Peak and Tune...

CB shops are all over the map. The ones with a competent tech and good equipment are rare because unless it's a guy in it for his own business, the owners are too cheap to pay what a decent tech is worth and too cheap to buy decent equipment. Shops will even argue among themselves what constitutes a peak and tune. At minimum, tuning the radio for max output into a 50 ohm dummy load on the bench, and tuning the SWR on the truck antenna.

The alignment of the receiver and the frequency should be right-on from the factory, and it has to be right as-shipped for type acceptance. I wouldn't touch them. Tweeking the receiver may degrade it in such a way that even though it sounds more sensitive, it may also be much more noisy.

The driver and final can be tuned up for more power. Just accept whatever that ends up being. Some radios have a low pass filter built in. The tech should know not to mess with it.

Don't 'clip the diode' in the modulation limiter unless you want it to splatter trash. The diode is mostly there to limit negative modulation, which is what happens during the portion of the signal where the power hits zero, not the portion where the power is peaking.

Increasing the mike gain and audio level can be done, but this needs to be done with proper equipment including a signal generator, scope, dummy load, etc. to avoid overdriving and distortion in the modulator and not like some guys using a screwdriver and whistling in the mike to max out a lying Dosy meter.

Rather than dink with that, I'd use a noise-canceling mike (maybe a power mike). I do use a noise canceling mike on the road and a 'power mike' at home.

Once the radio is tuned up and installed, yeah the SWR needs adjusted in your truck, but that should be a no brainer if the cable and antenna are good.

The most improvement in any system where energy is converted from one form to another is almost always to be had in those parts of it that are the "conversion interfaces".
In a CB radio, the mike converts audio power to an electrical signal to feed into the CB, and the antenna converts the RF electrical signal from the CB to an electromagnetic (radio) wave in the air.
->Assuming you want a clean sounding radio, The mike and antenna are most important.
(Same principle for an expensive turntable for records, and expensive speakers for listening - the stereo amp in the middle is not half as important as the turntable and speaker quality. Same principle for a lot of things.)

I repair and operate CBs and ham radio equipment. I also build ham radio equipment and repair and calibrate professional test equipment. That does not make me an expert. The above is just my opinion from experience.

 

The big question is "how often is it not?" I just picked up a bone stock Cobra 25 WX built in October of 1997 and was testing it today. I hooked it up to my 18 ft tall Shakespeare big stick base antenna with the feed point at 15 ft. I checked the SWR's and they were below 1.5:1. I asked for a radio check. A truck driver who was 3.5 miles away responded. He said "it sounds like it came out of the box". I could barely hear him as he was coming in at like a 2-3 on my radio. It was as if I had the RF gain dialed back but there's no RF gain on this radio!

Then I unhooked that radio and hooked up my Uniden Washington to the same antenna and called out again to the same driver. This time I could hear him a little better as he pegged my meter. He also commented I sounded a little louder.

So I'm wondering if the receive is way off on this Cobra 25 WX and if I need to just get the dang thing aligned.

 

Good point. Two different receivers. Not all are equal, nor are meter readings or volume & clarity for a given signal equal between different receivers. OCT 1997 was 13 years ago, maybe it needs alignment after so long, not surprising. No harm in an alignment if the tech has the manual and the gear. Just $, maybe it will improve it, hard to say.

There's a huge difference between how my 148GTL, Realistic TRC-458 Navaho, and Uniden-510 sound, what i can hear when conditions are difficult, and how they indicate. Inside most radios, one of the pots adjusts the meter reading, so who knows how one might have been set until it is checked.

Seems the more expensive the radio the better the RX has been. The transmit side is the cheapest and easiest part of the radio. The receiver is where the magic is.

If you can find an A/B antenna switch, you can do instant comparisons between all kinds of radios. That would remove all doubts but it looks like you already found the WX 25 to be suspect.

Workman makes a 'CX-3' 3-position switch for $6.95 sold on amazon. It's a POS because they lie and claim it will take 1000 watts which would eventually smoke it, but it will be OK long-term for maybe 100W peak.

