By Jason Reilly.....

 

Making the most of your CB I like to occasionally get back to where it all started for me.  I often visit the small sea side town where I grew up to go fishing and meet old friends.  My interest in radio is no different.  Hands up those of you who had their first taste of radio by building a crystal set.  Do I see lots of hands?  Keep your hand up if you still have a crystal set.  I know my hand is still up, how about yours?  Or what about CB?  How many of us spoke their first words on a radio with a CB?  I'm not too proud to admit that this is the case for me.  I still have a chat to friends via this medium.

 

As I write, I'm listening to the 27 MHz CB, and I'm hearing two things which I've not heard for some time.  The first is some decent 'skip'.  The second thing I hear is new or inexperienced CB'ers who have tried this 'skip chasing' and become hooked, and who instantly want to know how to give their signals a boost so that they can talk to further flung, more exotic places, or to just be 'king of the pile'.  With the next sunspot cycle slowly on the way up, it would seem an opportune time to present a few ideas on how to maximise the efficiency of your CB setup.  While most of this is directed at the 27 MHz CB'ers, you can adapt many of the principles for UHF CB, too.

 

Lets start off by looking at your setup and maximising the efficiency of what you already have.

 

First, the CB.  If you have a crummy old AM only CB, then your chances of working some really far-off countries will be limited.  Lets start out with a good quality CB, shall we?  My favourites are the Cobra GTL148 (and it's modern day cousin the Grant XL), the old Grant and the Washington base station.  I've also heard good things about the Uniden AX144 and it's copies and the PC122/Pro640e radios. 

 

For UHF, Sawtron (Kyodo) and Philips and the new breed of Electrophone rigs are darn good.   But no matter what radio you end up with, it can be improved upon.  When your radio leaves the factory, it is tuned quite well, but remember that the factory might be producing many thousands of radios a week and they won't have the time on the production line to tune the radio to the best it could be.  If you take your radio to a radio dealer who offers a repair service, they should be able to obtain better performance out of the radio, mainly on the receive side of things. 

 

I've the test equipment to be able to do this myself, and have found that maybe an extra 10% performance gain can be found in many radios on the receiver, making it more sensitive to weak signals.  Not bad for 10 minutes work.  Yes, the transmitter side of things can be improved, and in some cases this gain can look impressive (for example a 12 Watt PEP radio could have the capability to do 20 Watts PEP) but lets look at this a little deeper.  Firstly, the radio was 'type approved' to do 12 Watts PEP on SSB and about 4 Watts AM mode.  If you increase the power output to beyond these limits, the radio loses it's type approval and becomes illegal.

 

Secondly, if you do increase the output power, lets say to 18 watts PEP on SSB, you may only actually be getting an extra 3 watts on the frequency that you are transmitting and the other 3 watts that you can see on your watt-meter are probably harmonics and other crud-signals that your meter will be measuring, too.  Even if all the signal does go onto your transmitted frequency, it equates to less than 2dB improvement in your transmitted power, which will be hardly noticed at the received end.  A single S-point is 6dB, so you have increased your signal in this example by less than a third of an S-point.  In scientific terms, this is because of the 'inverse-square' rule, or in layman's terms, the law of diminishing return.

 

Thirdly, when you do increase the output power, you place an extra strain on your amplifier stage in the form of extra heat generated to make the extra power.  It may take months or it may take minutes for your amplifier stage to cease to work due to this excess heat, needing costly repairs.  Not only this, but in asking your amplifier stage to do so much work, it may introduce distortion to your transmitted signal, making you harder to understand and radiate lots of TVI (Television Interference) causing spurious signals.  So when you look at the risks and weigh them up with the small benefit, there really isn't much point in doing this modification to your rig at all.  But don't worry, there are other, more worthwhile ways of giving your transmitted signal a boost, which I'll cover soon.

 

Ensuring your radio isn't over-modulating is important, too.  The radio service centre that you take your radio to will be able to check this out and make any adjustment necessary.  Don't be fooled, a back-yarder job will not suffice.  As an example, I had one radio which was bought to me after a back-yarder got a bit excited with the screwdriver under the covers of one CB.  It was producing some of the most ugly 25 watts of SSB power (lots of harmonics and other yuk) and badly over-modulating on AM mode.  After setting the radio to factory specifications, the owner asked what I did to make the radio sound so good!  Modulation over about 95% is wasted.  It wastes your transmitter power, distorts your signal, and causes harmonics.  Three good reasons to leave your modulation control where it is!  UHF CB'ers take note of this point, too.  If you touch your deviation control, you risk not being heard due to over-deviation (extremely gross distortion and interference to other channels) or under-deviation (too soft to be heard).  Armed with this knowledge you can tell the idiot who boasts that their modulation has been wound up to 200% exactly what you think of that.  If he's telling the truth, chances are you won't even be able to understand him on the radio.

