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SAW filter design cascading SAW filters

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Good morning,

I made a spectrum analyzer (SimpleSA) according to the design of M0Wid.
You can see all the discussions on the ISO HBTE forum.


Unfortunately, the designer is not answering right now, and I have at least one point to clarify.
The analyzer can also do signal generator and also tracking.
The observation is that the spectrum analyzer works, but not the generator (and surely tracking).
I have been looking for a possible program problem for some time, but I am not a programmer and nothing special seen.

Today I think I detected the problem, I explain.
When one is in generator mode, the 2 SI4432 pass in emission.
One will be fixed at about 433.92 MHZ and the other will be at 433.92MHZ + FREQUENCE chosen. The mixer will make F1+F2 and F1-F2, the filter will let pass anything less than 433.92 mhz approximately.
  EX F1 443.92mhz and F2 433.92 MHZ will output a 10MHZ signal after the filter.

In fact, the assembly only works nice  if I shunt the 2 filters. (one by one has no effect).
So I wonder if the filter design is good.

Filter are ECPOS B3555
!!!see the adaptation to 50ohm and how it's made on the Simplesa schematic. I thing strange  (?)

I wonder if waterfall design is a problem because it is different from the one I find on a Tinysa that uses the same principle.
Attached files the SimpleSA 433.92 filter and the rf part of TinySa, you can see also the two saw filter (Not completly the same)

I wonder if the waterfall design poses a problem. I tried with a nanovna, but the result is bad (no form bell), well the test was done directly on the circuit.
if you can tell me the best way to do it.

Thanks for your answer

when i said:  EX F1 443.92mhz and F2 433.92 MHZ will output a 10MHZ signal after the filter.
it's the filter after the mixer. The 2 SAW filters only the 433.92 MHZ pass.
see picture


No answer at this time.
I simplify the question:
May you confirm that a SAW filter work on both direction.
Because my system is bidirectionnal.

I think yes, only confirm


For me, they are pretty symmetrical,
 but B3710 is a 50 Ohm filter without any ado.

... but watch your power level and allowed DC.

second pic is selection with 2 gain blocks and a variable pin attenuator
and 2 filters.


thanks for your answer

The filters are B3555 433.92 mhz.
Can you confirm that the electrical connection scheme is good compared to the datasheet.  (see first post)

I really have no spikes with a nanovna in test.

Possible that the filters are bad or the values of the components. (Components in strip without any indication except on the bag)
I’ll try again, I have some left.


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