HF with a cheap SDR Dongle

Using an Arduino controlled Si5351 PLL Clock Module, Mixer, and a cheap RTL-SDR Dongle I tuned in on the 40 meter ham band today using the SDR # software













I came across a Mini-Circuit ZAD-1 double balanced mixer (DBM) at the TRW swap meet this weekend in good condition for 7 bucks so I grabbed it. This DBM with BNC connectors turned out to be a standard Level 7 mixer.



I connected my RTL-SDR dongle to the IF port with several adapters and fed the output of the Si5351 directly into the LO port. The antenna is connect to the RF port.



Using NT7S Arduino Library and a Mega 2560 board I set the clock0 to 125 Mhz to feed the LO. Below is the basic setup.



This set-up worked great for the Medium Wave (MW) AM broadcast band too. On 40 Meters I listen to several SSB stations just fine. Using the NT7S library for 125 Mhz may be a bit out of range since I do seem to hear a warble to the clock when I listen to the 125 Mhz signal directly on another receiver. I need to experiment with the original Adafruit library and see if there is a difference. All and all a cool experiment. If I can get the warble out of the clock and maybe add some band-pass filters this could be a very usable SDR receiver for HF.

Computer Build

I am building a custom game PC based on the Gigabyte GA-Z97X-UD3H motherboard. It needs to be ready by Christmas Day, and I still have a lot to do before it is finished.

Desert Farm

This weekend I was back in Arizona at my buddies farm. We had a great time playing with all his farm machines and seeing what new things he is working on, like this pump system. He calls it "FrankinPump". This is 4 gas powered pumps connected in parallel that can empty his 50000 gallon water tank in 2 hours.



We enjoyed the trip and his solar system worked perfectly with plenty of power even with the short winter days.

Fix or Replace?

I have a 4 to 5 year old Samsung LCD Monitor that developed an issue where after a 20 minute warm up the monitor would go black. If you cycled the power switch it would come back for two seconds then go black again. I did some quick research and found that a frequent issue is with the capacitors in the switching power supply.















I felt that the effort would be worth my time, so I replaced all the capacitors after a fairly lengthy dis-assembly process and then reconnected everything without fully assembling it and re-tested it. Unfortunately the problem remained. I continued the research now after spending nearly a full day on the project and determined after some lengthy tests that the fault is in the back lighting system. The back lights on this monitor are compact florescent (CFL) units. To replace the CFL is not as simple however. These units are attached to the panel assembly on each end and there are two tubes in each. I think many hams and electronic tinkers hate to throw away hardware if it can be repaired and I have gone to great lengths on other items in the past to get it done, but sometimes you just need to call it quits, or it will consume all your time. I wish things were made to be repaired however many are not or the parts costs exceed its value.

So in this case I will be parting it out to the junk box. There are many good parts and who knows they may live again.

GKOS Keyboard Mockup

I spent some time this week mocking up the GKOS keyboard using some clay. I have the Cherry MX "Black" switches now and will need to make PCBs for each set of  the three switch groups. The mock up taught me that I need some thickness between the fingers and thumbs for it to feel natural and comfortable. Another discovery is that I believe I build can build this using aluminum "L" channel and PCB material to bolt it together. I may even be able to make it folding!

QRSS with Si5351

As I mentioned in my previous post, I have been experimenting with the Adafruit Si5351A Breakout Board and today I thought I would do some frequency stability tests using the QRSS tool Spectran. This tool will enable me to see variation in frequency with sub-hertz resolution.

Using the NT7S Library I setup the following in the loop() section of the Arduino code

Code Snippet

As you can see, all I am doing is setting the frequency to 7.083.000 Mhz (in the 40 Meter band), then after 10 seconds, I set the frequency to 7.083.001 Mhz which is just 1 Hz higher for 5 seconds and repeat. The plot below using Spectran is showing the clock board being received by my FT-817 transceiver with my dipole antenna. The bread board was in the house about 20-30 feet from the antenna with just a 4 inch piece of wire as it's antenna. From left to right, I had been running it for over 10 minutes then I powered it down for about 2 minutes and then powered it back up. When it powered up again, it was about 5 Hz higher than before being shutdown, then after about 5 minutes it was back to where it was before I powered down (pretty cool!). The full width of the plot is 10 minutes and shows less than a 1 Hz variation over that period (again, very cool!).

I would say that this board with a bare Arduino chip would be a great option for a QRSS beacon module as well as the other uses we have discussed. The more I use the Si5351, the more I like it.

Si5351 Clock Module

I ordered a couple of the Adafruit Si5351 Clock Modules that arrived this week, and quickly soldered up the header and plugged it into a breadboard.




I first tried the Adafruit library and verified its ability to generate multiple output clocks, however it is a bit crude compared the NT7S Library. To use his Library I did find I needed to use the latest Arduino IDE for his example sketch to compile. After that it was very easy to generate any frequency in the HF range.

This module will be useful in many projects. People are using them in place of the standard DDS modules. In fact M0XPD as released an awesome dual VFO sketch with LCD display and rotary encoder.