[hpsdr] Advantages/Disadvantages of Pin diode switching?

[Dick Faust]

Hi John

I am not a CW guy so I have a relay solution if you are interested in an 
alternative to Alex that would fit.
It is at the bottom of my Munin 2 page called an Alternate Alex 
Interface - 2 boards, one for T/R & filters and one for RX with 6M 
preamp and attenuators.
http://k9ivb.net/munin2/
Just getting the parts together to build the prototype

73, Dick K9IVB

John Marvin wrote:
> ***** 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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