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Hi, Just wanted to share success in getting the first scan of my own build 2GHz spectrum analyzer build almost completely from readily available modules from eBay. Total cost is less then $200. Here is the first scan of a 200MHz signal coming from a SI5351. The signals at 400, 800, 1200 and 1600 MHz are difficult to see on the black grid lines. I'll need to improve this  The SW I made (see picture) is still a bit rough, the signal at 1.84GHz is an alias the 2.0GHz low pass filter did not yet arrive. The actual resolution BW is 300kHz and the actual span is 2GHz All the modules are lying on a table, no decent shielding yet. Lots of unwanted signals below 400MHz Configuration: input->switchable attenuator(0-32dB)->mixer (LO 2.5-4.4GHZ) -> cavity filter(2.5GHz) ->IF amplifier->mixer(LO 2.489.3GHz)->resolution filter (10.7MHz, 15/300KHz BW)->AD8307 log detector->Arduino->Serial->PC Main components: switchable attenuator 0-32dB 2 * SIM-83+ 8Ghz mixer module 2 * ADF4351 35MHz - 4.4GHz generator module as LO Broadband amplifier 0-6GHz 20dB (to compensate for the 2*7dB mixer loss) Cavity bandpass filter somewhere between 2GHz and 2.5GHz with steep cutoff Bandpass filter at 10.7 MHz 300kHz/15kHz switchable BW (this I build myself from ebay cristal and ceramic filters and some other small components ) AD8307 Log detector module Arduino uno Set of SMA pigtails In the coming weeks I will add an additional 110Mhz IF stage to reduce images and spurs (although there are not many and I have SW spur elimination) and the input low pass filter to reduce aliasing The SW can be configured for 2 or 3 IF and any combination of IF frequencies. I did tests with 110MHz and 500MHz as first IF before receiving the cavity filter. A somewhat cheaper build uses 2Ghz mixers (ADE-11X) and a 1090MHz ADS bandfilter instead of the cavity filter. This will give you a 1GHz spectrum analyzer and due to the small BW of the ADS filter you will not need a 3rd IF I hope this inspires some creative building!
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Impressive! ?Any thoughts on publishing your circuit and methods of construction?
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I second the thought.? Very impressive.? Understand there are some bugs but, publishing what you have will encourage others to give it a go.? Maybe even me!
Gene N2IJF
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Impressive! ?Any thoughts on publishing your circuit and methods of construction?
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On Sat, Dec 15, 2018 at 07:58 AM, <erik@...> wrote:
I would also be interested in seeing what you have.? I am working on something similar only going up to 250 MHz.? It is using 31 MHz saw filters for first IF and second IF a t 10.7 Mhz.? I plan on using AD831 mixer modules and a si5351 with high pass filters for the first and second LO frequencies.? Will probably have 4 10.7 Mhz if band widths using available filters.? Will keep updates on my blog.
? -- DuWayne,? KV4QB
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This is the high level diagram  Regular dual conversion architecture with two mixers with first IF for image suppression at IF1 and second IF for resolution bandwith at IF2 and log detector for conversion to dBm I used IF1=2.5GHz and IF2=10.7MHz with the ADF4351 this gives me DC to 1.8GHz input range Attenuator is either a module for the right frequencies of fixed attenuator as required The low pass filters eliminates anything above IF1-IF2, I used a 1.8GHz lowpass filter module from ebay M1 and M2 are mixer modules with one port for DC to IF1 frequency and two ports with IF1 till 2 times IF1 frequency. I used SIM-83+ modules from ebay, a bit overspec as these go to 8GHz LO1 sweeps and goes from IF1 to max two times IF1. I used ADF4351 module from ebay IF1 filter has bandwith of less then two times IF2. I used second hand cavity filter from ebay (difficult to find) but you can build your own interdigital filter LO2 is fixed at IF1-IF2. I used ADF4351 module from ebay IF2 filter has bandwith for required resolution, 300kHz or 15 kHz or switchable. I build myself but there are 10.7MHz filter modules with bandwith of 15kHz available on ebay The amplifier compensates for the loss in the mixers. I used 20dB low noise amplifier module from ebay The log detector converts IF2 into measurement signal. I build myself with AD603 and AD8307 but there are AD8307 modules on ebay The ADC (AD1) is an analogue input port of a arduino. For the arduino you best use a zero or due as these are 3.3v just like the ADF4351 and attenuator modules If you need max 150MHz you can use a single SI5351 module for both LO1 and Lo2 and AD831 active mixer modules as mixers so you do not need the 20dB amplifier module. 150MHz IF1 filters are hard to find on ebay. I used 110MHz SAW filters and put them in a small enclosure with SMA connectors. Everything connects together with SMA pigtails from ebay.
