How much voltage would I loose on 5v linear power supply 5m cable to my LNA?

To work this out properly we need one key missing detail: the cable conductor size (wire gauge or cross-section) and ideally the current drawn by the LNA.

That said, I can give you realistic ranges that usually apply to LNAs, so you can see whether you’re in trouble or not.

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Typical LNA assumptions (reasonable defaults)

Most radio astronomy LNAs draw:

• Current: 50–200 mA
• Supply: 5 V DC
• Cable: two-core copper (power out + ground return)

Voltage drop depends on round-trip resistance, so the effective length is 10 m (5 m out + 5 m back).

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Voltage drop examples

1️⃣ Thin cable (≈ 24 AWG, ~0.084 Ω/m)

Common in USB leads or cheap hook-up wire.

• Resistance:
  0.084 Ω/m × 10 m = 0.84 Ω
• Voltage drop:
  • 100 mA → 0.084 V
  • 200 mA → 0.168 V

✅ Usually OK
⚠️ Marginal if the LNA really needs a clean 5.0 V

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2️⃣ Medium cable (≈ 22 AWG, ~0.053 Ω/m)

Better-quality power cable.

• Resistance:
  0.053 Ω/m × 10 m = 0.53 Ω
• Voltage drop:
  • 100 mA → 0.053 V
  • 200 mA → 0.106 V

✅ Very safe for most LNAs

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3️⃣ Very thin cable (≈ 28 AWG, ~0.22 Ω/m)

Found in cheap USB leads.

• Resistance:
  0.22 Ω/m × 10 m = 2.2 Ω
• Voltage drop:
  • 100 mA → 0.22 V
  • 200 mA → 0.44 V

⚠️ This can cause gain loss or instability in LNAs

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Practical radio-astronomy advice

For LNAs (especially at 1420 MHz):

• Keep drop < 0.1 V if possible
• Use 22 AWG or thicker
• Or send 9–12 V and regulate locally at the LNA
• Or use bias-T if the LNA supports it

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Quick rule of thumb

If your cable is:

• USB-thin → expect 0.2–0.4 V loss
• Decent power wire → expect <0.1 V loss

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