[hpsdr] Advantages/Disadvantages of Pin diode switching?

[Kjell Karlsen]

Hi John.

I see you mention Apollo in your mail. The first version had bot as  
options but the result with the diode switch is so good that the layout  
with a relay was dropped.

The signal loss in a diode switch is a bit higher than in a relay, around  
0,5-1 dB. That is both in TX and RX.

By the way, it seems as there is no need to use PIN diodes, 1N7000  
variants works as well at this power level. S1M is used by Elecraft for RX  
path and 1N5408 in the TX path in their 500W PA! But at this power level,  
you must use high voltage to block for the RF, at 10 W, 12 V is enough.

And if you are a CW man, the QSK is fantastic!

73, Kjell



På Mon, 03 Jun 2013 08:07:53 +0200, skrev John Marvin  
<jm-hpsdr at themarvins.org>:

> ***** High Performance Software Defined Radio Discussion List *****
>
> I've modified my hermes enclosure to prepare it to support a qrp amp.  
> What I've done is add 3 different boards (all mounted to the inside  
> bottom of my Hammond enclosure): 1) The Hardrock 50 driver amp  
> (available separately as a kit for $35 from HobbyPCB -- used to boost  
> the 0.5W Hermes output to 5W), 2) A small 5V keying circuit for the  
> driver amp (the driver amp requires 5V to key it, which is normally  
> provided from the Hardrock 50 amp board,  and 3) a T/R relay board based  
> on Gerd's Antenna Switch design.
>
> I split 2 and 3 above into separate breadboards since I'm not sure what  
> my final T/R switch solution will be, and I'll probably replace the T/R  
> board with either a better T/R relay board or a pin diode switching  
> board. After doing some research, my first choice amp is the Elecraft  
> KXPA100, which is not yet available. One of its features is pin diode  
> switching. I would lose the benefit of that as long as I am using a T/R  
> relay to drive the amp. After doing some research, I'm not clear on why  
> it appears that some people prefer relay switching to pin diode  
> switching. I understand that there are some limitations for high power  
> cases, but Elecraft seems to think it is an advantage for their 100W  
> amp. So I'm wondering why 1) Apollo has both choices, 2) it appears  
> prototype designs of the Hardrock50 used pin diode switching, but the  
> final design uses a T/R relay, and 3) most amps that could use pin diode  
> switching do not us it.
>
> There must be some disadvantages in using pin diode switching, but I  
> haven't found a discussion that points them out. I wouldn't think it  
> would cost significantly more. Are there some issues with reliability or  
> signal loss?
>
> Thanks,
>
> John
> AC0ZG
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