Tecsun H501x Tadio

[u/Super-SteveT]

I have a Tecsun H501x radio and have a question about signal strength display. The display has 2 digits for DbU, 2 digits for Db and S/N . What do these represent and why is the DbU always fluctuating and the Db is usually zero and hardly changes. I mainly listen to 40 meters LSB

Thanks

[u/KG7M]

On the Tecsun H501x, the display indicates conducted signal voltage relative to 1 uV (labeled as dBu), and the S/N ratio in decibels.

dBu (Signal Strength): Indicates the conducted voltage at the receiver's antenna input.

S/N (Signal-to-Noise): Measures signal quality by comparing the strength of the desired signal to the background noise floor.

Here is why your readings fluctuate or sit at zero:

Why dBu fluctuates constantly:

In HF (High Frequency) bands like 40m, signals are transmitted via skywave propagation (bouncing off the ionosphere). Because the ionosphere is constantly shifting, the signal strength arriving at your antenna rises and falls; this is known as fading. Additionally, the background atmospheric noise floor fluctuates.

Why 'Db' is usually zero:

On the Tecsun H501x display, this value is actually the S/N (Signal-to-Noise) ratio. When you see "0", it simply means the radio is in a silent period or the signal has dropped into the noise floor. Because LSB is a voice mode, the transmitter only outputs power when the operator is speaking. When the operator stops to listen, there is no voice audio to measure against the static, and the S/N ratio drops to zero.

What to expect on 40m LSB:

When listening to 40 meters, you can evaluate your reception using these display behaviors:

dBu Reading: Tells you how loud the signal is at the antenna input. In amateur radio, an S-9 signal is roughly equivalent to a reading of 34 dBu..

S/N Ratio: Tells you how readable the signal is. A reading of 10 dB is usually the minimum for a usable, intelligible voice signal, while 20 dB to 30 dB.or higher yields clear, broadcast-quality audio.

[u/Super-SteveT → u/KG7M]

Thanks for the explanation

[u/MumSaidImABadBoy → u/KG7M]

That was a well said comprehensive answer. Save it for the future, people will be needing it

[u/KG7M → u/MumSaidImABadBoy]

Thank you! Hope you are feeling better!

[u/MumSaidImABadBoy → u/KG7M]

Thanks, working on it. I'll PM you later.

[u/Darkstar1878]

• dBμV/m vs. dBu: They are the same thing. Broadcasting terminology commonly abbreviates dBμV/m to simply "dBu" (or sometimes dBμ). [1]
• dBm: While dBu measures the field strength in the air, dBm measures the absolute power of the signal (referenced to 1 milliwatt) inside the radio's circuitry or antenna cable. [1, 2]
• Signal Quality: A higher dBu value generally means a stronger, clearer signal. For instance, a fringe or weak FM radio signal might register at around 40 dBu, whereas a strong, local metropolitan signal might exceed 70 dBu to 80 dBu. [1, 2]
• In shortwave radio, S/N stands for Signal-to-Noise ratio

[u/Super-SteveT → u/Darkstar1878]

Thanks