Simple Radio - Frontend part choices

This is the "Elephant in room" for me, designing and building the analog part of the front end. I know the theory I can apply some intuition on top but in the end is open to experimentation.

Because I took the "brilliant" decision not to have a mixer in the front end and directly sample (actually under sample) the RF now I have to deal with larger frequencies (the opposite of simple) and I saved the cents to spend the dollars.

The VGA (variable gain amplifier) in front of the ADC now it needs a decent bandwidth so my previous choice (MAX9939) is not going to cut it. Well I found a proper ADC driver but is not cheap and it might sound like overkill for this project (and it is) but I have other projects where I can re-use it in the future.

This part is the Texas Instruments LMH6401 a differential input/output programable gain amplifier with very large bandwidth (and a price to match that)

Wideband VGA - ADC Driver

LMH6401 Datasheet Datasheet Here

I ordered the Demo board for this part which has differential input/output connectors so I need to add a baluns to work with single ended (ADC) and the rest of the RF chain. Is not all bad because I have other projects in mind where I have to drive the ADC in differential mode and will be a perfect fit in the near future. The demo board looks like the one in the picture below and it set me back approx. 150 Euros

VGA Demo board, Differential in & Differential Out

I need to build (or buy) some 2:1 baluns to interface this with the rest of the hardware but that should be straight forward.

Experimenting with small signals requires amplifiers (Gain Blocks) so I took the decision to use another TI family of amplifiers with good bandwidth which comes in different gain flavors.

TRF37x73 (x can be "A", "B", "C", "D" for different fixed gains)

TRF37x73 Datasheet

I found a demonstration PCB for this part on the TI website and the Gerber files for people which want to build this demo board (me) so I ordered a few (many) to JLCPCB I should get them soon, and of course I ordered parts with different gain so I can have flexibility for future experiments by optimizing the passives around the IC.

I'm not affiliated with Texas instruments I paid for all the parts from my pocket.

More updates soon.

73 de EI3HWB