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Re: TinySA construction
Or an Si5351, $1 on Mouser, cheaper than a mixer.
Assuming 250mhz or so max is sufficient. The Sig-Gen mode of the tinySA is interesting in that it might be able to emit a sine wave capable of going from 0 to 250mhz.? ?(The 250mhz LPF removes any harmonics.) But a square wave is fine for this tracking generator. Is it possible to approach the 120dB dynamic range of fig 31 on p61 of the datasheet? The RBW implemented in the Si4432 will not have sufficient stopband suppression to see this, but the SAW filters should compensate if RBW is set equal to SAW filter bandwidth. It will be interesting to build a tinySA with proper shielding, perhaps optoisolators on the SPI bus into the RX Si4432, a separate SPI bus into the LO Si4432 to keep the RX quiet.? See how far we can move the noise floor down. But the noise floor is flat, and doesn't vary much when we change the rx frequency? within the SAW filter passband.? So it's not just that the noise floor is some local oscillator harmonic.? Suggests to me that shielding may not be sufficient,? From p61 of the datasheet, the RSSI register gets updated once every four data bit periods, and each time it is updated there might be 10ns or so of invalid data if you happen to read it then. You can emit a data clock out an Si4432 GPIO pin, so perhaps interrupt the SPI master to do a read synchronous to that data clock?? No info on exactly where in the data bit period the RSSI gets updated.? Setting the data bit rate is a tradeoff between fast RSSI updates and having more frequent episodes of invalid RSSI data.? ?(We aren't actually using data bits here, but we may have to pay attention to this data bit rate thing anyway.) On p8 of the datasheet, Tlock of the Si4432 synthesizer is spec'd at around 200us for large changes in frequency (actually, Tlock is time to lock from initialization). I'd imagine it is much faster than 200us for the small changes typical of a scan. But must give it sufficient time when crossing a 10mhz band boundary. At line 675 of the Jan 17 tinySA.ino code, reg 0x69 is left with a value of 0x60. According to page 50 of AN440, that should leave the AGC enabled. Perhaps Eric determined that the documentation is incorrect? With AGC off by clearing bits 5 and 6 of reg 0x69, we can set the LNA and PGA gain with a register write, getting up to an extra 44dB of gain.? With this gain set high, keeping noise low becomes extremely important.? If it works, it may pretty much remove the need for the PE4302 attenuator.? And/or could conceivably adjust the gain for each sample. If an RSSI sample is out of range then adjust the gain and take the sample again. But as noted above, the noise floor is probably such that this is all moot. On page 9 of the datasheet, the LNA input impedance varies considerably with frequency. Not an issue for the current tinySA architecture since that input is always at 434mhz. The LO output into the mixer is overpowering, and can vary somewhat without issue. But something to keep in mind. Jerry, KE7ER |
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Re: TinySA construction
Speaking about shielding: Did anyone find a source for shields on ebay, aliexpress etc? Whatever search quires that I use I get 0 results. Can't find any on?LCSC either. On Wed, 5 Feb 2020 at 16:36, wb6ogd <garywinblad@...> wrote:
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Re: TinySA construction
You can output the LO and send it to a completely separate fully shielded tracking generator box with a mixer, SI4432 and any micro to setup the SI4432.
LO from tinySA to RF port of mixer, internal SI4432 in TX mode to LO port of mixer, output of tracking generator box from IF port. You may consider to add an amplifier after the mixer but the IF output of the mixer can deliver from zero Hz and adding an amplifier (with its capacitors) will create a lower frequency output limit. Even the leakage through the tracking generator mixer into the LO port of the tinySA leaking into the tinySA RX SI4432 may be a problem causing reduced sensitivity. So indeed using a separate box with two SI4432 and a mixer being slaved to the scan of the tinySA may be better. -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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Re: TinySA construction
¿ªÔÆÌåÓýThanks Erik..? I was assuming good shielding..? Do you have a recommendation?Two more Si4432s?? That's only $3 and two more nSel pins, minor Arduino code. Or just a noise generator I already bought the parts for.. If I can only find them around here... 73, Gary WB6OGD On 2/4/2020 10:54 PM, erik@...
wrote:
On Tue, Feb 4, 2020 at 08:26 PM, wb6ogd wrote: |
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Re: TinySA construction
On Tue, Feb 4, 2020 at 08:26 PM, wb6ogd wrote:
I tried and the 433MHz did deafen the RX SI4432 You can test by disconnecting the RF input from the RX SI4432 from observe if there is still a zero Hz peak. Only with VERY good shielding will a tracking generator that uses a static LO at 433MHz work ? -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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Re: TinySA construction
Ah, you're right.? One additional Si4432, not two.?
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? On Tue, Feb 4, 2020 at 08:26 PM, wb6ogd wrote: Jerry, |
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Re: TinySA construction
¿ªÔÆÌåÓýJerry,Yes, Si5351 is an excellent part, I have several. Another Si4322 programmed to TX at the IF (434MHz) feeding a mixer... and the LO feeding the 2 mixers will make a great tracking oscillator. 73, Gary WB6OGD? On Feb 4, 2020, at 6:43 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
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Re: TinySA construction
The Si5351 is a $1 part. common, very small, does 4khz to 250mhz,
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lots of DIY projects are already using it with Arduino boards. Not clear to me how two additional Si4432's and a mixer are better. Though if you are mass producing tinySA's, it is cool that one of them can be used as the tracking generator.? Jerry On Tue, Feb 4, 2020 at 05:10 PM, wb6ogd wrote: Erik already demonstrated using a Si4432. |
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Re: TinySA construction
¿ªÔÆÌåÓýErik already demonstrated using a Si4432.He just said to use another mixer and use the LO to do the sweep. ?I think it would ?need a peak hold or something on the display though? 73, Gary? WB6OGD? On Feb 4, 2020, at 5:02 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
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Re: TinySA construction
I assume that tracking generator need only do up to 250 mhz.
