Hammo Can 2.0

The project that was supposed to be but evolved into something else.

If you recall a few years ago, I built a portable battery box using a $5 plastic ammo can. It works phenomenal with my CB and ham radios. If I need a 12V source to test circuits with, I can also use it as a portable power supply. But what about my original idea?

Hammo Can 2.0

Well, it was supposed to be Hammo Can 1.0, but that ended up being my battery box.

Regardless, I've circled back to this idea because I purchased another mini radio, the Cobra 19 Mini. Since I'm putting this CB in my vehicle (and carrying the Baofeng again as an EDC radio), I have no need for the QYT-KT8900.

Or do I?

There's a fellow who posted EXACTLY what I originally had wanted to do with an ammo box. The website is here: https://reverendbow.wordpress.com/2016/12/13/the-50-cal-ammo-can/. He actually uses a KT8900 as well as one of the compact Radioddity CB-27 or the AnyTone Smart units. They're all the same exact form factor as the Cobra 19 Mini. These radios actually do surprisingly well and they come factory stock on 10 meters. This means that with some mods you now have a dual band 11 meter AND 10 meter radio, albeit without SSB/CW capability. However, 10 meter and 11 meter AM/FM QRP can go as far as you want on a good day with a good antenna, and it's been done before. Remember, even stock 4 watt CBs can talk skip as well.

This entire setup fits nice and snug in a .50 caliber ammo box. You could do the same with a .30 caliber ammo box, but it seems that only one radio will fit. I want two in there. :)

I wasn't planning on adding the speaker, however I was planning to add the following:

• 1x QYT KT-8900 - $80
• 1x Cobra 19 Mini (or similar micro CB) - $60-75
• 2x SO239 bulkhead connectors - $10
• 1x Volt/Ammeter - $7 (pack of 2)
• 1x Master I/O switch - $7 (pack of 5)
• 1x SAE 12V Receptacle - $10
• 2x RG58 Jumpers - $13
• 4x Angle Brackets - $6 (pack of 10)
• 2x SO239 Waterproof Covers - $10 (pack of 10)
• 1x .50 caliber ammo can - $15
• 1x SAE to 12V plug - $10
• 1x 12V Fan - $7 (pack of 4)
• 1x Power Distribution Box - $7

In total? About $160. $280 or so if you include the radios, but it's worth it if you think of the end goal.

In the end, I want to have a portable radio station that I can use in emergencies, for camping, or even on road trips. Something in case my Baofeng couldn't reach where I needed to talk or if for some reason license-based comms were irradicated. Pair this with a Linux-enabled Chromebook and you can do APRS, Winlink, and more!

Initially I wanted to go with Anderson powerpoles, but sets of Andersons can run anywhere between $20 and $40 just for a panel mount module! I instead stuck with SAE type connectors as those are the next best thing in my opinion.

This radio system has the following bands/services:

• HAM (10m, 2m and 70cm)
• GMRS/FRS (460MHz)
• MURS/Marine (150MHz)
• CB (27MHz)
• NOAA Weather Radio (162MHz)

Now...are there better radios out there? Yes. But these radios suffice me just fine, both in form factor and affordability.

Functionality

The Hammo Can must serve some functional constraints purposefully:

• It must hold at most 2 compact mobile radios
• It must be powered either externally or internally via a 12V current-appropriate supply
• It should self-contain any accessories needed for successful operation (namely microphones. Antennas are a bonus if I use something like a J-pole, dipole, etc.)
• It must be portable
• It should be easy to use and easy to understand
• It must be made with readily-accessible materials
• It must be at most water-resistant

My plan for this when the world isn't ending is to take it with me on trips. That way I can stay in touch and have 2 avenues of communication - license-bound and license-free. And besides, who doesn't want something cool they're lugging around as a talking point?

Portability is a huge factor with this thing. It needs to be portable so you could use it as a base station, in an EMCOMM situation, or even on long car trips. There are many ways you can also power this off of 12V. For starters, I could use the Hammo Can 1.0 or my car's accessory port. If I'm in a hotel room, I could use a small AC/DC converter. Out camping? Use the Hammo Can 1.0! The sky's the limit when it comes to power supplies!

