Introduction: Solar Powered APRS Digipeater for Amateur Radio

Picture of Solar Powered APRS Digipeater for Amateur Radio

This instructable will show you the steps I took in building a solar powered APRS amateur radio digipeater. Some of the info presented here can be applied to other projects that require power in remote places or where utility power is flaky.

It's assumed you have some tech background, basic tools, basic electronics knowledge, and of course some common sense. An amateur radio license is required to transmit on amateur radio frequencies. The license is not hard to get and there are plenty of study materials out there. A search for "amateur radio license study materials" or "amateur radio practice exams" should yield some results.

Step 1: What's APRS?

Picture of What's APRS?

APRS can be most easily described as amateur radio's version of lojack. Yes, this description tends to annoy some diehard hams but it really is the best way to describe APRS to someone that is not a ham radio techie. APRS stands for Automatic Packet Reporting System. Packet referring to data packets that are sent via amateur radio frequencies as data chirps that can be heard with a receiver on the correct frequency. These data chirps contain information on the sender's callsign, their location, and short amounts of text which can be additional data like that from a remote weather station or relay of someone else's data.

In short, APRS can not only be used to keep track of vehicles both on and off our planet (the ISS beacons an APRS signal that can be easily picked up with basic gear), it can also be used to send telemetry and messages.

As a licensed amateur radio operator in the USA, you can take advantage of the APRS network to keep track of your car, boat, plane, weather balloon, or other moving object. You can also use the APRS network to look at weather data from the thousands of amateur weather stations that are out there. While APRS can be used to keyboard back and forth much like instant messenger, it's most popular use is showing the position of moving objects.

In order for this whole network to work, it requires users with the proper gear and digipeaters. A digipeater is a digital repeater. The digipeater listens for data chirps that have been encoded with instructions to retransmit them and then retransmits what it hears when appropriate. This allows users with mobile or portable APRS stations to cover a wider geographic area. This is how a network of radios can send data back and forth for long distances without needing an internet connection. A digipeater can be a standalone dedicated device or it can be a feature incorporated into some of the more high end VHF amateur radios.

The internet is not totally banished from APRS land. It's actually blended in as an additional resource. Stations called I-gates can take traffic heard on the radio and bounce it over to the web allowing users with no APRS gear to still see what's going on. The pic above shows APRS traffic in South Fl via the APRS.FI website. Some I-gates are capable of taking APRS traffic from web based applications such as APRSdroid and putting it out on radio frequencies. This does get a little more complicated though as all users transmitting on the radio side must have valid FCC licenses. By interfacing with the web, it allows users to view APRS traffic will beyond their normal radio range. Should the web side go down though, the APRS network continues to work solely on radio providing there's enough stations within digipeater range.

In the USA, the popular VHF APRS frequency is 144.390Mhz. You can listen in on a radio scanner for data chirps and even decode them with simple software. You dont even need a computer. There are apps out there for both android and apple. There's no need for an amateur radio license if you dont plan on transmitting so if you're just curious, you can get your feet wet in the hobby with just a scanner radio and an old cellphone. If you just want to look at the web side of things, try the APRS.FI website to see what's happening in your area.

Why solar? I could easily have left this running off utility power and actually that's how it started life. Ham radio is a hobby with a strong emphasis on self sufficiency. Unlike utility power, the Sun always comes up regardless of what mother nature has unleashed.

APRS is fun to watch as folks drive around but it can have some very important uses. In times of disaster when street signs are gone and places look unrecognizable an APRS user can be guided to a destination in real time by another station viewing their movement and it can all be done without a cellphone network. APRS is also useful for keeping track of assets such as ambulances, food trucks, bike repair techs and so forth during large marathons or bike races.

Without digipeaters, the coverage area of the APRS network would be nil. Just like any other hobby, there's always folks out there doing things for the benefit of the hobby and that helps keep things going.

Step 2: Solar = Outdoors, You'll Need an Outdoor Enclosure

Picture of Solar = Outdoors, You'll Need an Outdoor Enclosure

Yes, you can build a digipeater that lives inside a building and runs off commercial power but this instructable is about building one that can be placed anywhere.

