Just like a bought one hey? This has been a while in the making and brings together many of the smaller project boards into one. We have 5 low pass filters, band pass filters, TX/RX switching, and + and – 20dB RF preamp. Low and behold, it actually all works right out of the box, no major issues, other than winding all those toriods is a nightmare LOL
In testing the losses were acceptable, 1/2 a dB on the low pass and 1.5dB on the band pass. With essentially 10 filters on the board, it was going to be interesting to see how much work they would require to bring into the correct band.
Most of the filters were actually just fine as you can see here with the 80m low pass filter. Only 1 low pass filter needs to have a turn taken out of each toriod to bring the corner frequency up a little so the corner is not in band, and 3 of the band pass filters need the same to move them up in frequency also.
I did my best to account for strays and variation in winding, but there is always going to be some error and fixing, especially in the band pass filters where I am using a specific value of inductance in the calculations for the filter and then using a turns calculator to get that inductance. These things are always rather hit and miss. With the low pass filters you can always set the corner frequency higher than needed, like with this 80m filter, our band here is from 3.5Mhz to 3.7Mhz, and I set the corner frequency to be 4Mhz, because if you end up with strays you always end up with more inductance and capacitance, not less and those lower the frequency response.
Anyway, thats it for me, I have another 6 boards to build now and I seriously hope that the receiver board is actually good, because if that works well enough to use, I will have a very useable and workable 5 band 50w transceiver. Wish me luck.
Its still not working, but it is getting there. All be it, slowly. So i fixed the oscillation in the PA, replaced the fet and now at least the PA is all working as it should be. Now I am still not getting anything out of the Mic. Not sure what is going on there, but there is power and it worked when i bread-boarded it. Obviously something is not right, but I will work that out soon enough.
Today I built the PA and have tried to test it out. As it currently stands, I think my design might have some legitimate design flaws. I am not certain yet, but tomorrow I will know more. For now, I am off to bed. I am done for today.
The fix for the Lo Leak was nothing more than a 2nd relay to disconnect the transmitter entirely when in receive. I am currently listening to 40m to whatever the contest is on tonight, and I am hearing everything other than my transmitter HAHA. I really should wire up the switching and make a few qso’s. But its late and its been a big weekend and I think i will go to bed instead. At least i know that this will work. I might take it portable up the road to one of the WWFF parks tomorrow and see if i can drum up the first qso or 2 with it.
I usually regret posting about something before I even know its working, I mean this blog is littered with the dead corpses of so many projects it probably should be called Robs Graveyard. Anyway, I thought i would post about where I am at with the 40m DSB Talkie Walkie. Other than having one small thing to test, everything has worked as designed.
Shock horror I know, but mayby after 5 years of killing parts, I am finally getting the knack. I have compacted the boards into 2. Yeah i could fit it all on the one board and in a future edition I might just do that, but for now I see a lot of advantages in keeping all the digital stuff on its own board with header interconnects.
All i am left to do is to send them off to China and have them made, build, test and make QSO’s with it. Wish me luck.
Slowly integrating all these bits together in software and currently all the relays are clicking in sequence when I change bands on the control board. If you look closely on the upper right, you will see an updated version of the Band Pass Filter board that uses different inductors and filter topology. I need to populate and test one filter to ensure its right and then build the entire board.
Something that I did not notice was that when I changed Ecad software my mounting hole pattern has changed slightly, so neither of the old filter board designs will stack with the other boards. So i have to redo the low pass filter board and I am going to redo the rf frond end board as well and move things around to make it a little more usable and to make sure the 3.3v regulator has a heatsink on it. With bugger all current running though it, it still gets burn your finger hot and that is not right. I am starting to wonder if these ebay parts are actually dodgy or something.
I updated the board and so its a bit better laid out than previously and have shortened the rf path by moving the SMA connectors Gerber files for the board can be downloaded from here: http://robs-blog.net/Files/Dual_Xtal.zip
Being invasion day here in Australia with not much doing, between watching the cricket, sleeping and doing not a lot more I managed to build and test the bandpass filter board.
Overall, well its MEH. The filters are nothing to rave home about, they will work for now, but I do think i am going to redesign the board using a different topology and get much better attenuation in the stop band.
I ran all the filters though the bode plotter and remembered to screen grab 3 of them which i will now present here for laughter and ridicule.
40m bandpass filter is a 2 humped camel. The width between the peaks is fine, but i will have to play with the coupling cap value to see if i can take some of that hollow out.
20m bandpass filter looks ok, its just to narrow.
The 15m band filter is also to narrow and the high side attenuation is kind of poor at best.
The 80m filter was also MEH but i forgot to screen grab it, It was double humped, but only -3db down in the middle and the high side attenuation was also poor. Anyway, these will allow me to get building and testing more parts of the radio and think about changing the topology and laying out a new board and having it made. I have 2 other board sitting there waiting to be sent to JLCpcb, the 3rd iteration of the audio board and the first of a final PA board. More on those to come.
So between the first iteration and the 2nd, I have changed from using Sprint Layout to using Diptrace. I have tried a few different programs from Kicad to the free version of Altium and I just could never get the hang of how to make components and footprints in either of them
Diptrace on the other hand I find to be much more intuative and straight forward to use and I can make components and footprints in it with easy, as will be seen later when i get the latest batched of board back from china and write a blog post. So many new parts all created by me in the one library so i can find all my parts easily.
Anyway, to the board at hand. Its still got a couple of minor mistakes on it, the cap footprints were in 2.54mm not 5mm which the caps I use mostly are, the 5v regulator and caps are in the way of the right angled SMA connector and I am not sure that the variable RF preamp is actually varying. Circuit wise it should work, but the spectrum analyzer was not showing any gain change.
Anyway, the design will not be changing now, its built, tested and it works. And i can stay like that :