Questions about Tayloe detector - Page 1
Forum section: electronics / rf-microwave

author: LM21
author_rank: Regular Contributor
timestamp: July 22, 2022, 03:49:45 pm
content: I found a nice schematic for a Tayloe detector here in this forum. I can give a link later when I have some time, but Googling helps. With it, it is easy to build a HF receiver. I have a couple of questions now.1. What about AGC. The detector is directly from RF to audio. There is no AGC, that is at one moment you'll get 1uV low noise audio, and the next 1V of audio. What is a good place for AGC. RF amplifier with a Vfet could be a good preamplifier and may be a gain control too, but I don't think it is enough.2. How to get audio from AM, USB and LSB. There are I and Q outputs but what then. How to get from I/Q to SSB or AM.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 22, 2022, 05:11:01 pm
content: For the AFSK digi modes on HF, conventional AGC is can be problematic as there are many signals in the 1 kHz or 3 kHz audio passbands.So if AGC acted on the strong one, the weak ones will be attenuated.Adequate dynamic range is necessary.My receiver is also having RF amp quieting problem with strong nearby signals. eg ft8, 10.136 usb (3kHz wide),affects psk31 on 10.135 usb (1kHz)Some of the ft8 users are trying with way too much level.The decoders in wsjt-x etc report level of each signal.fldigi (BPSK31 etc) also reports IMD of each.Putting all that aside, you could use a form of AGC for example for listening on an am broadcast , by adding a compressor as part of your audio processor.I have Calf on linux. use one of the AF filters and have not yet tried the compressor. Sound card dynamic range is typically from about -85 to +20 dBFS

author: LM21
author_rank: Regular Contributor
timestamp: July 22, 2022, 10:53:43 pm
content: So others have problems with RF levels, too. I think a fet with plenty of current could work as a preselector and preamp. Maybe even have some gain control. And I have built some audio compressors before, I quess I can build one more.What about different modulations. Can I hear AM and SSB?

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 23, 2022, 10:22:19 am
content: Most SDR do the IQ demodulation onboard these days, so there is no need to do it on computer.For example I have ordered this single board dual transceiver which gives/takes audio .https://apache-labs.com/al-products/1022/Open-HPSDR-Hermes-14-bit-ADC-EP3C25-Transceiver-Card-Assembled--Tested.htmlMost or all of the ham radio digital modes now use Audio FSK ( AFSK) , and the baseband audio is generated or decoded on computer using FFT3 etc and sent to/from the sound card to the transceiver.In your case you would need software to decode the I/Q. I am not familar with that.When I modernised an old HF receiver I considered all the above and decided to make a Gilbert demodulator ( instead of I/Q) . Gilbert sends baseband audio to the sound card.It has 3 selectable BFO XOs , handles all digital modes and usb/ssb.It works for am too, by adusting the DDS L.O. for << 1Hz beat. I also retained the original am detector in the old radio, and that can be used for am.For weak am there is a way to phase lock the Gilbert's carrier to the weak am signal. I did not try that.Although DRM never became popular, there are few stations in EU and Asia. I am not sure but I think DRM demod has some computer decoders that need I/Q to sound card. The DRM radios have mostly been kept proprietary, needing purchase of a dedicated receiver.

author: LM21
author_rank: Regular Contributor
timestamp: July 23, 2022, 01:50:44 pm
content: Is there a HW way to do the SSB->IQ->Audio demodulation?Here is what I could build:http://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdf.It gives out I and QI need a variable frequency board, these are cheap and an Arduino or similar. Then that demodulator and audio amp to drive loudspeaker. An easy HW receiver.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 23, 2022, 02:17:06 pm
content: Search:ssb phasing methodssb filter methodssb Weaver methodssb Hilbert transformThere are still a few IC and filters etc that can do these in hardware.

