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Very interesting, keep up the good work! I'm only on my build of the Specan, also a (re-)learning process:-)
Now we need a good diy description on how to build a 2.6GHz cavity filter. (I have searched ebay without luck)

I am using a raspberry pi for controlling my Specan.
/Niels

1: The SA can scan up to 1.8ghz with 1st IF at 2.6GHz. ADF modules go up to 4.4GHz
2: Some chinese. Some own build using ERA-1 on converted chinese bias tee modules
3: Only output balun. No input or LO balun to have the most generic module
4: AD603. As in the data sheet of the AD8307

Erik,

not much advice but number of questions instead besides saying that your posts are really interesting to follow.
1. Why not lower cutoff frequency on the first LPF somewhere around 1.3GHz?
2. What are you using as 10dB gain blocks, SPF5189Z modules?
3. Which version of the ADL5801 mixer are you using? With or without input baluns?
4. Typo, or why have you changed from AD603 to AD605 in the log detector?

Br
Marcus, SA5PMG

Now most of the modules are in, I combined everything into the complete signal chain.
The purpose of this post is to document the setup and performance of this configuration.

The +10dB after the ADL5801 should not be needed but the conversion gain of the ADL5801 is -8dB i.s.o +0.8dB. I still don't understand why.?
The Arduino Zero controls the ADF4351's and the 12bit ADC measures the output of the AD8307 which gives a 120dB range and 0.05dB resolution

The settings are (speed is actually in 0.1ms units):

The noise level, 1dB CP and IIP3 performance of the whole chain has been verified by doing the performance measurement including two tone IP3 performance of each stage starting with the last stage and working towards the input
The SW allows any mixer to have any role and all frequencies of all filters can be changed. Unused LO's can be used as signal generators or tracking generator. Even after building the total chain it is stil possible to sweep each filter

Scanning 0 till 1Ghz without input signal gives

The many spurs around 100MHz are from the ADF4351 as it runs with R=10 from a 25MHz reference.
Spur performance of the black ADF4351 eBay module is not acceptable. I still need to investigate the loop filter and improve supply decoupling
The 433MHz spur is not yet explained. At some point I had a terrible spur at 42.2MHz. After some testing I found it to be caused the keyboard of the PC. Shifting the keyboard to the other side of the bench did remove the spur.
The signal around 950MHz is leakage from the mobile base station close to where I live.
The absolute signal level is calibrated using a calibrated generator (which was checked using a scope with a 50 ohm input) up till 12MHz but I still need to check the sensitivity at higher frequencies.?
Scanning again 0-1GHz after connecting a 20cm antenna to the input of the SA gives:

Below 250MHz its AM, FM, DAB and some analog TV broadcast. around 550MHz, 800MHz and 950MHz there are mobile base stations and digital broadcast signals.

Connecting two old analog signal generators with a passive -20dB combiner to the low-pass filter gives the two-tone test

Do I read this correct as an IIP3 of around +10dBm? At least changing the signal strength of one or both signals always results in the IIP3 of around +10dBm and that would be consistent with the performance of the weakest part in the chain, the ADE-25MH.
With the current spur performance of the ADF4351 the active mixers seem to be the best choice, they have more noise but their LO rejection is better so unwanted mixing with the LO spurs (specially with R=1) will not obscures the measurement.

I see the following next steps:
- Investigate why the ADL5801 has so little output, solving this allows me to remove the +10dB amplifier and will motivate me to buy another ADL5801 module to replace the ADE-25MH
- Solving the spur problem of the ADF4351 will allow me to use passive mixers everywhere, I have mixers with an IIP3 at +13dBm, less then the active mixers but with much better noise performance so in total more spur free dynamic range. I ordered a green ADF4351 eBay module that uses a 10MHz reference with possibly a better layout around the loop filter
- Find the cause of the 433MHz spur.
- The 15kHz RBW filter as seen in the two-tone test has way too much BW below -50dB. The phase noise of the ADF4351 is much better (was verified using two ADF4351 modules 5kHz apart and a mixer to produce audio into an audio spectrum analyzer) I probably need to improve shielding

Any suggestions for further improvement or checking apart from putting everything in a box with good shielding?

Gentleman,

With Carlos KJ6ST permission , I call your attention to an outstanding, well documented, easy to implement, measurement technique.