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An Si5351 should be fine, spec'd for 225mhz, but does up to 290mhz. The tinySA will ignore any harmonics from the square wave.? Jerry On Tue, Feb 4, 2020 at 12:30 PM, wb6ogd wrote:
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Re: TinySA construction
Ok, its been a month or so, how are those tinySAs coming?
I am ready to build my next version.. the first is quick and dirty, see attached photo. It works beyond expectations for the quick and dirty construction! Does anybody have a PCB designed yet. I built the first with ebay modules, I think I want to try raw components on pcb next.? With shielding. I have modified a Arduino Nano for 3.3V, was easy and seems to work ok at 16MHz still... though I am not totally sure. Oh, do want a tracking generator too.. 73, Gary WB6OGD |
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Re: Spur Reduction
#tinysa
Jerry,
The scanning loop for the local display is different from the scanning loop for PC data, I was referring to the local display scanning loop -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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Re: Spur Reduction
#tinysa
Correction:
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So the RSSI read occurs delaytime*100*2/3 microseconds after the frequency is set. And perhaps the 2/3 factor is due to the processor specific execution time of this loop: ? ? ? while (micros() - old_micros < (delaytime * 100L)*2/3 ) { ? ? ? ? delayMicroseconds(100);
? ? ? }
Jerry On Mon, Feb 3, 2020 at 08:16 AM, Jerry Gaffke wrote:
So the RSSI read occurs delaytime microseconds after the frequency is set. |
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Re: Spur Reduction
#tinysa
Perhaps I misunderstand, but this doesn't seem quite right:
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>? The is no delay in the tinySA code between setting the SI4432 frequency and the RSSI reading. In the tinySA.ino code of Jan 17, I see the following under the 'M' command: ###################
? ? ... ? ? for(int i = 0; i < steps; i++ )? ?{ ? ? ? ...
? ? ? setFreq (VFO, modfreq);
? ? ? ...
? ? ? if (i>0)? ? ? ? ...
? ? ? ? serialBuff[serialIndex++] = ((byte) (sensor));
? ? ? ...
? ? ? while (micros() - old_micros < (delaytime * 100L)*2/3 ) {
? ? ? ? delayMicroseconds(100);
? ? ? }
? ? ? ...
? ? ? sensor = SI4432_RSSI();
? ? }
? ? ...? ? serialBuff[serialIndex++] = ((byte) (sensor));? ? ? ... ########################## So the RSSI read occurs delaytime microseconds after the frequency is set. Still curious about that weird *2/3 factor used on the delaytime. Jerry, KE7ER On Mon, Feb 3, 2020 at 07:42 AM, <erik@...> wrote: The RSSI is read on request as there is no guaranteed good latched value (no way to automatically capture a defined time after a PLL change).? |
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Re: Spur Reduction
#tinysa
The RSSI is read on request as there is no guaranteed good latched value (no way to automatically capture a defined time after a PLL change).?
The is no delay in the tinySA code between setting the SI4432 frequency and the RSSI reading. -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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Re: Spur Reduction
#tinysa
Thanks.? Will give it a try this evening.? I think I need to fit the matching parts to the 434MHz filters to flatten out the response and try and get a consistent peak reading as the IF changes.
Have you found any information on the time constant for the RSSI signal, or if it can be reduced in one of the registers?? I had a very quick scan of the register descriptions but didn't see anything.? It seems to take much longer than the specified 200uS to stabilise after a frequency change. 73 Dave M0WID |
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Re: Spur Reduction
#tinysa
Best is to take as offset twice the RBW, as long as 6*offset is less then IF BW
-- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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Re: Tiny low cost home build spectrum analyzer
#spectrum_analyzer
I am porting tinySA.ino to the Raspberry Pi.
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Code as it is now can be found at? ?/g/HBTE/files/KE7ER/tinySArpi00.c Need to shut this down for a couple weeks, have other urgent projects to deal with. Code compiles with gcc under Ubuntu with the GPIO pin handling stubbed out. Have #if directives to allow compilation for Raspberry Pi or for the Nano, but tot tried. Copious notes at the bottom of the file on what all is going on, may be helpful for those left confused by the original code in tinySA.ino. I'm sure Erik is quite comfortable with tinySA.ino as he wrote it, and I don't expect him to move all his work with displays and encoders and such into this new code base.? But for porting to the RPi it made the most sense to do a significant reorganization. Jerry, KE7ER On Wed, Dec 4, 2019 at 12:04 AM, <erik@...> wrote:
I won't mind if you tidy up the arduino code and post an updated version.... |
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Re: Spur Reduction
#tinysa
That almost works, see attached.
At each point in the sweep I take readings at the nominal IF, then with the IF at an offset each side, and take the lowest value of the three readings. Need to see how to speed the sweep up though, and avoid the different peak values.? The offset here is 50kHz. 73 Dave M0WID |
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Re: Early MiniSA .ino files?
On Sun, Feb 2, 2020 at 08:52 AM, Tony Jaques wrote:
Si4432 module warningThese so call "bad"? modules are mostly 250MHz or 333MHz modules used ad 433MHz. Make sure your supplier understands the different between the frequencies and only buy from a supplier (click on the name of the supplier and visit their store and look at their rating) that is selling many RF components and not someone that bought some leftovers and is trying to sell without a long established reputation. ? -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |
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