Let's fix the broken uBitx V3 HF Radio aka "Red Ferrari" of Jacobus ZS1JDJ

Image:  The "Red Ferrari" uBitx V3 HF Radio.  (Click on image for larger view.)

Jacobus ZS1JDJ recently acquired a  uBitx V3 HF Radio aka his "Red Ferrari".  He used the radio a few times and wanted to add the headphone socket in order to utilize headphones with the radio.  He followed the guidelines obtained from an Internet site only to find out later that the Audio IC  (TDA2822) let out the magic smoke.  He ordered several new TDA2822M IC's, removed the wiring to the headphone socket and inserted a new audio IC only to find that it also went up in smoke.

He contacted the author for assistance on how to fix the issue.  The author was willing to assist but he had to do all the soldering and de-soldering himself under supervision of the author.  This is how an Elmer share his knowledge after many years of constructing and fixing equipment.  Unfortunately due to bad eyesight the Elmer is not working on radios anymore.

Jacobus ZS1JDJ visited the author and the "Red Ferrari" was opened on the workbench to see why the IC let out the magic smoke. I told Jacobus to de-solder the IC and provided a IC socket to make it easier to remove the TDA2822M in future.  We gathered all the information on how to solve the issue from the Internet and also from the uBitx website.  

There seem to have been a problem with certain IC's that does not "enjoy" 12 - 15 volt DC (Pin 2 VCC.)

Herewith a short explanation of the problem: 

 uBitx v3 Radio audio IC damaged after trying to connect phones

Damaging the audio IC (TDA2822M) on a uBitx v3 when connecting headphones is a known issue caused by shorting the audio output to ground during jack insertion. The TDA2822 chip in the v3 is highly sensitive to this, particularly if using a mono plug in a stereo jack, which shorts the ring to the sleeve. 

Here is a guide to diagnosing and repairing this issue based on common uBitx community solutions.

Symptoms of a Blown TDA2822M:

No audio from the speaker.
The TDA2822 chip gets extremely hot when the radio is powered on.
Sidetone still works (if the issue is isolated to the receiver audio path).
A faint, distorted signal or a loud hum. 

Repairing the Audio IC:

Remove the damaged IC. The easiest method is to carefully cut the legs of the 8-pin TDA2822 chip, then use pliers to remove the remaining pins one-by-one while heating with a soldering iron.
Install a Socket: It is highly recommended to solder an 8-pin DIL (Dual In-Line) socket onto the board rather than soldering the new chip directly. This makes future replacements much easier.
Replace with a Robust Component: Replace the TDA2822 with a new one. Some builders have found that specific brands (like "WX" branded chips) are more prone to failure, so sourcing a high-quality replacement is advisable. 

Preventative Measures (Essential Mods):

To prevent this from happening again, you should implement one of these modifications:

Add Series Resistors: Add a 4-ohm to 8-ohm, 1/2-watt resistor in series between the uBitx output and the headphone jack TIP.
Rewire the Jack: Wire the headphone jack as a mono jack (using only the tip and sleeve) to prevent the shorting that occurs when a stereo plug is inserted.
Voltage Regulation: The TDA2822 on the v3 runs close to its maximum voltage. Providing a 6v-9v regulator for the audio stage can prevent future failures. 

Troubleshooting:

If the replacement does not fix the issue, ensure the capacitor C77 (470µF) was not also damaged by the surge, and verify that the 12V supply is not exceeding 15V, as the TDA2822 is fragile near its voltage maximum.

Wiring up the headphone jack

It is recommended that when you wire up the headphone jack, you do not wire it up as a stereo jack.  Inserting a mono plug into a jack wired for stereo (i.e. when connections are made to both the tip and to the ring connectors) will likely result in a short from the ring to shield when the plug is inserted.  Several constructors have blown up their TDA2822M audio output IC as a result of exactly this scenario.

If you do want to wire the supplied headphone jack as a stereo jack, add a series 8 ohm 1/2 watt resistor  (or perhaps a 4 ohm resistor) between the uBitx board and your phone jack.  This should safely prevent any damage, though it will reduce the maximum available audio slightly through the headphone jack.

Reference:

Wiring up the audio connector so that you can also use an internal speaker

The headphone jack can be wired to connect normally to an internal speaker, until a plug is inserted in the jack, whereupon the audio is routed to the headphones.  Again, it is recommended that the jack be wired up for a single channel (using the tip only) to avoid problems when inserting a mono plug into the stereo connector.

The jack’s tip has two connections (one is switched off when you insert a plug).  Because the sidewall on the jack is “see through” you should be able to see how this works in practice when you insert a 3.5mm plug into the jack. Wire the terminal that is switched off when a plug is inserted into the headphone jack, to the positive terminal of your speaker.   If your speaker’s polarity is not marked, it won’t matter which terminal on the speaker is connected to the jack.

