Transceiver Control Board

Control board PCB design files

It seems like now days every man and his dog has a DDS/Digital Synth VFO project happening. I have had a couple and I am pretty sure that there are even Gerbers floating about on my blog for that very thing and was one of the very first boards I ever designed and laid out.

Well, times are a changing and rather than just a simple VFO, I have designed a board to control all aspects of radio control. To fit all the functions into one microcontroller required a bit of a step up and the use of an ATMega because I needed that many digital pins.

So what does it do? Well:
1. Real time clock and keyboard for logging contacts, digital modes like RTTY and keyboard CW.

2. Rotary encoder for the SI5351a VFO obviously.

3. 8 push buttons for various functions like band changing, mode changing and setting the attenuation level. On my front end board i have a 32 step rf attenuator in 0.5db steps, and for selecting 1 of 2 audio filters, but this might change yet and become DSP audio filtering with a lot more options at a latter stage.

4. Setting relays both bandpass and lowpass filters for 4 bands and selecting one of 2 IF Filters.

Now i am only releasing the board files, the software is something you are going to have to write yourself, because my code is not complete and probably wont be complete for sometime. I have most of the basic functionality written, but it all needs fleshing out and cleaning up. Now its nice when someone does it all for you, but, this will be pretty slick when complete and well, i dont want anyone making a commercial product out of my work and so the code will probably never be released. But these board files will save you hours of work, even if you have to code it all yourself.

The latest iteration of the control board


Early prototype board working and functioning. 

Gerber files for this board can be downloaded from here: http://vk4ffab.info/Files/ControlBoard.zip

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4 Band Bandpass Filter Board

The relays are double pole double throw in a standard 18x9mm package size. The transistors are anything you have in CBE footprint, I used 2n3904 and the resistor is there for current limiting, just pick a typical value, i think i used 4.8K. The trimmer caps I use are 3 leg 100pf max value to tune and align each filter.

SMA edge connectors bring RF in on the left side of the board. By default all relays are in the OFF position and no RF can pass through. The 6 pin header brings control signals and power to the board. To turn a relay on, a 5v control control signal is placed on one of the first 4 pins to turn 1 pair of relays on. The last 2 pins are ground and VCC of the relays you used.

Aligning each filter can be a bit tricky, it is best to use a spectrum analyzer and tracking generator if you have one, or a noise source and spectrum analyzer or even in a pinch if you slow down the seconds/division on the oscilloscope so you can see the filter shape. The reason being, if your filters are not quite tuned right, you will end up with 2 peaks and some attenuation in the bandpass you just do not want.

The filters themselves are Double Tuned circuits. To design the values needed for each band I used some software called DTC.exe which can be found on a CD in the book Experimental Methods In RF Design. I have linked it here for download, but I am not sure if I am allowed to and i will pull it down if asked by the authors: DTC DOWNLOAD

The gerber files for the board can be downloaded from here: Bandpass Filters

Here is a schematic of the filters with values for 80, 40, 20 and 15m.


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4 Band Lowpass Filter Board

Board Design 

Ok, in the spirit of sharing and making things easy for people, I am going to start releasing some gerbers for the various boards I have designed for my various projects, that work HAHAHA, because, yes, not everything i do works.

I am not into this for making money, I do everything that i do simply for the love of it and for the learning experience. So selling boards and things is not high on my agenda. And besides, you can get 10 boards made and send to you from JLCpcb in China for not much more than it would cost me to send you one from Australia.


First cab off the ranks 7th order low pass filter boards. So you will notice there are no part values on the boards. Why? Well because i do not know what bands you might like to build for. The relays are double pole double throw in a standard 18x9mm package size. The transistors are anything you have in CBE footprint, I used 2n3904 and the resistor is there for current limiting, just pick a typical value, i think i used 4.8K.

SMA edge connectors bring RF in on the left side of the board. By default all relays are in the OFF position and no RF can pass through. The 6 pin header brings control signals and power to the board. To turn a relay on, a 5v control control signal is placed on one of the first 4 pins to turn 1 pair of relays on. The last 2 pins are ground and VCC of the relays you used.

For designing the filters I use an online calculator like this one at Calculators Edge: http://www.calculatoredge.com/electronics/bw%20pi%20low%20pass.htm Or a software tool like Elsie.

Lowpass Filter Board

Gerber Files can be downloaded from HERE:  http://vk4ffab.info/Files/LowPass_Filter.zip


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Radio Bebek 40m QRP Transceiver

Radio Bebek by the Bogor Homebrew Radio Community in Indonesia. Its an interesting little qrp radio that uses very common off the shell parts, mostly. There are a couple of oddities and absolutely no build instructions at all. So its not a build for the faint of heart, its a lot of reading the schematic and buzzing out the board to know what goes where because there are NO Part Designations on the board, only values and in some cases those values are wrong. But, i am having a go at building it and seeing how i get on with no instructions and only a schematic. Wish me luck. I do not think i will make this a transceiver, but will build it as a receiver only as i want to match this up to a 10w CW transmitter i have built.

