Tag Archives: EME

EME Station 2.0 Part 7 – Building Antennas

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M2 Antennas 2MXP28 X-Pol Yagi

M2 Antennas 2MXP28 X-Pol Yagi

The next step in our EME project is to assemble the four M2 Antenna Systems 2MXP28 Yagis. These antennas are large, cross-polarized yagis. They feature 28 elements each on 34 1/2 foot booms. The design operates as an independent horizontal and vertical Yagi on a shared boom and each plane have an independent feed point.

EME Antenna Array Assembly

EME Antenna Array Assembly on H-Frame

We are building four of these antennas to be mounted on an M2 Antennas 2X2 H-Frame. It is important that the four antennas be identical so they operate properly as an array. This includes things like symmetrical mounting and alignment of each antenna’s vertical and horizontal elements and the associated feed points. We will cover the assembly of the H-frame and Elevation Rotator systems in the next article.

Preparation

NOALOX Assembly Compound and Sharpie Pen

NOALOX Assembly Compound and Sharpie Pen

M2 Antenna Systems instruction manuals are very good and they specify the tools and procedures to properly assemble the associated antennas. A few additional items were helpful in our project. These included:

The assembly steps and procedures are similar for most M2 Antennas 2m and UHF Yagi antennas so I’m going to share some details and a few tricks that we’ve used successfully to build a number of their Yagis. You can see some of these other projects via the following links:

We successfully built all of these antennas using similar components and techniques.

M2XP28 Sorted Parts

M2XP28 Yagi Sorted Parts

The first step in assembling each antenna was to inventory and arrange all of the parts. I also took the time to wipe the boom elements with a solvent soaked cloth to remove dirt and aluminum dust that results from the manufacturing process. This makes assembling the antenna a much cleaner process.

2MXP28 Yagi Dimension Sheet

2MXP28 Yagi Dimension Sheet

M2 supplies detailed dimension sheets and boom layout diagrams with their antennas and we took the time to carefully identify each element and boom component according to the diagrams.

Element Measurement and Marking

Element Measurement and Marking

This step included careful measuring, sorting, and marking each element with its location and polarity (horizontal or vertical). This step makes the somewhat difficult step of getting all of the elements in the correct polarity and orders much easier. The marks allowed me to check and confirm the correct installation of all of the elements on the antenna boom before locking them in place.

Mast Clamp and Boom Truss Attachment Pre-assembly

Mast Clamp and Boom Truss Attachment Pre-assembly

We also pre-assembled things like the Mast Clamp and the Boom Truss Clamp during the parts inventory process.

Boom Assembly

Boom Assembly Details

Boom Assembly Details

The first step in assembling the antenna boom was to arrange all of the boom segments in the correct order and confirm their front/back orientation. This took some time to get right on the first of the four antennas. Each Boom segment was marked with the Sharpie to indicate its location and orientation in the final assembly.

We also installed the T-Brace Clamp to attach the rear of the antenna to the H-Frame’s T-Brace. It’s essential to do this step before assembling the Boom as the clamp cannot be attached once the antenna’s elements are in place. The correct location for the clamp was established via a careful measurement and the location was marked on the boom using the Sharpie.

Assembled Boom

Assembled Boom

The next step was to assemble the boom sections paying careful attention to the markings made earlier. We did not tighten any of the bolts that hold the boom sections together at this stage to allow us to re-clock each boom section for the best alignment of the elements later. A generous coat of NOALOX was used at the joint of the two largest diameter Boom sections to facilitate easier assembly and potential re-clocking later. NOALOX was also used on all bolts to provide anti-seize lubrication.

Once the boom is assembled, a 40-foot tape measure is used to carefully confirm that all of the holes for the elements are in the correct location. The Dimension Sheet is used as a reference to check and confirm that all measurements are correct before installing the Elements. This is also a good time to measure and carefully mark the location of the center of the Mast Clamp on the Boom.

The eye bolts that attach the Boom truss cable are also installed at this time.

