I originally made this intervalometer to photograph the 2017 total solar eclipse. I wanted to make a portable and simple intervalometer out of parts I had laying around. I had a small enclosure with a front panel cut out for a keypad, LED, and switch from an old project I didn’t finish, so that seemed like a good place to start. I used this with my Canon Rebel T6i, and it connects using the 2.5mm remote port on the DSLR body.
Although I really like the Kenwood TH-D74 for its long list of features, being an HT, the user interface is not well suited to satellite operations. In particular, for linear satellites where I may need to continuously vary the tuning throughout the pass, it is tough to come up with a good mounting scheme on my chest rig so that the tuning knob is accessible and the screen is viewable. To try to solve this problem, I thought I could somehow build an upward facing display so I can mount the radio vertically and have access to the knobs and a good display. The photo above shows the final product for this project which is built around a Raspberry Pi Zero W and the USB interface the TH-D74 supports.
After seeing a few people on Twitter with a a shortened Arrow Antenna for satellite operations (colloquially called a “Shorty Arrow”), I decided to try to build my own. Rather than three elements on 2m and seven elements on 70cm as with the regular Arrow Antenna, the shorty arrow has two elements on 2m and four elements on 70cm. This results in a more compact and lightweight antenna at the expense of gain, particularly on 70cm. In my experience, this limits the antennas use down near the horizon especially if you have foliage in the way, and it is definitely a bit more of a challenge to get into some sats. Still, I’ve made plenty of FM contacts using 5w radios and this antenna even on weekend passes. I particularly like using this setup when I travel somewhere via airplane as this is small enough to fit in a carry-on bag.
Since you’ll need the antenna elements anyway, I suggest you buy a full size Arrow if you don’t have one already and just share the elements between them. It also saves you having to bother with measuring and centering the holes you drill; just clamp the full sized Arrow to the shorty to drill like I describe below.
What you’ll need:
-2m driven element
-2m reflector element
-70cm driven element
-70cm reflector element
-70cm 1st director element
-70cm 2nd director element
–approximately 2 feet of 3/4″ square aluminum tubing – I found four feet of this at Menards for around $10
-handgrip of some sort. I used a foam grip from a garden trowel I found at the dollar store
–11/64″ drill bit
-a couple clamps
The build process is actually really simple and doesn’t require any measuring:
- Remove all the antenna elements and the hand grip from the full size Arrow Antenna.
- Take the square aluminum tubing and clamp it flush against the Arrow Antenna. Make sure you don’t place the clamps over any holes.
- Use the Arrow Antenna as a drill guide by drilling through its element holes and into the square aluminum tubing with the 11/64″ drill bit. This allows you to easily drill with the same spacing as the original Arrow Antenna without have to measure and center the holes. Do not drill through the holes that are usually hidden behind the hand grip on the Arrow Antenna – these are tapped for a 1/4-20 tripod mount.
- Remove the clamps, rotate the tubing and Arrow Antenna so the blank side of the tubing aligns with the other band’s element holes on the Arrow Antenna, re-clamp, and drill the holes for the other band in the same way.
- Using the hacksaw, cut the excess length off the aluminum tubing.
- Use a metal file to round off the ends of the tubing and remove any burs around the holes.
- Slide the hand grip on your new Shorty Arrow Antenna and install the elements.
- Go work some sats!
As I got interested in roving more for satellite operations, I was looking for ways to slim down the equipment I needed to carry, particularly on trips that require a flight. While packing one night, I noticed I had a Tronsmart WC2F USB power adapter that supports the Qualcomm Quick Charge 2.0 protocol. This is one of several protocols that let devices use higher voltages and currents over a standard USB A connector. There are a few versions, but in short, this protocol allows for the USB power adapter to supply 12V at 1.5A, among other less interesting voltages (to me anyway). This seemed like a perfect way to charge my 12V devices – my Kenwood TH-D74, Ailunce HD-1, and Yaesu FT-817ND – without having to bring along an additional wall wart.
After digging a bit, I found an article on Hackaday where someone made a custom power adapter using Digispark, a modified regulator, and some simple handshaking code. Going down into the comments, Sam Mallicoat mentions the handshake can simply be done with a couple resistors and a momentary switch. Even better, Horst Leykam replied that a regular old latching SPST could work instead of a momentary switch. Aha! Since I was trying to keep this compact, this seemed like a great option compared to adding a microcontroller to the system. My plan was to made a cable adapter with an in-line switch that contained the resistors. A USB A male connector on one end and 2.1mm barrel connector on the other would give me good compatibility with my devices.
For the switch, I ended up buying a simple Leviton in-line lamp cord switch which is large enough to hold the resistors inside and can be found online or a hardware store. I unfortunately didn’t take photos at the time, and I admit it wasn’t pretty inside; I had to use some hot glue to keep wires where I wanted them and rip out the regular lamp cord contacts. But still, it was not too difficult of a project. As this uses a SPST switch, the operation is as follows:
- Plug USB cable of adapter into Tronsmart
- Cycle the adapter switch to off (if it’s not off already)
- Switch adapter on
- Voila! After a moment, 12V will be coming out on the barrel connector
Note that this switch does not control power entirely; when the switch is in the off position and before cycling it, it will still be outputting 5V. This is likely not an issue for a 12V device, but of course, proceed at your own risk!
While I know my adapter could be prettier, I’ve been happy with it so far. I have 2.1mm y-splitter cable which allows me to charge two devices at a time, usually my D74 (with a small connector adapter) and HD-1 or D74 and 817ND. While it could actually run one of those devices at a time based on its current capability, the inexpensive switching regulator in the Tronsmart is expectedly noisy, so this really should only be used as a charger. Since the Tronsmart is a dual USB port charger, I can bring this adapter to charge my radios and iPhone or iPad all from the same outlet at the same time.