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Hi Erik
Your design is really good. At the cost level it is still reasonable considering the announced possibilities DC-> 1.8gHz For the software, did you start from the Ashar code for the Specan / Sweeperino or did you write it entirely. Can you, when you have finished making available the .hex or possibly the .ino?
Thank you in advance for your answers and congratulations for this achievement. Photos can be?
73 QRO Gilles - F1BFU / Fr
Le?jeu. 3 janv. 2019 ¨¤?14:59, < erik@...> a ¨¦crit?: [Edited Message Follows]
This is the high level diagram
Regular dual conversion architecture with two mixers with first IF for image suppression at IF1 and second IF for resolution bandwith at IF2 and log detector for conversion to dBm
I used IF1=2.5GHz and IF2=10.7MHz with the ADF4351 this gives me DC to 1.8GHz input range
Attenuator is either a module for the right frequencies of fixed attenuator as required
The low pass filters eliminates anything above IF1-IF2, I used a 1.8GHz lowpass filter module from ebay
M1 and M2 are mixer modules with one port for DC to IF1 frequency and two ports with IF1 till 2 times IF1 frequency. I used SIM-83+ modules from ebay, a bit overspec as these go to 8GHz
LO1 sweeps and goes from IF1 to max two times IF1. I used ADF4351 module from ebay
IF1 filter has bandwith of less then two times IF2. I used second hand cavity filter from ebay (difficult to find) but you can build your own interdigital filter
LO2 is fixed at IF1-IF2. I used ADF4351 module from ebay
IF2 filter has bandwith for required resolution, 300kHz or 15 kHz or switchable. I build myself but there are 10.7MHz filter modules with bandwith of 15kHz available on ebay
The amplifier compensates for the loss in the mixers. I used 20dB low noise amplifier module from ebay
The log detector converts IF2 into measurement signal. I build myself with AD603 and AD8307 but there are AD8307 modules on ebay
The ADC (AD1) is an analogue input port of a arduino.
For the arduino you best use a zero or due as these are 3.3v just like the ADF4351 and attenuator modules
If you need max 150MHz you can use a single SI5351 module for both LO1 and Lo2 and AD831 active mixer modules as mixers so you do not need the 20dB amplifier module. 150MHz IF1 filters are hard to find on ebay. I used 110MHz SAW filters and put them in a small enclosure with SMA connectors.
Everything connects together with SMA pigtails from ebay.
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The arduino SW is a rewrite/combination of various SW's
It can be used as a standalone tool controlled over the serial interface
The ADF4351 library is a rewrite of something I found but spur elimination and speed has been a big headache
The SI5351 library is partly rewritten to go to 300MHz (if you device supports it) and with substantial speed improvement.
Zip file with ino and libraries for SI5351 and ADF4351 attached. The libraries are still in continuous development.
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For the PC I started from scratch using .net libraries.
I like the Specan SW as its pure C but that also implies it is too much effort to add functionality?
The arduino SW can easily be made to work with the specan SW, it may even work now (did not test lately)
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Some pictures: The complete analyzer:  Signal left to right: Input low-pass filter (green), mixer (blue module), IF1 filter (big black brick) ,mixer (blue module), IF2 amplifier (green module), IF2 filter (tin box), log detector (tin box) ->arduino analog input Below two adf4351 modules (black PCB's) Above Arduino? The prototyping board is temporary till I get an Arduino Due (3.3Volt) to get rid of the 5v->3.3v resistors The IF2 filter. relays to switch, ceramic for 300kHz and chrystals for 15kHz. Not very beautiful but performance is good.  The log detector, hope you can see the 0602 components. Its loosely based on the AD603+AD8307 reference design but with single sided supply of 12 volt.? 
