Sometimes a hider may conceal additional transmitters around the area where the "main" fox is hidden, just so the hunters will have even more of a challenge, "sniffing" them out.
The use of these additional foxes may take on several variations, depending
on the whim of the hider, such as:
Such variations can be used to test the skill of even the most experienced hunters.
Multiple transmitters operating on or near the same frequency make it difficult to know which transmitter you are actually sniffing. Modern radios, with their wide-band "front-ends", usually cannot separate two close frequencies. Hiders may elect to have the transmitters operate with alternating on/off cycles, to give the hunters some relief.
If one transmitter is operating with a much higher power output than another, weaker, transmitter, it can be very difficult to find the weaker transmitter, simply because the stronger signal may overload or "de-sense" your radio, and you may have real difficulty in even hearing the weak one.
This latter effect can also be achieved with strategic placement of directional antennas. Jim (K5QQ) once did this by directing the signal of a strong transmitter through an eleven-element beam across a field in which a milliwatt-powered second transmitter was concealed. Even with intermittent signals, this can really test your ability and radio gear.