When you know stuff, You can do stuff!

 

Radio Society of Great Britain Webinar

January 11, 2021

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June 19, 2020

The RADIG is Repackaged

As Field Day Rig

 

 

 

The RADIG V.3 with Outboard LO using the Arduino Uno R3 and CLK0 & CLK1 on the Si5351.

 

 

 

 

 

 

 

 

 

Email Contact: n6qwradiogenius@gmail.com

I am happy to respond to reasonable emails but I do ask that you first read the information and instructions. 9 times out of 10 the info is here --but often the emails are fundamental information that has been provided like 2 + 2 = 4. Keep in mind most of my projects start with blank pieces of paper which I must fill. The least you can do is to read the info provided!

 

How to Load the QUISK Software
How to Setup the QUISK Software

 

 

A RADIG, Software Defined Radio Project

SBRYMH

The RADIG On The Air!

The RADIG V.2 Info

I have built two RADIG's and both are operational. Shown below is the V.2 main board

The V.2 differs in that it uses the revised Combiner/Splitter transformer at the front end. A good friend down in VK land put me on to this approach and it is now being tested with V.2. Essentially this splitter is flat from 0.5 MHz to 50 MHz. Information this device can be found at the following website.

Combiner-Splitter

Here is a Semi Schematic of RADIG V.2 and there are some other chnages including the coupling capacitrs from the S=ADE-1's which are now 100 Uf electrolytic and the modem transformers are slighty different but still 600 Ohm : 600 Ohm.

Note adjust the LO signal underload using the trim pots to about 550 Milivolts PTP measured at the LO Port of each ADE-1. Also note that the secondary side of the modem transformers are at isolated ground to keep noise and hum out of the sound card.

 

Here is the info on the wiring of the 74AC74

Finally the schematic of the DPDT relay and not the reversal of the I and Q on transmit (Line OUT).

The Band Pass Filter board has two filters installed with one for 80 Meters and the other for 40 Meters. At each of of the filters are RCA Jacks. To change bands I simply plug into the proper BPF and the the same for the LPF.

The V.2 has a module following/ahead of the BPF and this module contains the relay steered J310s, the 2N2219A Driver Stage and the IRF510 final. Relays handle the TR so that there are only two connections to this module with one being RF In/Out to the BPF and the other a 12 VDC control line. The module has the antenna connector and an external amp keying jack.It is also powered separately.

 

I am currently focusing my homebrewing efforts on scratch building an SDR RADIG. For those who don't know the term RADIG it is a contraction of two words that I coined: Radio and Rig. Radio in the sense there are many commercial product building blocks such as Raspberry Pi3 and a StarTech Sound Card. Oh lest I forget, software in the form of QUISK. The Rig part is the homebrewed detector board, the bi-directional amplifier board, driver board and the final amp.

A moment here to reflect on the progress so far. The RADIG has undergone several significant changes in the month since I first had it listening to 40 Meters. It is now in a full transceiver configuration and so far have made over 100 on the air contacts. The results are amazing! I now consistently get excellent on the air reports and the hardware is scant yet powerful! Here are some salient points of the current configuration and I should add that a second prototypes is now well underway. I will also highlight some future changes that will be included in Prototype #2

 

V.2 is Live on 75 Meters!

  • The RADIG is basically two direct conversions receivers (DCR) that take the incoming on the air signals and converts them into a two channel (I & Q) audio baseband. The conversion is done with simple ADE-1 Double Balanced Mixers -- thus two of those. The I and Q signals are passed through Modem Coupling Transformers to provide some noise isolation. DCR's are very susceptible to hum modulation.
  • Audio baseband signals are initially fed into an external USB sound card that works to feed signals into the computer ( a Raspberry Pi3) for processing with the QUISK SDR software and similaly takes the transmitted signals from the software and passes them back through the ADE-1's on to the transmitting hardware. A simple DPDT relay is the traffic director to interconnect received signals as well as transmitted signals through the DBM's. As a part of my initial work I discovered that in the transmit mode there was a sideband inversion. A simple reversal of the I and Q channels on transmit done with the wiring at the DPDT relay resolved that issue. A word about the USB sound card. Initially I used a StarTech 7.1 which costs about $32 and this has now been replaced with the Optimal Sound USB 2.0 a 5.1 unit costing $15 --less than half the cost. I am soon to evaluate another sound card that will plug directly into the 40 pin GPIO header of the Raspberry Pi3 --the cost about $15. This latest card will reduce interconnect cabling and make for a smaller footprint
  • Ahead of the two ADE-1's is a hybrid signal splitter / combiner. The purpose of this device is several fold. Firstly the off the air signal is split into two signals and fed into each RF Port of the ADE-1's. In this process it also matches the 50 ohm output side of the Band Pass Filter to the 50 Ohm Input side to the ADE-1's. On transmit it acts as a combiner to combine the I and Q signal channels into a single signal that is further amplified in the transceuver Linear Amplifier stages. This special transformer had several configurations and the current one is nothing more than 10 Bi-Filar turns of #26 on a FT-37-43 core (based on the work of ZL2CTM). The center tapped winding goes to the Band Pass Filter and each leg is connected to one leg of the RF Port of the ADE-1's. Bridging the two windings is a 100 Ohm resistor connected RF Port to RF Port on each ADE-1. This assures balance.

The website will now focus on the fabricating of a homebrew Software Defined Radio (SDR). The skills required to undertake such a project are very likely beyond the skills of someone who has never hombrewed a radio project or one with just a smattering of knowledge on which end of the soldering iron is the hot end.

Not to worry as there is a link above on how to have a serious SDR Transceiver with a commercial kit board (the Ensemble) that can be had for under $100. Thus all can join in on the fun.