 

I concur with M818 and Turbo. There are big differences in receivers in radios in the first place. And if the factory is a little lax on getting the last little bit of usable sensitivity dialed in, then they probably ship it as long as it meets their minimum specs so they can keep cranking them out.
At my place, I don't release *any* radio to a customer unless I've checked the alignment myself, whether it's a new radio sale or a repair. Once the gear is set up, it takes only 5 to 10 minutes to go through an entire radio with the service monitor & spectrum analyzer and make sure everything is running right. "Right" in my case means on-frequency, receiver hearing its best, and transmitter running at rated power and 100% modulation. Unless the radio has a factory seal, in which case I'll make sure it's doing rated specs and, if not, I'll give the customer the option of sending it back or having me break the seal and fixing it. (Cobra isn't currently accepting new dealerships, and they only certify dealerships to do warranty work).
Just like detailing a new car before delivery, I think it's part of what I should be doing, because every radio that leaves my shop carries my company's reputation. I make a point of letting the customer watch me certify it (I put my name & commercial license number on the spec sheet that I fill out and give out with the radio) and show them the readings on my gear. There's no extra charge for that, but we're a one-man shop, and I figure the extra 10 minutes I put into a sale will bring people back, or new business in.


Id be very wary of a place who offers to "peak and tune" (which seems redundant to me, BTW -- they might as well say, "peak, tune, align, and optimize"...) to wring every last fraction of a watt out of the transmitter. The final amp parts (transistor, MOSFET, etc.) are pretty spendy, and have to dissipate a lot of heat in the performance of their jobs. As was noted in an earlier post in this thread, some radios have "low pass filters" incorporated into their design. Some call a much simpler stage a "TVI Trap" or "54 MHz Trap", but they are intended to do the same thing: keep any energy from "harmonics", or multiples of the carrier frequency, from escaping to the antenna. A "real tech" will know how to do that test; a well-equipped one will have a spectrum analyzer, but there are other less expensive ways to do it. Simply tuning all of those stages for maximum watts on a meter runs the risk that a lot of the extra power is actually out-of-band, which interferes with other services and is likely to sound bad in-band as well.

Having your transmitter "peaked" from its rated output of 4 watts A.M. to 6 or 7 watts will never show on someone else's S-meter, but it *will* shorten the life of your final stage. If 4 watts won't do it, then neither will 7 or 8. And at least one major manufacturer stopped putting heat sink grease on the chassis side of the insulators for their power transistors, which is a delayed death sentence for those parts.

But if your radio shipped with a receive sensitivity of 1 uV ("microvolt") and you can get it to 0.3 uV, that's a BIG difference in how well you'll hear weaker stations.

And as was also noted above, most radios have an internal adjustment for setting the S-meter's reading, and factory alignment instructions tell the tech how much signal to pump into the radio in order to set it to S9. That would be fine if 1) all companies used the same signal level, and 2) all meter circuits were linear.

Neither is the case, though. I've got 3 different radios on my bench right now that I use for yakking with -- a modern one and 2 old "classics". One calls for 50 uV, one is 100 uV, and the third is 1,000 uV to show S9. So the one with the smallest signal required to show S9 will give others the best readings, cuz its meter is made happy by the lowest signal level. And away from S9, one or two S-units difference in signal strength doesn't necessarily cause the same difference on the meters.

My personal suggestion is to save the money for a "peak and tune" on a new radio and put it into a better antenna. The antenna will help *both* your transmitted and received signals.

And, as hams have said for years, "If you can't hear 'em, you can't work 'em."

Good audio is for talking; watts are for fighting

YMMV.

-- Handlebar --

 

Stay away from any one that offers "modulation" or "swing" kits. Also, if anyone wants to do the "whack-pack" mod, run the other way. That bs mod is where they hot-wire the radio by bypassing all the voltage regulators. The bottom of the radio will actually get warm. The radio will scream on the air for a few weeks until it burns itself up LOL

 

" And, as hams have said for years, "If you can't hear 'em, you can't work 'em." "

YEP !

