Re: QCX for 2m VHF? #chat #qcx #vhf #mods

Jim Mcilroy

Not quite, Jim

I worked on the basis that the 17m band was the top limit of what Hans offered and went from there, which introduced the term transverter.

To design for 2m CW without the use of the QCX range is a different thing: thought provoking nevertheless  :)

Jim  G4EQX

On 7 Feb 2021, at 21:33, Jim Allyn - N7JA <jim@...> wrote:

You seem to be assuming that Dick was asking about a transverter.  I don't think he was.  I think he was asking about a 2 meter QCX.  Dick, the limiting factor on receiving would be how fast the FST3253 can switch on and off, and a quick glance at the specs suggests it probably won't work well if at all at 2 meters.  According to Dan Tayloe in his paper, "Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier":

"The product detector’s upper frequency limit is set by the ability of a FET to be turned on for only a quarter cycle of the incoming RF being converted to baseband."

I don't think the FST3253 is fast enough for 2 meters.  It seems to me I read that somebody used one at 6 meters, and I think that is pretty much the upper limit.  However, if you have some fast switching FETs, the sky's the limit!

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