Best results are achieved with two people... one driving the vehicle and paying attention to road safety, and the other observing the D/F, reading maps, and observing the surrounding area. For "novice" users, it would be best to try a few "staged" T-hunts with a friend, to gain experience with the D/F. Try various different scenarios... transmitter located in an open field or parking lot, on top of a hill, down in a gulley, in a "civic center" area with lot of surrounding buildings, etc.... these different situations will help develop a "feel" for the behavior of the D/F, and will build confidence in its performance.

Doppler D/Fs are not as sensitive as Yagi D/Fs... they perform best when signal strength is moderate or strong, but poorly when signals are weak. They are vulnerable to multipath and reflected signals, but so are other D/F methods. In the presence of multipath, the indicator will often "flash" all around the dial, but will tend to dwell at some particular bearing, which should be followed. In general, it is best to seek high ground, where there is the best chance of getting a clear, direct signal path to the source.

There is one cardinal rule for using Doppler D/Fs... keep moving... the greatest virtue of a Doppler D/F is the fact that it instantly indicates the signal bearing... By remaining in constant motion, vast amounts of D/F information can be gathered and interpreted very quickly. It is not unusual for some D/F readings to be inconclusive, or even contradictory, so getting as much information as possible, as quickly as possible, from a variety of different locations is the key to success.

If the receiver has an S - meter, or some other form of signal strength indicator, its readings can be used to complement and augment the D/F readings. In fact, a Doppler D/F with a signal strength indicator is perhaps the most powerful combination of D/F "tools" commonly in use, today.


It is worthwhile to point out that this D/F is basically an audio instrument, operating at audio frequencies, on audio signals. This makes the unit much easier to build and de-bug than most "radio" projects, where careful parts layout and exact component values are often critical. It also implies that this unit is not strictly limited to operation on a single radio band.

In fact, it can typically be connected to a multi - band scanner receiver, and used to D/F on signals across a very wide bandwidth. Operation across a bandwidth of 20 per cent or more can be easily expected, with no modifications. ( example : 144 to 174 MHz ) For operation on other bands, a new antenna might be required, in which all the antenna dimensions are scaled up ( or down ) to represent the same values as those of the original antenna, expressed in signal wavelengths.

For results of the initial performance tests, ( performed with the prototype unit ) check the link calld "FIELD TESTS" on the home page, or click [HERE]

For more detailed information about the theory behind Doppler pulses, check the link called "PULSES" on the home page, or click [HERE]

For possible "pitfalls" with this Doppler, check the link called "CAVEATS" on the home page, or click [HERE]