Low Noise Differential Amp Cuts Noise By ~100x

The LNA 10 is a stock item, available at https://www.alphalabinc.com/products/lna10/ Most oscilloscopes don't go below about 1 millivolt per division because at high frequencies (above ~1MHz), the thermal noise is a significant fraction of a millivolt.Thermal noise is much smaller at low frequencies, but common mode noise is usually also present. It is also typically around a millivolt, but it can be eliminated if a low-noise differential amplifier is used. This type of amplifier is almost never built into oscilloscopes because it would require shielding from the scope electronics and a separate power supply. Up until now, the circuitry for low noise amplifiers has also been quite expensive. Most scopes do have a MATH function, which allows two inputs to be subtracted from each other, emulating a differential amplifier. It turns out that this method is terribly noisy and doesn't help at all to reduce common mode noise. Instead of subtracting the two analog signals, they digitize the signals first and then subtract those from each other. They will typically digitize with a thousand levels or less, and the two gains are not particularly well-matched. Also, scopes can’t display details less than about 1/20 of a millivolt simply because of the limits of vertical gain. (If a digital scope went down to a vertical gain of 10 microvolts per division for example, the entire screen would just be noise.) Common mode noise occurs anytime an oscilloscope probe contacts an external circuit, even if the inner conductor of the coax cable is perfectly shielded by the outer conductor and that shield is a perfect conductor. The only way to eliminate this noise is by amplifying both inner conductor and outer conductor signals, and then subtracting them from each other in a perfectly balanced way. To get the best performance from an oscilloscope at low frequencies, but without using a differential amplifier, turn on the bandwidth limit, and also set the scope’s low pass filter or notch filter to the most restrictive setting tolerable. Also make sure that the ground of whatever device you're measuring is well connected to the ground of the oscilloscope, if possible. If a direct connection is not possible because there is a DC voltage difference, connect them through a large capacitance, such as 10 microfarads or more. The LNA 10 Differential amplifier has two inputs with low-noise analog amplifiers matched to better than one part in 100,000. It is used up to 1 MHz, and has a continuously tunable low pass output filter from 1 Hz to 1 MHz. It features RF suppression and partial isolation between inputs and outputs to suppress ground loops. It is powered by 12 volts DC (typically 30 milliamps). A classic transformer-type AC adapter is included (the more common switching-type AC adapters should not be used because they create some noise). The included adapter is correct for the plug style and voltage for whatever country it is shipped to. This device can also be powered by an external 12V battery (not included).