The negative terminal of your speaker should be soldered to the shield connection on the headphone jack.  To be clear, the wire from the main board and the wire from the negative terminal of your speaker are both soldered onto the rear (shield) tab of the stereo jack.
 

More information from the uBitx Web-Site about the issue:

TDA2822 problems - Reasons for failure  CLICK HERE. 

Now how did we solve the problem of the "Red Ferrari"?

1.  Removed the blown IC

2.  Fitted a IC Socket

3.  Removed the 470µF capacitor (C77) and replaced it with a 100uF capacitor

4.  Lifted the leg of  pin 2 of the new IC which will be used to feed 7.5v DC to the IC

5.  Installed a LM2596 DC-DC down converter module which was set to 7.5v DC

6.  Connected the +7.5 v to pin 2 of the IC TDA2822M and pin 4 ground to the ground connection.

See images below for the above modifications

Jacobus fired up the "Red Ferrari" and tested it thoroughly.  Problem solved!

Comment from the author (Elmer):  

I am sure that Jacobus ZS1JDJ learned a lot from this event. (magic smoke release)  Whenever anybody want to make a modification to a radio you must ensure that you know exactly how to do it.  Google is your friend.  Read as much about the issue as possible. The cons and the pro's.  Do not be in a hurry.  If not sure consult an Elmer before the smoke release.  Any modification being done needs the correct equipment.  If you do not have the correct "tools" or test equipment forget about the modification or let an experienced homebrewer assist you.  Always have spare components available before you start.  As stated before due to bad eyesight the Elmer is not working on radios anymore.

Images:  (Click on images for larger view.)

Dedicated 5v Power Supply Distribution Board Project for your Raspberry Pi's

I have several Raspberry Pi's running in my shack on a daily basis.  Well some use the factory wall-warts you buy for the Pi and others run from cheap DC-DC Buck Converters.  It is always a schlep to find the correct wall-wart or converter lying somewhere underneath  a desk or on the floor.  I decided to build a dedicated 5v Power Distribution Board from items that I had lying around.

I found a switch mode power supply which I salvaged from and industrial appliance.  When I tested the output I found that it delivers 5v, 2v and -4v DC.  Unfortunately I could not find the amount of amperes it provides.  This will be tested under real operating conditions.  Looking at the construction of the power supply and the cooling fan, this unit is no small power unit and will work for my intended purpose. I decided to add a fan for cooling as in the original industrial cabinet the fan was built into the cabinet.  I removed the fan and install it on-top of the power supply.  Next I needed some means of distributing the output power.  I could add connection points to each 5v wire but decided to 3 D Print a "Bus-Bar" type  positive and negative feed point. I joined all the red positive wires and black negative wires to heavy duty lugs which I then added to each bus-bar.  The copper bus-bar is made of 20 mm copper pipe which I flattened in my bench vice.  Added brass-bolts and nuts which I had lying around and bolted both bus-bars to a piece of cutting board.  

That's it project nearly completed.  I just need to fit some acrylic covers to ensure that no short-circuits occur between the two bus-bars.  Once again a very cheap project with items that I had lying around.  Hopefully this distribution board will work much better than the wall-warts and DC-DC buck converters.  One could just as easily use the copper bus bars for building a 12 v distribution board.  Who knows might just do that one day.

Images:  (Click on images for larger view.)

 

Nico ZS4N build the DK3 Screwdriver HF Mobile Antenna

In this article we will be looking at how Nico ZS4N constructed his version of the DK3 Screwdriver HF Mobile Antenna.  I am sure many of you will agree that the construction of this antenna is not for the faint hearted. From the images it is quite clear that Nico ZS4N showed great building skills and craftsmanship in constructing this antenna.

Lets first look at the background of this antenna.  I will also add a few PDF files that explain the construction and performance of this antenna in detail.

Background of the Screwdriver Antenna

• The DK3 Screwdriver antenna was invented by Don Johnson (W6AAQ). The

DK3 is an HF antenna designed for operating on any HF frequency (10m through

80m) WITHOUT leaving the vehicle to change or adjust the antenna.

• The DK3 Screwdriver antenna is adjusted by remote control to give it multi-band

capability. A cordless screwdriver motor (which gives the antenna its name)

housed inside the lower mast unit of the antenna moves the embedded inductance

loading coil up and down. The portion of the coil that remains inside this lower

mast unit is inactive. The exposed portion of the coil provides inductance loading

to compensate for the capacitive reactance associated with short mono-pole

antennas like this one. The adjustable inductance loading allows you to achieve

resonance for a wide range of frequencies.