 

 

Lets get something correct, right here and now.  A clean, clear understandable transmitted signal will be far more preferable to a dirty, distorted signal, even if it is twice as strong at the received end.  That's why you should take particular care that your signal sounds good.  For communicating with distant stations under adverse or noisy conditions, a well modulated signal with punch is the go.  How do you get this modulation with punch?  A speech processor is the answer.  The human voice is a widely variable thing.  One thing that is common to most voices however, is the wide dynamic range.  During normal conversation, the average level of your voice is nowhere near the peak level.  If you use this voice to talk into your microphone, it will lack 'punch'.  A speech processor will increase the average level of your voice (reduce the dynamic range), and will ensure that the transmitter is being driven to it's maximum all the time without being over-driven.  A well adjusted speech processor can have the effect of increasing your signals understandability by 6 dB!  Note I didn't say power.  A poorly adjusted speech processor can be just as bad, or even worse as a power microphone driven flat-out, so take the time to adjust it carefully.  It may pay you to have two settings of your speech processor noted, one for local communicating where a nice 'studio' quality signal is preferable, and one for DX'ing where communications punch is called for.  The best speech processors are the RF (upconverting-downconverting) type, with those that have just clipping and compression next, followed lastly by those that just clip and amplify your microphone signal.

 

The way a good speech processor works is to firstly restrict the audio frequencies of your voice.  It has been found that you can restrict voice communications to between 300 Hertz and 3500 Hertz without any loss in intelligibility.  By restricting your voice frequencies to this band, you ensure that all the power of the transmitter will be used in transmitting the part of your voice that matters and not wasting its power on voice frequencies that don't contribute to intelligibility.  Almost all radios have internal filters that do this anyway, but doing this at the speech processor will help do its job more effectively.  The next stage is to clip the peaks of your voice which will help effectively raise the average level of your voice.  In clipping your voice, harmonics are generated, which are filtered out.  This is where an upconverting/downconverting processor comes into its own.  By upconverting your voice to a higher frequency, then performing the clipping operation, any harmonics generated will be of a very high frequency, and can be filtered out completely, and then downconverted back to normal voice frequencies.  Without this up/down conversion, clipping produces harmonics that can still be in the normal voice frequency range which can't be filtered out.  This adds some distortion to the process.  The final stage is to have a automatically variable gain amplifier work on your voice signal.  It will amplify soft components of your voice, and will reduce the peaky components, again raising the average level of your voice.  This is then fed to your rig, which will ensure that a signal with the highest possible average level will be modulated onto your carrier without overdriving.

 

This variable-gain amplifier implies that you will need a quiet location for the station to be operated, otherwise any soft background noises such as passing traffic, pets, the children etc. will be amplified and do nothing to help you put out a clear voice.  A room with suitable acoustic properties with carpet and curtains should be chosen, otherwise echo from the room floor or walls can again cause a few unpleasant effects.  Another thing to be wary of is turning the speech processor up too high.  This will have the effect of the receiving station hearing every little breath you take between words, and it will sound like you are gasping for air, prompting queries as to your health!  But carefully adjusted, they are a marvellous device.

 

Power microphones seem to be the hot item around here lately.  I definitely don't think that they are the panacea that others do.  Sure, they may make you sound louder, but they also amplify any noise in the room around you to the point that your voice just doesn't stand out.  Even the echo of your voice from the walls of the room can become annoying with a power microphone turned up too far.  Lets not forget that turning a power microphone up too far can cause the same over-driven effects as discussed above.  I see a power microphone as being useful in only a few situations.  If you are the type who has a naturally soft voice or likes to talk a few feet away from the microphone, then a power microphone, very carefully adjusted will serve you well.  If you are looking to get a little extra communications punch out of a power microphone, well, yes it can be done, but ONLY if adjusted properly.  Only a little extra gain is needed in most cases.  Don't fall into the trap of thinking that a little extra gain has helped a bit, a lot of gain will help a lot.  It wont.  Think of your rigs standard microphone as a glass of water, a power microphone with a bit of extra gain as being a large mug of water and a power microphone with the gain flat out as a bucket.  You can quickly drink the glass of water no problem.  Likewise you can drink the mug of water quickly too with a bit of extra effort, but try that with the bucket and you'll choke!  The same happens with your CB.  If it's communications punch you are after, save your money and buy a speech processor.

