Hi topband lovers, The basic concept that explains how power and signal to noise ratio works on low band is very simple. On high bands we need the signal to bounce back to the Earth. Without ionization, the signal does not reflect back and power does not matter, 1w 100 w or 10 Kw won't make the signal to bounce back to the Earth.
In last month's large contest, most stations worked more QSO's on 160m than 10m. The MUF was not high enough to bounce the signal back. Contrary to high bands ( 20 to 10 m ), on low bands the signal always bounces back to the Earth because the MUF is always above 3 MHz, even on the solar maximum the MUF is above 160 or 80m most of the time. Now that we are just entering solar minimum we can see that happening every day. If the signal on low bands always bounces back to the Earth we can say that we have propagation all the time on 160m, or most of the time on 80m, the issue here is just attenuation. Attenuation is the name of the game, and it plays on both sides, A to B and B to A location, Initial power minus the attenuation is responsible for whether the arrive signal is heard or unheard, local noise at the receiver side will compare to the arrival signal to make a QSO possible or not, if the signal is 3 db above noise level QSO is possible on CW, 8db above possible on SSB. The bandwidth is very important. On digital modes the real BW is the calculation inside the software that can result in less than 1 Hz of bandwidth. JT modes can hear below noise floor (500 Hz) because of that, the real BW is just few Hertz. If the signal always arrives at B, any one db power increase at A will increase the signal to noise ratio at B by one db. If your signal is at noise level at B location and you increase 3 db of power, 100w to 200w the operator at B will be able to copy you. If your signal is already 10 db above noise, increasing the power will just actuate the radio AGC and there won't be any real gain besides comfort. The local noise can be very different at A or B, A could be in a city lot and B could be in a very quiet Island with no manmade noise, B can use a narrow RX antenna with high RDF and the noise floor can be 10 or even 20 better than A. Most people call this one way propagation, but in reality it is just power budget difference at each location, local noise on the receiver side plays as much as power used on the transmit side. My take is that we can work on both aspects , reduce local noise with good directivity on the RX antenna, but power is limited by law, and ethic! A low band station with a RX near 12b RDF, 80 to 70 degrees front lobe and a KW can work 100 countries on 160m during any two month period of any year, and can work 150 or more countries during a 12 month period any year of the solar cycle on 160m. During solar minimum it is common for a good contest station on 160m to work 100 countries during a contest weekend. Understanding this basic concept can help any low band operator improve his or her performance. My two cents N4IS JC _________________ Topband Reflector Archives - http://www.contesting.com/_topband