Some si5351 Hackery and the Tayloe at 150MHz - FAIL!!

In this video I continue with the attempt to use my Tayloe Detector with a 150MHz input signal from my previous video

Here is that great rfzero site I mentioned

0:00 Intro
1:00 Success with 150 MHz quadrature output from si5351
2:08 si5351 Block diagram
4:33 Worked example for output of signal from si5351 at 20MHz
11:09 Changes I had to make to get quadrature output at 150Mhz
14:01 Testing at 20MHz input RF
16:00 Testing at 40Mhz
16:46 Testing at 60Mhz
17:51 Testing at 80Mhz - oh dear
19:46 Testing at 100 MHz and wrapup

[chrisherd]

Thank you for showing this it keeps my ancient brain exercised.

[td]

This is all a bit outside of my knowledge base, however... Some years back, I looked into using the Si5351A for various non-radio applications. In my research, I encountered a blog/paper showing the mathematical proofs that the Si5351 could not attain certain radio frequencies using the stock 25MHz reference oscillator that is included on most (all?) Si5351A breakout modules. This is due to the same fixed means of mathematics that you explain. Further, the author proved that the math did work at 27MHz. I would think that the typical cautions regarding fake chips would hold true for the 5351.. The assumption being that the AdaFruit module would have OEM parts. However, it comes with a 25MHz oscillator. Just some off-beat thoughts... Cheers.

[joshuablanton]

Sorry for asking technical questions WAY after your experiment was completed - but I re-watched this video and continue to have questions :) I'm surprised by the lack of symmetry between the I and Q channels in your mixer. Did you happen to look at the inputs to the mixer, to verify that your input splitter was behaving reasonably as you approached 100MHz? I suppose it's entirely possible that the mux silicon is significantly slower with some of its switches versus others, but the working channel works so well (relatively speaking, of course!) that I'm curious. I would have expected a more consistent failure between both channels, with mixer losses increasing as frequency increased.

Also, it might be interesting to look at third-harmonic behavior (using a 50MHz SI5351 input to receive 150MHz) - this would result in higher mixer losses, but should switch cleanly as in your 40-60MHz fundamental tests.

[RAUK]

Oh I didn't know one can overclock the PLL. Good to know. What I did in the past was underclocking it to 177 Mhz in order to get low frequencies (1.8 MHz and below) with a 90 deg phase shift. The reason why the MultiSynth divider in your case can't divide by values less than 8 is that it works only in so called integer mode and the CLKx_PHOFF register (the one used to get 90 degree phase shift) doesn't work in the integer mode. The details can be found in "AN619 Manually Generating an Si5351 Register Map for 10-MSOP and 20-QFN Devices".

[sullivanzheng]

It seems the speed limit of analog switch is really a headache when you try to down mix the signal above 100Mhz.

I did the same test as you did. It looks the analog switch IC has very limited turn on / turn off speed and doesn't function properly above 75Mhz~85Mhz (I tested a few samples.)

I also tested a faster, low voltage (3V) SN74CBTLV3253, which is 10% better in switching time according to datasheet. However, it still won't get me cover the full FM band and airband radio. So it seems to me a pure tayloe detector is not feasible to operate through all Airband. A downconverter is needed.


2 questions:

1. Do you know any alternative (much faster) analog switch IC ou would like to recommend?

2. The SA602/612 gilbert cell mixer IC has quite low IP3. I wondered if you can happen to know (and have tested) some mixer or downconversion IC with better IP3 that can downconvert 100Mhz+ signal to around 10Mhz for easy processing of a tayloe mixer?

[bendunselman]

That is why there is reason to counter intuition.

[RCBU]

I have wired my detector board so that it connects directly to the SI5351 module via SMA. Perhaps this will improve the situation a little. I think I need to check my version.

[curtstacy]

It sure looks like it might be an impedance difference between the two channels and it looks like it's the yellow trace is the bad one. just my observation. on another note what if you were to install a circuit, an IF stage of sorts/frequency divider, and bring the frequency into the range of the SI5351? essentially a transverter.

[vincei]

Wait? Arduino C/C++ allows spaces in identifiers? wtf. "SI5351 MULTISYNTH MAX FREQ" How is that possible ? Am I missing something here ?

[generalingwer]

These make better thermometers than oscillators.