The project can be found here on the authors website. http://blekokqrp.blogspot.com/2018/08/radio-bebek-40m-lsbusbdigital-qrp.html

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Vertical Antenna For 20m

I do not have a lot of space for antennas. So i have to get creative when possible to be able to work the bands of interest for me at this time, 40 and 20m. I have a low slung dipole for 40m in the tiny space called our backyard. Which leaves doing something for 20m.

I have had this old station master CB antenna sitting in my workshop for a while that i planned to use on 15 or 10m. Well, nothing much is doing on either of those bands other than some E’s so i have reconfigured the station master into a 20m 1/4 wave.

Its about 4.5m to the base of the antenna and the 5m of radiator on top of that and 4 radials to bring the feed impedance up to 50 ohms.

The fact that the 2:1 bandwidth is 2mhz kind of tells me that i have made a high quality dummy load. I am still unconvinced that its not a dummy load even though it does radiate.

This is the FT8 map from today. It certainly hears better than the portable dipole and reports are about the same so it is doing something.

Not to be outdone, reverse beacon reports similar reports around the pacific region. The jury is still out and I might still yet pull it all apart and start again to see if i can get that swr bandwidth narrower. For now, its what I will be using on 20m.Facebooktwittergoogle_plusredditpinterestlinkedin

Station Master CB antenna on 20m

I have had this antenna sitting under the work bench in the garage for some time. My initial plans were to use it on 15m by making it a little longer and going to town to get it close to a 50 ohm match and hope like hell it worked ok.

So, being the bottom of the cycle and not much doing on 15m at all and that i can tune the 40m dipole up on 15m and it will work ok, and 10m is pretty much a bust, I figured i would turn this thing into a 1/4 wave on 20m.

After a bunch of false starts and I want to smash this with an axe moments 🙂 I got to doing what was needed to make it kind of work. First part was to bypass the tuning coil as it is not needed, its about 5.2m long, a bit on the long side i know, but without going at it with a hacksaw it was not not becoming shorter LOL.

 

Put it on the vna and it looks kind of ugly. But We can fix that I hope.

 

A couple of radials later and its starting to look more like what it should. 2:1 swr across the whole 20m band. When i can be bothered to add another 2 radials that should come down even more.

Fired up FT8 and it seems to be working as good as the dipole. I dont think its any better, but it is certainly not worse. That gives me 20m at home now in a more permanent way until I can be bothered to buy a tri bander.Facebooktwittergoogle_plusredditpinterestlinkedin

Best Laid Plans And The Mind Of A Madman

So here’s the thing. LOL how many times have i started a new blog post with So. You know what it means though, that something did not go to plan, did not work and just became an exercise in learning. Yes, this is one of those times when I learned a lot and still have nothing functional and working at the end of it. 🙂

So JLCPcb were running a special of 30% off on boards. I had been tinkering with an audio amp and filter board for a while but it was no where near ready. I really had been lazy and just not put any time into finishing it. So while searching around for something else I came across this Indonesian site that contained downloads of Gerbers for some of their projects. So i downloaded one and looked over the schematic, it looked interesting so i then rushed into getting my audio board ready to make and sent off for the boards.

Now I did do somethings very wrong here, I played the main components like the relays, IC’s etc and locked them in place and used the autoplacer and autorouter to place all the passives and route it up. Obviously not the best idea, I also should have put a via fence around the negative voltage inverter and the same to isolate the 2 audio filters. So anyway, i got the board populated and started checking voltages. No 12v rail to the 2nd opamp, audio preamp or the audio amp. Seems that the 12v net did not get autorouted in 2 places and I did no checking to ensure things were right. Noob mistake, but i was rushing. Bust out the MOD WIRE.

So does it work? As pictured NO. The relay below the voltage inverter on the right hand side of the board is acting as an antenna for the voltage inverter oscillator frequency, which in turn is causing the audio amp to oscillate like crazy. Removing that relay and bridging the pads fixed that problem. The second major issue was the values I used for the filters.

Normally i would simulate in LTSpice just to confirm things are ball park. Turns out that the calculator i used, uses the frequency supplied as the -6db point. Kind of useless for a CW filter where you want 600hz peaked not attenuated by 3db LOL. So i will suck out the parts and replace them with something more appropriate now I have redesigned the filter response and simulated it.

 

These are not going to be the sharpest filters in the shed. They just have Salen-Key responses. I did not want brick wall filters, I just wanted something to make listening more pleasant. Eventually I will do the aggressive filtering in the IF using DSP. I have a partial design for this happening already, but it is a long way off being ready. Crystal filters it is for now, but DSP IF is coming, it just takes time.Facebooktwittergoogle_plusredditpinterestlinkedin

Sotabeams Linked Dipole 20m SWR

I had need to throw up the sotabeams 20m dipole here at home while I am operating as VI4LWF a special event call sign for the Armistice Day celebrations. I wondered why the autotuner went bonkers when i keyed up for the first time and so i thought i should take a look at it on the VNA, well it looks little on the long side to me, especially when operating up around 14.310 where most VKFF activators congregate. Its not bad, it just could be better.

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