Friday, August 8, 2014

Search and Rescue Radio in a box

Arlene is a member of the Incident Support Team (IST) for King County Search and Rescue (KCSAR).  She recently decided to purchase the standard KCSAR radio, which is a Kenwood TK-780.  Initially, she didn't want it permanently installed in her Toyota pickup, so I suggested putting it in a small box.  Apparently, I must really like building radio-in-a-box setups because below you will find photos of  the end result.

Before that here are some of the details that went into making the project.  Total build time approximately 60 minutes, except for the travel time to Harbor Freight where I purchase a small "aluminum" case on sale for just over $11 (always use your coupons!).  It has only an aluminum frame.  The black portions between the frame members are made of a fiberboard that comes very close to a highly compressed cardboard.  Yet, they advertise this as an aluminum case.

Case measures 7 1/2 by 11 1/2 by 4 1/2 outside dimensions.  Inside dimensions are 6 3/4 by 11 by 4 1/8.
Granted this isn't very big, but Arlene's request was to make it small enough to easily carry and store anywhere in her pickup. I believe that was accomplished, because it is in fact "Arlene Approved".

The weight needed to be light and to that end the entire setup weighs a mere 5 pounds, 6.5 ounces.  Optionally, there is enough room to include a direct connected 12 volt 7 AH battery, however this would nearly double the weight since the battery weighs  5 pounds, 4.4 ounces.  Although Arlene tested the "carry" of this option and said this would not be a problem for her, if needed.

A small aluminum bracket was used to raise the radio enough so it could be angled to make the display easily readable and the microphone jack is above the box edge.  The bracket was from an old tower PC, it was a 5 1/4 inch drive bay filler.  This came out of my projects junk box, so it was free.  The bracket is pop-riveted to the bottom of the case.  The radio included a mobile bracket, which was then screwed to the aluminum bracket.  That was the entire construction process.

Radio is attached to the mobile bracket, power and chassis ground cables were routed so can be used with the power accessory plug and chassis ground connection installed in the pickup, respectively.

The setup for in pickup operation is as follows:

  1. Open box, drag out the antenna pigtail, Anderson Powerpole connectors for power and chassis ground
  2. Attach antenna, power and ground wires already in pickup to the matching box items
  3. Turn on pickup and then radio
  4. Listen and talk!
The photos below can be enlarged with a click.  Purchased items were Harbor Freight case, KCSAR radio, Anderson Power Poles and  battery (from earlier project).  Recycled part was the aluminum bracket.

View from handle side, standing on hinged side.

View with box on base.

Opened box with basic setup.

Cables shown are VHF antenna pigtail, fused power lead,
chassis ground and microphone.

Optional battery is inserted to the right of the radio.

Packed for case closure, with optional battery.

Saturday, May 10, 2014

Power your laptop from your radio Go-Box battery!

First off, I am not any kind of electrical expert.  However, that never stopped me from experimenting.
Granted fuses fear me when I come near, but if you know someone who is skilled with electrical knowledge then you have every reason to give your ideas a path to reality.

Well, Jim, K7JGM gave me a new idea for my Packet Go-Box.  He mentioned that his Go-Box contained a Powerpole outlet to power his laptop computer.  This means that it is possible to tap the 12 volt power supply for the radio to power a laptop.  You just need a way to step up the 12V to something like 18 to 19 volts.  The specific output voltage depends on which laptop you own.  In my case the Toshiba  laptop I have dedicated to my packet station needs 19 volts.  I obtained this information from the power brick included with the laptop.  The power brick tag says output is 19 volts and 3.95 amps.  Being the trusting person that I am, I measured the voltage coming out of the brick and it read 19.6 volts.  Close enough.

The voltage step up is done by using a DROK DC Converter Voltage Regulator 8-32V to 9-46V 12/24V 150W Boost Step Up Power Supply Module which is available from  The regulator can be adjusted easily to match your output needs.  However, be sure the output range of the regulator is appropriate for your particular laptop.

For your Go-Box, you simply tap the 12 volts and install a Powerpole outlet somewhere accessible for you laptop.  In my case, I already had a Go-Box built with 12 volt Powerpole outlet so, I decided to make an external 19V converter.  Below you should see the convertor installed in a plastic "case" with  Powerpole connectors on both input and output.

The case for the converter is a $1 plastic box from the stationary section at our local Fred Meyer. Several holes were cut in the case to allow the Powerpole wires to enter the box and to allow the cooling fins to be exposed.

Finally 5 small holes were drilled to allow access to the screws which secure the wires AND the voltage adjust screw.

Lastly, the scary part is cutting the wire on the power brick that goes to the laptop. This way you can install Powerpole connectors on each side of your cut, as shown here.  This allows you to connect the laptop's power connector to either its original power brick OR the new converter you just assembled.   That's it, enjoy!

UPDATE (2014-05-10) :

So, you have a Dell laptop and it has a "smart" power brick.  Well guess what!  Instead of having the typical 2 connector power port, it has a 3 connector setup.  That center pin is a way for your laptop to tell if the power brick is the correct one. Unfortunately, if it thinks the charger isn't the correct one, then it allows it to power the laptop but not charge the battery, even if it has the correct voltage.  Some folks in the various forums have suggested to just send the 19 volts down the center connector as well, but don't do it.  That connector expects no more than 4 volts so more then that may kill the "smart" chip.  See for some background.

However, all that said it is possible to use the converter with a Dell.  Since I have a great appreciation for Anderson Powerpoles that is what I used to make sure everything connects correctly.  The images show how to wire the connectors to use all three wires when the power brick is connected and how the converter connects.  Note that the Center Pin is labeled for photo reference, since the Powerpoles are used there is only one way to actually connect everything.  Red goes to the + 19 V connector which is the inner shield. One black goes to the ground outer shield and the other black (sorry I didn't have another color, which they do make) goes to the center pin.

Everything works as usual when connected to the power brick.  However, when the converter is connected the laptop whines about it being the wrong charger and it won't allow battery charging. How rude!  If you leave this situation alone then the battery slowly discharges.  You probably won't notice it because the converter is powering the laptop.  The issue occurs when you disconnect the converter and expect the battery to power the laptop.  If the battery has fully discharged, well you guessed it, the laptop goes black when converter is unplugged.

An extremely simple solution is to remove the battery after the converter is plugged in.  The only change with the battery removed is that the converter's fins warm up just a bit more than with the battery inserted.

If someone knows a way to fool the laptop into believing it has the correct power brick, please let me know.