Sorry, confused you with @1design -- was about to leave and somewhat in a hurry... Apologies to you both ![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
Apology accepted, it happens to the best of us
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/xtongue.gif.pagespeed.ic.J5mTe0A2NA.png)
As you mentioned, it was surprising to see that Siglent decided to use EOL, and by now, obsolete parts in their design.
There are many ways to skin a cat when it comes to distributed filter design, what we see hare is blatant copying. No engineering went into that.
They did spin their own couplers and a few discrete filters, including the 10.7MHz IF section.
They did so little engineering that they even copied the 20dB fixed att + HMC307. There are better ways of doing it today, if they redesigned that, they would have been able to design it in a different way with modern components.
To me, it is more sad than anything else, the N9340B works, but it is far from being cutting edge design. It was a bottom of the barrel unit when released, it should have not been the reference for a design released 10+ years later. This is not a PXA level instrument.