ADF :- Automatic Direction Finder
ASSALAM O ALAIKUM
AUTOMATIC DIRECTION FINDER
THIS IS MUHAMMAD FAROOQ ATHAR TO STATE YOU ABOUT ............
ADF :
It is the instrument which is used to findout the direction or the right path as per with the rules of Navigation Guidence and Controls.....
By this instrument we can easily handle the direction the controls and the guidence navigation....
Handheld DIrection Finder which can be used to localize both AM and FM carrier-based sources using a single connection to the antenna input of an FM receiver tuned to the frequency of interest in the range of 45 to 450 MHz. It has been designed for bare-bone functionality as well as low power consumption, simplicity, and economy.
Except for adding a handle, fabrication is minimal. Two open-loop antennas are made from coat hanger wire bent into halves of a "bow-tie" shape and mounted directly to the circuit board.
The coax downlead is connected to an FM receiver and detects the carrier regardless of whether the transmission mode is AM or FM. The unit is switched on (UP) and rotated for a null in the audio tone that it adds to the audio coming out the receiver. The signal direction is perpendicular to the plane of the antennas. There is 180-degree ambiguity, but this is not a problem in actual use because multiple "bearings" must be taken anyway in order to establish a "fix" on the location. Once close in, the operator works toward the general sense of the direction, and again the ambiguity is not a problem.
The 3-position switch is moved DOWN to stop the tone but still keeps the antenna activated for monitoring and standby purposes, --or it is moved to the CENTER position to shut off the unit. Refer to the extensive discussion in the manual which describes construction variations, and the concepts behind the design.
THE OVERVIEW WITH TECHNICAL EXPECTS:
The electronic circuit is based on a design credited to Tom Feierabend SO/CM 03N18 circa 1979 which appeared in a manual published in May, 1980 by Van Field, DCP XVIII, entitled “VHF Radio Direction Finding Manual for Coast Guard Auxiliary Use”.
A similar circuit, referred to as the “Double-Ducky” direction finder (DDDF) designed by David Geiser, WA2ANU, is described in July, 1981 QST and reprinted in the 1983 ARRL Antenna Handbook.
The USCG AUX-03N18 version uses an LM555 driving two successive stages of 7404 TTL to provide complementary buffered outputs. Since TTL requires a 5-volt power supply, yet another IC, a 7805 or 78L05 is needed, to regulate the stated 6-30 volt input range.
One problem is that the LM555 does not easily put out a symmetrical square waveform, which is useful in this application. The antenna assembly consists of two vertical ½-wave dipoles (37” long) mounted 8” apart on a boom. This assembly is rather bulky and quite a bit of mechanical fabrication is required.
The QST circuit uses only one IC, the LM567 Phase-Locked-Loop Tone Decoder. This is a complex chip that contains an oscillator and other circuitry, including an output circuit which does put out a symmetrical square wave. However it does not have simultaneous complementary outputs. In the DDDF the single output is connected to the diode switches through a non-polar capacitor, and some adjustment is required to achieve the proper switching level. Data sheet specifications show that the LM567C typically draws 12mA. The antenna assembly consists of two “rubber duckies” mounted 10” apart on a 4.25” X 18.5” ground-plane. While the ground plane requires much less work to fabricate than the USCG-AUX circuit, two “rubber duckies” must be obtained.
HOW IT WORKS:
All three circuits described above are based on the same principle. An electronic switch alternately connects two antennas to the coax cable downlead going to the antenna input of an FM radio receiver tuned to the frequency of interest. First one antenna is connected, then the other, etc., back and forth with equal intervals. This is done at an audio rate, well within the audio bandpass of the receiver, and usually in the range of 400 to 1500 Hz. A good frequency is 1000Hz.
Of the two antennas, if one is slightly closer to the source, it receives the wave front slightly earlier in time (phase) than the other. There is a phase difference in the signal received by one antenna compared to the other. Since the receiver is being switched between the two antennas, the switching action imposes phase modulation on the incoming signal. This is detected in the FM receiver and is heard at the audio output as a tone equal to the switching frequency. The amplitude of the audio signal corresponds to the deviation, which depends on the physical separation of the two antenna elements, up to ½ wavelength. In other words, if the antennas are farther apart the circuit will impose a higher percentage of modulation or a larger deviation, producing a louder tone, but the modulating frequency will stay the same.
