| Electronics > RF, Microwave, Ham Radio |
| Actual gain of a Tayloe mixer |
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| mawyatt:
--- Quote from: RoGeorge on December 30, 2024, 11:07:09 pm ---Funny thing, got the exact same feeling after rewatching those 2 videos. In fact, I still have some untested ideas to try from a couple of years ago, when mawyatt brought the n-path filters to attention (at least for me, he was the initiator, thank you Mr. mawyatt for the very interesting topic). --- End quote --- You are quite welcome, hope others would find this DTCA N-Path/PP/Mixer/Filter interesting :-+ We certainly did way back starting in ~1980 with CZT RTSA and Commutating Filter (another name for N-Path), then in ~2000 with PolyPhase Mixer (N-Path Mixer). Fun stuff indeed ;) Happy New Year , Best |
| coppice:
--- Quote from: tggzzz on December 29, 2024, 08:44:32 pm --- --- Quote from: mawyatt on December 29, 2024, 08:29:03 pm ---DTCA is indeed a highly useful Domain, wish others would discover and delve into this more :-+ --- End quote --- Just so. While a DCTA circuit might be sufficient on its own, there's nothing preventing a DCTA+DSP implementation. But a pure DSP guy Matlab monkey is less likely to realise that; if you know how to wield a hammer, everything looks like a nail. --- End quote --- There. Fixed that for you. |
| mawyatt:
WRT to general Signal Processing and System Design. The best case one can achieve the important parameters of SNR, Interference Rejection and DR is by placing the BW defining Filter right at the input before anything. Early on we starting doing this even at low frequencies (under 1Hz while trying to detect certain nanovolt level signals in the presence of enormous interference), while the RF community has done this forever by utilizing "preselector filters" before the LNA and Mixer. In our case of the low frequency, we shoved an integrator right up to the input, so the 1st low-noise amplifier became a signal integrator, after some gain to isolate the later amplifiers/filters noise, we did the frequency band selectivity with integration compensation. This worked beautifully and was the signal processing chain for the Miles Signal Processor (MSP) based upon Magnetostriction Cable Intrusion Detection back in 70s. The PPM or N-Path Mixer performs a similar function that shoves the baseband integrating LPF right up to the antenna port by means of the unique bilateral transfer characteristics of the PPM. Very powerful technique that creates a large impedance mismatch as "seen" from the antenna port by the shunt capacitive baseband integrating LPF. Out-of-Band signals get reflected at the antenna port before entering the signal processing stage, while In-Band signals "see" a good impedance match at the antenna and are absorbed and passed along for post signal processing. This effect tracks the LO and because of the unique low noise characteristic (better than theoretical Bi-Phase Mixer NF) there's no need for an LNA, while simultaneously imposing harmonic rejection techniques to it's fullest!! Just a few features of this unique Mixer that is deceptively simple in appearance but quite complex in behavior and why once becoming public became an intellectual whirlwind throughout academia and the advanced research community. We can't stress enough for interested folks to study the various IEEE papers mentioned staring with the 1st public releases from Cornell. Happy New Year, Best |
| jwet:
The Softrock receiver was mentioned, I built many variations with DSP back ends to make HF receivers. They work well but have one funny habit explained by some of this discussion. When you're looking at a waterfall type display for tuning, the high Q of the front end makes the signal peak go away as you get closer to it. On a spectrum analyzer display, you don't have this- it is flat as you move a marker on a peak. I guess you could setup the Tayloe so it had low Q but the standard circuits and a lot of benefit come from this Q. Is this effect my imagination or real? |
| mawyatt:
If I understand the question (don't know anything about the Softrock Rx), this seems to indicate that the signal amplitude peak drops as it approaches tuned frequency of the high Q receiver? If this is the proper understanding, the input signal "sees" a poor impedance match which gradually get better as the Rx tuned frequency is approached. The input signal is reflected until approaching the Rx frequency, then becomes gradually absorbed by the Rx input match showing a dip in magnitude as the signal gets closer to the tuned Rx as "Seen Looking Towards the Rx Front End from the Outside", or as "Seen from Looking Towards the Antenna Port". Of course if one looks towards the Antenna Port from "Inside the Rx", or how the Rx responds, as the typical case, then the result is the usual narrow band high Q response. Not sure if this is what is being asked, but an attempt to answer such!! Happy New Year, Best |
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