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Fox Hunt Attenuator |
Technical Notebook
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The theory used here is a simple concept. If 50 ohms impedance is a perfect match, then anything other than 50 ohms is not.
The decibel markings on the attenuator use the inverse of the "rule of thumb" that if you increase a signal by 3 Db, the power is doubled.
Therefore if you add multiples of 50 ohms into the feed line, each multiple will decrease the received signal by 3 Db. (Example: 1000 OHMS / 50 = 5. 5 X 3 = 15 or -15Db. attenuation)
The decibel markings are not absolutely true for mainly 2 reasons.
The first reason is that impedance is a measure of effective resistance at a particular frequency and the internal resistors were chosen without regard to frequency. This leads to some large errors the higher the frequency of the signal is.
The other reason is that the attenuator was not designed with high isolation techniques, and as a result, there is allot of internal coupling going on due to lead inductance and capacitance's.
The purpose of the gimmick is to help reduce parasitic oscillations (ringing) in the presence of strong RF fields.
This circuit is not a "calibrated" device and should not be used for measurement purposes.
NEVER! NEVER! NEVER!
NEVER TRANSMIT THROUGH THIS ATTENUATOR, EVEN AT LOW POWER SETTINGS! SEVERE DAMAGE MAY OCCUR TO THE ATTENUATOR AND YOUR TRANSMITTER!
