[hpsdr] Advantages/Disadvantages of Pin diode switching?

[Kjell Karlsen]

Hi Greg.

If you look at the schematics for the Elecraft KPA500 TR Switch, you will  
see that they use e 1N5408 in the TX path. The bias current is not more  
than 500 mA as it is driven from 5V via a 10 Ohm resistor.

In Apollo ( max power measured= 25W PEP at 20V Vdd) I am using a Pin  
diode(MA4P7102F) with 35 mA bias but I have tested with S1M, a normal  
1000V silicone diode and I see no difference. The loss is around 0,5 dB in  
both.

73, Kjell





På Mon, 03 Jun 2013 11:59:33 +0200, skrev Greg - ZL3IX <zl3ix at inet.net.nz>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> The important difference between PIN diodes and ordinary diodes is the  
> bias current required in the ON state.  For ordinary diodes the bias  
> current must exceed the peak signal current, otherwise the diode will  
> switch off during the negative peak of the signal.  For 10 W in a 50 ohm  
> system the peak current is 632 mA, so you would need upwards of 700 mA  
> DC to hold the diode on.
>
> That is not true for PIN diodes, which are designed for slow turnoff.   
> Provided that the carrier lifetime of the PIN diode in use, is longer  
> than a half cycle, you only need enough current to keep the on  
> resistance reasonably low.  But beware, check the carrier lifetime  
> carefully.  Use on the lower HF bands needs really long lifetimes.
>
> Use of any diode switching in circuits intended for SSB, needs care, as  
> there is great potential for introducing intermod distortion. Use a  
> spectrum analyser or spare Mercury/Hermes module to check your  
> transmitted spectrum.
>
> 73, Greg, ZL3IX
>
>
> _______________________________________________
> HPSDR Discussion List
> To post msg: hpsdr at openhpsdr.org
> Subscription help:  
> http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
> HPSDR web page: http://openhpsdr.org
> Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/
>
>


-- 
Sendt med Operas e-postklient: http://www.opera.com/mail/

 1370331760.0