ZN414 type radio -question

Do you enjoy making your own equipment or antennas? Discuss construction and design in here.
Post Reply
User avatar
Road_Hog
Banned
Banned
Posts: 1313
Joined: 28 Sep 2008, 06:39
Location: Warwick

ZN414 type radio -question

Post by Road_Hog »

I'm putting together some small AM-MW radios using the ZN414 variant and to speed things up, I purchased some ready PCBs.

My question is, as I understand it, the chassis/ground leg of the tuning capacitor has to be AC coupled to the earth/ground part of the circuit through a capacitor. Also it is my understanding that the centre leg is the chassis/ground leg of the tuning capacitor.

But look at the PCB and the way it is set out, the outside leg of the tuner goes to the capacitor/ground and the middle leg goes to the input leg of the IC then ground.

Is this right, because when I tune the radio, my hand alters the frequency and that should happen.
AndyWestcott
Regular
Regular
Posts: 26
Joined: 17 Sep 2011, 12:12
Call Sign: M0WAN
Location: Exeter
Contact:

Re: ZN414 type radio -question

Post by AndyWestcott »

A peep at the schematic might be useful here, but yes, the main body of the capacitor should be grounded as far as RF is concerned, to avoid the hand capacity effects you have noticed.

As it's a relatively low frequency radio-wise, can you modify the board slightly to accommodate the contacts, or maybe simply connect the appropriate capacitor terminals to the right bits of the board using fly-leads? The slight changes to inductance and capacitance as a result of the fly leads would be insignificant in this application.
Post Reply