author: LM21
author_rank: Regular Contributor
timestamp: July 25, 2022, 10:25:28 am
content: Thank you but these use conventional method of SSB demodulation and they have very little to do with Tayloe detector and its I and Q signals.QuoteThis is closer but the links I found were too mathematical to me. I am looking for some HW.QuoteI want HW to go from I and Q to audio, when input is SSB modulated carrier.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 25, 2022, 12:58:55 pm
content: Phasing (with Hilbert) method and Weaver methods both use I & QFilter method just uses 1phase L.O.Added: Some notes after yesterday doing search and making a direct conversion IQ model in qucs.There were direct conversion receivers before DSP, but as far as I know, they had no (ie 0dB) image rejection in baseband.That would have been at least usable for phone ssb (which is becoming obsolete) but not good for the present digital ham radio modes.When DSPcame, the FIR filters could be implemented so there were receivers with hardware IQ signals into ADC than DSP.There was one receiver described, however the Motorola chip DSP (...) is obsolete.I don't know if there is a present chip with firmware, perhaps you should try on one of the ham forums.Another option if you want to use only hardware is to use Taloe I&Q converter to go down to a low IF then use another Taloe I&Q to go to baseband audio.The baseband demodulator will need two filters . I used 455 kHz because it was already in the old receiver.There is only about one suitable 455 kHz filter still available, being LTM455HW. Not as good as some olde receivers but it works OK.Ypu could also go down to a lower IF ( below 150 kHz etc) and try constructing your own filters from SMD.One of the present sdr is Open Source Hermes Txcvr card. you can read about it. That is the one I have ordered full build (if it ever arrives)That board would be way too complex for me to hand build.

author: mawyatt
author_rank: Super Contributor
timestamp: July 27, 2022, 01:56:31 am
content: There is a interesting mixer that creates a direct down conversion to baseband IQ that might be of interest. It has some remarkable characteristics including a measured noise figure below what mixer theory predicts (3.92dB), bi-lateral transformation that "moves" the baseband LP filter up to the RF input implementing a narrow bandpass filter at the RF input, RF input impedance matching by means of baseband components, high IIP, decades of frequency tracking and so on.Anyway, here's the brief discussions for those interested.https://www.eevblog.com/forum/rf-microwave/polyphase-or-n-path-mixer/msg3381802/#msg3381802Caution: this is a very deep dive and requires extensive time/effort and studying multiple IEEE articles to get ones arms around the actual mechanisms involved. So apparently simple, yet so involved, DARPA actually created a special workshop on such a decade ago.Best,

author: Kalvin
author_rank: Super Contributor
timestamp: July 27, 2022, 01:19:36 pm
content: ANALOG SSB-RECEIVERHere is a simple analog receiver using a Tayloe mixer/detector with I and Q signal outputs which are fed into a phasing network required for the SSB-detection. It is possible to select a USB or LSB sidebands with a switch.The receiver section with Tayloe-mixer, and I and Q audio signal outputs for computer based signal processing:http://qrp-labs.com/receiverCheck the first link in the Assembly Instructions for the schematics and receiver description.Here is the analog phasing network for USB and LSB reception with I and Q inputs, and an audio output:http://qrp-labs.com/polyphase.htmlCheck the first link in the Assembly Instructions section for the schematics and circuit explanation.DIGITAL SSB-RECEIVERHere is a simple SSB HF-receiver using a Tayloe-mixer. Actually this is an SSB HF-transceiver implemented using ATMEGA328 processor, but you can study the receiver signal path in order to get the idea.https://github.com/threeme3/usdxThat link contains a nice block diagram and good explanation how it all works. It also has an explanation how the AGC is implemented with a software.

author: LM21
author_rank: Regular Contributor
timestamp: July 28, 2022, 05:12:06 pm
content: I think this circuit is easy to put on PCBhttp://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdfpage 7. And after it a polyphase network for SSB.I like very much of this idea of making a receiver from counter, MUX, opamp, and some passive components.I have a board with programmable oscillator and Arduino libraries for it, to work as a local oscillator.