• The Z-match built into the bottom of the lower mast unit matches the antenna to a

standard 50-ohm coaxial transmission line. This eliminates the need for a tuner.

• Although the DK3 antenna is not plug-and-play, Don Johnson provides good

written instructions and suggestions, and even excellent telephone support to help you

set it up and make it work. 

• Due to its popularity, there are several different versions of the Screwdriver Antenna on the market. Some of the vendors offer improvements over the DK3(such as a plug-and-play version, 160m capability, or a lighter and more portable version of the DK3).

Diagram

DK3 Construction

More information  BIG DK3  By W6AAQ  (PDF Download)

Conclusion

The DK3 is probably the best mobile antenna for hf. It is also well known as the screwdriver antenna. It works on all hf bands (10m-160m) without changing the whip. Well, the DK3 is not really  inconspicuously, but still better than some other hf mobile antennas.

The whole antenna works as a quarter wave radiator. The body of the car is the ground.  There was a screwdriver antenna shootout at the parking lot during the International DX Convention in California (DK3, High-Sierra, Hi-Q, Drill Motor and one other brand). The DK3 took the first place in DX contacts at the convention. Please be aware for the cheep "remakes" of that fantastic antenna. Make sure you build or buy the original DK3 antenna by W6AAQ.

Congratulations Nico ZS4N on building the DK3 Screwdriver HF Mobile Antenna from scratch in your workshop.  

Images:  Click on images for larger view.

Building Low Budget Antennas - DIY Moxon Antenna for the 2m Band ( 144 - 146 Mhz)

In this article I will describe how I built my version of the 2m Moxon Antenna.

The Internet has an abundance of information on Moxon Antennas and I will not go into to much practical  and theoretical detail in this article.  Herewith a little AI information about the Moxon Antenna.

The Moxon antenna originated with British radio amateur and author Les Moxon (G6XN), who published it in his 1993 book, HF Antennas for all Locations, as a compact, high-performance two-element beam antenna (a radiator and reflector) with bent-back element tips, offering a great front-to-back ratio and 50-ohm impedance for easy coaxial connection, based on earlier explorations of folded-element designs. 

Key Aspects of its Origin:

• Inventor: Leslie A. "Les" Moxon (G6XN).
• Publication: Detailed in his 1993 book, HF Antennas for all Locations.
• Concept: A compact, rectangular variation of a Yagi-Uda beam, using bent ends (capacitive loading) on the radiator and reflector for efficiency and size reduction.
• Design: A two-element antenna (driven element + reflector) with folded tips, creating a directional pattern and high front-to-back ratio in a small footprint.
• Precursors: The design built on earlier ideas, including experiments with square-shaped antennas by Fred Caton (VK2ABQ) in the 1930s and 1950s.

Why It's Popular:

• Compactness: Occupies much less space than traditional beams.
• Performance: Offers good gain and excellent front-to-back (F/B) ratio.
• Simplicity: Easy to build, often from wire, making it great for amateur radio (ham radio) and field days.
• Direct Match: Its design naturally provides a 50-ohm impedance, connecting directly to standard coax.

In any project one needs a plan, diagram, guidelines and information.  At least that is my way of constructing any DIY Project.  I research the project thoroughly before I start any work.  I did exactly this before I started on this project.

Now the Internet is your friend but can also be your enemy if you just jump in and start constructing the first plan you find.  I was looking for the dimensions of  DIY 2m Moxon Antennas and ran into an abundance of information which included a calculator.  

The dimensions for the antenna was calculated using the free Moxon Antenna Calculator program (available for download from here). I set my frequency to 145.625 MHz with a wire size of 12mm to represent the 12mm aluminium tubing I was using. The resulting calculation is shown in Figure 1 below. 

Image:  Figure 1  (Click on image for larger view.)

The Moxon  antenna calculator was fed with the following data:

Frequency: 145.625 Mhz (I want to use the antenna for a repeater link.)

Diameter Wire size = 12 millimeters

Transmitter Power = 1 to 15 Watts

After calculating the information listed from A to E were provided.

With all the information now on paper, I was ready to move onto the next phase and that was to gather all the materials I was going to need.

Materials that I used:

1 x 150 millimeter x 50mm x 3mm Aluminium Flat Bar

3 x 12mm x 2mm x 2.5m Aluminium Round Tube  (The thicker the wall thickness the better. 2mm is rather thin.)

1 x 1 meter x 10mm x 2mm Aluminium Round Tube

1 x 1 meter x 10mm Wooden Dowel 

2 x 22 mm Plastic End Caps to fit into the 25mm Boom ends.