?/g/QRPLabs/topic/ocxo_short_term_drift/30321721?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,30321721

There is additional setup information in post 3 of his thread.

73
John
N3AAZ

Hand soldering 0603 is doable. I use regular fine tip solder iron and thin reason core solder. No additional flux. And +6 glasses

I tested the second one. The black board. It has a 25MHz reference.
The green board has a 10MHz reference. I ordered also the green to test because the layout seems better and price has come down and will report when it arrives.
I will upload the doc of the black board to the file space of this group

Which of the two ebay boards are you testing ?

or


I tried getting the zipfile for the second one but get stuck in the chinese:-)

73 de oz9ny, niels

The cheap chinese ADF4351 module is an attractive option as LO for a spectrum analyzer but is the performance OK?
This is the scan with only a -35dBm 1MHz signal with little parmonics


Terrible spurs on multiples of 25MHz, same as the reference on the module.
So so experiments with the ADF4351 settings are needed. The beauty of writing your own SW is you can add the required settings


Changing the R counter to 20 gives a much different result, many small spurs now.


Setting low noise mode or changing the channel spacing makes no real difference.
So it seems the loop filter does not work very well. Need to investigate.?

On Thu, Jan 10, 2019 at 12:07 PM, Jerry Gaffke wrote:

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, ...

Looks like the breakout boards aren't too bad priced:

This one looks interesting for versatility for the price:

I didn't notice any?3.2x5, 5x7 mm package footprints breakout boards and really not much for XO breakout boards other than this one which is sorta a start to modify though just as easy to make from scratch... maybe there is a small market potential if interest:

Was wondering about GPS disciplined benefit also if have already kit?

?

I just received all my modules today... now to see if they're working and I have enough components.? I want to order some 1206 and 0805 resistors and capacitors... I'm still hesitant on the 0603 though is probably better.? I was thinking about my old metallurgy blender to use to blend some solder into powder and make solder paste for the 0603 size.? Might be cleaner.? Any advice on hand soldering 0603?

?

Greetings everyone,
Just joined the group. Interested in making, homebrewing, etc. I have a small workshop space in my basement where the magic happens. Already have an old Tek 2213 (60 MHz, 2 ch) scope, hoping to eventually build an SA. Not entirely without experience, we have a nice array of different test gear at work (Tek [Keithley], R&S, HP [Agilent, Keysight], etc.)
73,?
Goran VE6GPO

I added one page to the already present file

I added a page describing the used measurement principle.
Hope this explains why it is possible to have only minimal HW and still very good performance.
Basically the performance is made possible by the extreme linearity of the PC audio signal path and a perfect DSP IQ mixer.
All IMD in the HW mixers is eliminated and the only requirement is to stay below if 1dB compression point
All harmonics from the SI5351 are also eliminated with the measurement approach.
Calibration will remove the imperfections of the Bridge

Thomas:

Thanks for sharing the procedure and your source code. I added both to my reference library.

On Wed, Feb 13, 2019 at 10:05 AM, Thomas S. Knutsen wrote:

The basic procedure is outlined here:

There is no need to use that given modulation meter, the important
part is to look at the change of the demodulated output. This can be
obtained with a diode detector and read with a oscilloscope. The
important part is that you calibrate to find the detector constant at
low levels, so it does not compress.

C# code for the above meter is here:


73 de Thomas LA3PNA.

Den ons. 13. feb. 2019 kl. 07:40 skrev Christian W. Correa <hk4qwc@...>:

--
With Best regards, Thomas S. Knutsen.

Please avoid sending me Word or PowerPoint attachments.

After playing around with the RF chain of my SA I discovered there where too many possible combinations and I needed some proper simulation and analysis tool
ADIsymRF is a free tool from Analog Devices and not too difficult to learn.

The signal path I calculate contains (perfect) filters, amplifiers based on ERA-1+ with resistive attanuators at the output to bring them at the right amplification level and to secure close to 50 ohm impedance, mixers twice a SIM-83+ and one ADE-11x and at the end a 120dB log detector based on a combination of AD605 and AD8307 as shown in the AD8307 datasheet
The input and output can be seen in one picture



The simulation, using a RBW of 30kHz,? predicts a maximum SNR of 106dB, noise floor at input -107dBm, SFDR of 74dB and input IP3 at 4dB so if my input stays below -30dB I should be about IMD free
First measurements confirm this performance.