Element Installation

Element Installation Details

Element Installation Details

Next came the installation of the elements. We began with the Horizontal reflector and worked towards the front of the antenna. The elements are held in place with insulated buttons and stainless locks. The elements are first installed in the correct location and carefully centered using a steel ruler. Vise-grip pliers are then used to hold the element in its centered position while the M2 supplied tool is used to push the lock on the opposite side of the element. The center is next checked again and if all looks good, the second lock is installed. This process is continued until all of the elements are in place. We pay careful attention to the markings on each element as part of the installation procedure to ensure that all of the elements are in the correct location on the boom.

H-Element Installation Complete - Ready for V-Element Installation

H-Element Installation Complete – Ready for V-Element Installation

Once all of the elements are in place, the antenna is rotated 90 degrees to enable boom adjustments to align the elements. It is common for the boom sections to be misaligned a bit after the initial assembly. A combination of clocking each boom section either a bit one way or the other or sometimes removing the bolts holding two sections together and turning them 180 degrees relative to each other will create a perfect alignment of the elements. Once this is done, all of the bolts that hold the Boom sections together are fully tightened taking care not to distort or crush the Boom tubes.

The same installation process is repeated for all of the vertical elements.

Driven Element Assembly

Feedpoint Assemby

Feedpoint Assembly

The Driven Element feed point blocks are installed next. The mounting screw and the Allen screws in the Shorting Bars all receive a light coat of Blue Locktite thread locker prior to installation.

Next, we loosely install the blocks in their correct location on the Boom and then install the Shorting Bars loosely on the Feed Point Block and Driven Element. Once these parts are in place, the screen that holds the Block to the Boom can be tightened fully, guaranteeing a perfect alignment of all of the parts.

The next step was to accurately set the spacing between the Feed Point Block and each shorting bar. I used a dial caliper to do this accurately but it can also be done with the careful use of a metal machinist’s or similar ruler.

The final step for each feed point was to install the 1/2 wave Coax Balun to the Feed Point Block. Be careful not to overtighten the coax connectors. Just make them snug and you are set. The supplied cable ties are used to secure the Balun to the boom.

The same steps are repeated for the Vertical feed point. It’s a good idea to install connector dust caps on the feed point Block connectors to keep them clean and dry prior to installation.

H and V Feedpoint Orientation

Vertical and Horizontal Feedpoint Orientation

It is critical that the relative orientation between the Horizontal and Vertical Feedpoint Blocks be the same on all four of the antennas in the array. If this is not the case, the pattern of the array will be upset which will have a major negative effect on the array’s performance.

Mast Clamp and Boom Truss

Mast Clamp Installation

Mast Clamp Installation

The Mast Clamp assembly is installed next using the center mark placed on the Boom earlier. I also marked the backside of the Mast Clamp plate to show its center to make lining things up easy. The clamps should be oriented according to the H-frame mounting diagram (show at the front of this article).

Boom Truss Assembly

Boom Truss Assembly

The final step in the assembly process is the assembly of the Boom Truss. The 2MXP28 Yagi is supplied with a Phillystran cable. The height of the Boom Truss will be set later when the antennas are attached to the H-frame so we just installed both ends of the Phillystran cable to the Eye Hooks installed in the Boom. The connections are made using the supplied Strain Relief Loops and small cable clamps. A drop of oil on each nut helps things go together smoothly.  We had some Phillstran cable end caps so I installed them on the Phillystran cable ends to protect against water ingress. The turnbuckles, remaining clamps/strain reliefs, end caps, and truss clamp assembly were stored in a plastic Ziploc bag and cable-tied to the Boom to be installed later when the antennas are attached to the H-frame.

Final Details…

Completed 2MXP28 Antenna Ready for Installation

Completed 2MXP28 Antenna

It’s a good idea to give everything one last go-over now that the antenna is complete. All bolts and screws are checked for tightness, the Elements are all confirmed to be in the right locations, and the feed point assemblies are given a final check.

