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Cobra 18 WX ST II (don’t laugh)

forest runner 98,

if you can find D21 near the back of the PC board next to the speaker jack and behind the big transformer, you can add more 1n4003 diodes in series with it to lower the deadkey by lowering the voltage to the driver and final.

each diode added in series will lessen that voltage by .7 volts.
you will have to keep adding them until you get your deadkey where you want it.

the advantage here over de-tuning the radio, is that if you de-tune the radio, you will lower your deadkey but you will also lower your modulation.

doing it this way allows the full swing potential of the radio to be coupled through the diode to the driver and final so you get a low deadkey but with full modulation.

the other suggestions are good and will work, just thought i'd add to the list.
good luck with it.
LC

Ah ok. That seems a little more involved but I will take any advice. If I adjust VR2 I think that also adjusts modulation.

Ok.....gotta ask.....from where and how much?

I knew someone would ask!!!LOL Let’s just say I paid a little more from a place that rhymes with DeeJay.:eek:
 
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yes, it's more work because it involves soldering, but there are chances for problems no matter what procedure you choose.
you might crack a ferrite tuning slug when trying to de-tune the coils.

yes, adjusting VR2 will adjust your modulation, and i see what you are getting at, but all i can say without typing a paragraph is that there's more to it than you think.

that being said, you should try your plans and see how things work out, who knows, it might be just how you want it.
LC
 
I once owned a kl300 about 15 years ago. Not a bad little box paired with a galaxy 33hml but back then they were known for the pre-amp failing just like mine did. Sold it to another driver and he used it for years with a cobra 29. Not bad for a budget box back then. I take it they've stepped up their game these days because I see them all over the web. Most guys bash them but in my experience one did me well. I've actually eyed that 505v with fans for quite some time now but just can't get myself to pay 300+ for one. I currently own 2 tinman built boxes and hardly even use them so that makes it even harder to justify the Italian job. Back to the subject, I'm curious to hear about the diode mod and that 18 driving the rm box. Please keep us posted!
 
Morning has broken! :)
Winter is over! :D
Life as we used to know it, has changed! :p

4 watts and a KL203 CAN be used in the same sentence! :ROFLMAO:

Thanks, guys!

Headed to Amazon. And newegg.com. (n)

Probably won't work out so good, the amp will have a monster carrier with very little swing. At least put a fan on it so it will last for several months.
 
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yes, it's more work because it involves soldering, but there are chances for problems no matter what procedure you choose.
you might crack a ferrite tuning slug when trying to de-tune the coils.

yes, adjusting VR2 will adjust your modulation, and i see what you are getting at, but all i can say without typing a paragraph is that there's more to it than you think.

that being said, you should try your plans and see how things work out, who knows, it might be just how you want it.
LC

I think I will try the least invasive attempt first. Even if I can get the DK down a smidge I should be ok. If I see smoke then no bueno. LOL
I'm curious to hear about the diode mod and that 18 driving the rm box. Please keep us posted!

I am curious to see where this goes too. I will post the results!!

This is where you really need the scope!

Ya...I will be adjusting blind without knowing what the numbers are.
 
Disclaimer: I haven't personally tested the values mentioned in this post...
I'm just winging it here without referencing datasheets.. so proceed with caution.
Now, with all that red tape out of the way...

If I was going to combine an "Export use only" "Juice maker", with a magnificent example of CB radio, such as the Cobra 18 WX ST II;
For export use and educational purposes only, I'd imagine something like this...
(Using a Watt meter, no modulation, a non-conductive/non-ferrous alignment tool & 50 Ohm RF dummy load)

Adjust L17 clockwise to lower RF output.
If you cannot reach a desirable power level
(and you have an oscilloscope to examine the waveform)....
you could modify the following component values.. among others..

Decrease capacitance at C139 (270pF)
Change to 220pF, perhaps even going as low as 180pF (wouldn't go crazy low like 100pF).

Between the RF Driver transistor and the Final RF output transistor, at R112 you can Increase resistance hoping to add a little attenuation. Change R112 (1 Ohm) to 2.2 Ohms, perhaps even try 4.7 Ohms?!

From the TX buffer "pre-driver" to the RF Driver, you can Increase resistance at R113 (10 Ohms)
Change to 12 Ohms, perhaps even 18-22 Ohms. Don't want too much attenuation here though..

Remember to re-adjust L21, then L20, then L17, (or just L17 if you're "in the blind")
check output level after each individual circuit change,
remember to re-peak the transmitter after each mod, checking Ch 1. against Ch. 40 as well..