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I added a third IF at 110MHz.?Now performance is acceptable. Two examples: Wide scan:?200MHz output of a SI5351 through 50dB attenuator to see the harmonics. The actual maximum scan frequency is 1890MHz  The spurs at 25MHz and related harmonics are probably from the 25MHz reference clock on the ADF4351 module. Limited mixer spurs. Small scan: Measuring a 1 MHz sinus signal at calibrated level of -80dBm  The power scale is 10dB off, actual noise floor is thus at -105dBm. Max input signal is -30dBm (actual -20dBm) so dynamic range is not very good (85dB, I was hoping for more then 90dB) but low frequency performance is usable and the zero hertz response small enough. Now I have to put everything in a nice box, not my biggest competence
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Erik,
?
can you please elaborate the following:
1. The 3rd IF@110MHz, was put after IF2@...? Or in between IF1 and IF2?
2. How and why did that affect performance? (Trying to learn here so links to relevant info is perfectly ok).
I have a stalled Specan build that might get some new inspiration from your build.
Br
Marcus, SA5PMG
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1: Between IF1 and IF2 so: 2510.7MHz -> 110.7MHz -> 10.7MHz
2: Got rid of leakage of LO's (bumps in first part of spectrum of first post) and got rid of mirrors. The IF1 filter is actually 100MHz wide, too wide for 10.7Mhz as second IF but OK for 110MHz as second IF?
Specan is OK.?
Its actually simpler and cheaper to aim for 1GHz as max input frequency. This enables the use of cheaper ADE-11X mixers (better isolation and higher conversion) and cheap but narrow ADS? SAW filters (see eBay, 10$ each, use two in series), or even active mixers (AD831) allowing to get rid of the IF amplifier(s) and you can go directly from 1090MHz to 10.7MHz because of the narrow ADS filter
I am having problems with the SIM-83+ mixers I bought. Not from cheap Chinese supplier so I assume they are original but only one has 7dB conversion los, the others 15dB and 25dB. I complained and will receive at least a replacement for the worst mixer. This may solve the current -10dB offset and improve dynamic range
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Thanks for taking the time to explain further Erik.
So sharp filters and mixers with good isolation is the key then, good to know.
Please keep us posted on your progress. And if I get around to building a SA myself I would certainly be interested in reusing your GUI SW even though I write SW for a living I find myself hard to motivate to when it comes GUIs :-)
Br
Marcus
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These SAW filters for the 915mhz ISM band are quite cheap at $2, under $1 in quantity, 40dB down at 15mhz out:
? ??
A clean 50 ohms so easy to stack.
Something like PX1002 SAW filters at 86.85mhz might be a better choice than 10.7mhz for a second IF, avoid image trouble.
Or just mix down from 915mhz to I/Q baseband and use SDR techniques?
The W7ZOI spectrum analyzer front end uses the mixer's IF port for the incoming signal,
RF port is outgoing, because the IF port can get down to lower frequencies.
Here's the entire line of MiniCircuits mixers:??
On the ADE-1+,? LO/RF ports are 0.5-500mhz, the IF port is good from DC-500mhz.
The ADE-11X is suitable for higher frequencies, but your minimum signal into the SA will be the 10mhz limitation imposed by the IF port.
The ADE-5+ might be a better choice,? LO/RF ports are 5-1500mhz, the IF is good from DC-1000mhz, so our SA could see from 0mhz to 1500-915=585mhz
And could perhaps press further than 1500mhz on the LO port.
Cheap as I might be, spending the extra buck on an ADE-5+ to be able to see the bottom 10mhz seems like a good deal.
.
I'm curious how well behaved that ADF4351 local oscillator of yours is.
The new si549 (like an si570, but solid coverage up to 1500mhz) would also work, with much finer resolution in selecting the frequency.