Much credit goes to Charlie Morris ZL2CTM who several years ago completely homebrewed an SDR transceiver complete with the development of the software using a Teensy 3.5 Microcontroller.

I did replicate his rig; but the current project uses a Raspberry Pi3B or an ASUS Tinker Board to do the heavy lifting. Aside from his initial scheme to use Double Balanced Mixers (SBL-1's and in my case ADE-1's) my current configuration has many differences.

  • I used a Commercial Sound Card versus the Teensy Codec Board. Several Sound Cards have been tested including the StarTech 7.1, the Creative Labs Xfinity. The Behringer UM2 is not suitable for this appliaction. However the Optimal Sound 2.0 USB (Amazon) at 1/2 the price of the StarTech 7.1 -- works!
  • My Detector stage is followed with two Modem Transformers to reduce any hum pickup.
  • The RADIG uses a relay steered J310 Amp stage that is the Rx RF Amp on Receive and the Tx Pre-Driver on Transmit. This has been revised to have a greater bandwidth covering 40 -15 M but useable down to 75M with reduced gain.
  • The Driver stage is the 2N2219A used in many of my projects.
  • The Final RF Amp is the stock IRF510, again a common design in many of my prior builds.
  • The Band Pass Filter is a 3 section versus my typical two stage.
  • The Low Pass Filter is the stock W3NQN.
  • The chosen band is 40 Meters but I have designed two other Band Pass Filters for 80 and 20 Meters. If a multiple band RADIG is contemplated then I suggest the use of plug in filters. ZL2CTM uses this approach.
  • I also have tested several versions of Hybrid Splitters with some very interesting results. The current version is the same one used by ZL2CTM in his rig. Later there will be a discussion about my experiences with"sideband inversion".

My blog (n6qw.blogspot.com) contains much information of the daily happenings on the project but I will use this website for an overall document repository.

 

Parts & Supplier Info

 

June 20th, 2019 ~ We have a working receiver using the RADIG Board. See the video below. Yes! Our next efforts will be to get that Microcontroller calibrated and finalize the Transmitter stages. Both of these tasks are complete and the RADIG is on Frequency as of 6/21 and as of 6/22 six QRP contacts were made with Field Day Stations and the farthest was Utah. This is exciting!

 

The RADIG IS ALIVE!!!!!!

 

The RADIG!

 

 

Our notional RADIG Configuration is nothing more than two direct conversion ADE-1 Double Balanced Mixers that on receive convert the received signals to I & Q signal channels. (I = In Phase and Q = Quadrature, out of phase by 90 degrees ). In the early days of SSB Transmitters the phasing method did this same trick.

Now on transmit the ADE-1 act as mixers to take I and Q audio signals and mix those with a local oscillator to provide a signal output at the operating frequency. Then it is with a simple hybrid combiner transformer that we produce the desired output.

A common Band Pass Filter used both on transmit and receive provides the signal filteing to assure we are transmiting/receiving on our band of choice.

The ADE-1's to operate properly are fed RF signals via our hybrid combiner out of the Band Pass Filter so essentially there are two signal channels. Like wise the Local Oscillator input (at frequency) must be quadrature so the you will have I and Q audio signals coming out of the ADE-1's. The I and Q signals are fed to isolated Modem Transformers so we reduce the possibility of hum. Remember this is nothing more than Direct Conversion Receiver technology and one of the problems is HUM!

To generate a quadrature LO so that the signals are indeed equal and 90 degrees out of phase we have a simple logic IC called the Dual D Flip Flop, specifically the 74AC74. When a signal is applied to this IC the outputs are square waves 90 degrees apart and at 1/4 the input frequency. Therefore the input signal must be 4X the operating frequency.

As an aside I mentioned about the early phasing SSB transmitters. One of the issues was that the phasing networks were all resistors and capacitors. Typically they were odd values and subject to aging (read changing values) thus there was frequent adjustments necessary to maintain the 90 degree shift. The IC replaces all of those resistors and capacitors --and no drift and no adjustments. One of the diagrams below shows the wiring of the 74AC74. You certanly don't know what is in a 74AC74 and cannot measure resistors and capacitors; but you know it works!!!

The photo below that shows a second prototype "detector" board. The empty IC socket is for the 74AC74 and the board has the on-board 5VDC regulator for the 74AC74. The four pads to the left of the ADE-1's is for the Band Pass Filter that was a two section. The new standard is a 3 section so I will just install a board overlay to accommodate the additional stages.

I have chosen 40 Meters for the build. But if you are a clever builder --you could fit this area with a socket system so to change bands simply means plugging a new BPF. The SoftRock transceivers did this trick!

I should mention that the board shown below in the current build (not the second prototype) used capacitive coupling between the ADE-1's and the modem transformers. After some experimentation with other coupling methods, while not the ne plus ultra, that is what is installed and seems to perform quite adequately.

The photo of the Band Pass Filter is a three stage that I "lifted" from N2CQR. Given that we are not using any real hardware elements such as a crystal filter, I believe we need a better BPF. It is imporatnt for you to invest some time learning LT Spice and simulate this filter. R1 is for simulation purposes and not used in the final design.

There is a photo in the mix of a block diagram / wiring schematic of how our pseudo Dual Gate MOSFET amplifier stage is connected as a single pass amplifier that is used as the Receiver RF Amp stage on receive and as the Transmitter Pre-Driver Stage on transmit. I have used this in many of my hardware (mostly) SSB transceivers and it is as slick as anything.

 

 

 

A Second Prototype Detector Board in work!

 

 

 

 

This is an updated Band Pass Filter and Hybrid Combiner

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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