Four 2MXP28 Antennas Ready for Installation

Four 2MXP28 Antennas Ready for Installation

Our EME project involves the assembly of four of these antennas with a total of 112 elements! It took me about 3 days to assemble each antenna (working about 3-4 hours each day). We stored the antennas on our deck to make space in our shop as we went. The antennas are well supported using low saw horses and woodblocks so as not the bend the Booms or the Elements.

The next step in our project will be to assemble and test the Elevation Rotator system. You can read more about our EME station project via the links that follow:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

Tech Night – VHF+ Weak Signal Stations Part 1 (Intro and 6 Meters)

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Tech Night - VHF+ Weak Signal Stations Part 1 - Overview and 6 Meters

Tech Night – VHF+ Weak Signal Stations Part 1 – Overview and 6 Meters

We recently did a Tech Night on building and operating VHF+ stations as part of the Nashua Area Radio Society’s educational program. I wanted to share the presentation and video from this Tech Night so that our readers might learn a little more about how to get started and build their own VHF+ Weak Signal Station.

There is a lot to this topic so we’re going to cover it with two Tech Night presentations. The first one in the series is included here and it provides an Introduction to the VHF+ topic along with details on building and operating a station for the 6 Meter Band.

July 2020 Tech Night Video – VHF+ Weak Signal Stations Part 1 – Introduction and 6 Meters

You can view this Tech Night session via the video above. Here’s a link to the presentation that goes with the video. You can learn more about the Nashua Area Radio Society’s Tech Night program here.

We have built a number of stations and antennas for the VHF+ Bands (6 Meters and above). Here are some links to articles about those projects and our operations on the VHF+ Bands here on our Blog:

Fred, AB1OC

Tech Night – Getting Started In EME Communications

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Tech Night – Getting Started in EME (Click to View The Presentation)

We recently did a Tech Night Program as part of the Nashua Area Radio Society’s Tech Night program. I wanted to share the presentation and video from this Tech Night so that our readers might learn a little more about how to get started in EME or Moonbounce Communications.

April 2020 Tech Night Video – Getting Started in EME Communications

You can view the Tech Night presentation by clicking on the video above. Here’s a link to the presentation that goes with the video. You can learn more about the Nashua Area Radio Society’s Tech Night program here.

The second Tech Night in the EME Series was about Building and Operating an EME Station. You can view that Tech Night here.

We are in the process of upgrading our EME station to include adaptive polarity. you can read more about that project here.

Fred, AB1OC

EME Station 2.0 Part 6 – Tower Grounding System

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Tower Ground System

Tower Grounding System

Now that spring is here, we’ve continued work on our EME station project. The most recent project was to build the tower grounding system for our new EME tower. The proper way to ground a tower is shown above. Each leg of the tower is connected to an 8′ ground rod via a heavy gauge ground cable. The cable is attached to the tower leg using stainless steel clamps meant for this purpose. The three ground rods associated with the tower legs are then bonded together using a heavy copper ground cable ring.

Ground Cable CAD Weld

Ground Cable CAD Weld

The ground cables are welded to the top of the ground rods using CAD weld on-shots. This creates a strong connection that will not corrode or fail. It is important that the ground rods be free of dirt, corrosion, oxidation, and burrs before performing the CAD welding. We used a combination of 3-wire and 4-wire one-shot CAD welds to build our ground system and connect it to the bonding system running from our tower to the entry to our shack.

Main Grounding System Bonding

Main Grounding System Bonding

The final step was to connect the bonding run from the tower to the perimeter grounding system around our house. This completed the tower grounding system and enabled us to complete our final permit inspection courtesy of our local building inspector.

Finished Tower Base

Finished Tower Base

With all of this work done and the inspection complete, we added a mulch bed around our new tower to make this area of our lawn easy to maintain.

