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

[Charlie Mazoch Jr.]

Charlie Mazoch Jr. wrote:

> Hi Bill:
>   The 1N4007 is a 1 amp 1000 PEV PN junction silicon diode mostly used 
> in HV power supplies. I agree about IMD when PN diodes are just 
> beginning to forward conduct. That's what diode mixer circuits are all 
> about. But if a diode is hard forward conducting as in switch 
> applications how does one get mixing?  It seems to me that one would 
> have to overcome this forward bias before mixing can occur. In my 
> Kenwood TS-2000 the unused band pass switching diodes have a reverse 
> bias applied. They use a resistor in an SMT transistor to accomplish 
> this novel bias scheme.
> I do agree about PIN diodes offering lower capacitance than a PN 
> junction diode in their reverse bias configuration. That's what the 
> intrinsic layer is all about.    73's
> Charlie  W5VIN
>
> William E. Sabin wrote:
>
>>In my homebrew rcvr (see QRZ.COM, W0IYH) I use 1N4007 PIN diodes in the 
>>front end AGC circuits.  A problem with significant IMD occurs when these 
>>diodes (or any other PIN diodes or ordinary diodes) are just beginning to 
>>forward-conduct.  I use 3 diodes in series at each AGC location and my IMD 
>>measurements show that this eliminates the diodes as a source of *increased* 
>>IMD, regardless of their state of conduction.
>>
>>I use MPN3404 PIN diodes to switch the 12 crystals in the first local 
>>oscillator because of their forward-biased storage time and low back-biased 
>>capacitance. I don't want the turned-off xtals to influence frequency via 
>>the turned-off diodes due to turned-off diode varactor effects. The 
>>interactions between the 12 xtals from 10.4 MHz to 38.4 MHz are negligible.
>>
>>For the nine hamband RF filters I use miniature Radio Shack (RS 
>>275-241)relays which are inexpensive and very reliable (over many years zero 
>>failures in many low power applications). The simplicity of this method and 
>>the reduction of DC power consumption are desirable (the off-relays consume 
>>zero power).
>>
>>Bill W0IYH
>>
>>----- Original Message ----- 
>>From: "Charlie Mazoch Jr." <w5vin at earthlink.net>
>>To: "Anders Janis SM4RNA" <sm4rna at telia.com>; <list at inrad.net>
>>Sent: Thursday, November 24, 2005 9:29 AM
>>Subject: Re: [INRAD] Switching diodes in roofing filter for the IC-775DSP
>>
>>
>>  
>>
>>>Hi:
>>> If you read W8JI's notes on switching diodes the 1N4148 is just fine
>>>as a switch. 
>>>    
>>>
>>
>>
>>
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>

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