Keep your Repeaters, Simplex Radio's and Raspberry Pi's cool

Image:  PWM Fan Contoller  (Click on image for larger view.)

Well this is a bit late to cool things down as we say good bye to summer and hello to winter.  I wrote several articles in the past providing information on building you own Thermo-Fan Controllers for use to keep radios, raspberry pi's and other electronic equipment cool during operation.  All of these controllers are still in operation on a daily basis and up to now I have not had any problem with any of them.

I recently noticed that my DMR Repeater fans are very noisy and I suspected that they are close to failure as they have been in operation for several years now.  Low and behold two days ago one of the TX fans decided that it had enough and failed as expected.

I considered to build another trusted IC741 op-amp Thermo-Fan Controller for use with the DMR Repeater.  As the years are creeping up on me and the eye-sight not being so good anymore I decided I would rather buy a ready to use simple/cheap PWM Fan Controller.   I ordered two different models.  In this article I will only provide information on the one model depicted in the images below.

The controller is designed as a model that combines manual control and automatic temperature control.

Here is more information on the specific model:

This single-channel PWM fan controller is designed for 12V DC fans, supporting both 2-wire and 3-wire fan types for precise speed regulation.

 

It enables smooth, efficient, and stable fan speed control, making it ideal for cooling systems, industrial equipment, and DIY thermal management projects.

 

Key advantages:

• Single-channel PWM speed control

• Supports 12V DC fans (2-wire / 3-wire)

• Smooth speed adjustment with low noise

• Compact module for easy installation

• Ideal for cooling systems and thermal control

 

Other detail:

Input Reverse Connection Protection: Yes
No output overload protection.
Power Interface: XH-3P Terminal Block (2.54mm Pin Spacing)
Fan current: 0.8A (not overloaded)
Fan Interface: KF2510-3P Terminal Block (Pin Spacing 2.54mm)
Temperature sensor parameters: NTC 50K B = 3950 Length = 50 cm.
Temperature Sensor Interface: XH-2P Terminal Block (Pin Spacing 2.54mm)
Temperature resistance of probe: ring probe 110℃
PWM Output Range: 5% to 100%
Operating temperature: -20°C ~ 60°C.
Dimensions: 43 x 18 x 9 mm. 

I am not going to go into detail on programming and setting up the controller as YouTube and Google is your friends here.

Finally:  I setup the controllers and tested them at different temperatures on the workbench.  So far they work as expected.  I will be fitting the two controllers in a 3D printed project box and install it at the back of the DMR Repeater to provide the necessary cooling when needed.

Images:  (Click on images for larger view.)

Videos:

 

What to do when your antenna rotator needs a new "starting" capacitor?

 

Image:  Antenna Rotator Control Unit.. Click on image for larger view.

I overheard a conversation recently between two radio amateurs in the Western Cape trying to scrounge a 130 mf 50-volt capacitor for a dead rotator.  The rotator suddenly died after several decades of faithful service.  The control unit of his Ham IV Rotator ceased to function.  A postmortem examination revealed a dead alternating current motor starting capacitor.

These capacitors are hard to come by in South Africa and if you can find one, it will be very expensive.  Ask me how I know that.  To solve the problem, two 150 mf, 50 volt electrolytic capacitors and two 100-volt, 3 ampere silicon rectifier diodes were used in the circuit shown.  The control unit was resuscitated.

Image:  Capacitor circled in red in the Control Unit  (Click on image for large view.)

For those interested in the theory of the functioning of the circuit, the explanation is simple. During any half cycle one capacitor is shorted by its associated diode. It might be presumed that having two capacitors in series, the resultant capacitance would be halved. This, however, is not the case because the diode acts as a bypass for the capacitor during every half cycle.

It is NOT a motor starting capacitor!!!

The purpose of the cap is to cause a 90-degree phase shift across the windings of the motor, which determines which direction the motor will turn. Some old capacitors dry out and the value changes.  This does result in the motor not starting to turn.  Replacing the cap (if you can find the correct value) will make the motor work again.

Note:  A larger value cap will allow more current to flow, but will also effect the phase angle, which will actually decrease the starting torque.  An infinitely big cap would be a short!  So don’t damage your motor!  A non-polarized cap if obtainable would also do the trick. If it is impossible to find the correct cap, well then back to our schematic.

Image:  Schematic Diagram of the Diodes and Capacitors (Click on image to enlarge.(

Use two back-to-back electrolytics as indicated in the above schematic.  Connect the negative sides of the electrolytics together, and connect the diodes so that the “bar” is at the positive end of each cap.  You want no current to flow through the diode when the voltage at the positive end of the cap is positive.

