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.
The Main PCB board
The Digital Board: Arduino and SI5351A
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:
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.
http://robs-blog.net/2018/12/22/receiver-rf-front-end/ To see where things have come from, here is a link to the original post:
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 :
The gerbers can be downloaded from HERE: http://robs-blog.net/Files/rf-frontend.rar
Got to do some building on this the other day and knock up the LPF board. Ran it though a battery of tests and other than Elsie screwing up the values of the filters, everything worked at designed. I gotta suck the inductors out and add some turns. Not a fun job but its gotta be done. Gerbers for the board can be downloaded, from HERE: http://robs-blog.net/2018/12/16/4-band-lowpass-filter-board/
This picture will give a bit of an idea on the stackup and how these things well all fit together. Using the 10w ebay PA for now for testing until I find a transmitter design i want to use and lay a board out for it. But as an idea, it will be using a pair of RD16HHF1 conservatively biased for 10w or so.
So today I populated the 2nd IF mixer, the 2nd mixer and some of the switching circuitry and gave all those elements a little bit of a test.
To follow on from the test of the first IF amp, I put a 10mv signal into the first IF amp and tested the whole IF strip through the Xtal Filter and out the 2nd IF amp buffer and it all seems to be working quite well.
But there is one issue and I am not sure what the cause is. The 470R resistor from voltage divider on Q6 does not go straight to ground and trying to find its ultimate path to ground has been elusive.
To make matters worse there are q Q10 in the schematic and Q10 and 21 on the board, there are 2 diode on the board not on the schematic and I cannot for the life of me work out what the actual cause is here. Either one of the Q10’s is not being biased on or there is some part missing or either VR7 or VR2 are not providing the emitter ground path on the emitters of those Q10 transistors.
Anyway, I think what i will do is pull both the Q10’s out and related circuitry, part of which is for a signal meter and just hard wire the 470R voltage divider to ground. That will at least leave me to be able to complete the receiver and actually test it.
At one point today I had fed a 9mhz signal into the IF strip and was getting a 600Hz tone out the audio amp, so that in itself is promising as I was worried about the dodgy design 2nd mixer. Which looks like a ring mixer but does not have trifilar windings on the inputs and outputs, but some crazy bifilar winding on one side and a variable resistor and cap divider on the other. I am not sure about this mixer design and I have not done any google foo to see if i can find it, but it does work
Oh and for the diodes in the mixer i did not use the typical 1n4148 diodes that everyone uses, but rather I used a Schottky Diode 1N5711, it probably means i have way to much drive from the BFO as the switch on of these are much lower, but its working and for now, I call that a win, particularly so when i really do not understand the mixer topology being used.
Oh and as far as audio goes, of the 2 AF stages, I am only using the LM386 first stage because the TDR2003 is motor boating or oscillating or just acting like a tard and I am not sure why here either
I do hope the next post will be a video of it receiving signals. Failure is always an option here, but so far this build has been very challenging, but its been rewarding and even if it ends up being a pile of junk, i will have learned a lot.