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Watts is the Question

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FiveFilter

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I just tested my three relatively new, unmodified compact CBs with a newly acquired Workman 3-P (read: cheap) watt meter and got the following results using a 50 ohm dummy load and powered at about 14vdc from my running truck:

Uniden 520XL = 1.80 watts
Cobra 19 DX IV = 2.90 watts
Midland 1001z = 2.20 watts

ASSuming the watt meter is accurate, it shows the factory settings are well below the nominal 4-watt legal limit. I'm OK with that, and I doubt getting them up to the full 4 watts would make a practical difference. I use the radios only for highway travel to get and give local traffic and road conditions. I've been happy with these radios and the three-to-five foot magnetic antennas I use with them. I remove the radios and antennas when not on the road, so this type of compact and mobile equipment is exactly what I need.

My question: Is there a case to be made for getting the CBs into a shop to achieve the 4 watt limit they were designed for? I.E., will the radios perform noticeably better with that extra watt or two, or is the benefit just theoretical?

One curious thing: I'm told the watts should go up by a factor of about four when a high-pitch screech or whistle is introduced into the microphone with the key down. When I try it with all three radios, if anything the watts go down by a decimal point or two rather than rising significantly. Any idea about what I am doing wrong with my testing for the modulation swing factor?

I will note that I want the radios to sound good rather than loud, so I don't want any "clipping" of modulation limiters or whatever Golden Screwdrivers do. I am not into the whole DXing, loud-and-proud, farting, echoing, Roger-beeping, Tarzan-screaming thing. I just want decent communications about local highway matters via simple, mobile equipment.

Again, I've been happy with what I got in terms of subjective performance. Should I be, in view of my more objective watt meter results?
 
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It can be done. I don't know what manufactures use to test their radios (if they even do that) but it's common with most radio manufactures in the CB industry.


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jackj

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Why try to fix what ain't broke?

You might be able to get another watt or two out of the radios but the only difference you'd notice would be on the watt meter. Your transmit range isn't limited by the "inverse square law", it's limited by interference and the only way to increase your range would be to overpower the interference. An added watt won't do that. You might add a RF power amp and turn your radio into a real blow torch but what about the guy you're talking to? If you can't hear him, you can't communicate with him.

Modulation will add power to your signal but will 'your' modulation? If your radio has 100% or slightly less modulation and if you modulate it with a perfect sign wave then you will see an increase but your radio might not be modulating the carrier with 100% linear audio. You should be more concerned with how your audio sounds than with the bounce of your watt meter.
 

jim202

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Please don't take my comments the wrong way. You asked a good question and I will try to point out a few things in what will follow here.

Let me give you just a little background on where I am coming from. I got started in playing with radios and originally obtained my ham license way back about 1962. When I got out of the military after working on voice scrambling equipment, I found a radio mentor that got me hooked on working around public safety radio systems and doing repair service work on mobiles, portables and the radio towers they used. I still am involved with public safety radio systems and work on public safety trunking systems now as a radio consultant.

Over the years I have collected a number of radio service pieces of equipment. As time goes on, you learn just how important it is to have calibrated equipment to measure the different aspects of how and what makes a radio system play well. One of these is a service monitor and another is a watt meter.

I check my watt meter reading against my service monitor about once a month. I take a radio and connect it up to the watt meter with a dummy load on the other side of it. Then move the same cable that fed the watt meter to the radio and use that same cable to connect to the service monitor and again measure the transmitter power and read it with the service monitor. They should come real close the providing the same RF output measurement to within a very small percentage.

Now back to your question of why the different radios and your watt meter readings are low. Did you use the same cables in the same locations each time you measured the different radios? The length of cable going between the radio and the watt meter, then the cable from the watt meter going to the dummy load could possibly effect the differences in output power your measuring.

As for your watt meter, I would try to find a friend that has a decent watt meter and use the second meter to compare your readings. Never trust a meter that you can't verify the reading it provides without using some other standard. I use a Bird watt meter that I know works and provides an accurate reading.

Don't point the finger at your radios until you know how accurate you meter is reading. Just changing the length of the cable between the watt meter and the radio can effect the readings in some instances. This has to do with the frequencies your trying to measure the power at. The other variable is how well the engineer did his homework on designing the radio and the transmitter output circuit.

So you see there are many things that can throw your readings off. Slow down and do some homework on the accuracy of what your watt meter is providing you. This is a learning curve that we all go through.

Depending on just how entrenched you get into the radio hobby, will determine what you end up with the toys of that hobby as many people call it when they come over to my house and step into my workshop / play area.
 
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jonwienke

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Your transmit range isn't limited by the "inverse square law", it's limited by interference and the only way to increase your range would be to overpower the interference.
Yes it is limited by inverse square, in all cases, no exceptions. The inverse square principle indicates how much power is required to increase the signal far enough above the noise floor to be received and demodulated.

Modulation will add power to your signal but will 'your' modulation?
Modulation increases peak power, but not average power if the radio is configured correctly. Average power is only increased if you increase modulation past 100%. Noobs do this, thinking that they are getting extra power, but the truth is that most of the extra RF is splattering across adjacent channels, and intelligibility goes out the window because the audio is clipped.
 

