Broadcast Reject, High Pass Filter.
Project built, into plastic project box.
612 ABC, 50kW AM Station 10km away from me, Before:
612 ABC After.
10mhz band spread before.
10mhz band spread after.
I just want to say that soldering TSSOP at home packages sucks big fat balls. What a pain in the arse this has been. I spent lots of tine chasing out solder bridges. But they are done now and I guess i can start to use them. Oh and if you want to know what it is, its a compander, to be used to make an audio compressor for the uBitx, Bitx and the receiver I am building, and maybe ALC as well.
So for the receiver I am building I figured that some sort of filtering is going to be required in the audio stages. Not entirely sure yet on the final make up of things, but to start with I thought that I would design and evaluate a high pass filter to cut out the low frequencies as this is likely to be fixed weather i am receiving CW or SSB. Though for the low pass filter, i do want either variable bandwidth or select able widths. More on that later.
As with all filters more orders, more betters LOL. And so i jumped online to a calculator tool and quickly designed up a 3rd order Sallen-Key highpass with a cutoff of 350hz. The simulation looked reasonable so i then simulated it in LTSpice just to confirm things and check the OpAmp i had chosen was going to be ok.
Schematic of 3rd Order Sallen-Key Highpass Filter.
Simulation Bode Plot
Next the circuit was built on a solder-less breadboard, the OpAmp is an NE5532 and negative supply rail is an LM2662 Charge Pump. This gives the OpAmp plenty of room to swing when powered with + – 5v.
For the initial testing the OpAmp was fed with 1vpp 600hz sinewave.
Dumb people do dumb things and I spend 10mins wondering why I had 10x gain in a circuit that should have unity gain, then i noticed i had the scope probe on 1x not 10x where it usually lives. There is my 10x gain.
For final shits and gigles i busted out the bode plotter and swept the filter from 10hz to 5000hz to see just how it really looks, and other than a little noise down close to DC, which i think is just the frequency generator not liking being that low, the filter itself is pretty much as designed. -40db at 100hz should be good enough for the kinds of girls i go out with.
Next job will be to either add in a couple of low pass filters for typical CW and SSB filter widths or have a crack with switched capacitor lowpass filters and make it variable. Thats a job for another day.
I have been slowly and by slowly I mean very slowly working on the audio amp stage for a receiver that I am building. Its a slow effort as i try things, fail things and then finally decide on an actual plan. So, I was looking at using a TDA2822 in bridge mode as i have a bunch of those in my parts box here, but after building it and blowing a few up I figured stuff it, its time for a different tack.
Then i saw these on ebay, I have used the PAM8403 boards before but in a different configuration with a dual gang pot on there, they are class E, uber efficient and sound nice, so i figured fuck it, lets stop trying to make the parts count high and lets just use something that works. And yes these things work.
So i busted out the digital calipers and took a few measurements and knocked up a component for Sprint Layout and can now get to the next stage in the audio stage plan, compression, filtering, pre-amp and AGC. That is, if i do not get distracted by something else shiny and play with it for a while. 🙂
Welcome to Dr Sheldon Coopers Fun with FT8. So i fired up FT8 last night for some receiving fun to see whats doing and certainly heard a lot of places. It looks like FT8 is the new black with many people using it. 51 countries heard and many more stations especially out of Japan. All in all, it was a bit of fun to see what I can here on my dipole. Flicked over to 15m now to see if there is anyone about.
Bottom of the cycle, bands will be dead they say. Well, perhaps not as dead as one expects. Little openings are there all throughout the day and in my case, VK2 was open most of the day. Bands are dead of course, not because there is no propagation, but because there is no one home to work. It is what it is and this WSPR thing is pretty cool. I did not learn anything i did not already know, USA in the mornings and Asia in the evenings. And a few other bits and bobs along the way.
I did have one interesting thing happen, a broken decode where I got no call sign but did get a grid square, I am not confident this is actually accurate, but if it is, then the station i was copying was in Egypt, someways south of Cairo. It would be cool if this was actually the case, but I won’t be holding my breath LOL.