
DANIELS
ELECTRONICS LTD.
TM
VHF Enhanced Extra Wideband Receiver Instruction Manual IM10-VR3H040-AB
3-9
3.2.4
RF Amplifier
The output from the preselector filter is coupled through DC blocking capacitor C8 to the base of
RF amplifier Q2. The RF amplifier stage is supplied by the reg9.5 Vdc line and
typically draws 60 mA of collector current. It provides a high third order intercept point and low
noise figure. Transistor Q1 actively regulates the bias to RF transistor Q2. The output signal is
coupled to an image rejection filter via DC blocking capacitor C10. Typically, the RF amplifier
stage has a gain of 16 dB.
3.2.5
Image Rejection Filter
The amplified RF signal is followed by an image rejection filter. This filter rejects image noise
after amplification. The low pass filter consists of C11 through C14, and L3 through L5. It is a
low pass filter designed to pass the desired frequency range of 29.0 MHz - 50.0 MHz and reject
the image band of 71.8 MHz - 92.8 MHz. Typical insertion loss is 1.5 dB.
3.2.6
Local Oscillator Filter
The local oscillator filter is a low pass filter consisting of C34 through C37, and L10 through
L12. Typical insertion loss is 1.5 dB. Input level to the local oscillator filter is typ5
dBm. Following the filter is a resistive attenuation network with an insertion loss of 7.5 dB.
3.2.7
Double Balanced Mixer
The Double Balanced Mixer consists of active mixer M1. The received RF signal in the
29.0 MHz - 50.0 MHz range is down converted to the 21.4 MHz first conversion IF frequency
by the use of high side injection. The mixer is driven by an LO signal of typically -4 dBm.
Typical current draw for the mixer is 100 mA. Typical conversion loss of mixer is 0 dB.
This Page Is Intentionally Left Blank