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Charlie Mazoch Jr. wrote:<br>
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Hi Bill:<br>
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.<br>
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<br>
Charlie W5VIN <br>
<br>
William E. Sabin wrote:
<blockquote cite="mid000e01c5f1c8$52665ac0$6402a8c0@DBYKXS51"
type="cite">
<pre wrap="">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." <a class="moz-txt-link-rfc2396E"
href="mailto:w5vin@earthlink.net"><w5vin@earthlink.net></a>
To: "Anders Janis SM4RNA" <a class="moz-txt-link-rfc2396E"
href="mailto:sm4rna@telia.com"><sm4rna@telia.com></a>; <a
class="moz-txt-link-rfc2396E" href="mailto:list@inrad.net"><list@inrad.net></a>
Sent: Thursday, November 24, 2005 9:29 AM
Subject: Re: [INRAD] Switching diodes in roofing filter for the IC-775DSP
</pre>
<blockquote type="cite">
<pre wrap="">Hi:
If you read W8JI's notes on switching diodes the 1N4148 is just fine
as a switch.
</pre>
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<pre wrap=""><!---->
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