2018 ~ The Year of SSB Transceivers

Building the Si5351 VFO/BFO Board!

11/07/2018 ~ Post Mid-Terms
I have transitioned to the remote console and the result are very satisfying. You will see that shortly and I want to tie in a program on the Velocity Channel which is a cable reality show 24/7 showing guys and gals homebrewing amazing cars mostly out of junk parts. So it was with the new console which formerly housed a linear power amplifier stage.

This box was fabricated from double sided copper PC board with an aluminum back cover. It was fully intended to be a totally shielded enclosure and it served that purpose when initially built as a power amplifier stage for a Ten Tec Model 540 that I acquired sans the linear amp brick. This was the prototype and a second one that was built was installed in the Model 540 which I later added a Digital Display effectively making it a Model 544. So I had a spare shielded enclosure in the "junk box".

When you undertake these zany projects there are often unexpected by products and one of those was RF noise coming from the Arduino/Si5351. A click click click sound would be heard as the Arduino went through loop and further evidenced by one of the on board LED's blinking at the same click rate. My thoughts turned into a completely shielded Arduino/Si5351 to see if it could cure the problem. The next light bulb was the enclosure I built that was hiding at the bottom of the junk box. TRGHS -- it was serendipity on two accounts as the enclosure was big enough to house the components and provided a neat "front panel" and the shielding solved the "click" sound. there are no more click sounds!

Should mention that I only heard the clicking when the antenna was disconnected or the band switch was in a position unrelated to the antenna being used. I did not hear the click sound on the transmitted signal but I did know it was there on the receive side (with no antenna).

The build itself has the display, encoder, band switch and USB/LSB select in one half, while the Arduino/Si5351 plus LO, BFO and power connectors on the back panel. This is a good way to do it since any reprogramming of the Arduino entails simple removing the back panel and you have access to the USB to Serial interface. [See the photo below.]

We are about to make some final adjustments and then we will button things up.






73's
Pete N6QW
11/06/2018 ~ Election Day

Yes I did vote (by mail) and so today I am electing to work on the Atlas RX110 and TX110. I just couldn't resist hooking up the Atlas Twins to 40M WSPR. I have a lot of data from other 40 Meter Rigs and thus can compare A to B. I am encouraged by what I see. My main concern was the transmitter, since it had problems and while I have moved forward I am still not there with the Twins where I think they can be.




Below is the hot off the press record of the Atlas TX110 on 40 Meter WSPR at 5 watts -- heard in South Africa. I was also heard in Japan.



You probably would never see an article in QST about "rebooting a Atlas RX110/TX110 with a Si5351" so you can work WSPR and as a bonus FT8. Even the Digi-Adapter is homebrew . Possibly the reason you won't see such articles is that the big commercial advertisers would not approve of hams building (or rebuilding) their own gear. This is a pure example where new technology let's the average ham to be able to work FT8 with really old boat anchors. All it takes is a bit of learning from the Internet (and blog's like this) and a desire to move out of your comfort zone. 

Then we have the new ARRL CEO wondering why the hobby is stagnant?




73's
Pete N6QW

11/3/2018 ~ See the You Tube Video of the Arduino/Si5351 Prototype Working with the Atlas Twins!



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!



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
Pete N6QW … Stay Tuned for more innovation and creative thinking. You are learning from the Master!

Comments

  1. Pete

    I don't know which Si5351 library you're using but many (most?) have a parameter that specifies the crystal frequency (25 vs 27).

    Joe
    W3JDR

    ReplyDelete
  2. Great job Pete,congrats.i m waiting tx part of Suden rtx.

    ReplyDelete

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