Pros and cons of no preselector filters

Hello.
I would like to get a SP145.
I’ve already done my research and compared it to alternatives in this price range.
Can someone from SignalHound team confirm my summary, which I’ve learnt from Justin’s videos?
I’ve understood that the lack of pre-selector filters in SP145 makes it less suitable at spur/harmonics analysis compared to BB60D and SM200 in wideband settings, but instead it has better phase noise (compared to BB), better noise figure, and also great dynamic range, making it more suitable for in-band analysis.
Is that an accurate summary?
I’m asking because I want it for 2 main use cases that are totally different:
1. Usage in the lab for testing various devices like signal generators
2. Use as RTSA to analyze specific channels (max 40MHZ)

Any additional info on this topic would be highly useful for me.

[Justin Crooks]

Mehdi,
That’s a good summary. A preselector really helps eliminate spurious responses from out-of-band signals, but adds noise figure.
Our products with preselectors (BB60D and SM200) are ideal for spectrum monitoring and harmonics measurements.
Our low-IF architecture products (SM200 and SP145) have the best dynamic range and flattest IF, making them ideal for modulation analysis.
For many applications, preselection can be accomplished with an external band pass filter. Mini Circuits is a good source for these.

• This reply was modified 3 weeks, 6 days ago by Justin Crooks.

Thanks Justin.
So SP145 is less suitable to do harmonic analysis on a signal generator’s output? (let’s say if I need to check the 3rd and 5th harmonics of a 2.4GHZ signal)
Because that’s a use case that I can’t put a bandpass filter for.
I’m curious: how would SP145 behave in this case? (e.g. would it show false artifacts like images that don’t exist?)

[Justin Crooks]

Mehdi,
The standard approach is a high pass (often with an attenuator) for checking harmonics without a preselector. There is still a bank of low pass filters before the mixer, but not before gain control, so you end up with harmonics that may be higher than they actually are. I think you can expect -40 dBc or better, but if you need 60 dB a high pass filter would be needed. Something like this would work for 2.4 GHz harmonic testing:
https://www.minicircuits.com/WebStore/dashboard.html?model=ZHFG-K4000%2B

• This reply was modified 3 weeks, 5 days ago by Justin Crooks.

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