Or an si5340 (4 channels, up to 1024mhz) followed by a clock doubler, cheaper and get multiple LO's for 2'ed IF, tracking generator, ...
?
Mostly armchair engineering here, but I am trying to build a simple single conversion SA?
using the ADE-1+, two PX1002's, and an AD8307.? (Also a couple MMIC's, front end LPF, si5351, Arduino Nano clone, etc)
Those PX1002's are $12 quantity one, but otherwise this is throw-away cheap to play with.
AD8307's can be had on ebay for down to $0.30 each, reportedly work well enough? Factory seconds, slightly out of calibration?
Jerry, KE7ER
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On Sat, Jan 5, 2019 at 07:57 AM, <erik@...> wrote:
1: Between IF1 and IF2 so: 2510.7MHz -> 110.7MHz -> 10.7MHz
2: Got rid of leakage of LO's (bumps in first part of spectrum of first post) and got rid of mirrors. The IF1 filter is actually 100MHz wide, too wide for 10.7Mhz as second IF but OK for 110MHz as second IF?
Specan is OK.?
Its actually simpler and cheaper to aim for 1GHz as max input frequency. This enables the use of cheaper ADE-11X mixers (better isolation and higher conversion) and cheap but narrow ADS? SAW filters (see eBay, 10$ each, use two in series), or even active mixers (AD831) allowing to get rid of the IF amplifier(s) and you can go directly from 1090MHz to 10.7MHz because of the narrow ADS filter
I am having problems with the SIM-83+ mixers I bought. Not from cheap Chinese supplier so I assume they are original but only one has 7dB conversion los, the others 15dB and 25dB. I complained and will receive at least a replacement for the worst mixer. This may solve the current -10dB offset and improve dynamic range
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On Thu, Jan 10, 2019 at 12:07 PM, Jerry Gaffke wrote:
Something like PX1002 SAW filters at 86.85mhz might be a better choice than 10.7mhz for a second IF, avoid image trouble.
Now I'm using 110MHz as second IF and 10.7MHz as 3rd IF (for the resolution filters)
Or just mix down from 915mhz to I/Q baseband and use SDR techniques?
I did this for my own build VNA that can run in SA mode with switchable DSP resolution filters
The W7ZOI spectrum analyzer front end uses the mixer's IF port for the incoming signal,
RF port is outgoing, because the IF port can get down to lower frequencies.
Doing the same
Here's the entire line of MiniCircuits mixers:??
On the ADE-1+,? LO/RF ports are 0.5-500mhz, the IF port is good from DC-500mhz.
The ADE-11X is suitable for higher frequencies, but your minimum signal into the SA will be the 10mhz limitation imposed by the IF port.
The limit actually does not exist. I'm using the ADE-11X in another project and it goes down to audio frequencies
The ADE-5+ might be a better choice,? LO/RF ports are 5-1500mhz, the IF is good from DC-1000mhz, so our SA could see from 0mhz to 1500-915=585mhz
And could perhaps press further than 1500mhz on the LO port.
Cheap as I might be, spending the extra buck on an ADE-5+ to be able to see the bottom 10mhz seems like a good deal.
.
All diode double balanced mixers will go down to DC on their IF port
I'm curious how well behaved that ADF4351 local oscillator of yours is.
Ah, indeed, not so easy to get rid of the spurs, low noise AND have a fast sweep. Lots of register tweaking. SI5351 are much simpler to use!!!!.
The new si549 (like an si570, but solid coverage up to 1500mhz) would also work, with much finer resolution in selecting the frequency.
Or an si5340 (4 channels, up to 1024mhz) followed by a clock doubler, cheaper and get multiple LO's for 2'ed IF, tracking generator, ...
?
Mostly armchair engineering here, but I am trying to build a simple single conversion SA?
using the ADE-1+, two PX1002's, and an AD8307.? (Also a couple MMIC's, front end LPF, si5351, Arduino Nano clone, etc)
How would you do the resolution filters?
Those PX1002's are $12 quantity one, but otherwise this is throw-away cheap to play with.