Putting gadgets outside comes with interesting requirements. First off your equipment enclosure needs to be rainproof. A totally sealed box is actually not a great idea. The temperature swing from day to night can cause condensation inside a perfectly sealed box. You want something good enough to keep the rain out but also able to breathe. Even equipment boxes used in coastal areas have some way to breathe. Remember we just need a small breather hole, ideally shielded from rain.

Bugs..

Bugs like ants and roaches love boxes. Any opening on your box (last pic) should have a screen of some sort to keep bugs out. Ants in particular are very industrious so dont skimp on this. Insect poop corrodes electronics. I've found aluminum scouring pad material to be great for stuffing into holes were you want gear to breathe but you want to keep bugs out.

Sun and Heat..

Plastic outdoor boxes are substantially cheaper than metal but sunlight can eat them up. If you can mount your equipment box out of direct sunlight then plastic shouldn't be an issue. An outdoor rated plastic box could last a few years but one day it will crack and chances are you'll find out once the damage is done to the electronics.

Thieves..

It's sad this is the world we live in but such is life. A lonely plastic box in a remote location is an easy target. Make them work for it! A heavy gauge metal box (pics 1-3) will keep curious folks and ill-prepared thieves at bay. Nothing is 100% secure but once again, why be an easy target?

Plastic - cheap, easy to work with, not secure

Metal - expensive, may require special tools, better security

I went with a stainless steel equipment enclosure. New, this box is probably in the $500 range. I got mine cheap as surplus from a local radio tech. My box originally held a strobe light power supply for a big antenna tower. These get replaced as a system so the boxes can sometimes be found at ham radio fleamarkets or by asking around to see who works on commercial radio stuff. The downside to a used box is it already has holes from its previous life. This is a small price to pay considering what they cost new. As an added benefit these strobe light boxes have a hasp for a padlock and require a crowbar to break into.

In the pics you see the lock hasp, wall mount tabs, and door seal on my commercial surplus box. Clearly, these are the way to go. I anchored mine to the side of the house using expansion bolts. This box isn't moving.

As an added bonus, some of the commercial surplus boxes will have a removable rack unit inside. This is REALLY convenient. I was able to build my entire digipeater on the workbench, test it, tidy it up, and then load the assembly into the box. It makes life much easier.

Step 3: The Gadgets

Picture of The Gadgets

What's in the solar powered digipeater box?

You'll need a 2 meter band amateur radio transceiver capable of operating on 144.390Mhz, a TNC that's been setup to operate as a digipeater, a properly sized solar panel or solar array, a battery with ample capacity, and a solar charge controller capable of handling the wattage of your solar array and consumption of your gear. You can have an optional RF amplifier to increase transmit coverage. You can also opt buy a radio that incorporates APRS functionality and have much of this gear all rolled into one unit but they are quite pricey and have high standby power drains that may not be ideal in a solar application.

In the picture you see my equipment rack. Starting at the top is the LCD display that shows traffic going through my TNC. Below the Display is the solar charge controller. To the right of the solar controller is the 2 meter transceiver. To the left of the solar controller is the RF amp with the TNC mounted on top of it. At the very bottom is the battery that runs the unit when there is no sunlight. To the left of the battery is the power distribution blocks and fuses. Let's look at these one by one.

Step 4: The TNC and the Optional RF Amp

Picture of The TNC and the Optional RF Amp

In the pic you see a blue plastic box that says TinyTrak and a blue LCD display. This is the Terminal Node Controller. It's purpose is to handle incoming and outgoing data traffic from the radio. Since this system operates at a very low data speed, data is sent as audio tones over radio. The TNC decodes that data, routes it according to TNC settings, and keys the radio's transmitter when it's time to send data along.

Since this is all done via audio tones, the connection from TNC to radio is not much different from that of a microphone and external speaker. There are countless resources out there that cover radio to TNC pinouts but my experience has been this is one area I'd rather just buy a pre-made cable. Most TNC vendors will also supply pre-made cables for the more popular radios.

