The AM Stereo Tech Zone - Hardware Modifications

Hardware Modifications

MC13028 Adapter Uses a surplus ±7½kHz 6 element ceramic filter from a cordless phone. An adjustable LC PLL Osc. NRSC De-Emphasis. 10KHz Notch Filter. Low Pass Filter with a +9dB High Frequency Boost.

TM-152 Added a window detector on the PLL loop volts for a center tuning indicator mounted on the dial indicator . Added 10KHz notch filters and 6dB buffer amp.Added wide and narrow IF filter selection via the mono/stereo switch for a ±7.5kHz and ±3kHz selection. Added synchronous detection for L+R and disabled cosine correction for L-R for true QuAM fixed at 90°. This can be overridden via a switch on back to select between QAM and C-QUAM.

Pioneer SX-2600 Designed and Built a MC13020P decoder that has a ±7½KHz 6-element filter with AGC. Pilot filter circuit has a 3rd order lowpass filter at 40Hz for good co-channel sensing with good rejection of the regular L─R signal. The pilot bandpass filter has a Q appraching 10 and a gain appraching 25. Post detection has 10KHz notch filters and 2nd order lowpass filters providing a boost of 7dB at 8.7KHz to help compensate for HF attenuation caused RF and IF filter response. Later I addd a synchronous adapter to it. This particular unit made it difficult to interface the decoder since the mono AM signal passed through the FM stereo decoder chip so I had to use a CMOS Quad Analog DPDT Switch to overcome this. Iterfaced the mono/stereo button for FM to also work on the AM stereo decoder. Interfaced the STEREO ID in the florescent display to the AM stereo decoder.

Basket Woven Ferrite Bar Antenna. This type of winding is said to improve the quality of the inductance.

Built a Homemade Select-A-Tenna using a heavy duty 10" embroidry hoop, an air core tuning capacitor, #19 enameled wire, some wood and cardboard for the pointer.