Theodolite Application for Locating the Moon

Theodolite is a multi-functional app that combines a compass, inclinometer, rangefinder, GPS, map, and camera with geo-overlay for augmented reality. It's essentially a digital theodolite, allowing users to measure angles, distances, and positions using their smartphone or tablet.  This is the perfect way to locate the moon in azimuth and elevation for pointing the antenna.  I purchased this app from the Apple Store for $9.53 and in my opinion it is well worth that price.

Below is my first attempt at using this app to locate the moon.  Local time was just after midnight and Full Moon is in 2 days so this moon was over 90% illuminated - it is bright!  You can see a tree to the left of the moon and also a portion of the edge of my garage.  This image was taken at the point where I plan to set up my Sub-Lunar Folding Dish.  At the time I took this photo the declination was -27° so the moon was not very high in the sky even though it was nearly due South of me.  You can see that the Horizon Angle on the left shows the phone was tilted 2.7° away from horizontal.  (Click on any image to see a larger version.)

I placed inside the Theodolite image a Yellow bordered box showing the Astronomical Data from WSJT-X for the same date/time.  You can see the app shows an Azimuth of 187° and WSJT-X shows 187.5° and since the moon is actually below the crosshairs, the indicated Elevation Angle on the right (of +25.3°) was a little off from the WSJT-X number of 23.7°  At the top of the screen the app also shows my latitude/longitude and elevation. 

I learned that I might want to set my iPhone on a tripod to keep it steady in the future.  Just holding the phone in my hands it was difficult to center the moon in the app.  Also, you can push the "Zero" button in the bottom left and it will put a box around the crosshairs in the center of the image.  This box changes color from Red to Yellow to Green then White as you get the image lined up with the horizon so the elevation numbers are correct.  What this button does is to zero all angles at a given orientation of the device, thereby showing angles relative to that reference until you tap the button again.  Once you tap zero again the true angles will be displayed and if the phone has not moved, the Elevation Angle will be correct (as long as the moon is centered in the crosshairs!) 

In the example below the Elevation Angle on the right shows -08.9° but the Horizon Angle on the left shows the image is -01.1° from being level.  And, the yellow box shows you are close to being lined up.  If you line up the image and "then" press the Zero button, it will adapt the image so that the Horizon angle is 0.0°

 

I don't think this app will take much effort to be able to dial in the location of the moon.  Once I have those numbers, I can set up my SL-1 Az-El Positioner to the current moon location and "hopefully" it will then track the moon automatically.  If I don't have visible moon, I "think" I can still use this app to align it with the dish feed and use that as the starting position for the Az-El Positioner.  The Theodolite User Manual is located HERE.

New EME Challenge - 23cm

After having completed EME QSO's on 6-M, 2-M, and 70cm, I felt it was time to explore a new EME band - 23cm (also known as 1296 MHz.)  Over the past few years there have been huge improvements in equipment for this band and it is possible to purchase all needed items off-the-shelf without the need to "home-brew" any of the needed equipment.  I had delayed moving to this band for several years because my location was not suitable for a parabolic dish antenna (mounted on the ground) to see the moon in the part of the sky which favors Europe.  Too many trees!  However, Paul Andrews, W2HRO, has developed and is marketing a lightweight, folding parabolic dish which uses space-age RF reflective fabric.  His company, Sub-Lunar, sells folding dishes in several sizes, patch feeds, OK1DFC Septum feeds, WinTrack Software/Hardware from N8CQ, Az-El positioners, and many other products to support EME operation.  This "portable" dish concept allowed me to consider other locations on my lot where I could "temporarily" install the antenna with a better view of the moon.

 

I decided to go with a 1.8M dish (just under 6-feet in diameter) because it was lighter and easier to install and remove.  The 2.4M dish would add about 2 dB to TX and RX signals but I was concerned that I might not be able to handle that larger antenna by myself.  The antenna folds and unfolds like an umbrella!  But it is not weather proof in any of its components and is sensitive to wet and wind!  For that reason, it is a "temporary" antenna.  I plan to only use it when the weather and moon conditions are favorable. UPDATE 2025-08-20 - After talking to several EME'ers and checking with W2HRO at Sub-Lunar, I opted to change my folding dish order to a 2.4M version.  Paul (W2HRO) said he felt I would have no problems with the larger dish.  The earlier models were a little tight but no more.  Bigger is better they say!

Considering this would be a "temporary" set-up, I decided to purchase a rolling cart that could hold all the equipment (power supplies, amplifier, laptop, etc.) and thus it would be extremely simple to just roll the cart out of the garage, erect the antenna, connect the feedlines, and be on the air.

A recent improvement in folding dish setups is the OK1DFC Lightweight Septum Feed.  Originally those stations with a folding dish used a "Patch Feed."  But on 23cm (1296 MHz) EME signals use circular polarization.  In order to get circular polarization from a patch feed, you need to incorporate a 90° hybrid to provide circular polarization. However, to switch between LHCP (Left-Hand Circular Polarization) and RHCP (Right-Hand Circular Polarization), a power relay and a set of cables are also required.  A key advantage of the septum feed is its ability to generate both RHCP and LHCP simultaneously!  This eliminates the need for a 90° hybrid.  Also many hybrids are not exactly 90° so that results is less than optimal operation.  And, 90° hybrids are limited in the amount of power they can handle - often only in the 200-watt range. 

Other major components include a preamplifier and a high power amplifier.  Thankfully AG6EE has been building both.  His pre-amp has about 30 dB of gain, with a built-in relay and dummy load - and can connect directly to septum feed.  His 23cm amplifier is spec'd for 600W out (max 700W) and splits the input into TX and RX lines, the RX line has sequenced DC voltage to feed the preamplifier through the coaxial cable.  I have ordered the pre-amp and amplifier from AG6EE and am anxiously awaiting delivery!

Since I have not operated on 23cm for 24 years (and all that equipment is gone) I needed to acquire a transceiver to operate on 23cm.  I chose the Icom IC-9700.  There is a know frequency drift problem with that radio on 23cm so I ordered a GPSDO from Leo Bodnar to incorporate inside the IC-9700 with an external GPS antenna included. In order to install the Leo Bodnar injection board inside the IC-9700, it is necessary to open the case of the radio.  That requires a special screwdriver. A P2x100 #2 JIS Cross Point Impact Screwdriver is what I ordered from Amazon. And, a laptop would also be required so I purchased a refurbished Dell 5500 Win10 from Amazon utilizing an 8th Generation Intel Core i7 with a 512GB SSD Hard Drive and 32GB DDR4 RAM.  To power the radio and the pre-amp I bought a PowerWerx 30A 14.1 VDC Power Supply, and to power the amplifier, I purchased a Mean Well RSP-2000-48 VDC Power Supply from DigiKey.

Several other minor items were also purchased - a 23cm 1kW element for my Bird 43 wattmeter, a 50-foot 12/3 extension cord, an AC power strip, a spiral ground anchor to hold the dish tripod down, an LED keyboard lamp, a Shielded/Filtered USB Cable for the IC-9700, and so on.  Then a fair amount of time was spent downloading and installing multiple pieces of software on the computer.  I work on this project every day with the goal of being operational on 23cm EME in time for the ARRL EME Contest on October 11/12.  Fingers crossed!