My choice of TNC is the TinyTrak 4. This unit was originally intended to be used as a tracker. In other words, part of a setup you would have on a vehicle you wish to track on APRS. The manufacturer added the digipeater function on this version making it a good option for digipeater service. Do you have to use this same model? Nope. There's plenty of other choices out there.

Why did I pick the TinyTrak 4?

It's a simple unit and very cost effective. The less bells and whistles you have, the less there is to go wrong and the lower the power draw. The LCD display is an add on option and not required. It's nice to have to visually verify your station is seeing data traffic. A word of advice though, this unit is a pain to program. One of it's drawbacks is that after 20 years or so of USB existence, it still requires a serial connection to program.

Programming the TNC requires setting various parameters correctly. Byonics, the guys that make the TinyTrak 4 do offer to ship it to you pre-programmmed which can be a great help. You may still need to go in and adjust in/out audio levels though.

Connection of the TNC to the radio is typically done via handmic jack on portables, front mic connector and external speaker jack on mobiles, and via user port on some ham mobiles and commercial radios. There are audio settings that need to be just right if not your TNC will not "hear" other stations and it's transmitted signal may be too weak or distorted for others to decode. Different manufacturers have different setup methods. If you're not familiar with getting these levels right I strongly suggest you get help from one of the experienced APRS or packet radio operators in your area.

What about that amplifier?

The amp is absolutely optional. In my case, I'm using the low power setting on the radio to drive a small amp that is capable is keying with only 1w input. I get 10w out of the amp. This gives me a huge safety margin. Should the amp fail in some strange way, the radio can surely deal with it as it's operating at only 1/5th its rated output. Should the antenna or cable fail, the amp is running at less than half it's rated output and will probably put up with it. If everything was running at full power, I'd have no safety margin.

My amp choice was an old Mirage B23 VHF amp designed for use with handheld radios. This amp has a heatsink that makes up the bottom of the amp and it's just a thick flat slab of aluminum. I bolted the amp to the rack inside my equipment box and used thermal compound, like what's used on computer CPU's to thermally couple the amp to the aluminum rack. This gives me added thermal capacity. The old Mirage stuff like this amp was made in USA, the new stuff is made in China. There has been a noticeable quality difference since MFJ took over Mirage.

Can you get a bigger amp? Sure but keep in mind a bigger amp means more current draw. More current draw means you need a bigger solar array and bigger battery to sustain the system on cloudy days and overnight. 10-15w on a good antenna can go a long ways.

Step 5: Choosing a Radio

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One of the cool things about APRS is you can use almost any old 2 meter (VHF) amateur radio to get the job done. You don't need PL (tone), you dont need memories as everything occurs on one frequency. Even an ancient (by tech standards) Icom IC2AT from the 1980's will work great!

Handheld radio Vs mobile radio..

A handheld radio has the benefit of being small and will generally have a much lower battery drain when idle. The downside to using an HT (handheld transceiver) is a max of about 5w output on most models and a lousy receiver. Older HT's may top out at 1.5w requiring an external amp to get reasonable power! The ICOM IC2AT (3rd pic) is one of those 1.5w radios BUT it has an extremely low battery draw as it has no fancy features and no digital display. it uses thumbwheels to set the frequency. An added advantage to those old thumbwheel ICOM radios is they go right back on frequency if the power gets cycled. No finagling with memory channels. The thing just works.

The receivers on most handheld radios leave much to be desired when it comes to selectivity. This is the radio's ability to ignore strong signals on frequencies other than those it's supposed to be tuned to. Seems the newer the HT, the worse this got. The IC2AT has a decent receiver in it as does it's more modern brethren, the IC02AT.

What about using one of the many cheap Chinese HT's flooding the market? While super sensitive on receive, it seems most of these are some form of SDR chip (software defined radio) type of receiver which have little in the way of filtering. The receivers on these get easily saturated by strong signals even if they are on other frequencies. They just don't work well for this application where you'll have a big outside antenna connected to them.

There is one semi modern HT that has become very popular with folks on APRS and that is the RadioShack HTX202 (shown mounted in rack on pic 1). This radio can provide 5w out AND has a receiver in it that's better than most mobile radios. Power cycling this radio will also result in it going right back to the desired frequency and volume settings. This is what I used and a great choice for APRS. 202's as some hams call them can be had for about $30 on the used market.

