[R-390] High Noise Floor in 0-1 MC Band

[Jordan Arndt]

FWIW, The biggest problem I have found with SM caps in the 390A is that they 
jump around in value from the heat in the radio, especially those with only 
RF voltages applied...

73...Jordan VE6ZT

----- Original Message ----- 
From: "Jim Whartenby via R-390" <r-390 at mailman.qth.net>
Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
Sent: Wednesday, October 23, 2024 12:48 PM
Subject: Re: [R-390] High Noise Floor in 0-1 MC Band


>I think that the assumption has been made that all mica capacitors are 
>silver-mica. If the capacitor is a dipped mica then perhaps this is true 
>but stacked mica capacitors, the "domino style" cased units, can be made 
>with aluminum or copper electrodes.
>
> From: https://madpcb.com/glossary/mica-capacitor/
>
>
>   - Stacked Mica Capacitors: These capacitors are designed with thin mica 
> sheets which are arranged one above another. The separation of every mica 
> sheet can be divided through thin metal sheets of aluminum or copper. The 
> whole unit can be enclosed within a plastic box to defend it from 
> mechanical harm s well as moisture. The capacitor’s both the terminals are 
> connected at every end of the capacitor where the mica sheets can be 
> arranged among the metal sheets which work like a dielectric material. 
> This material will oppose the current flow & aluminum or copper sheets 
> perform like electrodes.
>
> If the capacitor tolerance is equal to or greater then perhaps 5% then I 
> would think that this is not a silver-mica capacitor. Below 2% then the 
> capacitor is most likely silver-mica.
>
> Jim
> Logic: Method used to arrive at the wrong conclusion, with confidence. 
> Murphy
>