[hpsdr] Advantages/Disadvantages of Pin diode switching?

[John Marvin]

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