Here's our notes from this evening's conversations about the MEP receiver, using an FPGA.
-Michelle W5NYV
----- Original Message ----
From: Paul Williamson <paul.kb5mu@gmail.com>
To: Bob McGwier <rwmcgwier@gmail.com>
Cc: "mep-dev@uppermeadow.com" <mep-dev@uppermeadow.com>
Sent: Thu, April 15, 2010 9:15:07 PM
Subject: Re: [Mep-dev] FPGA 1.1 drawing and questions
This sounds really useful! Can you provide more details, or a reference to a paper, or the source code for an implementation, or something we can refer to?
73. -Paul KB5MU
On Apr 2, 2010, at 7:16 AM, Bob McGwier <rwmcgwier@gmail.com> wrote:
> In the FPGA prior to the costa's loop you will need a nonlinear
> equalizer and DC elimination. The QSD, done in this case with some
> fairly high speed switches and baseband filtering most likely, will
> have both amplitude and phase imbalance in the I/Q legs and further, it
> is frequency (rate of switching the sampling "capacitors") dependent.
>
> I have devised an algorithm which really makes the difference in the
> performance of these devices (out of necessity). Especially for digital
> signals, this is imperative.
>
> Suppose Z is the incoming signal AFTER the QSD. Z* (complex conjugate)
> is taken, and a filter is applied to Z*, and the applied to a delayed
> copy of Z. This sufficiently eliminates the image rejection imbalance
> to make it an unimportant part of the communications system.
>
> An ASSUMPTION of the algorithm is that there is NO DC component, so it
> must be eliminated before F(Z*)(n) is applied to Z(-n) and the
> reestimation of F is done.
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