misc

How To Suppress Voltage Spikes From A DC Motor With A Snubber Circuit

Being one who likes to be as self-sufficient as possible, I purchased a hand crank style grain mill. This augmented my weekly baking of Spelt bread. Now you are asking what does baking bread have to do with suppressing voltage spikes on a DC motor? That’s a fair question. Well the first time I tried grinding my wheat berries in my Wondermill grain mill, I quickly understood what they meant by ‘its not the easiest thing to do”.

This grain mill definitely needed a motor! After doing some research on motorizing grain mills I found all kinds of options. However for me, again wanting to be as independent as possible, I wanted to use a 12 volt motor instead of a 120 volt AC motor like most people do. Since my Amateur Radio station is off-grid and powered by 4 golf cart batteries, and a solar panel this seems like a logical choice.

Additionally, I had several radiator fan motors from automobiles laying around, running my grain mill on 12 volts DC made even more sense. This called for a mini road trip to the local industrial surplus shop near me, JDM Surplus to pick up some gears, pillow blocks, and chain.

Here is a video of the completed grain mill running for the first time on a gel cell battery:

As you can see in the video above, I am using a radiator fan motor. Typically these DC motors are a brushed type of DC motor, which due to the commutating of the brushes generates DC spikes that are much higher than the 12 volts that is running the motor. These spikes need to be suppressed so as not to cause damage to sensitive electronic equipment such as my Amateur radio gear, and the solar charge controller.

Pages: 1 2

How To Install Equipment Into A 19 Inch Rack

I needed to install a transmitter into a 19″ equipment rack. Since it was heavy, and having installed heavy equipment into a rack I needed an easy way to do that. If you have ever installed something heavy in a 19 inch equipment rack, it is rather difficult. Even with two people. Sometimes three people are needed. This is what I came up with to make installing equipment into a rack a lot easier.

Since almost all 19” equipment racks use 10-32 screws in their side rails, get two of them and put two 10-32 nuts on the screw, and jam them together. Then clamp the whole thing in a vise.

Below is a photo of what I am talking about:

How to install equipment into a 19 inch rack

Once the screw is in the vise, take a hacksaw and cut off the head of the screw. Then cut a vertical slot with the hacksaw right where you cut off the head. The purpose of the vertical slot is so you can use a screwdriver on it. so make sure you cut the slot deep enough. You will need two of these for installing equipment into a 19 inch equipment rack.

To use them, you need to figure out which holes in the side rails you will be using for mounting your equipment in the rack. In the top most hole that you are going to use on each rail, simply screw in one these special screws.

Now its time to mount your equipment. All you do is slide your equipment’s top mounting holes on to the screws. This will properly align your holes, and all you have to do is push the bottom of your equipment up against the rack, and these two screws will hold the weight of your equipment for you. Just put in the two bottom screws first, then the rest of them into the rails of your equipment rack.

Here is a photo of one of the customized screws after the equipment is installed:

To finish the job, simply take a screwdriver and unscrew these two screws and replace them with the proper screws and you are done installing your equipment into the rack.

This article was originally posted on www.mikestechblog.com Any reproduction on any other site is prohibited and a violation of copyright laws.

DIY Your Own Equipment Rack With a Lack Table – LackRack

Recently I needed a 19″ equipment rack. But being cheap, I decided to build one. While searching the Internet, I found what is called a LackRack, which uses IKEA‘s Lack Table. However further reading revealed a couple of things that I thought were lacking in the original design of the LackRack.

Upon doing further research on using a Lack Table for a 19″ equipment rack, I found out that the legs of the Lack Table were hollow, except for the top two inches, and the bottom inch. Which would probably be ok if you only needed to rack one piece of gear, but that sort of seems to defeat the purpose of having a 19 inch rack.

What I decided to do on my 19″ equipment rack was to use metal reinforcing strips as rack rails. But first, here is a photo of the completed 19 inch equipment rack using an IKEA Lack table:

DIY 19 inch Equipment rack Lack table lackrack

I chose to mount my equipment on the inside of the legs for a neater appearance, since I was mounting metal rails on the legs of the Lack table. This also gives me a more comfortable feeling when I put my coffee cup on top of the Lack table, as coffee spills are inevitable, mounting the equipment as shown will provide more protection from such accidents.

Pages: 1 2

Build a Phasing Harness For Stacking Antennas

Recently at work, I had the opportunity (or need) to make a phasing harness for a two bay antenna. But I had a problem. I found on the web a few years back how to do this for my particular antenna situation, but now the web page was gone! So I had to figure it out on my own. After many hours of looking through my (very poor) notes, I figured it out.

What I had was a pair of circular polarized antennas that were to be set up as a two bay antenna system. Each antenna had an impedance of 100 ohms. Here is what I came up with, and it seems to work.