 

Another trick is to find a microphone that is suited to your voice.  The signal you stuff into your CB/speech processor is only as good as the microphone you are talking into.  Imagine if your local radio station newsreader used a CB-type microphone.  Yuk, wouldn't the voice quality go out the window!  While you aren't looking for a Hi-Fi quality voice, you do want a quality communications voice, so a microphone that will provide you with this is needed for best results.  A chap I know has a real deep, almost muffled voice.  For his voice, I'd suggest a microphone with an electret condenser microphone insert which has a better high frequency response and tends to produce a 'crisp' voice.  Another chap I know has used a studio-type microphone with quite surprising results.  Other microphones will have different responses which may or may not be suited to your voice.  The ideal microphone would be one that can tailor it's response to any voice, a graphic equalizer for your microphone if you like.  I don't know of any of this sort of microphone commonly available at a reasonable price.

 

For a system that uses FM (such as UHF CB) a speech processor/power microphone would sound a little out of place and certainly upset the nice clear and crisp sound of FM.  However, obtaining the right microphone that sounds good for you can achieve a small improvement.  Ex CB Action writer Rod "furious" Fewster commented this effect as being similar to turning a voice that sounds like Donald Duck into one that sounds like Richard Burton.  That says it all!

 

Why have I concentrated so much on getting the voice side of your transmitted signal right?  It's simple.  On AM, two-thirds of the 4 Watts allowed will be the carrier signal.  That means the sidebands (the bits that actually carry your voice in AM) will be only one third of the total output power.  At the receiving end, the radio will only use one sideband to pluck your voice from the air, which means of that 4 Watts originally transmitted, only one sixth of this is actually used to carry the voice component, and that's assuming a 100% modulated carrier all the time.  Reduce this to the average level of a human voice and you have very little power actually representing your voice.  Maximising this will be where the greatest gains are to be had.  On SSB, the full power of the radio is used to represent the voice, so any improvement will have a directly proportional improvement at the received end.

 

So, now you have a good radio, tuned spot-on and a good quality, clean but strong voice to put into the air.  Lets look at improvements beyond your radios antenna connector.  For a base station, RG213 coax cable is a must for the serious operator.  Match this with high-quality connectors and you are well on the way to having a great setup.  UHF CB'ers should go for Belden 9913 or Heliax FSJ-50, maybe even LDF50.  RG58 coax may be fine for short runs, but remember that the RG213 will have a lower loss (which is applicable to both receive and transmit) and will generally have better shielding than RG58.  Waterproof the connectors with self-amalgamating tape if you can find it, or a small smear of vaseline or silicon compounds (pH neutral cure) with electrical tape wrapped around the outside to prevent weathering.  Water acts very much like an RF sponge in coax.  It pays to keep it out.

 

Coax connectors are one of the most common faults for intermittent signals.  Paying attention to getting them right is time well worth spent.  Making sure there is full continuity where there should be and no short circuits where there shouldn't is only the start.  Buying good quality connectors will ensure that you will lose as little signal as possible and assembling them correctly with properly soldered or crimped (I prefer crimped connectors - quick and reliable) connections.  Make sure that the coax is well tied to any masts and do not allow the weight of any vertical runs of coax to be 'hung' by the connector at the antenna.  Sharp bends, kinks and twists and loops should be avoided, too.

 

Finally we come to the antenna.  If your choice of antenna is an omni-directional one (that is an antenna the will radiate your signal equally in all directions) then you have three basic choices.  The most popular is the 1/2 wave type.  This type has few problems since it is ground independent.  The other most common type is the 5/8 wave (or .64 wave, same thing).  This will need a good groundplane to operate effectively, and the benefit of using this type of antenna is that it has a low angle of radiation.  I have a friend who has one of these, being fed by RG213 coax, with a Cobra GTL148 producing the goods, and a nice base-type microphone to go with it.  Somehow, he just seems to 'get out' so much better than others, despite his location being quite a bit lower than other surrounding stations.  The last type of antenna is the non-loaded 1/4 wave.  I've only ever seen one of these beasties, and considering they need a groundplane and have performance (from my own observations) about the same as the 1/2 wave types, you may wish to opt for the more foolproof 1/2 wave type.  If you are using a mobile whip for base operation, get rid of it!  A proper base station antenna really is the only way to go.  Of course, matching the SWR (please don't say swer, it is spoken as letters - S W R) to be as low as possible is essential.  You have only 4 or 12 watts, you can't afford to waste any of it.

