80 meter Homebrew Receiver by KE4ID
Here is a picture of my homebrew 80 meter receiver. This page was uploaded on January 19, 2009.
Here are the basic sections of the receiver:
-Double tuned FET low gain RF stage (tracks 455 kHz below local oscillator)
-Doubly balanced mixer
-Analog local oscillator, slide rule dial with fine tuning control
-Post mixer grounded gate JFET amp with tuned output at 455 kHz
-1st IF filter: 4 kHz wide 455 kHz Collins mechanical filter
-Low gain IF amp at 455 kHz
-Pass Band Tuning Module, using modified Drake eight pole crystal filter, about 3.5 kHz wide (455 kHz signal is mixed up to 5.645, filtered amplified with low gain amp, then mixed back down to 455 kHz)
-IF amplifier section in sealed cast box, containing 6 kHz wide 455 kHz ceramic filter,
low gain JFET amp, two stages of MC1350P IC amps (gain control is applied here), 6 kHz wide 455 kHz ceramic filter, and low gain JFET amp
-Product detector (doubly balanced mixer)
-One transistor BFO feeds product detector
-The AGC is audio-derived, with a full wave detector. This controls the MC-1350P ICs and is used to drive the S-meter.
-Audio section: audio diplexer, two stage audio amp, with IC power amp
Front panel controls are Power, Phone Jack, S-meter, Pass Band Tuning, AF Gain, IF Gain, Fine Tune, BFO Reverse and main tuning. An external Hi-Fi speaker is used.
The rig is built in a junked AM/FM stereo receiver purchased at a yard cell. The owner said it had been struck by lightning, so the price was right. I gutted the unit except for the power supply, lights, three section variable capacitor with slide rule tuning, a couple of switches and panel mount plugs. I hand calibrated the linear dial, covered it in clear plastic, and taped it down.
Here is an inside view of the front panel. Note the plethora of holes. I covered the front side with a black painted aluminum mini-panel, so I could use just the holes I needed. Labeling on the front panel was done with a P-Touch label maker using 1/2" wide white on black labels.
The various modules were built using ground plane construction on copper clad PC board. Most of the boards are mounted vertically on aluminum plates that double as shields between the sections.
The VFO and voltage regulation circuits are mounted underneath the main chassis. The use of double transformers is obviously overkill!
The rear panel is simple with connections for the antenna using either BNC or phono plus. 12 volts is available through a separate phono plug.
How well does it work?
The receiver is very easy to listen to due to the combination of wide filters for fidelity and the passband tuning to tighten the bandwidth when needed. The AGC is surprisingly smooth. The slide rule dial provides about a 23:1 ratio, and the Fine Tune control effectively provides an even greater reduction ratio.