YooFab RFLEGO - Page 5

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• The differential amplifier design employed here has low impedance inputs to

which the 1-1.5 meter loop of wire is connected.

Please note that this differential amplifier provides a certain immunity to common

mode signals. The circuit is based upon a differential pair that has an unusual

common base low impedance input design which is an advantage here as the

input loop wire presents a low impedance. (Designed by M0OOZ)

• Gain: The amplifier has a voltage gain of approximately 20dB (10X). This is

more than sufficient. If the gain proves to be too much for your receiver, do not

modify the Differential Amplifier circuit. Instead, place an attenuation pad of 10dB

at the receiver end of the coaxial cable. Note: that 20dB gain will allow for very

small signals appearing on the loop to be amplified to a level suitable for a half-

decent receiver.

• This antenna should operate across all HF bands and is a form of Low

Noise Amplifier (LNA)

• Its compact size makes possible a rapid setup. You may then receive HF

HAM radio signals with the much same ease as the use of a typical antenna

fitted to a VHF consumer type radio.

• This antenna is great for almost any type of HF receiver. However, it is

especially useful for direct conversion (DC) receivers, as it has a certain

immunity to emissions sourced from the DC receiver's own Local Oscillator. Such

emissions may cause hum when received by a DC receiver on an end fed long

wire Antenna (Zeppelin).

• The LOOP connected to the two terminals is something that can be

experimented with. It should be between 1 meter and 1.5 meters in length. A

bigger loop will probably not help with better reception and instead may lead to

instability and reception of more unwanted signals.

ASSEMBLY INSTRUCTIONS

RFLEGO Active Antenna Receiving Loop