Description
A weak RF signal can hide in the noise floor of a spectrum analyzer. The Keysight 87405B preamplifier lifts it out. This compact gain block covers 10 MHz to 4 GHz and adds 22 dB of gain, with a noise figure of 5 dB and integral bias regulation.
Why put a preamp in front?
An analyzer’s own noise sets the smallest signal you can see. A low-noise stage ahead of the input raises the signal before that noise joins the chain. As a result, low-level emissions, leakage and faint carriers become easier to read. However, extra gain also brings strong signals closer to overload, so watch the total input level.
Keysight 87405B preamplifier specifications
| Parameter | Value |
|---|---|
| Frequency range | 10 MHz to 4 GHz |
| Gain | 22 dB |
| Output power | 8 dBm |
| Noise figure | 5 dB |
| Bias | +15 V at 80 mA |
| Design | Compact gain block with integral bias regulation |
Typical uses
- Better spectrum analyzer sensitivity for low-level signal work.
- Extra gain at the test port in component and receiver checks.
- Portable, rack and automated RF systems that need a small inline stage.
In the photo, the body carries a coaxial connector at each end and a grey bias lead with its own plug. So it sits inline between a cable and the instrument.
Bias and good habits
The 87405B needs +15 V at 80 mA, and its built-in regulation steadies that supply inside the unit. Still, confirm your bias source before you connect it. Also respect the maximum input marked on the body. Because the output tops out around 8 dBm, the part suits small signals, not power work.
How to order
Lost in HCM rents and sells the Keysight 87405B preamplifier and arranges service on request. SMK Vietnam publishes this page; the supply and the terms come from Lost in HCM. First, note your analyzer model, band of interest and bias plan. Then request a quote from Lost in HCM. You can also look at other RF and microwave accessories, visit the Keysight website, or contact SMK Vietnam.
87405B FAQ
How much gain does the 87405B add?
It adds 22 dB across 10 MHz to 4 GHz, with a 5 dB noise figure.
What bias does it need?
It runs on +15 V at 80 mA. Ask Lost in HCM which bias source suits your setup before you order.
Can it boost a transmitter signal?
No. With about 8 dBm of output power, it works as a small-signal preamp rather than a power amplifier.
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