ZN414 peculiarities (by Gerard Larooy)
Category: RF IC's
This receiver chip was intended to allow simple radio receivers to be manufactured. It operated on a TRF principle and was intended for medium frequency broadcast reception.
-The TRF principle is the best approach for HiFi, not for sensitivity and selectivity but the 2% distortion precluded this.
-It was intended to be run on a mercury cell which isn't environmentally good but gives very constant output volts. The supply volts for ZN414 is very critical because it's tied to the internal AGC. Circuits with a 1.5V dry cell proved very temperamental with a touchy trimpot feeding the VCC/output pin. Different stations needed a different setting making the ZN414 more tricky than other circuits that it was intended to replace. Radios that run on higher voltages used diodes to regulate the ZN414. The diodes consumed more current than the ZN414 and stability was still marginal. By the way the ZN414 would oscillate at 1.6V or more and its sensitivity of 400uV/m implies that a 'miniature' receiver would need an eight inch long, half inch diameter ferrite rod or a six foot whip antenna for credible local station performance. The gain of the ZN414 was falling noticeably at 1.6MHz precluding its use at higher frequencies.
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