Hydrogen Line (1420 MHz) Pre-filtered LNA

Jarek presented his work at the Canada Wide Science Fair on the use of Software-Defined Radio to detect 1420 MHz radio waves from outer space.

In his words “A big problem has been the high cost of radio astronomy equipment with big antennas and expensive hardware. Now with computers and software defined radio there is a new age of amateur radio astronomy growing. My project will aim to demonstrate this low cost radio astronomy”.

Jarek used our 40 dB LNA as a pre-amplifier. Since then we have also introduced a new pre-filtered LNA for this application. You can read more about it here. We also have a version with a built-in Bias Tee.








What is a Low Noise Amplifier?

A low noise amplifier (LNA) is an electronic device that amplifies weak signals at its input without adding significant noise. These amplifiers are typically used in receivers. For LNAs the most important specifications are:

  • Gain
  • Noise Figure
  • Linearity


The LNA’s gain refers to its ability to increase the value of the input signal. It is most often specified in dB. Typical gain values for an LNA are between 10 and 30 dB.

Noise Figure

Noise figure provides a measure of the noise contribution due to the LNA itself. In the picture below, the LNA amplifies both the signal and noise present at its input equally. In addition, the output includes noise due to the LNA. This in turn reduces the signal-to-noise ratio. A good LNA contributes very little noise to the overall picture.



The linearity of an LNA is a measure of its ability to amplify the signal without distortion. When an LNA is operating linearly, the output power in dB is the sum of the input signal and the gain.  However, as the input signal level increases beyond a certain point, the output starts to level off and the LNA is no longer linear.

In the picture below, the LNA is operating linearly when the signal present at its input has an amplitude of -60 dBm. However, as the input signal is increased to 0 dBm, the device is no longer linear, the output signal is distorted, the gain is no longer 20 dB and the output signal amplitude is only +5 dBm.


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Airband Filter


A new Airband bandpass filter centered at 128 MHz. The filter has a bandwidth of 20 MHz.  The filter is designed to reject strong signals in the adjacent FM band. Here are the specifications:

Frequency (MHz) Typical Attenuation (dB)
78 43
88 35
98 25
108 10
118 4
120 4
125 4
128 4
138 4
150 11
200 39


The filter is available on Tindie 

FM Notch or FM Band Stop Filter


An FM notch filter is used to reject strong FM signals in receiver applications. A good FM Notch filter will reject FM signals and have low insertion loss for signals outside the band.

This is a 9th order Filter with excellent rejection in the FM band. The filter works up to 3 GHz with minimal out-of-band insertion loss. This product is ideally suited for Ham radio applications and Software-defined radio receivers where typically there is minimal internal filtering. In the absence of a notch filter, FM signals can saturate the receiver. The specifications of this filter are comparable to ones on the market that cost at least twice as much.


Frequency (MHz) Typical Attenuation (dB)
55 1
75 4
80 8
88 60
98 85
108 25
150 0.8
200 0.5
1000 0.3
2000 0.9
3000 1.8

In Japan the FM band extends from 76 to 95 MHz while in North America it spans 88 to 108 MHz.

NOTE: Connectors are SMA-F

Buy it here.