What is difference between balanced and unbalanced on microphone input?

This is one of those things that sounds boring until it suddenly explains all your noise problems.

Alright — let’s break it down in human terms.

🎙️ Unbalanced microphone input

An unbalanced connection uses:

• 1 signal wire
• 1 ground/shield wire

That’s it.

The signal travels down one conductor, and the ground acts as the return path.

Common example:
¼” TS jack (like guitar cables).

The problem:

Any electrical noise (mains hum, RF, lighting buzz, computer hash) gets picked up by that single signal wire. Since there’s no clever trick to remove it, the noise just rides along with your mic signal.

Fine for:

• Short cables (a few metres)
• Instruments
• Home setups

Not great for:

• Long runs
• Low-level mic signals
• Electrically noisy environments

And since mic signals are tiny (millivolt level), they’re especially vulnerable.

🎙️ Balanced microphone input

Balanced is where the clever engineering happens.

A balanced mic connection uses:

• 1 positive signal wire (+)
• 1 inverted signal wire (–)
• 1 ground/shield

So the same audio signal is sent twice:

• One normal
• One flipped upside-down (inverted)

Why this is genius

Any noise picked up along the cable affects both wires equally.

At the input stage (usually a differential amplifier), the inverted signal gets flipped back the right way and combined with the other one.

What happens?

• The audio adds together ✔️
• The noise cancels out ❌

That’s called common-mode rejection.

This is why balanced lines can run:

• 20–100 metres
• Through lighting rigs
• Across stages
• Past transformers and dimmers

… and still sound clean.

🔌 What connectors are which?

🎤 Why it matters for microphones

Microphones output very low voltage signals.

Unbalanced mic cables:

• Pick up hum easily
• Lose high frequencies over distance
• Can create ground loops

Balanced mic cables:

• Much better signal integrity
• Essential for studio/live sound
• Required for phantom power (48V for condensers)

🧠 Quick mental model

Think of it like this:

• Unbalanced = one person shouting through a noisy crowd
• Balanced = two people shouting the same thing, one upside-down, and the crowd noise magically disappears when combined

Pretty slick.

Which is best for RF inputs in radio astronomy?

Ahhh okay, now we’re in your territory 😄

Short answer:

Neither “balanced” nor “unbalanced” in the audio sense is what really matters for RF in radio astronomy.
What matters is impedance control, shielding, and common-mode suppression.

But let’s unpack it properly.

📡 For RF inputs (radio astronomy front ends)

In practice, almost all serious RF systems use:

Unbalanced coaxial transmission lines (usually 50 Ω)

Examples:

• RG-58 / RG-213
• Semi-rigid coax
• LMR series

Why?

Because coax gives you:

• Controlled impedance (50 Ω or 75 Ω)
• Excellent shielding
• Predictable behavior at high frequency
• Low radiation and low pickup
• Compatibility with LNAs, filters, SDRs, spectrum analyzers

Your SDRplay, spectrum analyzer, LNA — all are 50 Ω unbalanced systems.

🤔 But antennas are often balanced…

And this is where it gets interesting.

Many antennas are naturally balanced:

• Dipoles
• Yagis
• Loops

But your feedline (coax) is unbalanced.

So what do we do?

👉 We use a balun (balanced → unbalanced transformer).

Without a balun:

• The coax shield becomes part of the antenna
• You get common-mode currents
• Pattern distortion
• Extra noise pickup
• RFI coupling

In radio astronomy, that last one is deadly.

🧠 So which is “best”?

For radio astronomy:

✅ Balanced antenna

✅ Balun at the feedpoint

✅ Short, well-shielded 50 Ω coax to LNA

✅ LNA as close to antenna as possible

That’s the gold standard.

📻 Why coax wins at RF (especially weak signals)

At 1420 MHz (your hydrogen line obsession 😄):

• Mic-style balanced twisted pair would be disastrous
• Radiation loss would be huge
• Impedance mismatches would wreck SNR
• Shielding would be poor

RF systems care far more about:

• Standing wave ratio (SWR)
• Noise figure
• Return loss
• Common-mode rejection at the antenna

Not the audio-style balanced/unbalanced distinction.

🔬 In radio astronomy specifically

What matters most:

1. Lowest possible system noise temperature
2. Good impedance match (minimize reflections)
3. No common-mode pickup on feedline
4. Stable gain
5. Good grounding scheme

Balanced lines can be used (e.g., open-wire, ladder line), but:

• They’re rare above HF
• Mechanically awkward
• Susceptible to environmental changes
• Hard to shield

For weak-signal microwave work, coax + balun is king.