Month: December 2018

2019 A Years Projects

Its new years ever and I have been thinking about the things I have achieved in 2018 and its been quite a lot, but at the same time, there has been a lot that I have not completed or even made a dent in and others that I have failed at.

So this list is the list of projects I plan to complete in 2019. Some of these I have had for sometime, some are not even in existence yet but are coming soon and some might be absolute dismal failures. Some of these can be competed in an afternoon and others are going to take some time, but here we go with the list.

1. Bebek Radio

First on the list is to finish the bebek, at least to receiver level. I do not think i am brave enough to tackle the transmit side of it. Its been an interesting and frustrating project so far, the sooner its over the better.

The Radio Bebek

2. Pixie Transceiver

The Pixie Tranceiver

Ok, so i have build one or two of these before, but I have this one in the draw still and I should build it and attempt to make a contact with it, or at least get spotted on the Reverse Beacon Network calling CQ with it.

3. 49’r Transceiver

The 49r Transceiver

There is a similar kit on ebay called the Frog Sounds that I built ages ago. The receiver in it actually worked quite ok, but i never ever transmitted with it, let alone made a single contact with it.

So what I plan to do with this kit is modify it to use a DDS VFO and make it frequency agile. To achieve that i will add a bandpass filter to the front end and use a AD9850 DDS to inject a signal where the Xtal oscillator currently is.

4. WSPR

QRP Labs WSPR Kit

I was given this maybe 2 years ago from a friend, Simon VK6MSC. Its been sitting in my draw waiting and waiting to see the light of day and get built. Now that I can actually use digital modes, I am itching to get this happening and on the air every other moment I am not using my radio and antenna.

5. Super Rockmite

The Super Rockmite Kit

Another ebay kit i have has sitting around for a long time. I am not sure weather to build as standard to modify it to make it frequency agile. At this stage it might just be an afternoon build and see if I can make a contact with it. The built in keyer is a nice touch.

6. QCX

QRP Labs QCX Kit

Now we are getting into serious build territory. The QCX is more than a toy kit, it is a quality transceiver kit that I will take my time building and will enjoy using.

7. VK4FFAB 4 Band Receiver

PCB Board for the VK4FFAB Receiver Project

This has been an eternal project that has no end in site. I would like to have completed the board above built and connected together to see how it actually works as a receiver. Each of the boards has been built and modified in isolation and what is pictured above are 2nd and 3rd iterations of some boards. Along with just stuffing the boards there is a whole lot of software to write to control the whole thing. While its mostly done, there is still a lot of work to go.

8. QRP Labs QSX

QRP Labs 10w PA for QSX

Not a lot i can write about this, other than I will be dropping everything and building one once the kit is fully released. All i have at the moment is the 10w PA. This kit i am excited to get my hands on.

9. ZOI-40 Tranceiver

ZOI-40 Tranceiver

This is one of those projects that I may or may not get to. Its another board laid out by YD1JJJ from Indonesia. I have not taken a close look at things, but i kind of expect this to be a nightmare like the Bebek and something that I will have to buzz out and compare between board and schematic to complete.

10. Bitx 20

Bitx 20 PCB Boards

Where the BITX craze kind of went viral, the Bitx 20m will be something I tackle when i get time.

11. Other Notable Thoughts and Ideas

There are really only 3 other ideas floating around at the moment and that i would like to get to this year and they are all transmitters. A CW transmitter, a RTTY transmitter and a PSK transmitter. 3 individual or potentially combine into a single unit to pair with my receiver project. These will take precedence over some of the projects above and will make nice additions the the lineups.

To be honest, I have certainly listed out more stuff than I will probably get to, but these are the things I have in the pipeline and are my immediate list of goals. The hardest part with all this is not getting sidetracked and going off on a tangent.

Wish me luck.

Happy New Year to you.

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Radio Bebek LP and BP Filters

Ok, this has been a fun section to build. I spent the better part of an hour scratching my head over this and wondering why it was not working. Well, this is how I approached this section of the build.

First thing i did was rummage around in my parts bins for canned inductors. I do not have a lot of these things, but i do have a few and those are of a few different types. From what I understood from the few bits in information i have been able to glean from the internet, they used 10.7Mhz IF cans. This then narrows it down to 3 or 4 actual IF Transformers.

Of the ones i have in my parts trays, only one looked like it had suitable values for a 7mhz filter, with windings that measured 120nH and 2.2uH. That was going to get me ballpark and allow me to simulate the required capacitor values.

LTSpice Simulation of Bebek Bandpass Filter

The fun begins when you go to buzz out the actual pcb, because the input series cap is not on the board, but its on the schematic, first issue that did my head in. The output series cap is on the board and on the schematic. Simulating without the input cap seemed to make no difference at all. So i just left it out rather than cutting traces and soldering it to the bottom side of the board. This is not the first time in this build that i have found such discrepancies either. In fact, it would be a miracle indeed if someone could stuff the board with parts and it just worked.

