Boned In China

It was bound to happen eventually, anyone who buys parts off ebay gets stung and it was my turn. Looks like i got a packet of floor sweepings and rejects. Out of 120 xtals, 50% failed to even oscillate and the ones that did ranged in frequency from 11,996,000 to 11,999,600 with 4 being higher than 12mhz. Anyway, it is what it is and I will not be using that seller ever again and I will lodge for a refund. The 3 weeks wait has been the killer I wanted to get cracking on with filters for the receiver. ATM i do not have enough xtals the same frequency to even start. So, i just ordered some genuine parts from RS Components and will have them here within a couple of days and then I can move on.

That is the pile of dead or Q so poor that the amplitude of the sine wave was less than 1vpp compared to 4vpp on ones that were ok.


Rob’s Receiver Part 3: IF Amp and Xtal Filter

First IF amp and the Xtal filter is build. IF amp is perfect and works exactly as designed. The Xtal filter is a bit rough as you can see from the plots below. It needs to be a bit narrower, closer to 500hz would be nice. Its a bit ripply which is probably due to imperfect terminations and because the xtals are not very well matched, being more like + or – 300hz not 50hz. I have a better frequency counter and a couple hundred more xtals coming slow boat from China, so I should be able to improve things quite a lot when I can measure down to 10’s of hz.


Metal Bending and Chassis Building

I made a few minor mods to the homebrew bending brake and have improved the quality of the bends, with corner radius much tighter and improved the accuracy and repeatability of the bends. All in all its a much better unit now. I have added a set of sheet metal bending pliers and should now be able to make much more intricate boxes for my projects. The pictures below are something i knocked up rather quick and rough. Its 80x60x30mm and turned out ok. Nice tight fits.


Red Pitaya VNA

I got new toys. A VNA addon for the red pitaya. More on this as I work out how the hell it works LOL πŸ˜‰

Well i managed to get it connected and working and I ran a test on my 40m dipole. Seems to be working now i need to learn how to use it for serious things. Not just checking swr on antenna πŸ™‚


Rob’s Receiver Part 2: Band Pass Filter

Bandpass filter as designed in Elsie. In practice was a little low in frequency when built. I changed the end caps to to make them a little lower to bring the frequency up. The bandpass is rather ripply and if i remember latter I will Bode Plot it on the red pitaya.

Here is the schematic. It works but does not have the smoothest bandpass. I will see how it goes for now and if its not good enough, redesign it.