If the antenna is rotated so that the plane of the two elements is perpendicular or broadside to the direction of the signal, both elements receive the signal at the same time (phase) and there is no longer a difference in phase. Hence, the audio tone disappears. This is perceived as a rather sharp null in the audio as the antenna array is rotated into position perpendicular to the direction of the signal.
This type of direction finder has the disadvantage that it exhibits 180-degree ambiguity. However, it has several advantages:
1) It works on a nulling principle rather than a peaking principle. The null is sharp and much easier to detect than the peak from a directional or beam antenna.
2) When you null the superimposed audio, you are not nulling the carrier. This is unlike a conventional loop antenna or cardioid array, which nulls out the carrier. The problem with carrier-null, is that as you get closer to the null, the signal you are trying to hear in order to null out, is getting harder to hear! Also, when you null the superimposed audio, you can still hear the audio coming from the source.
3) Since audio is being nulled, the operator does not have to watch a field-strength meter. He only needs to listen, which is something he can do while driving, riding a bike or walking.
4) Since this method uses phase information, it works well with strong signals, so no attenuator is required. (By comparison, the signal from directional gain antennas must be progressively attenuated to keep the receiver RF within the range of the S-meter.)
REFERENCE INFORMATION:
The HANDI-Finder® is an evolving project which underwent several changes (hopefully for the better) during the early stages. However, the basic circuit remains essentially the same. This manual might be supplied to help you work on an earlier unit, as far back as 1986. If you have a model that does not correspond to the pictorial description in this document, you should be able to identify the components with only minimal tracing of the etched circuit pattern.
Your unit may also have component values that differ from the schematic. If you did not buy a kit, you may have obtained the circuit board and documentation from separate sources that copy and distribute such things and try to make them “public domain”.
The circuit board versions are identified by a prefix letter “A”, a 6-digit date code (YYMMDD), and an optional suffix. (The suffix, if present, indicates very minor changes.) As of this writing, the numbers used are: A861003, A860102, A870122, A890422, A01110, and A031123.
In general, if the board has a date code earlier than the documentation, the component values in the documentation take precedence, provided the integrated circuit type is pin-compatible. If the board has a date code later than the documentation, and/or a different IC pinout, you would do well to send a self-addressed-stamped-envelope (SASE) to the distributor for an update of the layout and parts list. Of course, be sure to furnish the number on your board, so you will be sent the correct information. Please indicate whether the RALTEC® or other trademark is present and we will help you figure it out. Try contacting the author at ral@ralserve.net. (If you have trouble, you can also find the author’s current snail mail and e-mail addresses through the internet Ham-Call database.) For information, try the website handi-finder.com.
CHECKING THE COMPONENTS
If you received this instruction manual as part of a packaged kit along with the circuit board and loose components, unpack all the parts and check the quantities and values against the Component Parts List before you do anything else because some parts have the same value but different mounting positions and lead lengths. Before proceeding with actual construction, it is suggested that you read this manual to see if there are any changes you would rather incorporate right away. Then proceed with “ASSEMBLING THE KIT” which is located at then end of this discussion.
NO PILOT LIGHT:
Considering that a small transistor radio draws about 10mA, it can be seen that the battery will last quite a while if the user remembers to turn it off. Unfortunately a pilot light would be self-defeating, since it would draw 5-10 times the current of the circuit itself!
How many times have you forgotten to turn of your HT? After a while you finally learn to double check. With the HANDI-Finder® it should even be a little easier, because you will probably be disconnecting it from your radio or otherwise storing it at the end of a “DF’ing” session. That action should help remind you to check that the switch is off. Better yet, remove the battery. That’s why we have included a top grade battery holder in the bare board version.