The HTX202 incidentally is extremely rugged despite not being a commercial radio. The one in the 2nd pic went through hurricane Irma. It was in a bin of random electronics in my back porch that the storm dumped out in my yard. The radio was found almost a week later laying in a puddle. Having zero hope it would work, I opened it up and gave it a bath in electronics cleaner. All the case fasteners had to be wire brushed as they were flaking rust. The radio survived! Receive and transmit are both fine with good audio.

One more note about using old HT's... powering them. The HTX202 can accept 12v directly via a barrel connector on the top of the radio. Most HT's require odd voltages like 7.2, 8.4, or 9.6vdc. Applying 12vdc to an old IC2AT will kill it. Luckily there are plenty of cheap Chinese step down DC to DC converters on ebay. Get one that handles a couple of amps of current and use that to take the 12vdc and convert it to something the radio can live with. Some even have digital displays that show output voltage. In pic 4 you see one of those boards mounted on the back of a cheap UHF HT designed to run off 3.7vdc.

If using an HT you will likely need an amp behind it to get a little more fire in the wire. You dont need much, 10-20w out is plenty when coupled to a decent antenna. Make sure whatever amp you choose can be driven by your HT. Not all amps will key with the low power an HT puts out.

What about using a mobile radio?

A mobile radio will definitely get you a respectable output signal without the need of an amp and in many cases have a better receiver than an HT. The big downside to using a mobile is they tend to have substantially higher idle currents than an HT. When running off solar, every little bit counts. The added current draw has to be figured in to your power budget. The power budget is calculations you make based on how much power everything will consume so you can figure how much your solar system has to produce not only to run your gear during the day, but also charge your batteries for night time operation.

Something else to look out for when using a mobile is make sure you pick one that will revert right back to your desired frequency, volume, power, and squelch settings when power cycled. It would be embarrassing to have your APRS setup run out of juice because of a few cloudy days and your radio resets to an unwanted frequency.

Step 6: Controlling the Sun!

Picture of Controlling the Sun!

Solar panels produce electricity, we all know that. The part some folks dont know is that voltage is rarely usable right off the panels. Solar panels produce an output that varies according to light levels. A cloud passes by, output varies, a bird sits on panel, output varies. When they are in full bright sunlight, they produce voltages that are too high or too low to be directly connected to anything. The output of the panels must be regulated in order to safely charge batteries and run electronics.

Regulators will be rated in max amps they can handle and have specs for max input voltage from solar panels and battery bank voltage. For the digipeater we are dealing with a 12v system. The amp rating applies not only to the panel input but also the load connection. To figure out have many amps your array puts out take the combined wattage rating of all your panels and divide it by the panels operating voltage.

*watts divided by volts equals amps*

Whats the low voltage disconnect for?

The LVD (low voltage disconnect) protects your battery from extreme discharge damage. Should your battery get heavily run down, the LVD kicks in and disconnects the load. Lead acid batteries can be damaged if deeply discharged. This of course means your digipeater is off the air until the sun recharges your battery.Your equipment should be connected to the LOAD connection on the regulator to take advantage of this option.

Thanks to mass production, the price of solar power stuff has dropped drastically. The regulator I used is a Morningstar brand unit which is really well made and priced at around $50-60. It's a real nice unit and feels of quality. Can you go cheaper? Yep. The regulator in pic 1 cost me less than $10 shipped!

The Chinese are absolutely killing the solar market with cut rate prices on panels and regulators. I have bought 20A regulators for $10-14 SHIPPED! Are they the same build quality and as efficient as the Morningstar? Nope. Do they get the job done? Seems so. I've got a few of the Chinese wonder boxes in service for outdoor lighting and such and they have worked flawlessly. The common downsides i have found have been they aren't as efficient as the American made units in converting the energy from the panel into a charging voltage for your battery bank and in the under $20 price range, most aren't weather sealed so they must live in a protective enclosure.

