The Garage Page 2

This page is a continuation of the Garage

Click here to go back to the Garage Index

Low Modulation

You can break squelch on other rider's CBs, but your voice is quiet.

 The  GL1800 CB (Clarion version) has always had a reputation for poor  transmit range.  In some respects, the reputation is well deserved.  But it is also due to unreasonable expecations.  Usually, this problem is not the transmitter itself that is the cause of the problem.  For some  reason, Honda and Clarion have done a poor job of matching the modulation levels to the common microphones in use today. In almost all cases, modulation alignment is set too low.

I will keep the following technical discussion basic for those who are  not familiar with the details of how transmitters work. After all, you  only care about fixing the problem, right?

To transmit audio over the air, there are two basic components needed, a  carrier, and modulation.  The carrier is what most people are familiar  with. The carrier is the sine wave that others tune to when they want to  receive your signal, The carrier is the signal that other CB's detect  when they break squelch.  It is also what you are adjusting when you  check your SWR.  The maximum legal CB carrier power is 4 watts.

There is no audio in a carrier however. If you just transmit a carrier,  all you get is silence. This is where modulation comes in. Modulation is  simply the audio signal you want to transmit. In the case of a CB, it  is our voices. The audio signal from your microphone is added to the  carrier.

For your voice to be heard the loudest and clearest possible, with the  least amount of background noise, the peak modulation needs to be as  close to 100% as possible without going over 100%. In reality however,  very few of the Honda Clarion CB's ever transmit anywhere near 100% modulation. In fact, it doesn't even hit 50%  on most bikes.  It doesn't matter how far the CB can transmit if the audio level is too low for anyone to hear it.  Just to add to the problem,  some headset microphones  have a lower output than others. When you combine this with the distance we have to keep out mouths from the mike due to the windsock, it just makes a bad problem worse.

To solve this problem, I now offer a service to correct the low  modulation problem. I modified Clarion's alignment procedures in order  to increase the modulation to a level that will enable the CB to reach  its full potential.  (At present, this is for the Honda Clarion CB  only.)  Before anybody asks, this alignment is unfortunately not  something that owners can easily do themselves. Not only does it require  a modulation meter and preferably an oscilloscope, but since the two  circuit boards can't be separated without unplugging them, you can't  access the alignments and power up the CB at the same time without a  specially made interface test cable.

To get your CB  re-aligned and enable it to reach its full capability,  see my Online Store. I have tried to keep the price as reasonable as  possible.

Two things should be kept in mind about this alignment.

  1.     Since all microphones are different, and each person speaks at a     different volume, the reference modulation level still has to be kept below 100%     to take worst possible scenarios into account.  This is a standard procedure for all CB's.
  2. If  you have the CB feedback squeal problem, the problem needs to be  repaired before getting the CB re-aligned. If you don't, this fix could  make the problem worse.  See the troubleshooting tips below for more  info on correcting the feedback problem. 

Back to Main Index

Feedback squeal during transmit.

 This  is a fairly common problem with the Goldwing CB. The problem itself is  actually quite simple. But finding and correcting it is sometimes not so  easy.

Transmit squeal is nearly always caused by a bad ground that is reducing  the effectiveness of cable shielding somewhere in the system. When  grounds go bad, shielding becomes less effective.  Shielding is used to  keep unwanted interference from becoming mixed with the audio signals  traveling in the cables. It can work the other way around too.  In the  case of a CB, you have a shielded coax cable which, when working  properly, prevents the transmitted carrier from being radiated outward.  That transmitter signal needs to be kept inside the cable until it  reaches the antenna, and if the cable's shielding is less than perfect,  it can't do that effectively.  Even though a CB carrier is only 4 watts,  the radiated EMI can be quite strong, and can be induced into the  bike's wiring. When this happens, you get feedback, which is heard as  squeal.  It is important that the transmitter carrier not be allowed to  radiate anywhere except at the antenna.

There are a few common ground points to check when you have the squeal  problem. The most obvious one is the battery cables. For some reason,  motorcycles are known for battery cables coming loose. The next place to  check is the bolts that mount the CB antenna. And check to see if the  reinforcing bracket for the antenna is cracked in half.

Other easy to check grounds are at the antenna cable connector, and the 3  pin CB power cable under the seat. It is hidden in a black rubber boot  to the rear of the relay box.  Check this connector to make sure they  are not oxidized or corroded. Spray it with a little contact cleaner or  WD40 Do not spray contact cleaner in the antenna connector. You can  screw up the impedance of the connection.