 

Beam (Yagi-Uda) antennae are your best bet if you are really serious about DXing.  These antenna concentrate your radios energy in one direction, making your signal (both receive and transmit) in that direction much stronger.  The smallest beam antenna commonly available is the three element type, with the five element type being the largest commonly available at 27 MHz.  The more the elements, generally the more the gain.  If you want more gain than these antennae can provide, try 'stacking' the antennae together.  This involves splitting the signal evenly and feeding the split signal in phase to two antennae.  Two antennae are better than one!

 

Where do you mount these antennae?  If you can get the antenna up high, at least 5 metres above your roof and any surrounding obstructions like trees, power lines, other house roofs etc. then you will be doing well.  If this is not possible, try to get as much clearance as you can from the obstructions in both the vertical and horizontal planes.

 

 A quick word about power supplies.  If your radio needs 4 amps peak to operate, try to get a power supply that can deliver 4 amps continuous.  That way, you can be assured that the power supply will not be stressed by long sessions.  Of course if you come across a 10 amp supply, then this wont hurt, so long as its voltage is regulated at a smooth and constant 13.8 volts.  Using a battery charger or model train power supply to power the rig is definitely out.  As for fuses: use the correct rated fuse that is specified for your radio, and don't try to put a higher rated fuse in it's place.  If a 5 amp fuse is used, then replace it with a 5 amp fuse, not aluminium foil, or a 20 amp automotive fuse, or bypassing it altogether.  The fuse is there to protect the radio.  If you compromise the protection of the fuse, you risk damaging your radio.

 

What about receive preamps?  For 27 MHz, I would recommend that these not be used.  They will amplify the noise heard on the airwaves just as much as the signals being received, and introducing some distortion in the process (all amplifiers do this) and will gain you nothing overall.  Let the receiver of the radio do the work.  But for UHF CB, they can be worthwhile.  The lower noise of FM lends itself nicely to preamps with a low noise figure.  With a really low-noise system and a preamp, the limiting factor for hearing really weak signals can end up being extra-terrestrial noise, that is noise generated by the sun and other outer-space sources.

 

Antenna tuners?  Well, if your antenna system is so bad that you need an antenna tuner (on the CB bands that is) then it would probably be best to scrap your coax and antenna and go out and buy some good quality equipment.  For minor antenna problems, lets say below 1.7 to 1 VSWR, an antenna tuner will help you match very close to the perfect 1:1, but in the same process will insert some loss, so what you gain with the better matching, you loose in the antenna tuner.  Don't get me wrong, antenna tuners have their place on the amateur bands and for shortwave receiving, but when you have dedicated, resonant antenna systems available for CB, then an antenna tuner really shouldn't be needed.

 

A few quick tips.  If your radio gets hot after some minutes of talking, you may want to add a heatsink to the back of the radio to keep things cool.  Yes, I know this means drilling holes in your radio and generally performing surgery to it, but the alternative is over-heated amplifier stages or voltage regulators, which won't do wonders for your signal.  You can buy commercial heatsinks from places such as Dick Smith.  Painting any silver surfaces with a matt black paint will help a bit, too.  Keep some clearance around the sides and rear of your radio to allow air to circulate and help carry some of the heat away.

 

Keep use of RF connector adaptors to a minimum, especially on UHF.  I had once used two right angle adaptors to help make the installation a bit neater, but these were sacrificing nearly one watt at the antenna end.  Guess where you can find these adaptors now?  That's right - at the very bottom of my toolkit!

 

Another little tip is to keep your antenna clean and corrosion free.  Ditto for the connectors at the antenna and any connectors exposed to the elements.  It pays to disassemble the antenna system once every couple of years to inspect for any such problems with both the antenna and coax.  Clean metal surfaces with dry steel wool and wipe with a damp cloth, and help protect any metal joins with vaseline or a lubricant spray like CRC.  Isopropyl alcohol can be used to clean antenna and coax connectors.   This is available from chemists.  Damage to coax that you should look for is UV perishing, cracks, cuts and nicks in the jacket which may allow moisture to enter, and any crush and cut damage where the coax is cable tied or squeezed into an opening like an air vent or window frame.

 

Keeping a close eye on your VSWR every now and then will assist you in finding any potential degradation of your antenna and coax system.

 

Follow these tips and you will be well on the way to having a signal that will stand out and be noticed the next time everyone gets on air and yells that obscure chant "CQ DX".