I think I'll find myself using a 1/4-wave vertical for both 2m/70cm and CB radio. 1/4-waves seem to be the de facto for 2m/70cm and have an excellent low takeoff angle for DX on CB radio and 10 meters.

Style

Oh Lord I'm going to go crazy with this one!

I have lots of ideas on how I can make it cool, with maybe a touch of aesthetic pleasure too. 

First, the faceplate. Yeah, plain wood looks good, but it could be better. Add on a dark walnut stain and water sealant and we're in business. It's more so to match the woodgrain of most vehicles. Add in wood-burnt designs for even more style.

Second, spray painted callsign on the side. Along with trailer reflectors on the other side, this will make it easy to find your equipment should you lose it. I'm not planning to throw it off of a moving truck (and I doubt it will survive), but if I lose it, it should be easy to find again.

Optional but cool? LED light strips that line the inside lip just above the faceplate. I saw someone else build a Hammo Can with this exact idea and while I won't most likely do it, it would be cool...

A Note on the Volt/Amp Meter

A volt amp meter is a crucial tool for this application. It can troubleshoot any electrical problems and can display real time current draw/battery drain.

You'll want to connect the meter as shown below as we are measuring the draw from the power supply:

I will most likely make some 3D printed bezels within the next few days so this module as well as the on/off switch will fit better in the wooden faceplate. 

The power supply comes from the toggle on/off switch, and the load includes the two radios and the cooling fan. With everything at the max (both radios transmitting high power, fan on high load) I'd imagine that this portable station would only use about 8A or less. Of course we aren't going to use that much though! A better estimate is probably around 3 or 4A with either radio on transmit and the fan on.

Actually 25W???

In the past few days I have been doing some research on the QYT KT8900 and I've determined that yes, this radio CAN do 25 solid watts. Here's why.

From the factory the QYT doesn't really come with any heat mitigation (see my previous post on the QYT). In its stock form, the QYT comes with an SIL foam heatsink under a piece of copper. Some manufacturers include a fan, some don't. Mine thankfully came with a fan.

Now...I have since replaced the stock heatsink with an aluminum one. However I initially failed to take note as to how the A5M06 or RD07MUS2B dissipates heat. There is a giant heatsink on the bottom that connects to the drain of the transistor (the largest pad on the package) that acts as the heatsink. However, for what I can imagine was cost and time, QYT failed to put thermal paste on this huge heatsink, which means that the transistor literally will cook on a flat top griddle. 

RF finals are engineered to get hot, but not catch-on-fire hot. This transistor has a maximum power dissipation of 50 watts, but this is 50 watts between heat and RF. The RD07MUS2B has an efficiency between 58% and 65%, which means that anywhere between 13 and 18 watts (25 watts RF output) of dissipated power is in the form of heat. This doesn't seem very warm, but pack that power into a small 1 square centimeter package and all that heat turns into the sun.

We also have to take into account junction temperature. The maximum junction temperature of the RD07MUS2B is 150C, and even at UHF frequencies, in theory, we are only dissipating heat that's 92C hot. Again this is all theoretically at 25 watts RF. The thermal resistance of the RD07MUS2B is around 2.5C/W, and with a cooling setup of a top-mounted aluminum heatsink, a large bottom copper heatsink thermal pasted to the external case and a fan pointing at the top-mounted heatsink, the transistor is within its safe operating limits. 

To operate on 25 watts, the following must be followed:

• Active cooling - REQUIRED
• Heatsink on the top and bottom - REQUIRED
• High-quality thermal paste on the bottom heatsink - REQUIRED

Therefore, 25 watts is plenty enough and realistic for this transistor AS LONG AS PROPER COOLING TECHNIQUES ARE USED. So yes, I will be turning this radio back up to around 25 watts!!!

And if it goes kaboom? I'll most likely buy an AnyTone AT778UV or for smaller form factor, the AT779UV.

Stay tuned for more, because now I have to do some testing on this radio!