The vertical dipole mode has lower noise floor (with 3-6 dB) and thus it is more sensitive in such conditions.

Our observations show that the small active loop antenna sensitivity when placed at low height is limited by its internal noise in quiet rural places at daytime when the bands below 10MHz are almost closed and the atmospheric noise is very low. Also directional antennas have much better reception for signals coming from certain directions etc. Of course, high placed full sized antennas have better reception for low angle signals and field intensities are probably higher due to the clear space around them. If this requirement is fulfilled the small active antenna will produce comparable S/N levels compared to a full sized antenna.

(This is the good old rule – if we connect the antenna to the RX input and the noise increases that means the RX has sufficient sensitivity). The atmospheric noise at the output of a good active antenna should be at least several dB above the output internal noise of the antenna amplifier. The atmospheric noise at the usable frequencies is the limiting factor which limits the RX sensitivity. What is the real sensitivity of the active antenna? in Description and Specification section and in Q&A(4.3 Cable) section. When using long length of the FTP cable it might be necessary to increase the sensitivity of the RX. Most of the RX or TRX have preamplifiers and their MDS is lowered up to -140 dBm. This sensitivity is very common between commercial equipment. The gain of both amplifiers is set in a way that the internal output noise of the amplifier (no antenna connection) to be greater with 8-10 dB than the input noise of the receiver with MDS of -128 dBm 500Hz BW. 12.2 to 12.8 V is the usual voltage given by the charged lead acid accumulators and they can be used to supply the amplifier if the cable is not very long. The amplifier can be fed also by accumulator battery. There is an internal 7810 IC (10 V) stabilizer in the amplifier and if the input voltage is too high the temperature might exceed the permitted limits. Be aware that there is also a voltage drop in the FTP cable, so higher voltage should be used. (the DC PS voltage at the terminals of the RJ45 connector on the amplifier board should not be less than 12.1 V and more than 16V because there are 2 chokes between the RJ45 connector and control points with voltage drop of 0.3 V).

The maximal voltage at the amplifier control points should not exceed 15.7 V. Measured minimal voltage between control points CP8 and CP11 should not be less than 11.8 V. What are the requirements for the DC power supply (PS) voltage?

Active dipole antenna op amp