The Initial Fit Check and Wire Job


Before starting any wiring it is really a good idea to A) have some wiring standards and B) have good wire from the git go. Lets cover wire first. AVOID using wire from Radio Shack as it is unsuitable and not very good for use with this project. For signal wiring I like to use #26 plastic covered and have adopted a color scheme which I will detail shortly. Get your wire from places like All Electronics . For power wiring you want something like number 18 as that is good for most power levels up to about 10 watts.

Wiring standards can be a huge benefit if you are troubleshooting a problem. In general I use the RED and BLACK leads for power and ground. For all circuits involved with receiving I use ORANGE colored wire. On the transmit side I use YELLOW. For any bias circuits I use GREEN. If I am wiring a pot I will twist the wires together and use WHITE, BLUE and BROWN. Brown goes to ground and White goes to the top end and Blue is always the center wiper. That is easy to remember and saves invaluable time.

With the Bitx40 project wired cables and connectors are provided. Fortunately VU2ESE has a standard in the black is ground and brown is the hot side. In the case of the three pin connectors used with the audio gain control, brown is the center wiper and the red lead is the top end of the pot. VU2ESE has provided a pictorial wiring schematic which is shown below:



It is obvious to manage the wiring that you will need those cable ties that were linked to in one of the earlier phases.


Scary as it may seem I frequently use pin headers on prototype boards and connect to those pins using header connectors. You can see these on the VU2ESE board and also on my digital VFO board. There are many types; but it is always good practice to use what is called the "locking type". Basically there s a "tang" on the locking connector that when mated with the board mounted pin header locking it in place so it will not simply come loose. The connectors are also polarized so it is a near impossibility to put the connector in backwards. This helps avoid smoking the board --notice I didn't say eliminate but avoid. You will have enough problems without having connectors coming loose from boards. Here are some links for these type connectors. (The P/N's below are for the two pin type.)

  • Jameco female housing with locking tang and polarized (prevent jamming in the wrong way)
  • Jameco straight friction lock headers
  • Jameco crimp terminals for the female housing

The items above are called crimp type and can be easily installed on the #26 wire using needle nose pliers. I am a firm believer of adding just a bit of solder to "seal the deal" and do not always rely on my crimping skills. With a bit of practice you can do it. No excuses about age or eyesight --get a headband magnifier and good needle nose pliers.

Below is photo of the completed wiring of the Bitx40 and look closely at the notes about how I did it. Noteworthy is that I liberally used cable ties to neaten up he wire runs!


* I used the cables supplied with the kit and only found it necessary to cut one cable and that was the one that connects to the antenna. VU2ESE is adamant that the length of this cable shall be no more than 2 inches long! Using the 6X10X2 chassis and positioning the board as I did the cables were almost the exact length needed. So that is indeed fortunate

* A word here about power connections and the ON/OFF switch. I recommend the use of two 5 lug terminal strips that are secured with a single bolt and include a lock washer. The reason the two are connected facing each other is that one of the strips will be used to connect a 9.0 Volt (LM7809) three terminal regulator which will supply power to the Arduino DDS assuming you use a homebrewed version and the second terminal strip is used to connect power to the Bitx40 Board and power to the Arduino/AD9850. The hot lead from the rear mounted power terminal is brought to one lug and the ground lead is soldered to the ground lug. A wire from the hot lug goes to the panel mounted min-toggle switch and the other lead from the min-toggle goes to an adjacent open lug. Thus power from the power connector is routed through the power switch to the radio and Arduino/AD9850. Now for my installation there are three connections made to the switch lug. One connection goes to the Vin of the three terminal 9 Volt regulator, and the other two connections go to the Bitx40 board. One of the 12 VDC leads goes to a two pin header located in the upper right hand corner of the board. There is a second two pin header located near the IRF510 and in the proximate area of the Antenna connector. With 12 volts applied to this second header the Bitx40 can pump out close to 7 watts. This is how I have it connected. But you can also apply 24 Volts to this second pin using a second separate supply and now the Bitx40 can Pump Out 20m watts! Hey we are smoking here. CAUTION --the IRF510 on board heat sink is only good for 5 watts and to run the higher power you must really up sized the heat sink. One possibility if you locate the ma inboard where I have located it is to get a copper spreader and using an TO-220 insulator kit mount the IRF510 to the copper spreader which is then bolted to the aluminum case. This will dissipate the heat generated at the higher power. It is suggested you locate the copper spreader 1st before locating the ma inboard. The second CAUTION --simply do not connect the power cable to 24 VDC! While the IRF510 can take the 24 VDC the other circuitry cannot and you will smoke the board.

* The next wiring involves the connections to the header that can be used to introduce the external DDS (or PLL) Local Oscillator signal. When using the varcator tuning pot that is shown in the above pictorial diagram. I found the varactor option only suitable for initial verification that the radio is working. There is just too much drift and difficulty in tuning (with fat fingers like mine). So make life easy a purchase the $14 digital VFO option and call it a day. Normal operation with the external digital VFO requires the disconnection of the tuning pot which effectively removes the varactor tuning option from the mix. In the case of the $14 add on "Digi" VFO there is isolation in the form of a blocking capacitor, The Pin header located almost in the center of the board provides access to the base of the first stage of the on board VFO. If you connect directly to this without the blocking capacitor --it won't work!!!!! In my situation I bought the board before the Digi VFO was available and I made my own DDS. It did not have the blocking capacitor and thus I initially had the problem. The photo collage below shows how I temporarily offset my connector and have a patched in 10 NF cap. Later I will install the 10NF on my Arduino/AD9850 board and then just simply plug into the board.

* VU2ESE has done a great job in including all of the parts to make this a working radio! Included in the $45 is an electret microphone element and even a small tactile switch. That is the good news --so now what do you do with it? I took a defunct microphone case that had a thin diameter cord on it. On the plug end I installed a 1/8 inch stereo phone plug and that works nicely. The microphone case I modified by inserting a small piece of plastic into the face of the microphone. Make it a snug fit! In the center of the plastic I drilled a hole and using my rat tail file carefully enlarged the hole until it was just slightly smaller than the diameter of the supplied electret cartridge. It should be a snug fit. I carefully pressed the cartridge into the hole and called it done. For those who screw up and make the hole too big --that is why they invented super glue. Prior to inserting the cartridge into the plastic. I drilled a series of holes so that as you speak some of the air would flow past the cartridge. The photo below shows the completed microphone. The Microphone had a PTT already installed and so did not use the supplied tactile micro switch.

*This completes wiring except for the power plug which comes supplied. I used #22 Red and Black wiring for the internal power runs. I did the same for the main power feed. A word about reverse polarity protection. N2CQR has posted information about how to do this on the hacks page which can be accessed through the main website. Invariably no mater how careful you are you will get the leads switched and smoke the rig. I like to use a diode and relay so that the power feeding the rig is on a normally open relay contact. If you have the leads reversed the field coil will not energize and no power is applied.

Purists and people whose only goal in life is negativity will pan my solution as wasting power energizing the field coil. I suppose if you will operate from the top of the Grapevine on batteries you don't want to waste watts closing a relay contact. A solution is to use a power FET. But hey I had a diode and relay in the junk box!