mount in a pickup bed. Most people mount the tool box on top of the bed rail only after sandwiching rubber between the bed rails and tool box. Now you have paint, primer and rubber preventing the electrical connection. I advise drilling two holes, one at each end of the tool box located so that a self tapping screw can be inserted to connect the tool box to the bed rail top. Clean the contact surface (the area the self tapper’s head will contact) to bare metal. Insert one on each side of the tool box. This will ground the tool box to the truck body. (Don’t use nuts & bolts)

Most people make the same mistake at the antenna mount itself. Four bolts holding the mount in place will not ground the bracket if the tool box is painted. Either clean the contact surface (the area the bolt’s head will contact) or drill a fifth small hole and insert a self tapper in place. The self tapper screw will bite into the tool box and ground the bracket.

The point is that the entire path must ground not just the antenna mount for example, and don’t even consider ground wires. At 27 MHz, ground runs on top of the wire not through it. It tapers off quickly normally within a foot or two. If using a ground wire, use a basket weave type material with much surface area and make it as short as possible. We use base coax, strip the shield out, flatten it, and apply heat shrink to clean it up.

Trunk lip mounts require special attention for proper ground. This type of mount normally uses two allen screws to tight the mount to the trunk (From the bottom side). The contact area on the trunk must be scrapped to bare metal removing ALL paint and primer. A short ground strap should also be installed at each supporting trunk arm close to the hinge.
Use self tapping screws and attach the ground strap from the vehicle body to the supporting arm.
The goal is to bypass the hinge. Many hinges have teflon or some other type of non conducting material built into its construction.

The final possibilities are antenna placement, height, and the way the antenna is reacting on the vehicle.

If using a center load type of antenna verify the bottom of the load is equal to or above the top of the vehicle. The majority of the signal radiates from this part of the antenna. The SWR will normally drop and your overall performance will improve if you follow this rule.

If the antenna is mounted to a Big Rigs mirror arm, try leaning the antenna forward 5-7 degrees. Signal from the antenna can strike some other object such as an exhaust stack, and reflect or (bounce back) striking the antenna and raising the SWR and degrading overall performance.

The antenna could be reacting badly to your auto body size & shape.
If all other recommendations have been followed and the SWR problem has not been resolved try relocating the antenna.
The antenna can quickly be relocated in order to rule out placement or to simply change the way it is reacting.
Antennas can react badly under some circumstances causing one to believe a problem exists when their is no fault with any part of the system.
Don’t be concerned with the look, you are not looking for a permanent mounting location, just another good grounded location away from anything that could interfere with the antenna system.
Once the antenna has been relocated check the SWR.
If the problem has not been resolved at this point try changing the antenna to a different type of antenna.

Vehicle resonance – ALL vehicles; cars, trucks, vans, motorcycles, etc., resonate at a particular frequency. This is called vehicle resonance.
The vehicle resonance reacts with your antenna system 100% of the time. Sometimes this reaction causes antenna systems to have poor performance and or high SWR.
Under this circumstance you won’t be able to pinpoint a problem.
Each piece of the system can be changed with no improvement.
The ground is good, all pieces of the system have been verified to be good, but the SWR is still high.

What do we do now?
Change the antenna to a different type. If the antenna is a base loaded antenna try a center load or a top loaded fiberglass antenna and recheck the SWR. If the antenna is a fiberglass or top loaded antenna try a center loaded or base loaded antenna.

If none of the above resolves your problem and you can’t find a local professional that can resolve your issue, bring it to us. We will resolve your issue.

Please call for an appointment before showing up as we may be booked for the day.
We can service your equipment – read more

 

The coax cable is a vital part of the antenna system. There are many brands and grades of coax.


The coaxial cable has basically four parts.


1) The vinyl outer jacket.


2) Just underneath the jacket is a copper braided material. This material is usually copper, and it is anywhere from 70 to 95% coverage. The higher the percent, the more surface area coverage. 95 to 100% is optimal shielding.


3) Just underneath the copper braided material is a dielectric material.

The dielectric is the insulator and insulates the center conductor from the outer shield.

There are two types of dielectric (the material that separates the center conductor from the outer shielding), polyvinyl and polyfoam.

Poly foam has more flexibility than polyvinyl. Therefore, many customers prefer the poly foam over the polyvinyl.

It’s easier to bend and installation is a little easier.

Polyvinyl is superior in its ability to withstand higher temperatures and hard compressions.


4) The very center of the coax is the center conductor. There are two types of center conductors. The solid wire and a multi-strand wire. High quality coax will have many strands making up the center conductor. The material will usually be copper.