Another idea is to move the cap/s directly to the rotator, properly weatherproofed of course.  This eliminates the cable resistance in series with the cap.  Now use the two wires in the cable which went to the cap, and double up on the motor wires, cutting the resistance down there to.

Image:  ZS1I successful test setup. Click on image for larger view.

Hopefully this article will resuscitate those dead rotator control units.

-  Compiled many years ago by ZS1I for QSX, the monthly newsletter of PEARS. 

- Source 73 Amateur Radio

DIY Overvoltage Crowbar Protection Circuit Project (Project 2)

(Click on image for larger view.)

I always seem to look for a simple crowbar circuit to protect my radios and other electronic equipment from over-voltage and reverse polarity.  Now I know there are many types of crowbar circuits that provides many types of protection.  I did not want to "re-invent the wheel" relating to crowbar circuits. In Project 1 I used the well known MC3423 Chip and a few other components.  More information available HERE.

In the images below is a protection circuit I found on the Internet. It blows the fuse if the voltage from the power supply rises above 15 Volts. It uses a 20 Amp thyristor so it’s more than capable of blowing a 15 Amp fuse. I’m using a 10 Amp fuse because that’s all I had. Also, most of my equipment running from this power supply aren’t current hungry. (More on the modified power supply in a future posting.) By the way, I wouldn’t rely on the modified power supply’s short circuit protection to cut the power.  I decided to use fuses instead of using a relay.  Once again some say a relay is better than a fuse.  I used what I had on hand!

I decided to add a TVS diode (transient voltage suppression diode) as used in the original design, as this would appear to make the BT152 thyristor redundant. If the TVS diode conducts at 15 Volts then, why use a thyristor? Well why not use double protection?  I suppose the TVS diode is fast when dealing with transient voltages. The TVS diode also protects against an accidental reverse polarity voltage connection. 

Now before you running of to build the Crowbar a word of warning!!  Using Vero Board is fine, but do bear in mind that the thin copper strips are not designed to carry 20 or 30 Amps! To solve this problem, I ran 3mm tinned copper wire alongside the heavy current-carrying strips. I also joined (soldered) clean tracks together that carry the 12 Volt in/out of the board.  The board can now easily carry the 15 Amp current without any issues.  If you upscale the Thyristor and other components for higher current then I would advise not to use Vero Board.  Dead Bug Style or a PCB might be considered. 

Parts List:

1.5KE 15 TVS 1.5kW 15v Diode

BT152 Thyristor 800v 20 Amp

27K 1 watt Resistor

10 Ohm 1 watt Resistor (I used a 2 watt that I had)

1 uF 50v Radial Electrolytic Capacitor

1N5245B Zener Diode 15v 1 watt

Vero Board (65mm x 35mm)

Red and Black Flex Wire (Copper diameter = 2 - 3 mm)

Optional:

Black and Red Terminal Posts

2 x Fuse Holders

2 x 10 Amp Fuses

1 x LED Holder

1 x Red LED

1 x 330 Ohm 1/4 watt Resistor for LED

1 x Project Cabinet

1 x Black Compression Gland 12.5mm CAB = 4-8mm

 

(Click on image for larger view.)

Construction:

Constructing this Crowbar is straight forward as indicated by the diagram and images.

Information on the two fuses.  I used normal automotive fuses which I had in my component cabinet.  I would however advise using good semiconductor fuses on the 13.8v input line to protect the SCR.  The I2T rating of the fuse should be less than that of the SCR.  You have been warned!!

What is a Semiconductor Fuse? Also known as ultra-rapid fuses, high speed fuses or rectifier fuses; a Semiconductor fuse is a high speed current limiting fuse that is designed to protect and isolate sensitive semiconductor components such as diodes, thyristors, SCRs etc. by minimizing the I²t, peak current let-through and arc voltage.

Summary:

I recommend you construct this unit that provide over-voltage and reverse voltage protection and fusing. This unit will ensure that your equipment is protected from inadvertent power supply transients, power supply over voltage failures or connection mistakes like reverse polarity. 

Note:  I will provide more information about the working of the Crowbar in a future article.

Images:  (Click on images for larger view.)

New Series - Building Low Budget Antennas - "1/4 Wave Ground Plane Antenna for 2 Meters - Project 6

I continue with the series "Building Low Budget Antennas" for Radio Amateurs. Nothing fancy or with high gain.... no just simple low budget antennas!