The next step in our project is to begin building the antennas that will go on our EME tower. You can read more about our EME station project via the links that follow:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

EME Station 2.0 Part 5 – Control Cables and Rotator Controller

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Control Cable Junction Box on EME Tower

Control Cable Junction Box on EME Tower

Snow is coming to New England this weekend so we wanted to get the control cables run to our new EME Tower before the ground is covered with snow. The project involved installing a Utility Enclosure on our tower and running three control cables to our shack for the following devices:

Az-El Rotor and Preamp Switching Control Connections

Az-El Rotator and Preamp Switching Control Connections

We began by install some barrier strips and a copper ground strap in the Utility Enclosure. The copper strap provides a good ground connection to the tower and associated grounding system. The enclosure is clamped to the tower using two stainless steel clamps.

We ran three new control cables through the conduits that we installed between the tower and our shack and terminated them in the utility enclosure. We only needed 6 leads for control of the planned MAP65 Switching and Preamp System which will go on our tower later so we doubled up some of the higher current connections using two wires in the 8-conductor cable.

Green Heron RT-21 Az-El Rotator Controller

Green Heron RT-21 Az-El Rotator Controller

The final step was to hook up our rotator cables to a Green Heron RT-21 Az/El Rotator Controller in our shack.  We do not yet have our elevation rotator so we tested the M2 Orion 2800 Azimuth Rotator that is installed in our tower. The azimuth rotator is configured so that the rotator’s dead spot faces north. This is a good configuration of our planned EME operation.

With all of our control cabling in place, we are ready to begin preparing our Antennas, Elevation Rotator, H-Frame, and MAP65 components to go on our EME Tower. We’re hoping that the weather will cooperate and enable us to get these steps completed during this winter.

Here are some links to other articles in our series about our EME Station 2.0 project:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

EME Station 2.0 Part 4 – New EME Tower Is Up!

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Three Tower Antenna Farm

New EME Tower in Our Antenna Farm

Our goal for this phase of our EME Station Project is to get our new tower up, install the Azimuth Rotator and Mast, and run the hardline and coax cables for our antennas from the shack to our new tower. Our EME tower is constructed using Rohn 55G tower sections. It will be 26 ft tall and will have approximately 18″ of our 3″ mast protruding above the tower. The tower is a free-standing/guyed hybrid design with the first section being cemented into the ground.

EME Tower

FInished Tower Base

The base section and the three guy anchor blocks were completed a little while back. The holes were backfilled and we’ve given the cement a couple of weeks to cure.

First Tower Section Installed Using a Gin Pole

First Tower Section Installed Using a Gin Pole

Matt, KC1XX, and Andrew of XX Towers began by installing a winch and a gin pole on the base section of the tower. They used the Gin Pole to hoist the second tower section into place and secure it. They also attached the top plate to the third tower section in preparation for installing it along with our mast.

Mast and Top Tower Section Going Up

Mast and Top Tower Section Going Up

It is always a challenge to install a mast inside a new tower. The mast we are using is a heavy, 22 ft 4130 chrome molly steel mast that weighs over 250 lbs. Getting the mast inside the tower was quite a feat! Matt and Andrew rigged the top tower section and the mast together and pulled both up together on the Gin Pole. Next, one leg of the top tower section was attached and a second pully was used to pull the mast up through the top tower section until it could be placed inside the tower. The last step was to raise the top tower section a second time using the Gin Pole to seat it on top of the rest of the tower. Finally, the mast was lowered inside the tower to the base and the top tower section was bolted on to complete the tower.

Upper Guy Anchor Bracket on Tower

Upper Guy Anchor Bracket on Tower

The next step involved attaching the upper guy anchor bracket to the top section of the tower and rigging the guy anchor cables. We decided to use Phillystran Guy Cable to avoid interactions with our antennas.

Guy Anchor Cable

Guy Anchor Cable

The completed cables are tensioned using turnbuckles. We adjusted the cables to plumb the tower and then safety-wired the turnbuckles so they will not come loose.

Azimuth Rototor in Tower

Azimuth Rotator in Tower

The next step was to install an M2 Antenna Systems Orion 2800G2 Azimuth Rotator in our tower. The use of the 22 ft mast allowed us to place the rotator about 5 ft above the ground where we can easily service it in the future. The long mast also acts as a torque shock absorber when the rotator starts or stops moving suddenly. With the rotator in place, we attached the mast and clamped it at the rotator and thrust bearing at the top of the tower.