KC4RAF

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+1 with Jim and Jon above.
The manufacturers of CBs don't adjust the output power to the limited 4 watts. They keep it just below, that way if the FCC check them, they are within the spec.
Be very careful of the golden screwdrivers out there. They can add insult to injury. Not saying all of them are bad, only to be careful.
Also, and I'm sure you are aware of it, put you money into the best antenna you can afford. A 350 dollar radio is useless with a 10 dollar antenna.
 

DJ11DLN

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This "deficiency" is nothing new. I have not fooled with CB for many years, but with that caveat out of the way, a friend of mine bought out part of a CB shop that was going out of business back in the mid '80s. The radios he acquired, and there were close to 50 of them, ranged from new/old stock 23-channel units to spanking new 40-channel ones factory-shipped just months earlier, with a scattering of refurbished units of various vintages and manufactures. We tested all of these -- I won't bore anyone with our reasons for doing so -- using a borrowed Bird 43 with the correct slug and a 12" piece of RG8 into a 50W-rated dummy load. Not a single one of them scratched 4 watts when keyed on AM (there were a few AM/SSB units). The worst were just under 2W and the "best" were right at 3W. But when attached to a 5/8-wave ground plane up about 30', they all talked, and all got OK to great audio reports. They were re-boxed and sold to various folks and we made a little $$$ on the deal...none of the buyers were unhappy with them. Some were used as-was, some no doubt got the golden screwdriver treatment, good or bad.

I was a little surprised at the low factory power ratings too, but then I had to remember that the antenna is a lot more important than the radio.
 

mmckenna

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I agree.

After 15+ years without a CB radio, I purchased on and installed it in my truck for a long road trip to Texas from California.
Using a Bird 43 with a 5 watt slug that covered the CB band and an accurate 50Ω 100 watt load, it too tipped the needle at about 2.3 watts out of the box.

I could have messed with it, but I didn't. The difference between 2.3 watts and 3 or 4 isn't going to make a difference.

Just about anyone will tell you that the antenna will make a bigger difference in the performance. I had an old (30 years) NMO-27 installed on a permanent NMO mount on top of my truck. Used by work analyzer to nail the tuning right on 19, 1.03swr, 1.3 on 1 and 40.

In reality, I rarely (almost never) talk on the CB, I primarily use it for listening only. Worked just fine for that. The few times I did use it, the person I was talking to heard me just fine.

I wouldn't pay someone to try and bring the power up. Not only will no one notice the difference, but you risk having the guy accidentally make something worse. I wouldn't even try messing with it yourself unless you wanted to do it purely for the exercise and were willing to write off the radio afterwards.

And, SWR meter accuracy is a good point. Workman ain't top of the line. Still, your numbers sound correct, at least from my experience.
 
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Good answers addressing your question. You mentioned you were taking your measurements using your truck as a power source. You may have slightly better reading if you used a regulated power supply, you may have some slight voltage "sag" by powering from your truck.
 

AK9R

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You may have slightly better reading if you used a regulated power supply...
Not only the power supply, but the power wiring should be checked. Many radios have been labeled as under-performers only to find out that the power wiring presented too much voltage drop when transmit current was being drawn through the wiring.
 

FiveFilter

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Thanks for the great replies guys!

I did run my tests with a 50 ohm load and the same coax. Everything was identical with the three radios lined up and tested one after the other in the same session.

From the responses here it seems these factory-issue radios are operating about like all the others have operated for the past 30 years or more. I.E., at varying wattage output levels, all well below the 4 watt legal limit. That's the bad news. The good news is that it doesn't make any practical difference, because a watt or two isn't discernible in the real world anyway.

I like to see such equipment comparisons because they help to give comfort (or discomfort) to others who might be having the same results and question why.

As I noted, I'm happy with my factory-grade junk because it gives me the results I want, which is the ability to communicate locally with other drivers about immediate road and equipment hazards. Such communications can be very useful for conducting a good, safe trip, and I've proven that to myself on a number of occasions.

So, I'm leaving my radios as they are.

Best wishes to all.
 

prcguy

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My experience testing newer CBs right out of the box on an accurate wattmeter and at 13.8V is higher than you saw and from memory they were closer to 3 or 4W dead carrier. I suspect your wattmeter is the main problem.

You are correct that the peak power should be 4X the carrier power or an increase of 6dB going from a dead carrier to full modulation and you need a peak reading wattmeter or oscilloscope to measure that properly. The difference between dead carrier and peak power can vary a lot between mfrs and depends partially on how the modulation limiter is set up and also the design of the radio.

The last CB I played with was a Uniden 980 that was not so good out of the box (like most) with maybe 80% AM modulation and after a simple adjustment its now very close to 100%. As a coincidence I used that radio just last week to drive a home made amplifier into a load and using a peak reading wattmeter it was doing right at 4X or 6dB increase from dead carrier to full modulation even through the amplifier, so its working as it should.
prcguy
 

FiveFilter

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Yeah, my new Workman 3-P watt / SWR / field strength meter cost about $30, so it's certainly not up to par with professional grade equipment. However, it should serve my purpose of keeping some check on the radio, antenna and coax performance to make sure they are within some semblance of propriety.

That's a big step ahead for me compared with flying blind without it.
 
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