There are three more connectors that have grounds that can cause squeal,  but they all require a lot of disassembly. The large 13 pin CB  connector up near the radio, the radio connectors themselves, and the  main radio ground under the gas tank are possible culprits.

Before doing a major tear down, there is one simple fix you can try.  Sometimes, even with proper shielding and grounding, an RF signal can  still be induced into the bikes audio system. This is because rarely is  consumer grade shielding perfect. If you look under your seat, you will  notice that your antenna cable either crosses over, or runs right  alongside your passenger headset cable. This is a potential problem.  Those cables should be separated as far away from each other as possible  to minimize the chance of the transmitted carrier being induced into  the headset cable.

I recently saw an installation where the owner decided to run his CB  antenna cable along the bottom of the trunk directly to the CB instead  of routing it under the seat as the Honda instructions suggest.  My  first reaction to seeing this is that it was just a case of somebody  being lazy. But the more I thought about it, I realized this was a great  idea because it gets that antenna cable as far away from the audio  cables as possible. I wonder if this installer even realizes what a  genius he was!

Back to Main Index 

The LCD display shows "CB Error".

 The  CB Error message is generated by the radio's microprocessor.  It is  displayed if there is any loss of communications with the CB while the  CB function is turned on. Data is constantly being shared between the CB  and the radio whenever both of them are on. That communication can't be  interrupted.

Now that you know what causes the error message, you are probably  already imagining some of the possible sources of problems. The 3 pin CB  power connector under the seat is a major suspect, as is the 14 pin  main CB connector under the top shelter. The two radio connectors  themselves are also a possible cause. Anything that can cause an  interruption in data flow between the radio and CB can cause this  problem. The antenna or antenna cable CANNOT cause a CB Error message.

One seemingly unlikely cause for the CB error message is a bad battery  or loose battery cables. If this is the cause, you will know it, because  it will only happen if you start the bike while the CB is turned on,  with the error message popping up a few seconds later. When you start  your bike, the high current draw from the starter causes your battery  voltage to momentarily drop. This is normal, and is expected. But if the  battery is weak or the cables are loose, the voltage can drop too low  and play havoc with the bike's electronics.  When  the battery voltage drops too low, electronic devices can momentarily  power down. If the CB powers down, even for a second, the result can be a  CB Error on the display.

I have not been able to duplicate the battery problem on the bench, but  some owners have reported that it caused their problem, so I am throwing  it out there as a possibility. Checking the battery and cables should  always be the first step whenever experiencing an electrical problem  anyway.

One unfortunate possible for the CB Error is a possible internal   failure in the CB, and most CB failures are due to circuit board  corrosion caused by water damage. This is one of the drawbacks of the CB  being located in the bottom of the trunk. Any spills in the trunk will  head directly for the CB. If this happens to you, the CB is usually  unrepairable.  Severe corrosion is obvious, with white residue on the  circuit boards and visual signs of rust. Discoloring of the circuit  board is also a sign. Most boards are green. Visual signs of large black  splotches on the circuit board are a possible sign of corrosion  going  on underneath the top layer.  But sometimes corrosion is hidden, and not  easily detected by the untrained eye.  

Back to Main Index

A Few Thoughts about SWR

 I have read the opinions of many owners who say that you do not have to check the SWR on the Honda CB, because the antenna and radio are matched to each other.  It is certainly true that by using a CB designed specifically for a single model of vehicle, with a specific antenna, the manufacturer is able to tune everything to work properly together.  And in the past 20 years or so, discrete components have become ultra precise, meaning that there is very little performance deviation from unit to unit. But like most things, there is more to it than that.

In most cases, you can indeed install the Honda CB with the Honda antenna,  and the SWR will be acceptable. But you can usually still make it better.  The lower your SWR is, the farther you can transmit, and the cleaner your broadcast will be.

There is an even bigger reason for checking the SWR after installation however. Sometimes a new CB, or antenna, or coax is defective, or something could have gone wrong during installation. Checking the SWR verifies that your installation and equipment are good. In my opinion, no shop that is interested in doing quality work would ever install a CB without checking SWR, and you shouldn't either. it is just the proper way of doing things.  Meters are cheap to buy, and you can sometimes borrow one.  Keep in mind however that Honda uses Motorola connectors instead of standard PL259 RF connectors, so you will also need adapter cables to test the SWR.

When adjusting the SWR, in many cases you have to cut 1/4" or so off the  antenna to get the lowest match. This is done intentionally by the mfr.  It is easy to cut off some length if needed. You can't add length  however. so they err on the side of caution. There are many very well written procedures on how to adjust  SWR on the Internet. I may add something here in the future if I get the  time and find that it is necessary. 

Back to Main Index