Tower Base, Coax Feedlines, and Guy Anchors

Tower Base, Coax Feedlines, and Guy Anchors

The last step in our project was to install our coax cables and hardlines on the tower and run them through a 4″ underground conduit to our shack. We pre-made the two LMR-600 coax cables for the receive side of our EME Antenna System previously. We cut a section of LDF5-50A 7/8″ Hardline to approximately the same length as the LMR-600 coax cables.

Pushing Coax Cables and Hardline Through the Condui

Pushing Coax Cables and Hardline Through the Conduit

We used a cutoff plastic bottle to protect the ends of the coax cables and hardline as we pushed them through approximately 50 ft of buried 4″ conduit. The conduits were constructed to create a gradual turn into and out of the ground and the cables went into the conduit smoothly.

Coax Cables Exiting the Conduit Near Our Shack

Coax Cables Exiting the Conduit Near Our Shack

With the cables in place, we installed N-female connectors on each end of the 7/8″ hardline. We used rubber reducers to make it easier to deter water from entering the conduits where the cables exit.

Coax Cable Ground Block Connections

Coax Cable Ground Block Connections

We expanded out main shack entry ground block using an 18 position tinned cover ground bar from Storm Copper to make room for additional static arrestors for our EME Antenna System. The LMR-600 receive-side coax cables and the 7/8″ hardline connection for the transmit-side of our EME antennas terminate on N-connector Static Arrestors from Alpha Delta.

Completed EME Tower

Completed EME Tower

Our new EME tower is up and ready to accept the Elevation Rotator, H-Frame, and Antennas from M2 Antenna Systems when they arrive. We plan to complete the grounding system and get the Azimuth Rotator hooked up and tested with our Green Heron Engineering RT-21 Az/El Rotator Controller in the near future.

Here are some links to other articles in our series about our EME Station 2.0 project:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

EME Station 2.0 Part 3 – Phase Tuned Receive Coax Cables

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Measuring Coax Cable Electrical Length Using a VNA

Measuring Coax Cable Electrical Length Using a Vector Network Analyzer (VNA)

Our new 2M EME station will have Adaptive Polarity capability via MAP65. MAP65 requires that received signals from the Horizontal and Vertical planes of our antennas arrive at the receivers in our shack precisely in phase with each other.

We decided to use a pair of LMR-600 coax cables for the receive side of our feedlines. We made these cables from an unterminated length of LMR-600 coax measured to cover the distance from the top of our planned 26 ft EME tower to the ground block at the entry to our shack. The cables are approximately 82 ft long and they must be cut to be equal in length to within 1/16″!

The easiest way to measure the length of an unterminated coax cable is to determine the minimum frequency of resonance of the cable when the opposite end is an open circuit. One can then use the speed of light and the velocity factor of the cable to compute its exact length:

Length = (Speed of Light X Velocity Factor) / (Resonant Freq. X 4)

Doing these measurements with an open circuit at the far end of the cables enables trimming the length of the two cables to be matched in small increments until our two cables are exactly the same length.

VNA Measurement of Open Coax Cable Resonance

Vector Network Analyzer (VNA) Measurement of Open Coax Cable Resonance

We used an Array Solutions VNA 2180 connected to a Windows PC to precisely measure the minimum Resonant Frequency of our LMR-600 coax cables as we trimmed them. Once they were equal in length to within 1/16″, we installed an N-Female connector on the unterminated end and re-verified each cable’s length. A frequency-accurate antenna analyzer can also be used to make these measurements.

We will need to repeat these steps of the receiver-end and antenna preamp box jumper cables which will make up the rest of the receive side feedlines for our EME antenna system once these components are installed. We also plan to make a final end-to-end measurement of the receive-side feedline assemblies to fine-tune the phasing of the completed feedline runs.