ON-OFF SWITCH STATUS INDICATOR:
For models prior to A890422, here are a couple of things to help you tell OFF from ON in the absence of a pilot light. First, the “ON is UP” convention has been followed. This is fairly commonplace on most equipment. Second, you can make a “passive” indicator by using a dot of bright paint, for example, typewriter correction fluid such as “whiteout”. Push the slider to the ON position, then paint a small dot on the lower part of the slider that is now exposed. Let the paint dry thoroughly so it doesn’t rub off. When you slide the switch to OFF, the painted part should be hidden; when ON, it should be visible. On Model A890422 and later the switch has 3-positions: OFF is in the center, UP is for DF’ing, and DOWN is for straight receiving or Standby. (Notice the design date is embedded in this code as YYMMDD.)
ON-OFF SWITCH MECHANICAL VARIATION:
There are a couple of subminiature slide switches available from “experimenter” sources such as Mouser and Digi-Key, but they differ slightly in the spacing and style of the connector pins. Circuit boards A861003 and A860102 used the CW Industries switch available from Digi-Key as SW103-ND.
Starting with circuit board A870122, the switch pads were made larger and the spacing changed to use the Mouser 10SM007 or 10SP001. The larger pads allow larger holes to be drilled to allow for the wider flat pins. If the switch you have does not go right in, do not force it. Study the problem and carefully enlarge the holes only where necessary. A small modeling file is handy for this purpose. Don’t make the holes any larger than necessary, or you will have trouble bridging the gap and getting a good flow joint when soldering. When you do solder it into position, use ample solder and heat it enough so the solder surrounding each terminal flows evenly into a nice even form similar to an “Indian tepee.” A890422 and later use a DP3T switch with 6 pins, which will not fit the previous models, but that gave the ability to add the “standby” position which is very useful.
BATTERY HOLDER:
The 9-volt battery holder is fastened at one end by soldering the two terminal tabs that pass through the board. The other end of the frame can best be fastened by using 1/8” diameter “pop-rivets”, but you may alternatively try hot-melt glue, epoxy, small screws, etc. However, make sure that whatever you use won’t protrude and prevent the battery from seating in the clip.
ANTENNAS:
The adf is quite versatile in the way it can be used with different kinds of antennas. First of all, you can get it running immediately without extensive fabrication because two simple wire antennas can be attached directly at the circuit board. For 150 MHz, take two EQUAL lengths of stiff wire about 19 to 20 inches long and bend each one into a neat square “U” shape. The bottom of the “U” should be about 6”. Form the ends into a hook and fasten them to the screw terminals on the circuit board. Looking at the component side of the board, you will see there are three terminals along the left side and three along the right side. Fasten one end of one antenna to the very top terminal on the right side. Fasten the other end of that same antenna to very bottom terminal on the same side. Then repeat this procedure for the left side.
Note that the bottom terminals are merely mounting points. They are electrically isolated. On some board designs there are circuit pads to allow installation of a grounding jumper. DO NOT INSTALL THIS JUMPER! It is desired that the antennas be open loops. If you ground the bottom of the loop, you will create a closed loop that will cause a carrier null in the direction of the signal. This is not desirable. On later circuit boards provisions for grounding was eliminated to avoid confusion.
The wire you use should be thick enough to provide desired rigidity, but thin enough to allow fastening under the screw terminals. If it is too thick, you might be better to first solder on some spade lugs or similar terminations. Of course, it helps if the wire is a good conductor, but steel coat-hanger wire or welding rod will work satisfactorily.
Note the ACTIVE ELEMENT of each antenna in this application is the vertical part of the open loop supported in space by the horizontal part. A greater separation of the vertical elements will produce a larger deviation and more audio. However, the longer a vertical element is, the more signal it will receive, provided there isn’t some gross impedance mismatch. This shows up as more carrier, better quieting, or a stronger S-meter reading. Of course, when that vertical section is maintained in space by an unshielded horizontal section, determining the resonance or tuning gets very complicated. Also consider that the horizontal part does receive some signal, and this degrades the intended signal. Therefor, larger loops may work worse. Feel free to experiment; that is the whole object of this project!
Alternatively, the circuit board is designed to accommodate connections by coax cable to other kinds of antenna arrays. Just below the top antenna mounting screw on each side, is a ground screw. This is not used with the open loop antennas, but is used for the coax shield. Thus, if you do wish to make a “Double-Ducky” direction finder as described in the ARRL Antenna Handbook, you can connect the two equal-length coax cables to the HANDI-Finder® circuit board. Similarly, you can fabricate the dual half-wave vertical dipole array described in the Coast Guard Auxiliary Manual and run it with the HANDI-Finder® board.
One suggestion for a more extravagant system is to position two multi-element Yagi antennas with vertical orientation at opposite ends of a horizontal boom. Support the boom at its center on a vertical mast so that it can be rotated. Use equal lengths of coax from each beam and connect them to the HANDI-Finder® board which should be mounted in a protective enclosure at the center of the boom. The beams will give greater forward gain and reduce the 180-degree ambiguity. It is just a little hard to use with the mobile.
FOR ASSEMBLING CHECKOUT THE FOLLOWING STEPS:
1) Check the circuit board and make sure all the holes are drilled and it is otherwise finished and ready to accept the parts.
2) Having read the discussions about the ON/OFF switch, locate that item and make sure that the type you have does indeed fit the hole pattern on the circuit board. Do not install it yet.
3) Locate the integrated circuit socket, carefully straighten the pins, and insert it onto the component side of the board with the proper orientation. You may have to study the IC socket to determine how its design denotes the position of pin 1. Some sockets have a beveled corner at pin 1. Others have an indentation at the end between pins 1 & 14, some are not clear!
Note, for packing purposes, the IC may have been installed in the socket. It is NOT necessary to remove it, unless you can see it has been inserted in the socket incorrectly. The IC will incur much less handling and there will be less chance of damaging it if you just leave it in place when you solder the socket onto the board. Make sure the socket is properly oriented and seated flat against the board when you do the final soldering.
4) In the following order, mount the diodes, resistors, and capacitors, starting with the smallest parts first. If you have only one capacitor with long leads, SAVE that, and use the precut ones first. There is one location that needs the capacitor to be formed with longer leads.
5) Examine the ON/OFF switch and make sure that the terminals are clean and not tarnished, before soldering. If needed, carefully scrape them with a small hobby blade. Then mount the switch and solder it in position. The 6-pin switch also requires that the two diagonal frame tabs be soldered as well. NOTE: if you later use a solvent to remove flux from the board, be especially careful not to get any into the switch. Some literally melt. Some have four frame mounting pins. Carefully clip off only the two diagonal pins that prevent insertion.
6) Refer back to the discussion about the battery holder and mount that item.
7) Prepare the end of a length of RG-58/U or the miniature RG-174/U and attach it to the board. Note that the hole for the shield should be 1/8” so that the shield can fit through. The excess braid is cut off so that only about 3/16” lies flat against the circuit foil where it is soldered down. Install a nylon cable tie through the holes provided in the circuit board. Pull it tight so that it anchors the coax securely against the board to prevent flexing at the cable end. This is known as a “strain relief.” Clip off the excess. Depending on what type of handle you use, you will need to figure out how to route the coax so that it crosses to the center and comes down the handle equidistant from the two antennas for best symmetry. Later circuit board layouts have the coax routed down the centerline in the solder side of the board on the side opposite where the handles should be attached.
8) Slide on “tinnerman” nuts (if such nuts have been supplied) at the four points used to attach the open loop antennas. These are the two top-most and two bottom-most locations.
9) Fashion two open-loop antennas according to the instructions described previously and attach them to the board using the 6-32 x ½” screw hardware. That’s it! Refer to the section “TRYING IT OUT”.
The manual includes discussions of several other options and variations in the way the unit can be wired.
NOW AT THE END CHECKOUT THE VIDEO THAT HOW IT WORKS AND FOR WHAT PURPOSES IT IS USED IN THE AIRCRAFT OR MODERN VEHICLE :
GOOD LUCK !
posted by Unknown @ 9:02 AM