Efficiency used to be very important back in the days when panels were pricey but now it's easy to find 100w panels at $100 or less shipped. When I started dabbling with solar power, a 45w panel was around $400. With panel prices so cheap, it doesn't hurt the wallet so much to get a bigger panel than you actually need.

Regulators fall into 3 basic categories.. shunt, PWM, and MPPT.

Shunt is the oldest type and they basically just turn the feed from the panel on and off while watching battery voltage. These can cause problems with electronics if you're not careful as the voltage is always bouncing up and down everytime the thing switches on and off.

The PWM ones are the way to go for low cost installs. The Chinese units I'm using are all PWM. Instead of switching the feed from the panels on and off at a slow rate that is obvious to the user, the PWM controllers switch it much faster resulting in quick pulses that yield a somewhat smooth voltage. Once the capacity of the battery comes into play, all you see is a smooth rise in battery voltage when the sun comes up.

Finally we have MPPT controllers. These cost a little more but are the most efficient. Long story short, they can sense what the best load is to get the most amperage out of the solar panel. Many MPPT controllers can also make good use of panels that are of significantly higher voltage than the battery bank.

Say you have a 12v battery to charge off the sun. If you use a non MPPT regulator you are limited to 17~v panels. Once the Sun starts setting your panels wont produce enough voltage to charge the battery. If you use an MPPT regulator you can run panels intended for 24 or 36v systems for example and the regulator will produce what you need for the 12v battery. As the sun sets, the higher voltage panels are still producing enough power to keep charging your 12v system albeit at a much slower rate. This is where an MPPT regulator with higher voltage panels excels.

There's plenty to read out there on regulator tech. My experience has been good with the Chinese regulators but do your own research before deciding.

Epoxy sealed?

Epoxy sealed regulators have all their electronics sealed up in glue (pic 2). This can be a good thing if humidity or insects are a concern. Ants seem to love electronics. Either get a bug proof box for your gear or buy a sealed regulator. The last thing you want is a $12 regulator getting shorted out by bugs and destroying gear or batteries.

***a word of caution with regulator connection***

All the regulators I have owned so far stipulate that you connect the battery FIRST if not you risk damage. Some of the Chinese regulators I own can work on 12 or 24v systems. Hooking the battery up first tells the regulator what the system voltage will be. Don't mess this up or you risk putting 24v on a 12v system.

Step 7: Grabbing That Free Power!

Picture of Grabbing That Free Power!

Solar panel prices are the lowest ever. There's plenty of brands to choose from and it can be daunting. What I look for in panels is correct voltage range, wattage I need, a glass face, aluminum frame, and blue cells. Yes, there's other specs to consider but being "thrifty" I work with whatever I can afford or get a deal on. Blue means silicon cells which is what you want. You do not want the brownish amorphous panels. Amorphous panels produce less power per square inch and have a shorter lifespan.

Panels will be rated in wattage and voltage. Open circuit voltage is what the maximum voltage of that panel will be in bright sunlight with nothing other than a voltmeter connected. Open circuit voltage should never exceed that maximum input voltage of your regulator.

On the backside of the panel you will see a label giving you panel specs and one or two connector blocks. You can see the 2 black connector boxes on the back of the panel in the second pic. This is where your cables going from the regulator to the panel will go. Some panels have built in diodes to prevent reverse discharge. Solar panels can act as resistive loads at night and discharge batteries. This was a problem at one time but modern regulators have built in protection to prevent that.

Some panels will come pre-wired with MC4 connectors. The MC4 connector is a twist type that provides a solid connection and seals it from weather. This is the industry standard outdoor rated connector for solar power systems. Do you have to use it? Depends..

Are you building something that will be in a hard to reach place and possibly exposed to extreme weather? Then yes. Are you building something that has to meet building or insurance codes? Then yes again. Are you a hobbyist on a budget and dont have to worry about meeting codes for your project? Then no. I have always wired straight in to the blocks with outdoor rated cable and never had an issue in over 20 years. My solar installs have been purely hobbyist stuff so I haven't had to deal with any permitting. If I was doing a proper home system for example then I would use MC4 and associated wiring.

What about mounting?

