Check out the Open Source Radio Telescopes Project. They use our Red LNA with a bias-tee in their Amplifier Box B.
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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
Gain
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.
Linearity
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
Spectrum Scanning Projects
Jon has some spectrum scanning projects in which he uses our LNA and FM notch filters. It’s interesting how he puts them into die-cast boxes. This is something we get asked about all the time. You can read about the projects here and here. Jon’s wireless projects are definitely worth reading about.
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.
SPECIFICATIONS
| 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.
FM reception using the 40 dB LNA and HackRF
David Goldstein sent in a few pictures that show FM reception without and with the 40 dB LNA. A significant gain in performance with the LNA. Thanks David!
Considerations when using high-gain LNAs
Some of our LNAs provide in excess of 40 dB of gain and operate over a wide frequency range. The primary application of these products is to amplify weak signals by increasing the signal-to-noise ratio at the receiver.
One important consideration when using these LNAs is that they amplify everything across their frequency range of operation. If your receiver does not have any front-end filtering, you might find yourself having to deal with a large assortment of strong unwanted signals. Most software-defined radios are wideband and therefore susceptible to these strong signals. A strong signal present at the input of a receiver can cause it to saturate and produce garbage at the output.
When using these high gain LNAs we recommend using a bandpass filter for your frequency range of interest. We have a number of such filters for GPS, 426, 433 MHz, 915 MHz and 2450 MHz bands: http://stores.ebay.com/gpiolabs/Bandpass-Filters-/_i.html?_fsub=28020158018
and we are looking to add new filters. If you would like to see us develop a filter for your application, get in touch.
