After some first functional tests I have measured the AD-FMCOMMS1 RX sensitivity from 400 MHz to 4 GHz. The maximum sensitivity seems to be around 1800-2600 MHz. Sensitivity at 4000 MHz is ~ 4 dB lower. At the low end of the frequency range the sensitivity is ~ 10 dB lower at 900 MHz and ~23 dB lower at 400 MHz. The reason for the large degradation at the low end seems to be the balun between the RX input and the ADL5380 Quadrature Demodulator.
In the ADL5380 datasheet it says “Due to the wideband nature of the ADL5380, three different board configurations had to be used to characterize the product. For low band characterization (400 MHz to 3 GHz), the Mini-Circuits TC1-1-13 balun was used on the RF and LO inputs to create differential signals at the device pins. For midband characterization (3 GHz to 4 GHz), the Johanson Technology 3600BL14M050T was used, and for high band characterization (5 GHz to 6 GHz), the Johanson Technology 5400BL15B050E balun was used”.
On the other hand the FMCOMMS1 documentation says “The AD-FMCOMMS1-EBZ enables RF applications from 400MHz to 4 GHz. The module is customizable to a wide range of frequencies by software without any hardware changes”. When I first read this I had the impression the wide range of frequencies was 400-4000 MHz. It seems that this was too optimistic and that we have to change baluns in order to use the lower frequency range. Maybe this should be mentioned in the FMCOMMS1 documentation?
First question: The balun on the board has no text on it. Is the board delivered with the Johanson Technology 3600BL14M050T mounted?
Second question: I assume that the Mini-Circuits TC1-1-13 does not fit on the board? Can you mention a balun for the lower freq range e.g. 400-2500 MHz, that is compatible with the board layout?