Sometimes when laying out a board you have to create your own footprints. Out comes the digital calipers and you start making measurements, but, what if you make a mistake, the board becomes a waste of time. So, i like to print out the board layout at 1:1 resolution and then overlay my parts and where possible push the pins through the page to check everything lines up right. Saves in the long run 🙂
On thing i manage to do well, is make a mess. Not so great on the cleaning up or being tidy and organized. But i got a little excited the other day and started to sort out all my stuff and make it into some sort of organized mess, where i can at least find things.
Starting with my component trays, I have them all stacked together now in the one location, the only thing i need to do is to add front lables so i know what is in each tray. Each tray has its own theme so its just a one word label that is needed, resistors, transistors, IC’s, Arduino etc.
So after getting all my componentry away and tidy, i had some bench space left over, and do i cleaned up and organized my work and test area of my bench. Things are nice and clean for now, I just need to find a place for my current project, the 3 boxes on the upper shelf and fill that gap with something nice like a spectrum analyser. HIHI.
So we got some nice winter sun today and I was able to test them out in typical sun conditions and we are making pretty much close to the theoretical maximum they can make, peaking at 550mah and averaging about 440, all in all this is rather good and well suited to the purpose i have in mind for them, keeping a portable rig running longer on a 7ah deepcycle.
So today i thought i might be fun to whack together a VXO for 80m and see just where i landed me. Now i know that pulling crystals very far is not an easy thing to actually do, especially when they are on the lower end of the spectrum. So with this in mind, i set my initial goal as 1khz pull. I figure if i can get that, its kind of usable in other projects.
First job is to get on google and find a simple schematic, with that out of the way, I can get to putting the ugly back into ugly style home brewing and slap something together on some scrap board.
And slapping together is just what I did, a pair of 3.6864 xtals, with 10uH series inductance and 170pF of capacitance in the polyvaricon.
Give it some power and connect up the scope and freq counter and am greeted with this ugly waveform, harmonics, bias, its a mix of everything that is wrong in the world. So let see how far we can pull these bad boys.
High freq is 3.6867
Low freq is 3.6863 HAHA we managed a whole 400hz agility, as good as useless, but it was rock stable, pun intended. So i did a but of goggle foo and found that I can get much better pulling power with more inductance, 10uH is orders of magnitude not enough, so i added another 200uH in series and got a total pulling power of 2khz. 2khz is not much in the scheme of things, but, for a cw 80m rig, 2khz is a nice slice of spectrum to be frequency agile on.
So, whats next? rip out the xtals and drop in a ceramic resonator and adjust the series inductance to suit. Should see a good pull range with that.
I got to thinking the other day, as I was pondering placing an order for a couple more books from Pages of Cobram that i have started to amass a bit of a library and I probably should write a bit of a review of them. Oh and if you are looking for a bookstore that is not going to mess you about and is competitively priced, give Peter as pages of Cobram a call and place your order there. Just about all my books have been purchased there and never had an issue, ever. I found a book that was not listed and they even ordered it in for me, a 1 off, cannot complain about that.
Anyway, on to the books:
Homebrew Cookbook and Building a Transceiver by Eamon Skelton: Skelton is a good writer and these books are and interesting read, however, cookbook contains a lot of the same material covered in transceiver. If i was buying all over again, i would pick one, either one and be done with it. I am not sure how useful transceiver is in actually being able to build a transceiver from whoa to go, but it is a good read that documents many of the decision making processes the home builder faces. A worthy read, with limited scope for developing the documented project. 6/10
Experimental Methods in RF Design by Hayward et al: This is a book I love to hate, now dont get me wrong, this book is a tomb and a beast, jam packed with masses of information and probably the best text book we have on all things RF and Amateur Radio. Its just that it is hard to find the information you need, the flow is somewhat haphazard and illogical and it just tries to be all things to all men and does not really do any of them well. In some places its practical, in others massively theoretical. I think for me, I am always wanting the pertinent information and less of the fluff. Often times, bits of a schematic are just missing, like the number of turns on a bifilar winding, with a note to look in the transformer section, which is then masses of theory and I still do not understand why or how the turns ratio is calculated, other than most times in HF rigs, its 8T bifilar. Love it or hate it, or as i do, have a love hate relationship with it, its the best we have, but could be so much better and designed much more towards the practical person, rather than theory. 7.5/10
Hands on Radio Experiments by Ward Silver: These books are copies of what was written in the Hands On column in the ARRL mag. The writing is great the projects great, its just its not a complete copy of the column and they are not in chronological order. Its a little frustrating when a project references a project not in the books, or if it is, you need to search all over to find it. I find myself reading bits and pieces of these books over and over, generally before bed. 7/10.