LTSpice Simulation of Bebek Lowpass Filter

Not feeling very confident at this point, I thought it would be best to simulate the lowpass filter just to make sure it was ballpark and surprise it was actually quite ok. Perfect in fact.

Radio Bebek filters built and ready for testing

Ok now this is where the fun began. First thing i do when building something is buzz it out to make sure there are no shorts. Well the low value windings on the canned inductors are only 100nh. They look like a short to ground at DC. So sticking my continuity meter on both the antenna pins caused it to go beep and I spent the next 30mins trying to track down the mystery short to ground, before i worked out what was happening

Testing the Bebek filters

So finally I wired up some power and injected a signal and started to trace it though the board all the way to the input port of the mixer footprint. Initially there was nothing, so i probed around and found RF at a mystery pad showing a 6.8uh inductor, which is in series with the 7pf coupling cap. After some head scratching, I think that this meant to be a capacitor so that you can series 2 caps together to get a lower value. I dropped a wire link in there and things finally worked.

Signal scoped at the RF Post of the First Mixer

0.02V signal injected at the antenna port, through the lowpass filter, through the bandpass filter into the RF Preamp and we have 50mV. I do not think the losses in the filters are all that high.

So that end this nightmare 🙂 Its all worked so far, just some IF amps, IF filter and 2nd mixer to go to have the receiver working. Still plenty that can go wrong from here, but its getting there.

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Radio Bebek RF PreAmp

Radio Bebek RF Preamp
Powered Up and Testing
100mV in and 500mV out

So the RF preamp has about 5x gain. On 40m its probably not really needed unless there is a lot of loss in the filters. Which in this case might actually be the case as the RF path from the antenna goes through the LPF, into the Relay and then into the BPF. So a little gain ahead of the mixer might be a good thing.

One thing that I left out for now were the back to back clipping diodes. I am only building this as a receiver pretty much to begin with and I am not sure clipping diodes are really necessary. Next I will be working on the LPF and BPF. Need to do some LTSpice here to make sure my values are correct.

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Radio Bebek LO Buffer Amp

Ok, back to doing some work on the Bebek. In this block the only real issues are that there is an extra DC blocking cap on the board that is now shown on the schematic and that the Cap values on the schematic are not the same shown on the board. In this case I have defaulted to using the values on the board. 10nf and 100nf on the board are 1nf and 10nf on the schematic. The former values just seem more logical to use and the latter are most obviously an error on the part of the designer.

Bebek LO Buffer Amp
250mV in and 2.5V out

So the LO Buffer Amp has a 10x gain. I injected it with a 250mV signal to get 2.5V out. Now obviously this is not good if you are using a SI5351A as it puts out 1.5V. But this should work quite well with an AD9850 which puts out 200mV. It still might be a little to much drive for a -7dB mixer, but it should be ball park upper limit.

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Uzbekistan, Another New One

Seems like its every other day that I am posting about working a new DXCC entity on my blog. Well, here is another one. Uzbekistan. From the looks of it, this guy does not LOTW, so its either pay for a card or not have it confirmed. Not sure what I will do here, I am not into paying for confirmations, but, I will always have this screen shot of the FT8 window as proof I worked him. Even if that does not count towards DXCC. 😉

Uzbekistan on FT8

Not to be outdone, I also worked Kazakhstan not once, but 2 times. And even have the NON AG card from eqsl to almost prove it LMAO, lucky i do not take this collecting numbers all that seriously. I have Kazakhstan confirmed on LOTW.

Kazakhstan on FT8

Eqsl Card from Kazakhstan

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Receiver RF Front End

VK4FFAB Receiver Front End

Ok, I am posting this mostly because I can, but I wont publish the gerbers yet because I actually want to layout the board better, fix some footprints and have the boards remade. Not because they are bad or do not work, but because I know i can make them so much better

So this it my receiver front end. RF comes in from the antenna, through the TX-RX relay into a 0-31dB attenuator module, into a 5 to 15dB RF Preamp.

The RF amp is a pair of J310 as a dual gate mosfet as designed by Pete Juliano here: SimpleCeiver

Variable RF Preamp Schematic
Prototype Built and Tested
PCB as originally laid out.

I might add some more info here later, or will just post anew when i have redesigned the board. The main thing i want to do is to remove those wire links joining the attenuator to the rest of the circuit and replace that with some right angled SMA connectors as the attenuator board comes with SMA connectors on it already. I will probably change the relay also as I now have some better RF relays, not just chinesium grade floor sweepings.

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Ecuador, Another New One

I have seen HC2AO pop up a few times on 20m over the last couple of weeks. Have put out calls, but he could not hear me. So today when he again came up on FT8, I put out a couple of calls, got on PSK reporter to see that I was being heard, then persisted calling. A couple of QSO’s later and I was in the log. Thats another new one in the log and another new one confirmed. Not bad for 30w and a 1/4w vertical.

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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://robs-blog.net/Files/ControlBoard.zip

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