 

The coaxial cable can be terminated with terminals or a PL-259 connector. PL-259’s of high quality are coated in either nickel or silver.

Amphenol and Astatic are two of the best brands on the market.


Coax cable for transmitters is 50 and 75 ohm impedances. A single antenna system must use 50 Ohm (RG58) coax and will normally be 18 feet long.


Dual antenna systems must use 75 Ohm (RG59) coax cable and will normally be 18 feet to each antenna.


The coax types can not be interchanged. RG58 must be used for a single and RG59 must be used in dual antenna system configurations only.


The length of the coax to be used is controversial only because most people have not educated themselves concerning this matter. At 27 MHz 18 feet of coax is the correct length and will provide for minimal loss with an optimal SWR match.


When using other lengths a phase shift will occur causing a loss in Db gain even if the SWR matches. This means that the carrier is either lost in the form of heat or the coax cable itself acts as part of the antenna lowering the Db gain. Stay with the 18 foot rule. If an 18 foot length is to short to reach the antenna use a 27 or 36 foot length. The system is in phase with 18, 27, & 36 foot lengths.



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Posted: 01/06/2012 in About Coax Cable
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About Citizens Band

Posted: 12/21/2011 in About CB
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Citizens Band (CB Radio Service) is a private two-way voice communication service for use in personal and business activities of the general public. Its communicating range is normally from one to ten miles. License documents are neither needed nor issued and there are no age or citizenship requirements.

You may operate CB radios within the territorial limits of the fifty United States, the District of Columbia, and the Caribbean and Pacific Insular areas (“U.S.”). You may also operate your CB radio on or over any other area of the world, except within the territorial limits of areas where radio-communications are regulated by another agency of the U.S. or within the territorial limits of any foreign government. You may also be permitted to use your CB radio in Canada subject to the rules of Industry Canada. Travelers to the U.S. may operate CB radios within the U.S. as long as the unit is FCC certificated.

The highest point of your CB radios antenna must not be more than 20 feet above the highest point of the building or tree on which it is mounted, or 60 feet above the ground.

Rules & Regulations
The FCC rules and regulations for CB radios are codified in Title 47 of the Code of Federal Regulations (CFR). They are initially published in the Federal Register. The FCC does not maintain a database of its rules nor does it print or stock copies of the rules and regulations. That task is performed by the Government Printing Office (GPO). After October 1 of each year, the GPO compiles all the changes, additions, and deletions to the FCC rules and publishes an updated CFR.

The rules for CB radios are provided in text version and in portable document format (PDF) and can be viewed using the Adobe Acrobat Reader.

You can check the Federal Register to review rule changes since October 1, 2004.

There are basically three types of mobile CB antennas.

1) The base load.
A base load antenna has coil or load at the bottom of the antenna.  Base load antennas  usually have a three to four foot long whip made out of stainless steel. Base loaded antennas have a wave length of 1/4.  A 1/4 wave antenna has an angle of radiation of 45 degrees. Signal radiates off the antenna at all angles and directions but the strongest point is at a 45° angle.

2) The top loaded antenna.
A top loaded antenna is usually fiberglass with copper wire wrapping a round a fiberglass rod loosely until it approaches the top of the antenna.  This is normally the top 6 inches to 1 foot where it is wrapped tight. This tightly wrapped area is the load.  That is why the antenna is called a top loaded antenna. Top loaded antennas have a very low angle of radiation.  Fire stick antennas for example are normally 5/8 wave antennas.  5/8 wave antennas have an angle of radiation of seven degrees from the horizon.  A Tiger SOTT antenna is a 1 1/2 wave length antenna.  Its angle of radiation is lower than seven degrees. As a rule of thumb the higher the wavelength the lower the angle of radiation.

3) The center load antenna.

A center load antenna is called a center load is because the load is at the center of the antenna.  The center load antenna will have a shaft below the coil and a whip above the coil. Center load antennas are also 1/4 wave length antennas.  Therefore, they have an angle of radiation of 45° as well.

There is not an antenna made that is best for all applications. Our recommendation changes depending on the type of auto, preferred mounting location, and required bandwidth.

Generally these are typical recommendations.

Vehicle Type: Car

Mounting location: Roof top  or trunk lip type mount.

Antenna recomended: base load such as the Wilson 5000

Mounting location: Side body

Antenna recomended: Lite weight fiberglass  such as the FL series Firestik. A spring or antenna quick disconnect can be added as a precaution

Mounting location: Bumper (older metal bumpers)

 

Antenna recomended: 102 inch steel whip, or a 4 to 5 foot fiberglass whip. The SOTT Tiger 1 1/2 wave is an excellent choice for this application.

