[INRAD] Switching diodes in roofing filter for the IC-775DSP

[Charlie Mazoch Jr.]

Hi:
  If you read W8JI's notes on switching diodes the 1N4148 is just fine 
as a switch. Go to his call on QRZ and look up his home page. I have 
been using the Shottky diodes as switches in the bandpass filters on 
receivers as they generate less thermal or electronic noise, also called 
resistor noise in low amplitude signal paths. I've gotten some negative 
response about 3rd IMD product mixing in the shottky and also silicon  
PN diodes. These comments come from people who advocate using PIN 
devices. It's my assertion that once a diode is hard forward conducting 
the only way for products to mix is by overcoming this bias. That would 
take one whopper of a signal. The PIN devices are meant to be used as 
transmit switches and due to their elevated barrier voltages prove to be 
noisy.  I plan on using DIP reed relays, two for each filter to switch 
roofing filters in my IC-756. I already have the relays, (4) SPDT and 
some ground plane PC board. The filters will tie to the swingers and the 
unused filter will be at ground potential through contacts to prevent 
capacitive feed through of the signal. I agree diode switching of the 
filter networks would be more reliable. I'm ready for INRAD to get the 
filters in stock.
73's   Charlie  W5VIN

Anders Janis SM4RNA wrote:

>Hi all!
>
>I have been lookking at teh schematic for the IC-775DSP roofingfilter. How well do a 1N4148 work as a switching diode? Im just thinking about the discussions about changing switching diodes in some high end radios to improve ability to handle strong signals and to minmize noice.
>
>/Anders
>
>_______________________________________________
>INRAD mailing list provided as a service by International Radio
>INRAD Web Site: http://www.qth.com/inrad
>
>To Submit Message to the List: list at inrad.net
>List Help:
>http://mail.inrad.net/mailman/listinfo/list_inrad.net
>
>  
>