HF Operation From Low ASL (Above Sea Level) November 30th, 2014
Many newcomers to ham radio make the assumption that height above sea level is important. Well so it is on VHF, but that is by no means true for HF. How can that be?
Well let us look first at VHF. The important part of radiation from a VHF antenna is the part that is horizontal or near horizontal. In other words, the part that runs parallel to the Earth’s surface. For maximum distance your antenna needs to be as high as possible and likewise your location needs to be high above surrounding ground. That way your horizontal signals will travel furthest. This is the most common mode of propagation used for normal VHF contacts. In fact all VHF antennas also radiate energy at higher angles, but this energy usually travels out into space to be lost forever. There are rare occasions when some of this energy is reflected back to Earth. But by and large, the most successful operators have high antennas on high ground.
When it comes to HF propagation, almost the reverse is true. The horizontal signals are quite quickly attenuated, whilst the signals travelling at angles upwards from the Earth are, for most of the time, reflected back to earth at significant distances away, frequently thousands of miles. This kind of propagation benefits little from antennas on tops of hills. Stations on lower ground are not disadvantage, and in many cases there may be a benefit. Low ground frequently means moist ground and this gives better ground reflection and stronger signals. So on HF a low sited station is certainly not a disadvantage.
But, do not confuse this with antenna height above the immediate ground beneath it. The higher the antenna above the local ground, the better the performance because the angle of radiation is lower as antenna support height is increased, and therefore there is a longer skip distance before the signal is bounced back to Earth.
These are somewhat simplistic explanations, but hopefully helps to encourage those potential HF operators who thought they were not likely to achieve good performance because they were not located high enough above sea level. Peter G3OJV
Elecraft KX3 Battery Life November 29th, 2014
Several customers have recently asked the same basic question: “if I run my KX3 from an al battery, how long will it last?” And the answer always begins, “well it depends . . . ”
I use 2Ah AA cells within the KX3 transceiver. On receive it draws around 200mA. That means around 10 hours on receive. On transmit running 5W the peak current drawn is 1 Amp. But if that is the peak, the average is around 600 mA. Now we can refine this even more because there are pauses between words and so the average can fall below 500 mA. So 500 mA is a generous approximation. That equates to transmitting for up to 4 hours. Let us build in a safety margin and go back to 600 mA. That is still over 3 hours transmit. As we normally spend more time listening than transmitting, it would be realistic to expect 6 hours plus from a new set of cells that are fully charged. Pretty impressive!
Many owners don’t realise that the KX3 has a super battery saver mode when the power is reduced to 3W or less. In which case the life cycle us even greater. Peter G3OJV