[hpsdr] Advantages/Disadvantages of Pin diode switching?

[Rick ve3mm]

At Dayton this year, I was trying out one of the Flex 6000 series radios.
 The Flex rep told me that there are two TR switching systems in the new
radio.  A pin diode system is used for cw and a relay based system is used
for all other modes.  The QSK on cw seemed to be good during my very
limited exposure to the radio.

Maybe this is a scheme that would work for our radios.

73 Rick ve3mm


On Mon, Jun 3, 2013 at 5:59 AM, Greg - ZL3IX <zl3ix at inet.net.nz> wrote:

> ***** 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
>
>
>
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