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Re: [Amps] rotary switch - shorting/non-shorting

Subject: Re: [Amps] rotary switch - shorting/non-shorting
Date: Fri, 31 Aug 2007 16:20:57 +0000
List-post: <>
Peter and all.

This has been MY understanding of a shorting (progressive) rotary switch.  On 
smaller switches the contact bar on the rotor is continuous and progressively 
shorts contacts together as switch is advanced.

I do have several Radio Switch model 86 switches with a progresive shorting 
feature. Instead of a continuous bar they use multiple contacts on the rotor 
(call them tongues, fingers, whatever).  I have not seen the progresive 
shorting feature on switches larger than the model 86.

The break-before-make or make-before-break switches define a different switch 
function.  If a constant load must be maintained when switching then a 
make-before-break switch would be appropriate to use.  Can not think of any use 
in my station.  If just switching a source from 1 path to another (constant 
load not required or desired) then the break-before-make switch would be 
appropriate.  As stated previously, its the width of most of the contacts (in 
many switches) on the rotor that determines which switch is what.

Two very common uses of the progresive shorting switches are in RF amp output 
tanks circuits,  shorting coil taps as ones goes from 10 to160M, adding 
additional fixed capacitance to both the Tune and Load capacitors (used mostly 
in the Load side of the circuit).

Example:  The SB-220 uses a progresive shorting switch on wafer 2 (taps on 
coil). Wafer 1F is NOT progresive (its 2 pole 5 position)

Arne N7KA 

-------------- Original message -------------- 
From: Peter Chadwick <> 

> In my experience, in the UK, 'shorting' means 'progressively shorting', and 
> is 
> used for shorting out bits of tank coil. It can also be used for receiver 
> type 
> circuits, where unused coils are shorted out, usually by means of a ring on 
> the 
> rear of the switch. 'Shorting' and 'non shorting' in US terms are defined 
> when 
> you design the switch onto the switch manufacturers templates - it depends on 
> the width of the tongue which it is. 'Oak' switches which came from a company 
> called NSF and from AB Metals allowed the choice. AB seem to have dropped 
> out, 
> but NSF is still going well, and they still do ceramic switches. 
> >From experience, you can have great fun optimising a rotary switch design to 
> get the number of wafers and contacts to a minimum. A bewildering set of 
> choices 
> too - reversed clips , reversed long clips, short clips, reversed short 
> clips, 
> insulated clips (generally to be avoided on reliability grounds) etc...... 
> 73 
> Peter G3RZP 
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