There's plenty of vendors out there for solar mounting hardware. At the end of the day, you have an aluminum frame that needs to be mounted to something to face the sun. This doesn't require expensive made for purpose hardware. In the second pic you see the backside of one of my panels with wall brackets attached to it. Those are common wall brackets from Lowes hardware that have been drilled and attached with nuts and bolts. The brackets are steel and quite sturdy. Other mounting configurations can be assembled with some creativity at the hardware store. Just remember your panels need a good view of the sky and they need to be well supported. The aluminum frames are sturdy but you still need to support the panel from at least both ends.

Wiring?

For many years I have used heavy gauge malibu light type cable for my solar experiments. The stuff looks like real heavy duty lamp cord. It's outdoor rated for low voltage applications and stands up well to sunlight. Is this a professional solution? Nope. I recently disassembled a portable array I built about a decade ago and wired with said malibu light cable. The cable was still good and pliable with no cracks in the insulation. It works for me.

How much panel do I need?

Math time! You first need to find out what your solar insolation is. This is a measure of how many hours on average you get of good sunlight for your area. In my area, I've seen books that say 7.5 and maps that say 6. While your panels will produce power in less than ideal sunlight, if you calculate solely on this number you wont fail. If you err on the good side, you wont have a solar project run "out of gas" due to insufficient sun.

For the sake of this calculation, let's pick 7 as our lucky number. 7hrs of strong sunlight multiplied by the wattage rating of your panels will give you the total number of watts produced per day under ideal conditions. If I used a 50w panel that's 350w per day of production. 350w divided by my operating voltage (12vdc in this case) gives me 29A per day. I read that 20% is about average for losses from charging and other electrical losses. 29 minus 20% leaves me with 23A of daily production back into my batteries or what have you. This is a very conservative number considering we are basing it solely on the strongest sun of the day.

So 100w of panel under these same conditions would provide up to 46A a day into the battery bank. A 300w panel would provide up to 138 amps a day into the battery bank.

These calculations are based on using panels intended for a 12v system. If you use an MPPT controller with higher voltage panels you will produce a little more than these calculations say. This is because of efficiency and the fact the MPPT controller can make use of higher voltage panels which will produce usable power in poor sunlight conditions when your 12v system panels fall short . Remember this is my failsafe way to calculate what I need for my projects to work. I'm not an engineer, just a geek! please feel free to search the web for other methods of calculating these numbers.

In pic 3 you see my temporary 100w panel for this project. It so happens to be the sun is arcing east to west on the side of the house where the APRS cabinet is mounted. I just rested the panel on the cabinet until the bracketed ones are mounted up on the wall with tapcons. This temporary arrangement allowed me to test out my solar setup over a few weeks of varying weather before bolting things up permanently. Solar panels can be crook bait so be careful where you setup loose panels. They can also be blown down easily so be mindful of weather while in your test phase.

Step 8: Storing the Power

Picture of Storing the Power

Solar panels will grab the power for you but you still need to store it. The most common batteries used in solar systems are lead acid. Lead acid batteries pack the best bang for the buck. They can have very long lifespans if cared for properly.

The most common lead acid battery is the wet cell battery used in cars and trucks. This is not the one you want if your battery will live in the same box as your electronics. Wet cell batteries vent and can corrode stuff around them. If your battery box is separate from your electronics then this may be an option. make sure and use a deep cycle battery like a golf cart or marine grade battery. Wet cell batteries intended for deep cycle applications like what we are doing also require maintenance. The electrolyte levels in the cells should be checked periodically.

Another type of lead acid battery that is perfect for our application is the SLA (pictured above). Sealed Lead Acid batteries are commonly found in UPS units for computer systems, kids ride on toys, and adult mobility scooters. The acid in these batteries is in jelly form. With proper care, they can last a long time without fear of venting or leaks. SLA's also have the benefit of generally not having all the B.S. fees associated with buying car or truck batteries.