It dosnt matter if it is a CB or a HAM radio you pay for a better RECEIVER much faster than a few extra watts. This is why weak signal guys run PREAMPS and DSP and use radios with adjustable bandwidth ....Radios the high end ones allow you to do this.

On CB CHECKING the radio to see it is working right is ok if your receiver is really out of alignment it can cause you not to hear the weak stations but "PEAK and TWEAK " is pushed a bit far ..... the use of advanced receiving devices on AM had little value since bandwidth is fixed and the cost of DSP would make the radio way too costly.

"S" meters have little meaning the old standard was "S" 9 was 100 uV but that went out with the first jap CB 45 years ago .....Today many meters are just a digital display with little use except to look nice .... or to help you point a beam ....

People like Handlebar and my self who work on other kinds of radios are REQUIRED to have stations that are NBS traceable and even the old ones we use here IFR-1200S built in the 1980's and cost $1200-1500 to get calabrated EACH YEAR EACH STATION to buy new are $20,000 or more. This is one reason the workmanship out of many CB shops is so poor .....they lack the equiptment and remember no training is required anyone can call them selves a CB TECH

Sadly Many just have a rusty screwdriver and a cheap watt meter .... and just get hacking on you radio ....

This is a mid level HAM radio with DSP ....

 

The way I look at Peaking and tuning is that the radio is checked over and "fixed" so that it does what it is suppose to do. In other words, fixing the problems that come from mass production. No two radios are the same out of the box. Some do what they are supposed to do while others do not. You can bring the radio back and exchange it for another but how do you know the new one will be better.

So to me Peaking and tuning is just chcking the radio to make sure it is putting out the proper amount of power with clean modulation and is tuned so that it puts out its power directly on the frequency it is supposed to and not in the middle somewere.

Some will go as far as adjusting the modulation a little higher while making sure it is clean sounding etc.

There are some places out there that will just open up the radio and clip a few things, spread a few things and remove a slug or two and not even look at the radio on any equipment other then a watt meter. This is not a peak and tune, this is a hack job.

As far as antennas etc. This is not really part of a P&T. If you are at the shop and they offer to check your truck out then go for it but it is not required of a P&T. If it was then you would have to have the place send a tech across the country when you buy a setup over the phone or on the net.

 

I have a brand new stock cobra 29 ltd chrome edition and it has never been worked on I've had it since this Christmas and it is ok but people im trying to talk to far away can barely hear me but i can hear them fine. My uncle is a trucker he told me I needed to get it peaked and tuned but there are no local cb shops and don't want to take it to a truck stop to get hacked on so I was wondering if it would still sound fine if I turned up the vr4 modulation pot myself and I don't know if I should turn it to 100 or turn it up to 100 and down just a little I want to reach out and hear just as far but I still want it to sound good. And I'm running a 102" ss whip from radio shack on an old firestik mirror mount with the old firestick spring and bolt on the alluminum toolbox with a ground wire to the frame and a 20ft length of rg-58 coax. The swr meter on the radio reads about 1.3 it just hits the s on swr on the meter.
Thanks for any help

 

Backwoods it sounds like everything in your set up is ok. You could turn up the VR...it will make you a little louder but might not make a significant difference...just be careful as if you turn it too much it will make you sound distorted. I wouldn't turn it up anymore than maybe 3/4 of what it can do.

I went thru this a few weeks ago, had a guy tell me I was bleeding into the adjacent channels plus I sounded distorted. I backed VR4 back down to about 3/4 and all was ok.

You say you can hear others far off but they can barely hear you, what kinds of antennas were they running? You have one of the best antennas possible, but if your other party doesn't have as good of an antenna, that in itself will pose some issues.

Of course perhaps it might just be better to skip cranking on the modulation pot and just get yourself a nice 2 pill amp?