Circuit Overload and RF Design Basics by John Fielding. Circuit overload is great lavatory reading, a useful schematic followed by an explanation of how and why it works. I have learned a fair bit from this book, all while sitting on the toilet. The sections on filters are almost identical in both books, and of all the books i have, these make the best explanation on how to design LC filters of anything i have read and for that info alone, make these books useful. 6.5/10
Radio Projects for the Amateur 1,2,3,4 by Drew Diamond: I find these books to be inspirational, while i am not all that interested in anyone project to build in its own right, when i am stuck for an idea, or a solution, these books seems to have it. The books themselves are copies of articles Drew has written for other publications, the explanations and descriptions are good, and generally give you all the information you really need to know without too much fluff. I will often pick one of these books at random and read an article or 2 before i go to sleep. 8/10
I have a couple more books i will add to this list later, and I have some new ones coming soon that I will also add to this list. Happy home brewing.
An interesting story with this one. I had been calling cq for a while, having a qso with the odd station here and there, when i got into a ragchew with Cliff, a ZL station. We had been chatting away for 15 mins or more when John said his call during a pause, he was a little low down to me, but, 5mins later when he was called into the qso, he was a nice easy copy. I could only have a brief qso with John as i needed to use the loo, i was about to explode, but, we made an exchange and a few other pleasantries and I do hope to catch him on the bands again. Tu 73’s John.
I have worked Michel a number of times, always a big signal, with those antenna is it any wonder 🙂
First time i have worked Dennis, was nice to get another Philippines station in the log.
I was really pleased to have a qso with Gunter, he was calling VK/ZL and with next to no takers i was able to get him 2nd call, this was also my 2nd African country.
For anyone who watched the Mythbusters, the catchphrase “Failure is always an option” is one you will hear often. It is also one that i subscribe to in general, where, no matter how well you research and plan, no matter how great your methodology, failure is always a very real possibility.
I was reminded of this in the last couple of days when an audio stage for a DC receiver did not produce the intended results. The audio output from a mixer in a direct conversion receiver is very low and needs a lot of gain to bring it up to speaker driving levels. With that in mind, i have a preamp prior to the mixer giving 10x gain to the incoming RF, and then lots of audio gain post mixer to bring the AF up to a nice listening level.
With that in mind, i thought, OP AMP preamp would be a good idea followed by a LM-386 at 100x gain. Trouble is, I also set the OP AMP to deliver 100x gain and that is 10,000x gain too much and obviously something is going to distort. Changing the gain of the OP AMP to 10x was tried next, and while the audio was nice, it was much lower than the LM-386 in isolation, and the whole point was to have nice sounding audio that would drive a speaker, this was certainly not that. I am guessing there is some impedance miss match there, that i have not accounted for, but to be honest, i really have no idea.
Now, i could run the LM-386 by itself, the audio will be a little lower than i would like, and lets face it, they sound like arse when it comes to CW, which is the main mode this RX will be used on. So i am back at square one, needing to find an audio stage that both sounds nice and gives 150 to 200x gain and is power efficient. Wish me luck HIHI.
The offending circuit and its implemented circuit board.
The above picture is a block diagram of the receiver section of the 40m direct conversion transceiver i have been building for some time. There is nothing ground breaking in the design, it is fairly typical fair for a direct conversion receiver, taking elements from many different designs and bringing them all together into, hopefully a cohesive whole.
This is all part of the “5 x 7” CW Transceiver project i started to outline here: “5 x 7 Tranceiver”
A few things have changed with this, especially so in the front end where the original circuit as been totally replaced with something a lot more simple.
Band Pass Filter: The band pass filter is a 7th order Chebyshev 50ohm in and out with 0.1db ripple.
Pre Amp / Mixer: The pre amp and mixer both use Mini Circuit devices, MAR-6 MMIC for the pre amp and either TUF-1 or ADE-1 for the diode ring mixer.
Local Oscillator: The LO is an Arduino microprocessor controlled AD9850 DDS VFO.
Buffer Amp: Is a simple common emitter, common collector, gain buffer stage to take the LO amplitude to 10dbm.
Audio Diplexer: This diplexer, out of EMRFD starts to narrow up the bandpass and increase gain of the AF.
Active AF Filter: An active 500hz wide CW filter, 8th order design using a Quad OP Amp.
Audio Amp: Finally, the audio amp using an op amp pre amp and LM386 driver.
The only things left to actually build are the 3 audio stages and then test it all together and see if or how it well it works. Failure is always an option as they say.
At anytime, there might be half a hundred dozen different things on my work bench slash radio desk that can take up my interest for a fleeting moment. It might be a new toy, a new component, or just something shiny.
I was reminded of this today when i picked up part of the Direct Conversion CW rig i have been building for what seems like forever. I had some boards build to house a micro controller and DDS unit and I started to fiddle about with it and noticed that the output was very low.
The DDS should be putting out about 250mv rms at 7mhz, but i was only seeing 50mv rms on the scope. Something was up and i had never noticed what or why before. Pulling things apart and checking things separately showed everything was working right, but when plugged into the board it all went wrong again.
Turns out, I was measuring things at different frequencies and amplitude out of the DDS depends on frequency. Measuring 40mhz in the board and 7mhz out of the board, but being distracted i did not notice my error til much later. So, i have now cleared off the work bench, the only things on it now are stages of the DC receiver and everything else i have been tinkering with has been shelved. Time to get some focus and get this things build already. So tonight, i will build the DDS buffer amp and add the mixer as well.
More to come on that soon. 🙂