Lithium rechargeables are out there and pack a heck of a power density but they present unique charging issues not easily addressed by cheap regulators. I have seen countless Chinese solar regulators advertised as safe to use with lithium batteries but a careful study of the item pics shows nothing but a common lead acid battery capable regulator. Lithium batteries will explode violently if overcharged or abused. I'd stay away from them until the tech matures more. If you decide to go with a lithium battery bank, steer clear of the offbrand stuff and deal with a reputable source.

What capacity battery bank?

There are complex formulas you can use to calculate this OR you just learn over time by experience. I'm at level 2 on this but what about the newbie? Here's my non scientific method.

Take an ammeter that can handle at least 10A and put it in series with your load. Watch what it draws while on and not transmitting. Whatever this number is, it will be a constant draw over 24hrs so multiply it by 24. say it's 1 amp. That's 24 amps a day.

Now either wait for radio to transmit or push the transmit button if you can and read the current draw. This is an intermittent draw that will vary drastically depending on how often your digipeater ID's or how much traffic its digipeating. Packet transmission are relatively short and obviously things get pretty quiet at night. In places with light APRS traffic you may have a full hours worth of transmit time in one 24hr day. Some places have more. I'd start with that 1hr number. What did the ammeter read on transmit? Let's say it was 5 amps (pretty consistent with a setup like mine). Add that 5 to the previous 24 and we now have 29 amps. Your battery bank needs to provide 29 amps for a full days operation in this scenario with no help from the sun.

Next question is hows the sun situation in you area? You see, more sun, less dependency on battery. If you're somewhere that's overcast often then your battery bank will be taxed more, you may go several days without a good charge. Take this into consideration when planning your battery bank capacity. It's better to err on more capacity than have your system going into low voltage disconnect on a regular basis. My system is running on a 20Ahr SLA and doing fine but then again I'm in sunny South Fl and APRS traffic is light at my location.

Step 9: Electrical Protection for Your Gear

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The cabinet I repurposed had a nice power distribution block and fuses. This is yet another nice thing about repurposing an old commercial cabinet. While this is all nice, you can accomplish the same with cheaper stuff. Many online vendors sell cable assemblies that have built in inline blade fuse holders intended for use with aftermarket car accessories. These will work just fine. You can use DC circuit breakers as well if you wish.

What to fuse?

The feed from your panels should be fused. Some regulators have built in fuses for this. The lead from the batteries to the regulator should be fused. The lead from the "load" terminal on the regulator that will power your gear should be fused. These should all be fused at ~150% of whatever their expected operating load will be. If in doubt, consult an electrician.

Don't forget to ground it for lightning protection. The gear should have lightning protection. Antennas can attract lightning. Even a nearby hit can wreck unprotected gear. If you're new to lightning protection for radio setups, ask the local amateur radio guys for help. Someone who works on commercial radio gear installs will be of great help with how to do this.

Step 10: */RADIATE\*

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All this stuff is useless without a decent antenna to radiate your signal and hear local traffic. There's plenty of choices out there for VHF amateur radio antennas. You've got everything from DIY to $1000+ options. My choice was the TRAM 1481 three section dual band antenna. This monster is 17ft long and has plenty of gain to make my 10w go further. Quick calculations reveal this antenna makes my 10w transmitter as powerful as a 45w signal on a no gain antenna. As an added benefit, it's a dual band antenna which means I can use a UHF radio on it without interfering with my APRS stuff. The TRAM 1481 antenna was about $100 at time of writing.

In the pic you see my TRAM 1481 sharing an antenna mast with my TV and WISP antennas. The low transmit power from the digipeater causes me no problems with TV reception. This may not always be the case so it's good to test things out before making a permanent install decision.

If you're in a windy location you may have to give up gain for strength. The single section TRAM dualband antenna is good for 100+mph winds and cost under $50. If you want to make your own look up "copper pipe 2m j-pole antenna" online. Its an antenna completely made of copper pipe and one antenna connector that can be scavenged from an old cb radio. They work very well but you must follow directions carefully and know how to sweat copper pipe.

When it comes to antennas, the higher the better and the higher gain the better. Antenna gain not only helps with a low power transmitter but also helps pull in weak stations. The best antenna in the world is only as good as its feedline. Don't skimp on your feedline (antenna cable). Lousy antenna cable introduces losses. At bare minimum I suggest LMR400 or comparable cable.

