Direction Finder

Frequency accuracy has been a topic of special interest to many amateurs and experimenters since the early days of radio. Until recently, the best frequency standard available to most hams was a crystal oscillator carefully adjusted to zero-beat with a station of known frequency, such as WWV.

This GPS receiver is powered by 2 AA batteries. They are only strong enough for the GPS to stay on for about two hours, and this seems like quite a waste. I would like to be able to use a larger battery, and sometimes even an AC adapter.

When designing an EIA-485 control bus to link widely separated machinery and process controllers, devising a scheme to control the repeaters can be one of the more awkward tasks. In long buses, bus segments are joined with repeaters if the distance exceeds the maximum allowed by one cable segment.

This application note will focus on a simple, low-cost, hand-held digital compass design using a Microchip PIC18F2520 microcontroller.

The µPC8211TK, µPC8215TU, and µPC8226TK are silicon germanium (SiGe) microwave monolithic integrated circuits (MMIC) designed as low noise, high-gain amplifiers for GPS and mobile communications. These ICs are manufactured using our 50 GHz fmax UHS2 (Ultra High Speed Process) SiGe bipolar process. The use of these three devices in evaluation boards implementing LNAs (Low Noise Amplifiers) at 1.575 GHz GPS is described in this document.

The goal was to make a compass sensor compatible with the RCX and have it only take one sensor input port to take a compass reading. We decided to use a Dinsmore analog compass part that has two outputs that need to be combined to determine the direction the compass is pointing. With our design, it takes two readings by the RCX to get one complete reading from the compass sensor.

This application note will focus on a simple, low-cost, hand-held digital compass design using a Microchip PIC18F2520 microcontroller.

The sensor used on the PC Board is the 1490 digital compass manufactured by Robson Company, see figure 2. This sensor is a solid-state Hall effect device. It is sensitive enough to detect the Earth's weak magnetic field. When rotated it can display the position of the four cardinal points on a compass, North (N), South (S), East (E) and West (W).

Many years ago I decided to build myself a Direction Finding (DF) system just after I had won my first VHF "fox-hunt" with the DF-Antenna in the Cambridge & District Amateur radio Club. I achieved all of the above criteria, although fitting to a car did require a roof rack to carry a 1000mm square aluminium or tin plate for the antenna array. If you have the time and money then make this plate bigger, if possible. 5-meters would be ideal for a home base.

The basic idea of the system is to use *two* additional GPS antennas. Antenna #1 is used to receive the GPS signal from the satellites, and is placed wherever it has a good view of the sky. Antenna #2 is used as a *transmitting* antenna, and is connected to antenna #1 via coax cable. The transmitting antenna is then placed close to the GPS receiver's own internal antenna, and the GPS signal is coupled into the GPS receiver's antenna through the air.

For the Garmin 45, GPS II, and some other Garmin units, there is a set of power & data connector/harnesses available. (Ham Radio Outlet and West Marine sell one cable only for $40, or the cable & cradle for $65, approximately.) However, the leads are long. Rather than cutting them down for our use, we recommend preparing the end according to the specification shown below, and then coiling the excess cable.

This is a project that I started back late 2003 when I just starting to learn PIC programming. I wanted to building something that actually did somthing useful. This project is based on a PIC16F84. I actually came up with this idea and then after doing some searching I found that a few people had the same idea. But, I wanted to build my own that I could call mine, developed by me.

The GPS interface can be fed in 2 ways: with a stabilized 5V supply or with a 10 to 25V unregulated DC supply. In both cases the power is fed into the RJ45 connector on point 8. Pin 7 is DC ground. The power supply current is first secured with a slow 315mA fuse (in socket). Then there is a Transzorb device to ground. This device is a short-circuit for reverse polarity voltages and for voltages above 27V. It causes the fuse to blow and in doing so, protecting the other electronics and GPS module.

Some Garmin GPS receivers are capable of running off external power ranging up to +32VDC or more, whereas others can only accept a maximum of +8VDC.

A strap-down inertial-navigation system uses silicon sensors to measure displacement without entailing the bulk and expense of moving parts or GPS receivers. For example, a three-axis accelerometer and three angular-rate sensors can determine the position and velocity of a vehicle such as a robot or radio-controlled aircraft.

This highly integrated GPS receiver IC improves upon earlier-generation devices by including more components in a smaller package with a reduction in power consumption.

APRS stands for Automatic Position Reporting System and now is taken to refer to a protocol that uses a subset of AX25 packet radio to provide a range of facilities not available to amateur radio before. The cornerstone of APRS is that the packets are sent using the BEACON text format - and do not require 'connects' to occur first.

Detects and counts inputs and outputs. Photoelectric detectors are usually unidirectional, i.e. they are able to detect when someone enters a particular area but not when leaves it. On the contrary, a system able to detect movement in both directions could be useful to control shops, rooms etc. If installed in a shop it could allow to know if all customers entering the premises have left them at the end of the day. Or, at home, it could be used to switch on the light (or any other electric device) when one enters the room and to switch off the electric device when he or she leaves it. Suited to control Lamps, Household Appliances etc.

Similar to the system used in modern aviation where an antenna array modulates the phase of an incoming signal. The commercial system is known as Commutated Aerial Direction Finding (CADF) where a ring of 18 identical antennas are each switched on in sequence, just like winding a rotary switch round and round so that one antenna is always connected to the receiver. Consider: