The following chart and the discussion after it were presented as hard copy at the APCO conference in 1985. Click to down load as a GIF Image. Its name is GRADED.GIF.
vector Vector Beam L-Per Adcock loop Doppler 'scope Finder SuperDF Ease of Use C B C D A A D A Multipath A B B F B B D A Sensitivity A A C F B/C A/B D A Accuracy C A B B C B C A Versatility D D C C C C C A Bat. life NA 8 hr NA NA NA NA ? 60 hr Speed C B C D A A+ B B Safety D B C D B B B A Maintenance A ? A A D F ? A Horz / Vert VH VH VH V V V VH VH Documentation NA ? NA NA ? ? ? A Base, mobile- BH BMH BH BH BM BM BH BMH in-motion, handheld Freq Range 5% 5% 10:1 2:1 3:1 108- 108- 100- 174 250? 1300 Cost $<100 $<300 Hand Hand $<300 $2000 $140 $217 to made made $775
A = Excellent B = Good C = Fair D = Poor F = Unacceptable NA = Not Applicable ? = Unknown
NOTE: The ratings given these systems are to some extent the subjective opinions of the writer. Explanations of rating criteria are given in the following paper, "RDF Rating Criteria".
(At the APCO Conference this section was not presented verbally, but was available as hardcopy.)
This section explains the criteria used to obtain rating shown on the chart titled "Grading of RDF Systems". In that drawing some of the entries are self explanatory. Those items are "Cost", "Frequency Range", "Battery Life", "Polarization", & "Base, Mobile, Handheld". The criteria for the remainder of the ratings are described below. Where the writer has no experience or data available, a "?" is entered.
Factors considered here are the number of separate manual or mental operations which must be done to obtain a bearing. The following items tend to reduce the ease of use:
These items lead to higher ratings:
The more sensitive a system the higher the rating. Systems which can DF signals so weak as to be undetectable by a human listening to the receiver output are given a rating of "A". Systems requiring a relatively strong signal, such as the loop antenna, are given a rating of "F" (failing grade) because if the RDF can't see it, you can't hunt it or find it.
To earn an "A" rating the criteria is an accuracy of 1 to 2 degrees, which is about the accuracy most people can obtain in reading a handheld compass. A system with 10 degrees of accuracy or resolution is given a rating of "C". Note that an error of 10 degree at a distance of 10 miles is the equivalent of a miss-distance of 8260 feet (1.56 miles).
An additional criteria is ambiguity. For this evaluation the basic accuracy of an ambiguous system has been reduced by a factor of 2. Thus a system with an ambiguous accuracy of 2 degrees is reduced to 4 degrees.
Versatility rating includes all factors which increase the number of signals that can be hunted, the number of environments in which the system can be applied, and the total amount of information which can be obtained with the system. Included are:
If the time required to obtain a bearing and display it seems to a human to be instantaneous the system is given an "A" rating. Five seconds or under earns a "B". A beam earns only a "C" because of having to swing 360 degrees and having to adjust the RF level. This could take 20 seconds to 2 minutes. To a loop stick operation, one should add the time to search in elevation as well as azimuth. Also, multipath can cause the loop to be difficult to interpret, thus its "D" rating.
Factors considered here have to do with road and personal safety while the system is in use. Two situations need to be discussed. First, what are the operation actions needed if the equipment is being used by the driver of a vehicle? Second, what are the considerations which dictate the locations from which it is desirable to operate the equipment?
Note that BMG Engineering, Inc. strongly advocates that Radio Direction Finding equipment should not be operated by the driver of the vehicle. Because of the possibility that a driver may not follow this recommendation, we include the following comments about driver-operated RDF equipment.
If operated by the driver, how much attention must he give to the equipment? What adjustments must he make? Does he have to look at the equipment (take his eyes off the road) to take a reading while moving? In general, the less attention needed by the equipment, the safer it will be by producing fewer distractions while driving. Ideally the operator should not have to look at the equipment at all, leaving his eyes completely free.
There is a safety factor even when there is someone other than the vehicle driver operating the RDF gear (which is strongly recommended). In the case of the beam, usually the team is on the alert for good locations to pull over to take bearings. Sometimes these places are recognized at the last second, and the driver makes a split-second decision and takes action to get off the road. These sudden decisions and actions can be dangerous. Ideally the system should be able to take good bearings while in motion, making stops unnecessary. This is safer, and also means less time is taken to reach the transmitter.
There are similar safety consideration when operating on foot. The writer knows of at least two incidences where a hunter has tripped, hurting himself and damaging his equipment while walking and watching his hunting indicator at the same time. Again, it would be desirable to have an "eyes free" operation.
The equipment should be readily maintained by the owner. The factors involved here are:
Documentation should be complete, clear, accurate, and helpful. It should provide information needed by the operator while he or she is learning to use the equipment. Once the basics have been learned, the operator should have available discussions of practical applications in varied environments in the field.
Documentation should provide the information required by a radio maintenance shop to do repairs, should they be needed. This includes schematic diagram, parts list, voltages, waveforms, adjustment procedures, troubleshooting information (such as a debug tree), common operator errors, and theory of operation.
George (Russ) Andrews, K6BMG BMG Engineering, Inc. 9935 Garibaldi Avenue Temple City, CA 91780 USA Phone: 1(626)285-6963 FAX: 1(626)285-1684 (dedicated line, automatic) Web: http://members.aol.com/bmgenginc
(31 Jan 1996)
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