[hpsdr] Alex BANDPASS filter

[Marc OLANIE]

Hi Tony

>As the noise level is high I have disconnected the ALEX bandpass filter - what I found there was no change.

In RX mode, Alex is a simple high pass filter (or à least a hpf followed by the antialiasing lpf) . And yes, it is absolutely normal to have the same level of noise level, as this filter is mostly useless, except in certain urban area with a permanent industrial QRM. 

>How do I ensure the bandpass filter is functioning or not - OR the switching for 20meter is taking place correctly

Even if the band switching is ok, it is always possible to have some bad capacitors or a short in the protection circuit due to a violent static discharge.
Check the power supply on J1/2 (12 V) and the 5V rail going to the TPIC6B595 (pin 2)  
Check D5-D10
Check if your input attenuator is on or off (I know, it's a stupid detail, but "I "am a stupid guy and spent 3 hours looking for a filter problem without seeing that my attenuator was stuck on the -30 dB position) 
Plug an analyzer between X1GS1 and the input connector (x4gs1 by default) and sweep the bands from 1 to 60 MHz
Attenuation should be less than 0.7 dB on each band (except the 6m band which has a LNA and therefore a 10 dB gain

Alex is incredibly robust. I'm pretty sure you'll find the gremlin. 
73'
Marc f6itu