What will you hear or see?

APRS traffic sounds like a beep followed by a short data burst. If you can monitor the traffic on your TNC or get the display option like I did for my unit, you'll see the senders callsign, SSID, location, and some other tidbits of info. On packets being digipeated you can even see the path it took through other users radios to get to you. Packets intended to be digipeated will be heard by your system then immediately retransmitted.

In pic 2 you see the display on my unit showing what the data grouping looks like in a packet. It can all be decoded to figure out who initiated it, who retransmitted it, and what the stations informal name is.

If you want to know if your station is seen by the web side of the network go to aprs.fi and search by your zipcode. If there's an i-gate within radio range of your digipeater and you have configured things properly, it will show up on the aprs.fi website.

Comments

chichimus (author)2017-11-13

Nice project. I have been thinking of putting an I-gate up in the top floor of my shed with a solar panel outside. We have reasonable coverage here but I live down in a small valley so there are a few gaps locally. If nothing else it would allow my wife to follow me on APRS.fi when I am out rambling about :)

ggriffith1 (author)2017-11-07

Nice article.
I have been running a solar powered 2m repeater for over 20 years, and your instructions will help many people. I also almost remember using packet radio prior to the internet.
But I wonder why you use a gain antenna. I built a yagi for packet but only to reach the nearest node station which was over some hills. But the repeater always used verticals to get all round coverage.
Regards. VK3CQ

ke4mcl (author)ggriffith12017-11-07

I used a vertical gain antenna to get omnidirectional gain. The goal of my setup is to pickup local stations and be able to bounce them along to the next digi for extended RF coverage.

Wild-Bill (author)2017-11-07

Cool - I feel that the Internet has had its effect on reducing the people who might have become interested in HAM radio. I find your project fascinating and I have just learned some thing new. Years ago I looked at building a repeater based data transfer system for a forest products company (I was the IT weeny). The idea was floated to me by by a HAM who developed a business creating remote security monitoring systems. I encountered him as he was looking into real time open source video compression. Unfortunately my company wasn't willing to consider the proposal. It would have been so simple to pull off using just handhelds. We already had most of the physical locations (for out radio network) and we only really needed one new location to get the data network to work to fully cover out operating area, thinking of things like remote portable cutblock weather stations. I never thought of using it to monitor the logging trucks. I think, that the potential scope of the project and what it could do for the company, scared them. Looking at the APRS.fi is interesting. Thanks.

ai4px (author)2017-11-07

Very nice! You know what would be cool? Co-locate it at your local 2m repeater site and use the discriminator audio from the input freq of repeater to feed the input of the TNC. Then you could scavenge mic encoder packets from the 2m input and spit them back out onto 144.39. Bonus points if you tie the carrier detect LED to mute the audio going into the 2m repeater, especially if the repeater has an audio delay board in it.

ke4mcl (author)ai4px2017-11-07

Would be a cool idea but repeater owners and just ham activity in general in soflo is kinda weird. We just don't get the general comraderie amongst system owners here like they have in other parts of the country. Sadly you either have to rub someone's ego or just build your stuff on your own. We have a repeater and aprs digi on a 1200ft tower within visual from my place. Its all been busted for well of over a decade and nobody can get up there due to politics. Just an all around bummer.

MikeD11 (author)2017-11-07

Check out the LiFePo4 batteries. They don't explode like the other Lithium technologies. $145 will get you 80 5AH cells that can be put in series (4) to get you 12.8V so you'll have a 100 amp hours at 12.8V battery. Best thing is these battery's can be charged/discharged many thousands of times. They way outperform lead acid! Just don't go below 2.8V on any cel or will wreck em.

ke4mcl (author)MikeD112017-11-07

I've been messing with lithium's but on a smaller scale. I know they can pack plenty of punch but paid $25 shipped for the 20Ah 12v SLA in this project. Hard to beat deal on Walmart.com

SamWoT. (author)2017-11-07

Wow, nice and thorough and easy to understand

Tominaz (author)2017-11-04

wow great project, I'm sure the folks in your area will appreciate the added capability

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