1 x PL259 Connector

2 x Electrical Eye Lug (Terminal)

3 x 12mm Stauff Clamps (Insolaters between boom and elements.)(See images)

6 x 45mm x 5mm Stainless Steel Bolts + Washer + Lock Nuts

2 x 65mm x 6mm Stainless Steel Bolts and 2 x Lock Nut

8 x 6-16mm Stainless Steel Hose Clamps

2 x Stainless Steel TV - U Clamps

1 x 150mm x 80mm x 5mm Alimunium Flat Plate to mount antenna to boom.

1 x 500mm RG58 CU Mil-Spec Coax Cable (50 Ohm)

2  x 300mm x 4.6 Hellermann Cable Ties

Odds and Sods:

Hot Glue Sticks

Self Amalgamating Tape

Solder

Solder Paste

Marine Silicone Sealant

Heat Shrink Tubing

 

Tools:

 

Metal Punch

Drill

Various Drill Bits 3mm - 8mm

Hack Saw 

Hot Glue Gun

Soldering Iron

Screw Driver (Small flat)

Alen Keys 

Spanner Set

Small Pipe Bender (See images)

 

Test Equipment:

 

SWR Meter

Antenna Analyzer (If you have one but not compulsory)

Amateur Radio Transceiver

Coax Patch Leads

Mast (Non conductive)

Coax feed line cable  5 m  RG58CU 50 ohm

Power Supply for Radio 

Building the Antenna:

My final dimensions is listed in the image below:

Images:  Figure 2 and 3 (Click on image for larger view.)

I am not going to go into detail how I constructed my version of the antenna. I will however describe my findings in constructing and testing the antenna.  The images below provide good detail of how I constructed the Moxon Antenna.

More information on the build and use of the antenna available at the following sites:

 

(Click to view website) 

 

The Moxon-Beam  by DK7ZB  

The GW3YDX Super Moxon 11 by GW3YDX

 

 

My build observations and findings:

 

Now how did I bent the 4 elbows of the antenna?  I used a small pipe bender.   The 10mm aluminum tubes are cut to 4 x 200mm.  I made a mark in the center at 100mm and then two marks 20mm on each side.  The first mark on the left is placed on the 0 | 0 mark of the pipe bender.  Now start bending until the 0 on the top lever reaches the 9|0 mark on the bottom lever.  You now have a 90 Deg elbow that fits into the 12 mm antenna element.

To fit the elbows and hold them in place I used stainless steel hose clamps.  This allows me to easily tune the antenna for a low SWR to a frequency I want to use.  I had two options to join the elbows to the element.  I could have used stainless steel self-tapping screws or the hose clamps but I opted for the latter.

Mounting the elements I manufactured 2 x Element Brackets as displayed in Figure 3. I used stainless steel bolts and nuts and Stauff Clamps to install the 12mm thick elements.  

The last observation and finding pertains to the feed-point and co-ax connector.  No rocket-science here.  I used a short piece of co-ax and PL259 + Barrel Connector for the feeding point.  I add a ferrite bead / clip to the piece of co-ax as before installing the antenna.

 

Just a word on the isolated wooden dowels between the two elements.  I left the two 90mm dowels for 2 days in furniture oil to protect the wood from the elements.  The oil was soaked up by the dowels  and  should now last for many years to come.

Fitting the dowels to the elements is easy. Ensure there is a 50mm gap separating the ends of the folded elements on each side of the antenna. Lay the two 90mm  next to each other and measure and mark the dowel as follows -  20mm - 50mm - 20mm.  Mark the measurements with a permanent marker. Ensure that the spacing between the elements is 50mm. Now slide the dowel inside the aluminium element up to the 20mm mark on one side and also on the other side. You will now have 50mm dowel showing between the elements. I drilled small holes through the tubing and dowel and then secure them with stainless steel self-tapping screws  Re-adjust the antenna assembly as necessary to make sure the outer dimensions are still correct. 

Preliminary Test Results:

 

(Click on the images for larger view.)

 

I really did not go into a full out testing and use of this antenna at this stage.  The only testing I have been doing is with the Nano VNA and a test or two on air RX and TX "excursions".  See images above for the test results.

The next step will be to install the antenna.  I installed the antenna only for test purpose.  Two meters above the ground and drooping forward as per image.  This was just to check the SWR.  I also connected the antenna to my Baofeng UV82 and gave a call on the 145.625 Mhz repeater.  Danie ZS1DL returned my call and indicated that there are rain on the signal but that my audio is understandable.  Well once the antenna is installed about 6 meters from ground I am certain that I will receive the repeater full quieting at my QTH. Update to follow once antenna is installed.

Images:  (Click on images for larger view.