Egg quad updating discriminator
For the best receive system sensitivity, one puts the preamplifier outside and at the receive antenna to minimize coax losses. It is worth remembering, then, that the more amplifier gain one puts in front of the receiver, the more susceptible it would be to overload from strong signals - such as those from passing aircraft, paging systems, or even nearby ham transmitters.By designing the receiver to have "adequate" gain, that meant that it could be used (with "good" but not stellar) performance without the preamp, but it wouldn't be as likely to be overloaded once the preamplifier was added.
In the list of "design parameters" above, the second item - "adequate" sensitivity" - deserves a bit of explanation.A few of the critical design goals were: Figure 2: Top: The "Tall and Narrow" Quadrifilar Helix Antenna with the mast-mounted preamplifier used for weather satellite reception.Bottom: A look inside the enclosure containing the Ga As FET preamp (left) and bandpass filter. In reality, it wasn't the desire for a weather satellite receiver that was the main motive for its construction, but rather that I'd always wanted to build a receiver entirely from scratch - plus, I wanted to try out a few circuit ideas, including: For receiving signals from polar-orbiting weather satellites one must either have an antenna that tracks the satellite or use an antenna that is sufficiently non-directional to allow it to receive signals that come from anywhere overhead where the satellite might be.Starting from the upper-right: IF/Audio section (on perfboard), CPU/Control board (mounted on front panel), LCD (mounted on front panel), Local oscillator compartment (just behind ribbon cable), mixer and post-mixer amplifier (left of the local oscillator, behind the display), RF amplifier and filter (the coil and the compartment with the cover) and the frequency reference/PLL board (the one with the box with the white label.) Click on an image for a larger version.For the preamplifier (see Figure 2, bottom) I constructed a simple Ga As FET amplifier.