To protect my SDR UHF receivers on hilltop sites, I needed some filtering to reject local FM broadcast and repeaters.
I looked on Aliexpress what bandpass filters were available. Most of them are SAW filters.
Here are the results of my findings and testings.
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The first filter I bought was a 403 MHz bandpass for my radiosonde receiver. Advertised for less than 2.5 dB insertion loss +20 dBm maximum admissible power |
This measurings confirmed the good advertised characteristics.
The insertion loss is within characteristics and the return loss is quite good for such a low cost filter.
Very low ripple within the bandpass.
This filter makes its job !
Being confident in these filters, I than bought a similar filter for the 433 MHz band in a different shop.
Big disappointment ! Bad mechanical and electrical quality as can be seen on the pictures.
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Both filters I bought from this seller had the same very bad characteristics. Almost no bandpass and bad return loss.
Did I get a bad batch or are they all like this ?
Don't buy here ! The seller was very relunctant to refund me and I had to return the filters at y expense despite the Aliexpress rules.
Bad seller : https://fr.aliexpress.com/item/1005004340532266.html
I decided to try another 433 MHz SAW filter :
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This 433 MHz SAW filter advertised on Aliexpress, was given for less than 3 dB insertion loss. For the price, it looked to good to be true. Once measured, it apperead to be much more lossy and with a high ripple in the bandpass. Forget this one ! |
Here the measuring results. (click to enlarge)
As can be seen, the insertion loss is at least 5.5 dB and return loss is very bad.
Conclusion :
The first SAW filters are quite good, but you have to find a good seller !