In many wireless systems – for instance FM radio, TV, AIS, ADS-B an amplifier can be used to boost the signal and improve performance. So how about in the case of Helium – can an amplifier be used to increase the number and range of witnesses?
The quick answer is No
Before we discuss the reasons, let’s first cover some basics. Amplifiers are used to amplify or increase the strength of an RF signal. An amplifier only amplifies signals in one direction. The following picture shows an amplifier inserted between an antenna and a radio receiver (which could be an FM or ADS-B receiver).
The amplifier increases the level of signal received by an antenna. It is easier for a receiver to process a stronger signal than a weaker signal.
In the following example, the LNA is inserted between a radio transmitter and the antenna. Once again it amplifies signals at the RF input such that the signal emitted from an antenna will be stronger than if the LNA were not present.
In both the above cases, the amplifier only increases the level of signals present at the RF input. This is the case in both the examples above. An amplifier will not amplify signals that are injected at the RF output.
The Helium hotspot is a transceiver
Many of the radio systems we use – such as FM radio and TV – are receivers. In other words, they only receive signals. An amplifier can be used to increase signal levels at the receiver.
The Helium hotspot is a transceiver that both transmits and receives signals. Both of these operations are essential to earning HNT. To maximize the number of witnesses you would need to amplify both transmit and receive signals.
To amplify both transmit and receive signals, you would need to know when the hotspot is transmitting and when it is receiving. Based on the above discussion, when the hotspot transmits, you connect the RF port to an amplifier that increases the signal level in the outward direction toward the antenna. When the hotspot receives, you connect the RF port to an amplifier that increases the signal level into the hotspot.
Essentially, you would have to switch back and forth between two amplifiers or reverse the direction of a single amplifier.
Is there a device that does this? Yes there is and it’s called a Bi-directional Amplifier.
So will a Bi-directional amplifier work?
It really depends on the design of the amplifier. Some bi-directional amplifier designs require knowledge of when the hotspot is transmitting and when it is receiving signals. Since this information is not easy to determine from the hotspot, such a design will not work.
On the other hand a bi-directional amplifier that is automatically able to detect when a hotspot is transmitting and receiving might work assuming certain signal timing constraints in the circuit and the modulation scheme are met.
What if I use a Low Noise Amplifier between the antenna and the hotspot?
Unlike in an ADS-B or AIS system, you cannot simply connect a low noise amplifier to increase the reception range for reasons mentioned in this post. An LNA will not amplify in both directions and it will in fact attenuate transmit signals to a point where your beacons will not be heard by other hotspots.
If a Bidirectional amplifier works, is it legal to boost the signal in such a way?
The answer is no.
You can amplify a received signal and there are many amplifiers on the market dedicated to boosting signals for various applications. However it is illegal to boost the transmit signal as this would potentially exceed the FCC limit. As well, the Helium algorithm is designed to detect such situations and declares such events as invalid. Invalid means no HNT.
A Low Noise Amplifier cannot be used with a Helium hotspot to increase the number of witnesses. In this article we have provided some tips on how to maximize your HNT earnings.