11/3/2018 ~ See You Tube Video of the Arduino/Si5351 Prototype. Scroll Down
I frequently receive inquiries about building the Si5351/Arduino boards and the last blog posting was sort of a stop gap measure to answer some specific questions; but I am sure for those who don't like to read or to look at photos that was not enough. Or alternatively they don't want to invest the time to read and study.
Note, not all Si5351 boards are a simple drop in the circuit and move on. I use the Adafruit boards or clones made by others based on the Aadfruit design. Boards are available from Hans Summers website; but he uses a different clock frequency than the Adafruit or Clone boards. Thus if you have the Summers boards you will need to make some adjustment for his clock frequency. I don't know how to do that and got lost in the process that was described to me. So if you have those boards, contact Hans Summers for any adjustments that may be required. (Possibly nothing.)
Recently I was asked about the source for the Color TFT I use in my projects. Despite having a series of webpages on the Sudden Transceiver on my www.n6qw.com website with one being specifically about the Arduino/Si5351 and a link to the supplier and a matrix of pin wiring for the several Color TFT's --I get the question where can I buy one?
Let us start at the beginning of the current Arduino/Si5351 build. Yes there is another $100 "bought on eBay commercial radio" on the bench going through the Pete's reboot process. For about $100 I managed to purchase the "Atlas Twins" radio set which is comprised of two boxes. The first box is the RX110 Receiver which has embedded within it some of the circuitry needed to convert it to a transceiver. The RX110 is a five band SSB receiver complete with a built in AC power supply. It is a single conversion design with a 5.595 MHz six pole crystal ladder filter. As is the case with many of the economy rigs of this vintage it operates on LSB on 80/40 Meters and USB on 20/15/10. Thus only one BFO crystal is used. There are no heterodyne crystal mixing schemes! To operate on 10 Meters the VFO is running at 24 MHz and for 20 Meters it is running at 9 MHz and needless to say drift will always be a concern. [NOTE: Go to www.n6qw.com and there is a detailed link on the Atlas Twins.]
The RX110 can be operated standalone or mated with the TX110 module that now makes the unit into a complete five band transceiver. The TX110 is about 1/2 the physical size but with some slight of hand and additional mechanical hardware the two boxes are physically mated as a single unit. All interconnect wiring is done through a 12 Pin plug on the back of the RX110 and where the antenna is normally connected to the RX110 and jumper plug connects the antenna port to the TX110. The TX110 in the normal configuration is a QRP type rig with about 10 watts on 80 Meters and a lot less on 10 Meters. There was an internal add on power amplifier "brick" that would boost the output to over 100 watts on 80M and perhaps about 50 watts on 10 Meters.
All I can say is that there was a lot of internal heat in that very small box. I say this because of my observation of the actual space in the TX110 and the fact that a prior owner hack sawed openings in the case on the bottom and top of the case where the amp board was installed. Crude is a really good word. It was obvious that my unit had the amp board but it was no longer installed. Without the amp board a jumper cable is installed so that the rig can be operated "QRP". In passing, a bit 'hokey" but there are two bands switches so at times you have to remember that both switches must be on the same band!
All I can say is that there was a lot of internal heat in that very small box. I say this because of my observation of the actual space in the TX110 and the fact that a prior owner hack sawed openings in the case on the bottom and top of the case where the amp board was installed. Crude is a really good word. It was obvious that my unit had the amp board but it was no longer installed. Without the amp board a jumper cable is installed so that the rig can be operated "QRP". In passing, a bit 'hokey" but there are two bands switches so at times you have to remember that both switches must be on the same band!
I don't buy things without having some specific plan for the reboot. I saw the Atlas Twins as a spring board to install the Arduino and Si5351 to enable two things: 1st is an accurate and highly stable LO generation complete with Color TFT display and 2nd to provide USB/LSB capability so that the rig could be used on the digital modes on 40 Meters. Thus why I am spending time on this post to take you through the Arduino/Si5351 sketch process and then the actual building of the hardware.