 

Overview

SWR stands for standing wave ratio. Basically it is a very simple concept. When you transmit a certain amount of the wattage is reflected back into the transceiver. Damage to the radio will occur If the amount of wattage that is being reflected back into the transceiver is to high.

So the SWR is a measurement of how much signal is going out the antenna, versus how much signal is reflected back into the transceiver. An SWR level of a 3.0 will damage the transmitter. A 2.0 SWR is about an 11% loss and the transmitter of the radio will run hotter as compared to a lower SWR. Amplifiers do not like high SWR’s. A radio with a built-in amplifier should not normally be used if the SWR is above a 2.0. While they might get away with it the duty cycle on transmit is reduced. The transmitter will warm up much quicker with a higher SWR as compared to a lower SWR.

Let’s talk about setting the SWR’s

All CB antennas are tunable. Antennas that have an easy, often mechanical, tuning device are referred to as a “tunable antenna”. Accordingly, many people think the other antennas are not tunable and so they make no attempt to have the antenna tuned. This is a critical mistake.

Wire-wound antennas (without mechanical tuners), that test electrically long (higher SWR on ch 40), can be tuned by removing wire from the top. Remove the antenna cap, remove one wrap of wire and cut it off. Put the cap back on and recheck the SWR again on ch 40 & ch 1. As long as the SWR is higher on channel 40 continue to cut. Do not cut more than one wrap at a time. If SWR testing indicates the antenna is electrically short (higher SWR on ch 1), test for a ground problem. Touch the antenna bracket while keyed and watch for SWR fluctuation. Do not touch or even get close to the antenna. Move the coax around bending it, again watching for SWR fluctuation. If the SWR fluctuates a ground problem exists and must be corrected before proceeding. If there was no fluctuation bend the end of the wire straight up the fiberglass shaft and lap it over the very top of the fiberglass shaft. Check the SWR on ch 40 & ch 1. The goal is to reverse the situation so that ch 40 has a higher SWR than ch 1. If ch 40 is higher cut 1/8 inch of wire, put the cap back on and check the SWR on ch 40 & ch 1. Continue with this process until ch 40 & ch 1 are relatively the same.

Wire-wound antennas (with mechanical tuners), that test electrically long (higher SWR on ch 40), can be tuned by adjusting the mechanical device at the top of the antenna. Remove the antenna cap, and adjust the rod down or if threaded turn the device clockwise. Put the cap back on and recheck the SWR again on ch 40 & ch 1. As long as the SWR is higher on channel 40 continue to adjust the rod down or if threaded turn the device clockwise. If SWR testing indicates the antenna is electrically short (higher SWR on ch 1), test for a ground problem. Touch the antenna bracket while keyed and watch for SWR fluctuation. Do not touch or even get close to the antenna. Move the coax around bending it, again watching for SWR fluctuation. If the SWR fluctuates a ground problem exists and must be corrected before proceeding. If there was no fluctuation adjust the rod up or if threaded turn the device counter-clockwise. Check the SWR on ch 40 & ch 1. Continue with this process until ch 40 & ch 1 are relatively the same.

Solid fiberglass antennas (straight or helical wire impregnated in fiberglass resins) that are electrically too long (higher SWR on ch 40) can be cut shorter with a hacksaw or grinder. Cut only 1/4 of on inch at the most at one time. If the SWR test on one of these antennas indicates that it is electrically short (higher SWR on ch 1), the addition of a spring or quick disconnect (or both) is the only way to correct for the short condition.

Base loaded & Center loaded antennas with steel whips have a set screw (or two) just below the area that the whip is inserted into the loading coil. By loosening up the set screw(s) you are able to slide the whip up or down as required. If the SWR is higher on ch 40 slide the whip down, If the SWR is higher on ch 1 raise the whip.

Antenna Tuning when using an amplifier

Setting the antenna SWR with an amplifier can get involved. The antenna SWR is calibrated at the back of the amplifier with the amplifier in line and turned off. Once the antenna is properly tuned the meter is removed and re-installed at the radio with the amplifier in line. The antenna SWR level is then measured with the amp off and then with the amplifier switched on. The SWR level must be at an acceptable level at the radio under all conditions. The conditions are with the amp off on channel 40 and 1 and with the amp turned on, on all power levels of the amplifier on channel 1 and 40. Most shops don’t check the SWR match at the radio with the amplifier turned on. This is a critical mistake. With these steps added the SWR calibration can turn into a multi hour event at times.

Posted: 11/29/2011 in Antenna Tuning
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