Why Choose a +45 dB Line Isolator? The Benefits Over Standard Chokes

One of the most common questions we get is: "Why would I choose a +45 dB line isolator over a standard +25 or +30 dB one?" After all, if some common-mode suppression is good, isn’t that enough?

The short answer is: not always. And in many stations — especially high-power or problem-prone ones — the extra attenuation makes a real-world difference. Here’s why:

1. The Suppression Gap Is Massive

  • +25 dB = ~316× suppression
  • +30 dB = ~1,000× suppression
  • +45 dB = ~32,000× suppression

This is a logarithmic scale, meaning the jump from +30 dB to +45 dB isn’t minor — it’s over 30× more effective at stopping common-mode currents. This extra suppression can make the difference between minor improvements and truly solving persistent RF issues.

2. More Reliable RF Interference Elimination (1.5 to 30 MHz)

If you’re dealing with any of the following between 1.5 MHz and 30 MHz, a +45 dB choke significantly outperforms a +30 dB unit:

  • Instability in auto-tuners
  • False triggering in digital modes (FT8, RTTY, PSK)
  • USB disconnection or PC glitches during TX
  • Local equipment picking up your RF unintentionally

The +45 dB isolator greatly reduces the chance of these issues recurring — even at full legal power and with long coax runs.

3. Lower Receive Noise Floor

In urban and suburban areas, man-made noise often couples onto your coax shield. That common-mode noise rides directly into your receiver. A +45 dB isolator can dramatically reduce this conducted noise, especially noticeable on 160, 80, and 40 meters.

Standard chokes might help a little — but the high-attenuation model can lower your noise floor by several S-units depending on the environment.

4. Improved System Stability

Inconsistent SWR readings, unstable tuner behavior, or devices acting differently depending on the frequency or mode? These are often signs of insufficient isolation.

A +45 dB choke offers much better stability and predictability across bands, especially in multi-band systems where common-mode behavior varies with frequency.

5. Ideal for High-Power Stations

Running 400W, 1kW or more? The risk of RF feedback and re-radiation increases significantly. A +25 or +30 dB choke may still allow common-mode currents strong enough to:

  • Interfere with nearby electronics
  • Stress sensitive components

A +45 dB isolator provides a much deeper buffer, helping you run clean even at full power.

Final Word

While a +25 to +30 dB choke might be “enough” for basic setups, anyone serious about minimizing RFI, lowering noise, and protecting equipment within the 1.5 to 30 MHz range should consider a +45 dB line isolator as a key part of their station infrastructure.

It’s not just more suppression — it’s peace of mind, stronger receive, and rock-solid performance across all bands and power levels.

Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.