In this article I will be looking into building a 1/4 Wave Ground Plane Antenna for 2 Meters. Now I know there are thousands of ways to construct this antenna, but how cheap can you build one? R10, R20 or R50. You decide how much such an antenna will cost.

General Specifications:

Resonant Frequency: 145.550 Mhz

Frequency Span: 145.000 - 145.800 Mhz

Modes: FM ( Local repeaters and simplex)

Polarity: Vertical (Note: Repeaters use vertical polarization.)

Antenna Impedance: 50 Ohm or very close to 50 Ohm

Gain: Approximately 2 - 3 dBd

I found a very useful quarter wave calculator if you want to change the measurements to suite your needs. This calculator is used to determine the length of each element of the antenna. That includes the vertical monopole radiating element and the 4 radials.

The calculator is available HERE

Enough said let's start building the 1/4 Wave Antenna.

Materials I used:

3d Printed Ground Plane Support Parts (3 items) Available HERE (Note you do not need these parts. I will explain later how to build the antenna without these parts.)

1 x PL239 Socket Connector (Not ideal rather use BNC or N-Type Connectors but I used what I had on hand)

1 x 1 meter 25mm Electrical Conduit pipe

1 x brass 5A Electrical Connector Block ("Chocolate" Block)

1 x 1.5 Meter (2.5 mm) Copper Wire (Ideal would be brazing rod but I used what I had on hand. Brazing rod is far sturdier but more expensive.)

Odds and Sods:

Cable Ties

Silicon Sealant

Insulation Tape

Solder

Solder Paste

5 -10 m Coax Cable (RG58CU Mil Spec) 50 ohm with 2 x Connectors (Feeding line to radio)

Self Amalgamating Electrical Tape

Tools:

Hack Saw or PVC Pipe Cutter

Soldering Iron

Sharp Utility Knife

Screw Driver (Small flat)

Test Equipment:

VHF SWR Meter

Antenna Analyzer (If you have one but not compulsory)

VHF/UHF Radio

Coax Patch Leads

Mast (Non conductive)

Power Supply or Battery for Radio

Building the Antenna:

I am not going to go into detail how I constructed my version of the antenna as there is more than enough info via the links and images how to construct this antenna. A word on the 3d Printed parts. You can use the SO239 without the 3D printed parts. Just fit the bottom threaded part of the SO239 and the PL259 in the one end of the 25mm electrical conduit pipe. To make it fit tightly you can use self amalgamating tape around the connectors and then push it into the pipe. Hot-glue can also be used to hold the connectors tight in the pipe. Improvise is the answer here. You can also make an aluminum L bracket and secure the SO239 to the bracket.

Testing the Antenna:

I ran a quick test on the antenna with my HT just to see what the SWR was like. Well the images speak for themself. SWR was 1: 1 between 145.000 - 145.800 Mhz. With the antenna just above the roof, I can work the 145.750 Mhz Aasvoelkop- and all the other repeaters in the area. I did some more tests with the VNA Antenna Analyzer. See the images below.

Side Notes:

I found that the antenna works just as well on 70 cm's. SWR 1.2:1 on 70cm. Unfortunately I did not do any measurements with the VNA on 70 cm's .

Conclusion:

This antenna will be good to download SSTV images from the ISS. It is lightweight and easy to setup/install. To the new radio amateurs this antenna is an ideal first time antenna project.

I am very happy with the performance of this 1/4 wave antenna on 2m and 70 cm's. Well worth spending my time on building this antenna.

Final cost to build this antenna: R45.00 ($2.5 US)

Images: Click on images for larger view.

 

Building a Drive-On Car Stand for Portable Masts

During my preparations to erect a amateur radio station over Easter Weekend in Gamkaskloof, I realized that I sold my heavy duty Drive-On Car Stand and that I needed a stand for my portable mast.  The previous stand was a real heavy duty unit that was difficult to move around and took a lot of space when transporting.  I looked around my scrap metal and found a few pieces of metal to construct a much lighter stand.  The plate with four holes in it lend itself to quickly put a new stand together.  Not the neatest metal work  but under the circumstances it will have to do and I did not want to spend money on buying metal for the project.  Every single piece of metal used in this project was salvaged from my scrap metal box.  The beauty of this design (not the stand) is that you do not need a car to hold the stand into place.  Stones, sand bags or any other heavy weight placed on the stand will keep it in place.  I am not going to go into construction details as the photos is more that sufficient to enable those interested to build their own.

I am looking at a few other designs and might build a few to sell if their is any interest.  The above stand is really not an artwork nor a thing of beauty but I used what I had on hand and it works great!

Images (Click on images for larger view.)