HANDBUILT - H.F. SUPERHET
3 - 13 MHz


Based heavily on a design in Amateur Radio mag' (Australia) of May 1995;
(TCF {twin crystal filter} 40 metre transceiver by Drew Diamond VK3XU).
With L-C circuits as shown; tunes 3 to 13 MHz approx.
First mixer is the well regarded SA602;
manuf ' data states - The SA602A is designed for optimum low power performance.
When used with the SA604A as a 45MHz cellular radio second IF and demodulator,
the SA602A is capable of receiving
- 119dBm signal with a 12 dB S/N ratio.
Casing is recycled PC power supply metal box, with new painted front panel.
Speaker is small 1" permag tweeter unit from colour TV.
IF Crystal lattice filter, and 2nd L.O. are recycled 4.43 MHz colour sub-carrier xtals (from old CTV's)
Second mixer MC3361 is salvaged from disgarded cordless phones (the older "clunky" 30 MHz FM types)
Tuning capacitor is a salvaged bc'st air-spaced dual-gang using the smaller (oscillator) section (40~150pF).
Mounted on pillars with a 2" dial-cord drum, it is rotated by spring-tensioned dial cord from the 1/4" tuning shaft
(4 1/2 turns around an abraded section) which passes underneath at mutual right angles. (see photo's)
Tuning shaft is anchored by a rotating fixing screw at rear panel
and through a threaded brass bushing, (ex volume pot') on front panel.
This is a reduction ratio of 8:1
Tuning-scale 'drum' is a recycled cut down aluminium soft drink can (light & strong)
which screws to the dial-cord drum.
A printed paper calibration is taped to the surface
and rolls past a wire cursor in the 1" square window in front panel.
To produce this dial scale calibration; I monitored the VFO on a good receiver (ICOM R8500)
and marked up the dial in 1 MHz intervals consistent with a "swish/plop"
in the receiver at ...MHz + 4.4336 MHz (High side local oscillator injection)
I then flatbed scan the "working" paper calibration
and artwork and print an aesthetic dial scale using the PC.
VFO (1st L.O.) is housed under a metal enclosure soldered to the copper side of the PCB
(cut-down mustard tin)
Circuitry is fabricated on two pieces of vero-board.
One is RF and the other is AF
and are affixed by soldering on opposite sides of a hinged piece of naked PCB.
Makes it easy to swing-out for upgrade/service/measure etc.
PCB should act as a ground plane.
I think this is a variation of ugly-board, or Manhattan style hand building ?
A 3 terminal 7808 VR supplies stabilised +8V to the electronics.
BFO pitch is acheived from potentiometer tuning of a varicap (varactor) diode
in the detector xtal oscillator circuit.

Pictures : scroll down and across.





Still a work in progress {WIP} ..........