Actual gain of a Tayloe mixer

[jwet]

Thanks Mike- yes I believe that's my observation and its explained by the selectivity.

I noted that the Tiny SA doesn't do this.  It has a pair of Gilbert Cell type mixers (SA612 type) up front driven by a quadrature LO and so you don't have selectivity.  If you see a signal on a spectrum plot and move your quadrature LO over to center it, it doesn't change.  I might have to make a short video of how a Tayloe type front end works on a waterfall display- its very confusing.  I think another artifiact of this is that the harmonic sensitivity gives you a lot of artifical signal on the spectrum.  Most superhets have some birdies but these artifacts are really odd.

The fact that the Tayloe also has this selectivity quality makes it useful in a receiver but less so in SA type app.

[mawyatt]

....I think another artifiact of this is that the harmonic sensitivity gives you a lot of artifical signal on the spectrum.  Most superhets have some birdies but these artifacts are really odd....

WRT the harmonic response, not sure about the Tayloe Detector, however the 8 phase PPM has a harmonic response that employs harmonic rejection mixer concepts which pushes the harmonic responses above the center frequency out to believe the 7th or 9th harmonic. We've mentioned this somewhere discussing the PPM, and it's also discussed in the Cornell IEEE papers.

This is another remarkable feature of the PPM that's not usually observed/appreciated but one quickly becomes aware when building actual sensitive Rxs based upon the PPM where conventional mixers have multiple low order harmonic responses that must be dealt with by means of some form of preselect filtering.

An important observation with the Tayloe Detector as shown earlier and here:

https://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdf

Is the discontinuous nature of the input dynamic impedance as "seen" from outside the input looking in. This is caused by the non-symmetrical switching load impedance at the switching outputs which gets "reflected" to the input by means of the bilateral transform of the switching process. This creates large switching artifacts as well as harmonic responses at the input which causes issue if not filtered before hand. Thus the Tayloe Detector requires preselect filtering of some sort as shown in Dan Tayloe's reference and related schematics.

Way back in 2000s this was addressed with the PPM, as one application was for EW use and LO radiation from the antenna port was a major concern as any type of LO radiation or dynamic impedance effects are discoverable. Since the PPM has a completely balanced input from LO phase to phase, dynamic impedance effects are minimized as are harmonic responses. Later in one of the Cornell IEEE papers discussed a means to reduce the effective LO radiation of the PPM to acceptable levels (vaguely recall less than -90dBm as seen directly from the antenna port without any filtering). 

Best

[mark03]

I've been following this conversation with interest.  I remember skimming some of the papers the last time PPM mixers came up in a forum thread, and I sense I need to go back now and re-read them!

One thing I have wondered, is how many of the benefits mentioned here are achievable using the readily available analog switches / bus switches which are the standard thing for amateur Tayloe designs.  The academic papers, obviously, are written by folks doing their own advanced CMOS designs.  Can the amateur throw together an 8-phase PPM from off-the-shelf parts and still do clever things like integrated antenna impedance matching?  Or do you really need to design at the transistor level for that?

[mawyatt]

You can certainly do a lot of things with off-the-self components. The only limitation is the upper frequency limit since a sweet spot for the PPM is with 8 clock phases, so the logic generating the 8 phases becomes the limiting factor.

You are bound to have loads of fun with the PPM

Best