The Receiver
This looks so complicated. And over whelm the new person trying to read the schematic. So lets block this together to make it a bit easier.
Let’s get to know what is happening in the AM receiver of this Cobra 29.
Go here and look at the block diagram:
http://www.cbtricks.com/radios/cobra...m_pg1_pg11.pdf
RF signals are picked up by your antenna, converted into energy and sent to the so-239 on the back of you radio. We will call these 26.965 to 27.405 mhz signal. This signal is brought to
TR 7. This is your
RF amp. This amplifies the signal to make it more usable. The signal is then fed into
FET 1. This is the
first mixer. Lets say you radio is tune to channel 1. The frequency is 26.965 Mhz.. At the same time the PLL (IC 1) with the respect of the channel selected, IC 2 the VCO mixer sends the signal of 16.270 Mhz to FET 1 also. The signal produced at IC 2 will be from 16.270 to 16.710 (1 – 40).
The signal of 16.270 is then subtracted from the 26.965 Mhz signal yet producing our
10.695 Mhz signal.
26.965
-16.270
=10.695
From there the signal passes through the 10.965 Mhz filter (FL1) and delivered to
FET 2. This is our
second mixer. At this point we are getting a 10.240 Mhz signal from TR20 (10.240 OSC) This is mixed with the 10.695 Mhz signal
10.695
-10.240
= .455 Khz
The signal is then passed through the
455 Khz filter (FL2) and then sent to the second IF amplifiers,
TR8, TR 9, TR 10. After the amplification the signal is passed through
D4. This is our detector. Its purpose is to demodulate the signal for speech signal recovery. The recovered speech signal is sent through the volume control, to IC 4 (audio chip) and finally to the speaker. Where we plainly hear “Breaker 19, anyone got yer ears on comone?”