Fortunately, manuals for the RX110 and TX110 exist on the Internet and so I didn't have to guess some things. The original VFO/BFO scheme was that the VFO operated above the incoming frequency (by the amount of the BFO) for 80/40 Meters thus subtractive. For the higher bands the VFO operates below the incoming frequency (by the amount of the BFO). So on 80 Meters you have a 9 MHz range VFO and on 20 Meters a 8 MHz range VFO. One crystal BFO frequency would yield LSB on the lower bands (sideband inversion) while giving USB on the higher band (no sideband inversion). Thanks Herb.
A single three ganged band switch on the RX110 simultaneously switches in the correct VFO coils while connecting the input and outputs of the Band Pass Filter. My initial thoughts were to "rip out" the VFO section, install a Color TFT is the frequency window and install on small toggle switch on the front panel for USB/LSB selection. Inspection of the actual hardware led me to conclude a separate small "Remote VFO" console that would house the 3rd band switch to shift the Arduino range, have the color TFT and the USB/LSB select. I might even include the Mic connector and a stereo headphone jack and even the CW key --it can do CW. This way for digital operation in my new configuration, all connections are made to the Remote VFO. I am even considering the use of a commercial sloping front panel aluminum box from Bud or Hammond.
Long ago with a lot of help from others I decoded how to band switch an Arduino for five band operation and thus minimum sketch development was needed. For the Atlas Twins all LO's will be above in frequency and the BFO will be switchable above and below the Crystal Center Frequency by an initial starting point of 1.5 kHz. The RX110/TX110 Manual describes the setting of the BFO by visually observing the power output at 1000 Hz and then 300 hertz. A drop of a specific level between these frequencies is the BFO set point without identifying the actual frequency. This may require several runs to get it right but we will be in the ball park perhaps not in the exact seat on our initial attempt. So we have the sketch and now to the hardware.
Having a standard layout for the Arduino/Si5351 makes for rapid prototyping and minimizes the footprint. The last blog post talked about using the Nano as that offered the most bang for the buck. Recently I bought a three pack and the cost was $4 each ($12) so that is very cost effective. Thus I will use the Nano and the Adafruit board without connectors. Connections to my standard Board are made using Pin Header Sockets and Connectors. A total of 20 connections are made to the board as follows:
- Four pins are used for the Encoder and Step button
- One pin (to Ground) is used for USB/LSB Select
- Seven Pins are used for the Color TFT Interconnect
- Six Pins are used for the five position Band Switch
- Two pins are used for the Source 12 VDC Input
The below photo shows how using #30 bare tinned wire that I wire from the Arduino socket to the 30 pin header (15 each side). Then wiring is taken from the pin headers to the header sockets as shown in the photo above this one. Thus I have two forms of access to the Arduino with one being the pin headers which fit standard jumper plug wiring and the second the header sockets. I can't tell you the number of times I wanted to see what is happening on an Arduino pin and posing about on the top of the Arduino board you risk shorting something out. Thus I can safely insert a jumper wore and measure to my hearts content. Two bolts/nuts secure the Si5351 to the perforated board and I will wire wrap the connection to this board. At this point the signals are digital not RF!
As I add more of the wiring I will add shots to this blog post.
Yes Virginia another transceiver in the works only this time a reboot of the Atlas Twins. In summary the plan is to leave the internal VFO/BFO intact but disconnected and all operations will be done with the Remote VFO. This modification could be noted for other Atlas owners (Models 180, 210, 210X, 215) where you can have a Digital VFO with a Color TFT display.
I have had the Atlas Twins on the air using the stock VFO/BFO and have made about a half dozen contacts with most on 40M and one on 15 Meters. The TX110 needs some work to get the power out up to spec. But I was surprised at the stability of the Analog VFO. The main Analog VFO issue is the actual readout (too macro) and of course there is a bit of a drift. It would be a near impossibility to set WSPR frequencies with the analog VFO!
73's
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