Nano Controlled Step Attenuator Pt 2

Finished the project today. At least as far as getting the board to work. Still need to think about how I'm going to package it up.

I did a quick scan of the attenuator from 1Hz to 2gHz and looks to be pretty flat . But I'm not all that interested in such high frequencies so I concentrated 1Hz to 50mHz.

There is about a 2.5dB insertion loss and stepping through at 10dB steps up to 60dB shows a linear plot of 2.8dB on top of the dialed in attenuation. In other words, add 2.8dB to the dialed in setting. Exception however was found at 50mHz where it was 2.4dB.

I think I'll adjust the code in order to take into account the insertion loss so what you see is what you get. No need to do math in the head, as easy as it is. I'm sure I'll be busy concentrating on other things while using the attenuator.

Back To Basics

Time to get back to some basics so I built a direct conversion receiver. The design is based on the MRX40 Mini Receiver by K8IDN.

I did not use a crystal that was used in the original design and used my homebrew signal generator instead. I removed all components associated with the crystal circuit except for the capacitor across pins 6 and 7 of the SA612 mixer.

I ended up removing the 220uf capacitor on the output of the regulator as it was shorting to ground.  Fortunately not enough smoke was let out of the regulator that it quit working. Got very very hot though. Another self inflected problem was during the initial power up and testing I used a signal generator to supply the signal source. What I didn't anticipate was that signal was strong enough that it ended up blowing the LM380 chip. I had another one on hand and lowering the source down to an appropriate level proved the circuit worked. 

The receiver worked great and pulled in signals on the 40m band better than expected. Bench testing showed I could an injected signal down to the -120dBm area.