In a transmission line, such as coax, the impedance of the load repeats itself every half wavelength. Since each antenna is tuned to 100 ohms at resonance, all I have to do is cut two lengths of coax exactly to a multiple of a half wavelength, and connect them to a Tee connector. What this does is takes the two 100 ohm impedances of each antenna and put them in parallel with each other. The end result is a 50 ohm feed point, which allows me to connect my 50 ohm coax for proper match.

However there is one problem. When coax is manufactured, there is a 10% tolerance in the velocity factor of the coax. So as far as I am concerned, just taking the published velocity factor of the coax could be problematic. So I needed a way to measure or tune the individual lengths of coax to some multiple of a half wavelength.

By way of background, here is a diagram that is similar to the antenna system I was setting up. The two pieces of coax I had to precisely cut are labeled “Phasing Harness“:

How to build coax phasing harness for stacked antennas

So what I had on hand was Belden 8237 RG-8-U Type coax. This has a velocity factor of 0.66 and a characteristic impedance of 52 ohms. So based on these numbers, and the spacing between the two antenna bays, I chose to use a length of coax that is 7 half wavelengths long. Actually this is way too long for my needs, but that’s ok.

Here is what I came up with, I will simulate both antennas at resonance with a non-reactive 100 ohm resistor. So I built my own dummy load inside of a male type-N connector, as well as on the back of a female type-N connector. Next, I calculated the electrical half wavelength of a piece coax using the following formula:

L (inches) = (5904 * VelFactor) / Freq. (mHz)

This will give you the length for one half wavelength. In my case, I chose 7 half wavelengths, so I multiplied the result by 7, then added about 15%. This length is deliberately too long so I can tune it in to the desired frequency. On one end of the coax, I put a connector on it. The other end is the end that I will be trimming to length. So on this end, I put a connector on it, but I don’t solder it, which is ok for temporarily measuring its length.

Here is a diagram of my test setup using a MFJ-209 antenna analyzer:

Start your frequency sweep slightly above your desired frequency, then start sweeping down. As you tune through the frequency range, you will find a point where the SWR goes to almost 1 to 1. Typically I sweep the frequency several times to the low point of the SWR in both directions. This insures an accurate frequency reading for the coax. Make a note of the frequency.

Next, trim the coax by an inch, and repeat the steps above until the SWR dips at the same frequency as your antennas are resonant for. Do this for both pieces of coax, which comprises the phasing harness.

When you are through with both pieces of coax, you now have a completed phasing harness tuned to the same frequency of your antennas.

This article was originally posted on www.mikestechblog.com Any reproduction on any other site is prohibited and a violation of copyright laws

How To Bond Ground Rods With Exothermic Welding

At work, I recently put in a ground system for our new antenna system, which requires a good ground system. A critical part of that is properly bonding the copper ground wires to the ground rod. The best way to do that is exothermic welding.

A lot of people call it CADweld, which is a registered trademark of Erico, which is one source. However their less expensive One Shot has been difficult to acquire. In searching the internet, I found a different company that makes the same thing. They call it a Uni-Shot, made by Harger and can be found at tessco.com.

Using this method of bonding ground wires to your ground rods, prevents corrosion, and high resistance connections to your ground rods. If you use a clamp, or other compression method to bond your ground system, it will require cleaning the connections regularly, and still won’t insure a good ground connection.

In this blog post, I will show you how to use a CADweld uni-shot to exothermically weld your ground rods. The photo below shows all of the components of the CADweld uni-shot.

Cadweld Exothermic Weld Components

bond Ground rods with exothermic welding

From left to right, you have the following items:

Uni-shot mold
Ceramic Disk
Metal Disk
Starting powder
Ceramic Lid

Pages: 1 2 3 4

How to fix scp: Ambiguous Target Error Solved

Recently I needed to copy a file using scp to another server and encountered the following error: “scp: ambiguous target” In doing some testing I figured out that the space in the file name was the problem. Here is how to handle a file name with a space in it.

I even tried putting the file name in quotes, and that didn’t take care of the ambiguous target error message. For example, I was trying to use the following command:

scp myfile.txt user@192.168.1.100:”/file path with spaces/myfile.txt”

In trying to put the quotations marks in several different places, it still didn’t work. What you need to do is escape the space with a backslash. what is meant by this is that you need to put a backslash in front of every space in the file path name. So the above command then becomes:

scp myfile.txt user@192.168.1.100:”/file\ path\ with\ spaces/myfile.txt”

This takes care of the scp: ambiguous target error message from the command line, but what about running inside a shell script. In that case, you would add two backslashes. So the above command then becomes:

scp myfile.txt user@192.168.1.100:”/file\\ path\\ with\\ spaces/myfile.txt”

This article was originally posted on www.mikestechblog.com Any reproduction on any other site is prohibited and a violation of copyright laws.