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All, Education

TV Signal Power Units Explained

TV Signal Power

How strong is the signal in the air where I am? Since the government wants you to watch TV, the FCC provides this handy tool online:

FCC TV Channel Signal Power Tool

“dBμV/m”, Decibels, Signal Strength, and Confusing Units

The FCC’s site uses the unit dBμV/m or “decibel microvolts per meter amplitude” for signal strength. This is really a debacle of a unit. Units like this prevent people from understanding physical concepts, make people hate science in school, and even prevent technicians and probably many engineers from understanding the underlying concepts of their daily work (in my opinion). The proper way to write this unit is “dB (re: 1μV/m)” which means ‘decibels of power relative to a signal of amplitude 1 microvolt per meter.’ The unit “dBμV/m” further explained in 8 steps across two posts:

Step 1: your frustration at the many layers of confusion here are justified. Accept it and move on.

Step 2: Volts per meter. An electric field in the air is measured in volts per meter (V/m). For example, air breaks down at about 3 million V/m, very visible when lightning strikes. You might also say ‘3 megavolts per meter’ or ‘3 MV/m.’

Step 3: Amplitude. Any radio signal generated by an antenna for communication vibrates the electric field in the form of a sine wave at a specified frequency* and amplitude. The amplitude is the maximum at the peak of the sine wave.

*The frequency determines what channel the signal is and must remain within a tight range to not interfere with other signals in the air. Frequency is measured in Hz, MHz, GHz, etc. For example, 88MHz to 108MHz for FM radio. This is separate from the signal strength discussion.

Step 4: μ = micro. Being a Greek letter that looks like a ‘u.’ this is often written with a ‘u.’ It means ‘micro’ which is one millionth, so we are dealing with millionths of volts per meter, i.e. one-trillionth (1 / 1,000,000,000,000) of the unit used to measure air breakdown for lightning.

Step 5: Decibels Explained here.

In our case dB appears in front of μV/m, so you would think you would multiply by 10^(__ / 10) to get the μV/m amplitude of the signal. Nope, see the description of decibels and … in our case here, 100dBμV/m is a common strong signal level for TV stations and it means a signal with a power of 100dB above a signal with 1 μV/m amplitude. 100 dB  = 10^(100/10) = ten with ten zeros = 10,000,000,000 = 10 billion. Does that mean 10 billion microvolts per meter or 10,000 V/m??? No. Since the power of a signal is the amplitude squared, the actual amplitude in volts per meter only has to multiply by ten with five zeros to reach 100dB power above a signal of amplitude 1 μV/m, or 100,000 microvolts per meter = 0.1 V/m. Very manageable.

The signal received by an antenna is very weak compared to pretty much all signals powered by electronics on-site. The problem with receiving a weak signal is usually not that the signal is too weak to amplify, but that the noise has to be amplified with the signal and the signal can’t seen over the noise. There is always some level of noise and the signal has to be strong enough to be distinguished from the noise.

All, Electronics Repairs Attempted, Jobs

Job 3 – Plasma Cutter – Attempted

Customer brought in a plasma cutter that had popped when first powered on then did not power on after that.

I fixed the obviously-damaged arc drive lug, but the device still didn’t power on. It was not worth troubleshooting the rest of the device at the time as it is difficult to disassemble. No charge to the customer, but I probably should have checked the primary power section of the cutter first.

I didn’t take a picture of the final solder

The customer still has it. I may try troubleshooting again sometime …

All, Electronics Repairs Attempted

Data Recovery – Attempted

A customer brought in a hard drive hoping to recover the data. The data wasn’t worth paying a laboratory so she brought it to me for an attempt.

I was not able to recover the data, but I was able to diagnose the problem so for no charge she got the peace of mind of knowing the data was gone forever. The platter was badly scratched. I called the lab and they told me they couldn’t recover the data even for $100,000! Impossible?

All, Electronics Repairs Fixed

Megatouch – Fixed

A customer brought in a Megatouch (bar solitaire touch screen arcade game, see photo) in which he had replaced the permanent-memory battery and it would not power on.

I verified the battery charge level, configured the CMOS settings properly and returned it to him with brief “step-by-step” showing how to factory reset in the future.

Thanks for bringing it in!

All, Services and Products

Data Recovery

If I cannot recover your data, you don’t pay anything.

If I can recover your data, $50 charge for it and I give you a download link if the data is not sensitive, or a thumb drive if your data is sensitive. I make some quick attempts and may be able to recommend something.

The next option would be a laboratory. I can diagnose and try to give you some idea of your chances if you send your media to a laboratory.

If your data is worth $500+, I recommend Data Recovery Labs. They have a “no data, no charge” guarantee.

Last resort, I can open the drive and make an attempt. Opening a hard drive does not usually cause damage that would prevent a laboratory from recovering data if you decide to send it, but it can increase the recovery cost and the laboratory will know if the drive has been opened.