While you're on the 50 Ohms dummy load, modulate your carrier and examine the waveform, look for any signs of unwanted oscillation "run away" or other distorting disturbances in the force!

Carrier power should now be "low enough" to keep the "Juice maker" happy..
Approx. 1 Watt or less keeps my 203 very happy on the test bench.
Your output may even be too low now depending on what values you've chosen!

Adjust VR2, and attempt to set AMC for approximately 95% modulation
(using a 5 mV 1000 Hertz sine wave at the mic jack)
If you are having trouble keeping the modulation in control, consider modding the AMC..
Perhaps change R107 (2K7) to 1K (increasing this value could create a less effective AMC circuit)

The following changes may be unnecessary and could create a sluggish or quicker responding AMC!
C76 (33 uF) change to 47 uF or 22uF
C82 (3.3 uF) change to 10 uF, or 4.7uF, or 1uF
C126 (1uF) change to 2.2 uF or 0.47uF
R62 (15K) increase to 30K or decrease to 7K5 Ohm
R63 (1K) increase to 2.2K or decrease to 470 Ohm
R64 (1K) increase to 2.2K or decrease to 470 Ohm

I think this would be a better way to go, compared to the diode string method or "JP36 variable mod".
*Remember to observe all regulations in your area, and to always operate accordingly.*

If your going to modify these circuits, understanding how the pieces work together will be important!
I'm not an E.E., I just think I know what not to do so that I (hopefully) don't burn anything up, lol.

If any members would like to comment on the technical accuracy of my approach for this "modification", I'd really appreciate the input; thank you.
 
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My ears just perked up!
Everybody and their dog says the KL amps can only handle 1.5 watts or they blow up. Am guessing an out-of-the-box 980 does 3.5.

Slowmover, what’s the story with your setup? It could mean a boatload of new 980 and KL203 buyers. Me included. :D

I’ve reported before that I’ve run the KL203 I own with Uniden 880 & 980 without issue. Radios untouched.

I respect the advice to match the pair by turning down the radios from where the factory set them.

But the problem of those of us without the know-how to do this is having to trust an unknown tech. Likely, advice on a tech from this site would work. Just add shipping X2 plus expertise $.

Thus my advice (fellow truck drivers) is to keep costs low and performance a high baseline with:

1). Uniden AM/SSB Model 980 straight from the box
2). RM ITALY KL- 203 baby amp
3). WEST MOUNTAIN RADIO CLEARSPEAKER to add what all
CB & 10-meter radios lack, and that’s digital signal processing of the audio.

The above is roughly $400 with appropriate mike upgrades, an antenna plus miscellaneous.

IMO, better performance than a Golden Screwdriver $500 radio alone.

Find the Harbor Freight APACHE-brand pick/pluck foam-filled transport case large enough to hold all of the above (the complete mobile rig sans antenna (for that build a transport case from called PVC tubing), and one has a do-it-all rig ready for mobile.

The transport cases are where most fall short in putting together a package. But moving radio gear in and out of vehicles is where damage is most likely to occur. And it’s ideal to use for sending that gear to a shop. Or as a gift to someone.

I don’t consider this a debate on merit, but on price vs performance. It’s a radio with high marks in reliability and value, coupled to DSP which brings out the best in it (any mobile radio would benefit).

Is a Stryker 955 a better radio? Probably. But against the above one will be close to $600 poorer. Versus $325 for 980 & ClrSpkr alone. For less than the $600 outlay one will have a complete system.

For mobile, this same rig — radio, amp & speaker — will run off of a big truck 15A supplied CB radio circuit.

A 980 with a 70W amp is “enough” to get out. With the CkrSpkr, one can now hear around the noise so well that conversations previously hidden are now fully legible.

Sure, a poor antenna system isn’t cured. Nor is all vehicle noise, etc.

But you’ve more money available to spend where best results can be obtained in optimizing a vehicle.

Save the big radio for another day. Get on the air, and track down any problems. Come that future you’ve always an outstanding backup at hand.

Are the radios I own a fluke (880, 885, 980)? Maybe not set to 4W by factory. Is my KL203 exceptionally hardy? It’s been dropped more than once here in the truck.

Would it be best to match the pair? That’s my eventual plan. Hasn’t mattered up till now (knock on wood).

A 980 with 203 is a straight from the box 70W AM/SSB rig for $200 is my experience. Add the ClrSpkr and it’s better than a comparable $525 radio.

But that’s not expertise. It’s called “get on the air” with minimal headache.

.
 
