HT Modification Reactions

[Blaise]

Hey all,

I just ran across this Baofeng modification video.  Brass tacks, just how bad an idea, from a technical standpoint, is the power mod in this video?
 

 

[Lscott]

8 hours ago, Blaise said:

I just ran across this Baofeng modification video.  Brass tacks, just how bad an idea, from a technical standpoint, is the power mod in this vi

Generally not good.

1. Transistors are not great for linearity. As the amplitude increases for more power the waveform likely deviates further from the ideal sine wave shape. Any departure indicates harmonics of the base frequency are present. That's why there is a band pass filter on the output stage of the radio. The UV-5R's, particularly the older models, were known for having poor filtering on the output. If the radio meets FCC emission standards before the mod it might not afterwards.

2. All power transistors have a power dissipation rating, and thermal resistance from the transistor's junction to the heat sink. The power amp stage, transistor, in the radio is no exception. Whatever power is going into the final amplifier stage and not coming out as RF is turned into heat. It's not unusual for the efficiency to be around 50 percent. So if you get 10 watts out that means you're dumping 10 watts of heat into the radio's case. That can turn the radio in to an instant hand warmer. Maybe even too hot to hold and likely fail the output power transistor.  The junction is going to be very significantly hotter than the case due to the thermal resistance. This is why I'm not a fan of tiny radios. Not enough case size to dissipate the waste heat generated during transmit.

3. In the case of number 2 above for lets say 10 watts out, 50 percent efficiency, the drain on the battery pack is 20 watts. Just how long do you think that tiny battery pack is going to last? You'll likely will need to carry around extra battery packs if you transmit at high power a lot, and don't manage to kill the radio from excessive heat before then.

[SteveShannon]

Nobody can answer that but you. There are always trade offs, such as definitely shortened battery life, probable shortened electronics’ life, slight possibility of battery rupturing and catching fire in a spectacular way, possibility of generating interference, and/or spurious emissions.

Do you have test equipment to see what happens to the signal? Why didn’t the manufacturer do it? 
 

 

[WRKC935]

In addition to what Steve said.  Mind you I didn't watch the video.  But does it more than DOUBLE the power output?

Doubling power output is an increase of 3dB.  To change a standard S-meter fro S-1 to S-2 is a change of 6dB.  Which of course isn't a real big change on the receiver end far as being able to hear a signal. 

My point is that you are not accomplishing much even doubling the output signal.  So when you apply the stuff Steve said above to the whole discussion, it's really kind of pointless to do it.

 

[SteveShannon]

On 10/16/2024 at 7:04 AM, Socalgmrs said:

I’m addition to the other bad things mentioned a some point rf starts killing your rain cells and causing cancer.  That point is around 10w soooo?  

No. I think you just make stuff up.  It’s more likely to affect your eyes and your testes.  RF is non-ionizing radiation, and although excessive RF exposure can have harmful effects the calculation is more complicated than just some arbitrary power level. It involves frequency, distance, cumulative time of exposure,  antenna gain, and power output. ARRL makes a free calculator.  https://www.arrl.org/rf-exposure-calculator

[WRKW566]

This becomes interesting to me as I want to turn down the power on my illegal radio so that it generates 0.5W at Low power setting.

[Blaise]

22 hours ago, WRKW566 said:

This becomes interesting to me as I want to turn down the power on my illegal radio so that it generates 0.5W at Low power setting.

I was thinking about that too!  Although, I think this would decrease power for all of the settings at once, not just low power, but I haven't dug into it...

[WRKW566]

2 hours ago, Blaise said:

I was thinking about that too!  Although, I think this would decrease power for all of the settings at once, not just low power, but I haven't dug into it...

I'm not so much bothered by the reduction of power overall, honestly I can't reach anything from where I live but it would make me more comfortable wrapped in the feeling I was trying my best to use what I have as close to "legal" as I can get. If GMRS turns out to be something I'm interested in pursuing, I will invest in type approved equipment.

[WRKC935]

I was thinking about this more and something that was mentioned but not really explained about having the PROPER test equipment when doing this.

A standard watt meter is going to measure the power on ALL frequencies passing through it.  Meaning if I connect a watt meter to a 10 channel combiner that has 3dB of loss in each port to the output, and I connect ten 100 watt radios to that combiner and key them all up I will see 500 watts of output in that watt meter.  The meter is NOT specific enough to see the different frequencies, it only see's the TOTAL power passing through it.

Why is that important?  These CCR's are notorious for generating spurs on transmit.  This can't really been seen with a watt meter, you have to have a spectrum analyzer to see them.  But if there are 10 spurs at .5 watts each and a center carrier frequency of 5 watts.  The radio is ONLY producing 5 watts on the frequency of operation, the other 5 watts of signal being produced is effectively noise.  This is how the CB guys would get the big silly power numbers out of a CB radio back in the day.  THe meter being used was seeing the primary carrier AND the second harmonic at double the frequency that was a couple watts.  The meter just put in on the display.  This is why a BIRD watt meter is more accurate.  THe slugs are specific to frequency range.  Outside that range, they don't work well and don't display the spurs.  Of course no CB shops had spectrum analyzers that were actually in use, because they would show this and someone knowledgeable would see their BS for what it was.

Same thing here with the 15 watts out of a portable radio.  It might show it on the meter, but it's probably not all on the correct frequency, and the radio will NOT operate like that for very long.

 

[SteveShannon]

The thing is it takes a lot of transmitted power difference to result in a very audible reception difference.  This video really demonstrates that point. The presenter demonstrates the difference in received signals at different power levels starting very low (5 watts) and goes all the way up to 600 watts where the signal is received with full quieting. This is for SSB rather than FM and the distance is heard over a 600 mile distance: 

 

[Socalgmrs]

I’m addition to the other bad things mentioned a some point rf starts killing your rain cells and causing cancer.  That point is around 10w soooo?