AD8307's can be had on ebay for down to $0.30 each, reportedly work well enough? Factory seconds, slightly out of calibration?
Suggest to look at the AD8307 data sheet and consider adding a AD603 as shown in one of the examples in the datasheet. I did and it gives you 130dB measurement range, even when build in dead-bug style!!!! Success with your build
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> Now I'm using 110MHz as second IF and 10.7MHz as 3rd IF (for the resolution filters)
Should work fine, cheaper too.? But the PX1002 is drop in with no tuning required.
> I did this for my own build VNA that can run in SA mode with switchable DSP resolution filters
Have you put up a description of that thing?
> The limit actually does not exist. I'm using the ADE-11X in another project and it goes down to audio frequencies
Sounds right.
They fully characterize their parts, and something undoubtedly doesn't meet spec at audio.
But likely good enough, especially if you calibrate the variance
Worth exploring the various parts.
But since I am mostly interested in HF at this time and not 1ghz+, I'd probably tend toward the ADE-5+
Asking it to deal with a 2ghz LO is cheating by 33%, whereas asking a 10mhz minimum part to do audio might be much worse.
Incidently, G0UPL found that the si5351 doesn't crap out till 292mhz, well above the 225mhz spec.
I'd guess the loop filter is not optimized for that, so jitter could be getting bad.
If the ADF4351 needs replacing, I'd probably go for the si5340 (plus doubler, if need over 1024mhz).
Much cheaper than the si549, multiple independent outputs, has a fast spi interface so you can sweep?
as fast as your filters allow.? Jitter spec on the si5340 is an order of magnitude better than the si5351.
Though likely a few days of fun involved to write suitable firmware for either the s549 or the si5340.
?
> How would you do the resolution filters?
Well, the PX1002 bandwidth seems about right as is for looking at spurs and harmonics.
To see IMD and other close in stuff, I was thinking a second mixer from 86.85mhz down to baseband audio.
So a simple DC receiver, no attempt at image rejection.
Inspect the result on a soundcard based audio spectrum analyzer as you scan through the signal,
images will be moving the opposite direction and thus easily ignored.
An idea stolen from Arv, of HBTE fame.
But mostly I'm interested in harmonics and spurs, and probing RF signal levels through each stage of a receiver.
None of that requires the final DC convert to audio, so scans can be fast and fully automated.
And once bored with that simple spectrum analyzer, maybe move on to a full featured direct to baseband IQ
using something like the AD8348 quadrature demodulator, 50 to 1000mhz in.
Below 50mhz, could upconvert first to 86.85mhz using the front end of that PX1002 design.
Don't hold your breath, will likely get distracted with a dozen other unfinished projects
before any of that happens.
> Suggest to look at the AD8307 data sheet and consider adding a AD603 ....
Yup, that caught my eye as well.
Good to know it works well!
To bad they haven't integrated the two of them into one device.
Jerry, KE7ER
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On Thu, Jan 10, 2019 at 11:53 PM, <erik@...> wrote:
On Thu, Jan 10, 2019 at 12:07 PM, Jerry Gaffke wrote:
Something like PX1002 SAW filters at 86.85mhz might be a better choice than 10.7mhz for a second IF, avoid image trouble.
Now I'm using 110MHz as second IF and 10.7MHz as 3rd IF (for the resolution filters)
Or just mix down from 915mhz to I/Q baseband and use SDR techniques?
I did this for my own build VNA that can run in SA mode with switchable DSP resolution filters
The W7ZOI spectrum analyzer front end uses the mixer's IF port for the incoming signal,
RF port is outgoing, because the IF port can get down to lower frequencies.
Doing the same
Here's the entire line of MiniCircuits mixers:??
On the ADE-1+,? LO/RF ports are 0.5-500mhz, the IF port is good from DC-500mhz.
The ADE-11X is suitable for higher frequencies, but your minimum signal into the SA will be the 10mhz limitation imposed by the IF port.
The limit actually does not exist. I'm using the ADE-11X in another project and it goes down to audio frequencies
The ADE-5+ might be a better choice,? LO/RF ports are 5-1500mhz, the IF is good from DC-1000mhz, so our SA could see from 0mhz to 1500-915=585mhz
And could perhaps press further than 1500mhz on the LO port.