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FWIW, I took my GALAXY 99v2 to Clays and a bench check with an RM-Italy k7505v showed 180w +/- with a 2.5w deadkey, IIRC (I posted results).

Cranked, it was well past 200w.

Would that get me “more”? Not as I understand it.

A KL203 with less than 4W input is probably best. I can’t prove Uniden sends them out with less than 4W, but it makes sense. Lower still makes MORE sense.

One can buy a pair of 203s for about $100. (I use DNJ Radio). Step up to the 7405 or 7505 and now $$ power cabling plus tools becomes an issue. Etc.

An “ideal” set of power cables for a 203 powered rig is minimal as you likely already own what’s necessary for a no more than 3% voltage drop set.

As I see it, I want the tech with expertise not only with radio but antenna analyzer as well. I may/may not acquire skills and/or tools. Would rather drive up and have an old hand go over the whole of the installed mobile rig.

Caveat Emptor
 
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Hello everybody!

I am new to the CB world. I originally got my radio just for off roading BUT I kinda got the bug for CB. Also the radio was DIN sized.

Does anybody know how to lower deadkey wattage on this radio? Reason is I wanted to add a RM Italy Kl203. I believe the radio is already under powered by the factory but I didn’t want to kill the amp with high input watts.

I appreciate all your responses!! Thank you!!

Bill
Welcome! I run a few of the little 203 amps and I believe they are a great value. I have run them with a Cobra 29, uniden 980, and even a Galaxy 99 turned down to 15w peak. If you get a 980, it is one of the easier ones to set the dead key. It has a trim pot inside just for the carrier power. I turned mine down to 1.5w and gives the 203 a 25w carrier. Sure it will work with a 4 w dead key, just keep an eye on the amp temperature and if it gets hot then quit talking for a while and let it cool down. A small fan on top would help too.
 
With my SRA 198 mike I use the setting at either 3 or 4 with good reports. When running my RF LIMITED 2018 I use either 2 or 3 on the radio's settings with the mike's internal gain turned up about a quarter of the way.

Also anyone running one of the RM 203 amps should make sure there is plenty of cooling air for this amp. It can get hot during heavy use. I would recommend putting a small fan on it.
 
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Slowmover,
Regarding your mic, what settings are you using on it and the radio’s mic gain? All voices are different, but it will be a good ballpark starting point.

Thanks! (y)

I’m using the stock mic in the big truck at present. Max gain. (#4).

In a different truck and with a “better “ noise cancel mic, it was (#3).

With a Red Devil it was (#1) and adjust mike for listener irritability.

Truth be told I think it would be best to use another radio across the radio as receiver and adjust for “quality”. That’s my plan once I get home. Much, much easier to play with mikes than to rely on truck drivers still acting like they’re speeding in a 55-mph zone (“oh, no, my anonymity”) and won’t take time for distance and audio quality checks.

With power mics, these Uniden (my experience in big trucks) need only a little juice at the mike. And less than max gain at the radio.

Now, you come on down to mixmaster at downtown Dallas, you’ll want to know maximally irritating radio settings on a Galaxy with robotic voice changer, echo amount plus delay, and how to eat that mic with aplomb. Then instantly (innocently) switch back to complain about THAT GUY.

Your two radio shack investigation to setting audio level puts you on the road to the exalted King A-Wipe Driver Level.

I just made it past St Louis by running back roads from 70 down to 64 thence to 255 around the south side to 44 (Tulsa today) only to find some neckbeard got hisself kilt right as I was onto 44 thinking I was home free.

Still arrived at a truck stop a half hour ahead of a driver who passed me with 5-mph to spare 45-miles back into Illinois. Saved myself more than 30-minutes which today I need.

Be ready for all eventualities.

I’ve had this 980 & ClrSpkr cranked hard today.


.
 
And while you read all of the above...

Print this out, or snapshot it - take it to the bathroom and while you're in a movement moment - study and see if this can work for you...
Cobra18Swingkit.jpg

I did this work to a previous Cobra 18 radio but for a different purpose. So the L19 is different - I used my own coils for radios to try a mod for a high-drive unit. The above was a prototype for an Asymod radio for customer that back out and wanted to have more control over variable power.

The variant is the additional 33 ohm 1watt rated carbon composition resistor (no wirewound) and a 33uF 50WVDC cap applied to squeeze into the bottom or overhead as necessary to develop swing and drive your amp.

The 33 ohm resistor should be the right value you need to keep the 203 working and hold in the "Relay" to allow for swing from low-to-high.

The above reduces the need to "de-tune" the radio to accomplish this. It'll look like hell but the covers keep it under the hood and out of your way...
 

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