Solar Powered Portable Cross-band Repeater: Extending your HT Range.

When it comes to emergency comms, there is no more important element to consider than the HT (Handi-Talkie) or “walkie-talkie” that operates simplex on the 2M / 70CM bands.

When you consider a grid down scenario the importance of short range “tactical” communications can’t be over emphasized and the HT fits the bill perfectly with its small size, minimal power requirement, accessories like ear piece / speaker mike combos, and VOX operation, etc.

On the other side of the coin is the fact that the average 5W signal from them is fairly weak and ranges of < 2 miles should be expected as is out of the box.

Because they are “line of sight” signals, terrain features easily block the signals.

In Oregon where I live, its common to have 300-500ft draws and gullies on “flat ground” areas that we tend to live in. In the Oregon woods, you are looking at several thousand feet of disparity in elevation within just a few miles.

w7pra_map
Even though they are less than 17.8 miles away and on a 4200 ft mountain and my house sits at an elevation of 700 ft by comparison, the terrain prevents reception on either end.

Although line of sight issues are reduced when one of the transceivers is elevated ( that’s why repeaters are on mountains 🙂 ), living close to the “knife edge” of a 300ft hill like I do, does not allow reception of the elevated repeater.

In my case that results in no comms to the most important 2M repeater system in Oregon, the Peak Radio Association (W7PRA) repeater system which has 20+ linked repeaters that tie all of Oregon together on one net.

Even if I could hit the repeater without an issue, there is still the problem of depending on other peoples gear in an emergency which is never a good idea.

Few repeater stations are setup for long term use on E-Power and getting to their sites in Winter presents an issue as well as any other time if the grid is down as there is no fuel readily available to drive there.

After a few weeks of a downed electrical grid, you are going to want to patrol your immediate area for security reasons and eventually expand those patrols out further for information gathering purposes. That means you will need to have reliable comms that can reach past the < 2 mile limit of simplex communication as well as a system that can circumvent terrain issues.

While two man-portable radios like my FT-817 could be used in NVIS formation to accomplish this, there is a lot to be said for the simplicity of being able to hand someone a pre-programmed HT verses trying to procure several HF rigs and teach each person how to be an experienced HF operator.

With that in mind, I present my solar powered cross-band repeater.

The portable repeater fills the gap between simplex 2M and HF NVIS very well. Being able to place it on any surrounding hill greatly extends the range of my dual-band HTs. It also has the benefit of allowing MANY users on the system with NO EXPERIENCE needed versus the 80M/40M NVIS radios where extensive knowledge of equipment and propagation is needed.

When I first got my Tech license in Medford, I would routinely hit the 2M repeater on King Mountain over 50 miles away with a 5W HT. Granted it sits at 5200ft while I was at 1500ft, I also made a simplex connection to a guy in Klamath Falls (100+ miles away) while calling CQ and driving up Sexton Pass (1690ft) one day.

The point is that given elevation your signal will go a lot farther than you think.

I had previously played with the idea of a remote cross-band repeater when I lived in Medford, OR. but our house was on flat land then and patrolling around it in a 1-2 mile diameter did not cause any comm issues.

For this reason, I kept the Kenwood D700A mounted in my truck, planning to drive it to a location if needed set it up as a repeater.

Now that my current location does not allow for even a 500 yard perimeter with comms, I decided to move the project up on the priority list and what you see here is the end result.

I should note that at first I went cheap on the solar charger and even considered using a cheap spare 3W panel, but in the end had to upgrade because the controller was DOA from China. When I think about how much of a force multiplier the device can truly be in a grid down scenario, I’m ashamed that I initially went cheap on the build.

Use quality components, you won’t be sorry!

Because the actual airtime is going to be minimal, I could have used a smaller solar / battery system, but due to my location and the many overcast days I felt it necessary to overbuild to ensure that the juice would remain on at all times.

Be sure to test your install for several weeks in the worst sun conditions possible!

I already had a Kenwood D700A with cross-band repeat function so that is what I used, but if I were to purchase a radio for a similar build it would likely be the much cheaper and something like the Tytera TH-7800 or Yeasu Ft-8900R.

My Kit Build Components:

What I ended up with is reliable comms from my house out to 20+ miles in all directions with this device placed directly above my house on the 300ft hill behind it. Compare that to the previous limitations of < 2 miles and it’s easy to see the value of such a setup.

Placement needs to be high and secure!!!

I have controlled access to my install because it is at the top of my property which butts up to several hundred acres of timber land and I’m continuously monitoring the area via one of my MURS Dakota Alarms which is being scanned at the house for alerts during grid down conditions.

You do not want to put all the money and effort into such a system only to have it stolen. Be sure you select a secure site to install your repeater.

Don’t forget to lock it down!

It kinda goes without saying since anyone who will make one of these is likely an experienced HAM, but don’t forget to use CTSS to block unwanted use of the repeater.

Being a crossband unit, it would take the average HAM two scanners and decoders one on 2M and the other on 70CM to be able capture your freqs and CTSS. Most will only hear the output side and not notice that its a repeated signal.

The great thing about the D700A is that it has another mode besides “cross-band” repeat that I prefer to use. It’s called “locked-band” repeat which only allows signals in on one band and out the other, making it impossible to use the box without capturing the input freq and CTSS, which is not the one they hear. They could only hear it if they were within simplex range of my HT.

Unfortunately this project ended up being abandoned.  For an update and field test report see Field Test of Portable Solar Powered Repeater.

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6 Comments

    1. There is a link to it at the bottom of the page.

      The only difference is that I added threaded connectors to Ed Fong’s design for easier breakdown and painted the PCV.

      Like

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