Cheap as I might be, spending the extra buck on an ADE-5+ to be able to see the bottom 10mhz seems like a good deal.
.
All diode double balanced mixers will go down to DC on their IF port
I'm curious how well behaved that ADF4351 local oscillator of yours is.
Ah, indeed, not so easy to get rid of the spurs, low noise AND have a fast sweep. Lots of register tweaking. SI5351 are much simpler to use!!!!.
The new si549 (like an si570, but solid coverage up to 1500mhz) would also work, with much finer resolution in selecting the frequency.
Or an si5340 (4 channels, up to 1024mhz) followed by a clock doubler, cheaper and get multiple LO's for 2'ed IF, tracking generator, ...
?
Mostly armchair engineering here, but I am trying to build a simple single conversion SA?
using the ADE-1+, two PX1002's, and an AD8307.? (Also a couple MMIC's, front end LPF, si5351, Arduino Nano clone, etc)
How would you do the resolution filters?
Those PX1002's are $12 quantity one, but otherwise this is throw-away cheap to play with.
AD8307's can be had on ebay for down to $0.30 each, reportedly work well enough? Factory seconds, slightly out of calibration?
Suggest to look at the AD8307 data sheet and consider adding a AD603 as shown in one of the examples in the datasheet. I did and it gives you 130dB measurement range, even when build in dead-bug style!!!!
Success with your build
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I read somewhere about using a si4432 as log detector with 120dB range directly at 400mHz or higher with buildin sw defined resolution filter 6khz to 600khz.
This way? you only need one mixer, once LO, one roofing filter and the SI4432 directly after the roofing filter
I ordered some si4432 to test, they are dirt cheap
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I'd looked at the SiLabs ISM band data transceivers pretty hard before,
hadn't dawned on me that they could be useful as a UHF spectrum analyzer.
Very cool.
Datasheet says works from 240-930 mhz, has an "RX Channel Bandwidth" down to a min of 2.6khz.
And "RSSI Resolution" of +/- 0.5dB, accuracy not stated but that could be calibrated.
Indeed, they are cheap.
And lots of breakout boards for them too.
On the downside, with just 18ma of current draw on Rx,
it can't do a good job of looking at weak signals in the presence of strong signals.
For example, looking at -50dBc spurs in the presence of the carrier.
Also, "Image Rejection" of 30dB with "IF=937khz".
But still, quite useful.
Way better than a diode RF detector.
Or the 8 bit DVB-T dongles as well (except for that 240mhz minimum spec).
Jerry
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On Fri, Jan 11, 2019 at 12:28 PM, <erik@...> wrote:
I read somewhere about using a si4432 as log detector with 120dB range directly at 400mHz or higher with buildin sw defined resolution filter 6khz to 600khz.
This way? you only need one mixer, once LO, one roofing filter and the SI4432 directly after the roofing filter
I ordered some si4432 to test, they are dirt cheap
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An FCC document with actual measurements.
Seems that for an adjacent signal 1MHz away the rejection is at least 50dB
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That thing I threw out there:
?> with just 18ma of current draw on Rx,?it can't do a good job of
> looking at weak signals in the presence of strong signals.
doesn't quite hit the mark.
The si4432 just can't handle very large signals, but that's what attenuators are for.
Dynamic range could be quite large, determined in part by the ADC's they use
and the noise figure.? So could be pretty good.
And as you say, with a mixer and local oscillator and filter to upconvert,
it could easily be extended for use below 240mhz.
An appropriate local oscillator for it might be a second si4432 set up as a transmitter?
Qualcomm RF360 series SAW filters (perhaps for the 315mhz ISM band) are around $1 up on Mouser.
A promising direction to go for a cheap SA.
Jerry
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On Mon, Jan 14, 2019 at 07:37 AM, <erik@...> wrote:
An FCC document with actual measurements.
Seems that for an adjacent signal 1MHz away the rejection is at least 50dB
?
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DuWayne Schmidlkofer