[regenfreak]

Originally Posted by G0HZU_JMR

The TSC-2-1 combiner has fairly good performance at 100MHz. The isolation is just over 30dB. It's at its best across the HF bands.

However, I think you can get better isolation performance at 100MHz if you make a 6dB combiner. Try both and see if it makes any difference.

The TFM-2 mixers should perform well for level 7 mixers at 100MHz because these little mixers are good to 1GHz. The port isolation is about 54dB at 100MHz. You should see an output TOI of over +10dBm at 100MHz. With a conversion loss of just 5.5dB the input TOI would therefore be about +15.5dBm or so.

I used the level 10 TFM-2LH version a lot back in the late 1990s and it worked very well. The level 10 ADE-1LH was also a very good performer across 30MHz to 200MHz. The input TOI can be expected to be about 3dB higher with a level 10 mixer.

My only signal source can only go up to 100MHz is FY6800. It has spurs in the upper and lower sidebands at very low levels. Normal Butterworth and Cheryshev filters won't work as they reflect all the band-stop frequencies back to the frequency sources creating more distortion products. So I have to make "absorptive" diplexers to bypass the band-stop frequencies to the 50-ohm loads.

I have to look for schematics for crystal oscillators with good frequency stability, low phase noise,low load pushing and pulling.

The Siglent has 751 frequency points per sweep. For RBW = 10Khz at 10MHz, if the noise floor is measured to be 130dbc/Hz and TOI = +15db for the 1st mixer based on HMC499 datasheet:

Maximum dynamic range = 2/3 (TOI-DANL)=2/3[15-(130)]=96.7db

Optimal mixer lever=1/3[2xTOI+DANL] =1/3(2x15-130)=-33dbm.
The mixer level is spectrum input minus the spectrum analyzer's internal attenuation. So the optimal spectrum analyzer input should be around -23dbm with 10db attenuation.

The distortion relative to the mixer level is the distortion power relative to the mixer power input in dBc. The TOI has a slope of 2 in the distortion relative to mixer level graph because 1db increment in the mixer level corresponds to 3db TOI distortion, the increment is 2db. The graph for the DANL relative to mixer level has a slope of -1 ( it is equivalent to N/S). For every 1db increases in mixer input power, the S/N decreases by 1db.

I guess the 1Mhz frequency spacing for the two-tone is industrial standard, regardless it is 1GHz or 10MHz fundamental. However, the phase noise around two tones' double sidebands at a particular frequency offset starts to mask the distortion product as the RBW increases. The phase noise is a horizontal line in the dynamic range chart and it can be added to the broad noise. It is advantageous to use smaller frequency spacing to improve the DANL. So this 1MHz two-tone spacing puts a significant constraint on measuring DUT of very high TOI.

Radio Wrangler The more cross-isolation a combiner/splitter offers, the touchier it is to having good impedances presented to it. Eventually you hit a limit and get bulldozed into small power amps and attenuators.

I suppose the level of isolation between ports of a Wilkinson resistive or hybrid splitter can be upset by any mismatch of one of the ports. It is a fine balancing act.
Perfect isolation only happens when all the ports are perfectly terminated with 50 ohms.