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?

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

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

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

I  found 2.4GHz SAW filters at mouser. Bought some and tried to put one on a pcb. That failed, but will try again
eBay has 1.090GHz filters with SMA connectors that shoul work.
1GHz is much easier than 2.6GHz and the only reason I try 2.6GHz is to make use of the ADF4351 rang.
I may also build a 2.18GHz interdigital filter myself. The calculations are ready.
Using 2.18GH will allow using a direct conversion to I/Q baseband on 192kHz samplerate audio. Not sure mirror surpression will be good enough when doing audio fft for very small RBW

I would suggest skipping the cavity, and building a interdigital
filter: https://www.changpuak.ch/electronics/interdigital_bandpass_filter_designer.php

Altough the link shows it as some nice, milled aluminium boxes, you
can make them by soldering pices of brass sheet or even unetched PCB
together. Brass tubing and screws from a model shop, and brass sheet
or PCB and you should be able to make a decent filter at a low cost.

The only thing that is somewhat critical is the length of the
resonator. Try to get this to 0.1mm, but err on the short side. You
can always compensate a bit with the tuning screws if the resonators
are a bit too short, but not if they are too long.

Interdigital filters should be the workhorse of homebrew UHF (sub 3GHz) filters.

73 de Thomas LA3PNA.

søn. 10. mar. 2019 kl. 21:05 skrev <niels@...>:

--
With Best regards, Thomas S. Knutsen.

Please avoid sending me Word or PowerPoint attachments.

Thomas,

That is indeed the calculation I used.
The height of the interdigital filter is calculated a 1/4 labda. How critical is this? Its not easy to make a very accurate box.
If only the rod length is really critical I may try to build one.

Hi all,

In my opinion, pipe cap filters are best suited above 3GHz. I have
used them up to 24GHz without problems, but their size compared to
bandwith and loss makes them little suitable below approx 3GHz. Just
as I would not build a Interdigital filter for frequencies below
400MHz, below that regular LC filters work quite fine if built
correctly.

73 de Thomas.

Den man. 11. mar. 2019 kl. 13:54 skrev Marcus Gustafsson
<mankan@...>:

--
With Best regards, Thomas S. Knutsen.

Please avoid sending me Word or PowerPoint attachments.

For the rest of the box, a couple mm here or there does not matter as
much. It is only the resonator length that is critical.
If the box sizes are far out, you may end up with a filter that has a
different input impedance (tho that is related to tuning of the filter
as well) or needs long screws to be in tune.

Err on the larger side for the box, and shorter side for the
resonators, and it should be possible to tune the filter.

73 de Thomas.

man. 11. mar. 2019 kl. 09:40 skrev <erik@...>:

Thomas,

That is indeed the calculation I used.
The height of the interdigital filter is calculated a 1/4 labda. How critical is this? Its not easy to make a very accurate box.
If only the rod length is really critical I may try to build one.

--
With Best regards, Thomas S. Knutsen.

Please avoid sending me Word or PowerPoint attachments.

On Mon, Mar 11, 2019 at 05:54 AM, Marcus Gustafsson wrote:

what about pipe cap filters?

Reminds me of this design of Cavity Filter that almost looks like a combination of the Interdigital Filter and Pipe Cap Filter (coupling difference only looks like):

http://lea.hamradio.si/~s53mv/spectana/sa.html (see link below for more details, this is the SA link)

http://lea.hamradio.si/~s53mv/cavity/cavity.html

Here is the home link: http://lea.hamradio.si/~s53mv/index.html

Thank you for the interdigital filter link.

On the same site you can also find a very interesting 199MHz Spectrum Analyzer design (As an alternative to Specan). Especially the use of a SI4432.as IF and log-detector.

73 de oz9ny niels

The log detector of the SI is good but the ability to see a small signal close to a big signal is to be investigated. According to the data sheet at least.
I ordered one to test.

I'd be interested in the RPi software you are using. Much of what others have done seems to be Windows based. Or are you using Wine?

Thanks,

Dave L.

Not sure who you are asking.
My sw is also on windows using .net.

I am asking Neils. It was his message I quoted/included in mine and he stated (in that message) that he is using a PI to control his specan.