With this step complete, we are ready to put up our new tower and attach the feedlines. Here are some links to other articles in our series about our EME Station 2.0 project:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

EME Station 2.0 Part 2 – Excavation, Footings, and Conduits for New Tower

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EME Tower

FInished Tower Base and Cable Conduits

The first part of our EME project is to put up a new tower to support our antennas. Our plans call for a 26′ tower built using three Rohn 55G tower sections. Four feet of the first section of the tower is cemented in a concrete footing to anchor the tower’s base. The tower is also going to be guyed to ensure that it is very stable.

EME Tower

Digging Footings for our New Tower

We are working with Matt Strelow, KC1XX, and Andrew Toth of XX Towers to put up our new tower. Matt brought out his tractor and dug the footings for our tower and for the associated conduits that will carry coax and control cables to our shack. The photo above shows the completed hole and form for the main tower base. Matt is working on the footings for one of the three guy anchors.

EME Tower

First Tower Section and Rebar Cage

Here’s a closer look at the tower base. The footing includes a rebar cage to reinforce the concrete footing. There is also 6″ of crushed stone in the bottom of the hole that the tower legs sit it. It is very important that the bottoms of the tower legs remain open and do not become plugged with cement so that water in the legs can drain. If the legs cannot drain properly, water will accumulate and freeze. This can split open the tower legs and ruin the tower.

EME Tower

Cable Conduits with Drains

We also installed two conduits (a 4″ and a 2″ run of schedule 80 conduits) from the base of our tower to our shack. These conduits will carry coax feed lines and control cables to our new tower. We used a pair of 22° elbows to create a smooth transition to bring the conduits out of the ground. This will ensure that our hardline and other coax cables can be placed in the conduits without creating excessive bends.

Conduits will fill with water even if they are sealed. This happens as a result of the condensation of water in the air. To prevent our conduits from filling with water, we created two drain pits at the bottom of the trench at the two lowest spots in the conduit runs and filled them with stone. We drilled a few holes in the bottom of the conduits above the drain pits to allow the water to drain so our cables will remain dry.

EME Tower

Cadweld’ed Ground Cable Bonded to a Ground Rod

We also created a bonding ground cable run from our new tower to the ground system at our shack entry. The bonding system was created by driving an 8′ ground rod every 10′ in the trench between our new tower and the perimeter ground around our house.

#2 stranded copper ground cable was Cadweld’ed to each ground rod to create a ground path to bond the tower to the perimeter grounding system around our house. Using a Cadweld system is simple and produces strong connections that will not deteriorate.

Here’s a video that shows our a Cadweld is made. We’ll cover completing the ground connections to the tower and the perimeter grounding system in a future article.

EME Tower

Completed Footings – Ready to Pour Cement

Finally, we used some sections of rebar to firmly support the guy anchor rods prior to pouring the cement. If you look closely, you can see a portion of the rebar material in one of the guy anchor footings in the photo above.

EME Tower

Cement Mixer

The next step in this part of our project was to pour the cement. A large cement mixer brought the proper cement mix to our QTH and Matt used his tractor to transport the cement from the mixer to the forms. We did a bit of finishing work on the cement base for our tower and let the cement dry for a few days.

EME Tower

FInished Tower Base and Cable Conduits

The last step was to remove the forms and backfill the footings. A little work with a cement finishing block was done on the cement base to round off the rough edges left by the forms. The cable conduits emerge from the ground next to the tower base. You can also see one end of the copper bonding cable next to the conduits as well.

EME Tower

Completed Guy Anchor

Here’s one of the completed guy anchor rods after backfilling. We are going to let the cement harden for a couple of weeks and then we’ll complete the construction of our new tower.

Here are some links to other articles in our series about our EME Station 2.0 project:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

EME Station 2.0 Part 1 – Goals and Station Design

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The Moon

The Moon

EME or Earth-Moon-Earth contacts involve bouncing signals off the moon to make contacts. EME provides a means to make DX contacts using the VHF and higher bands. There are also some EME Contests including the ARRL EME Contest that provides opportunities to make EME contacts.

We made some 2m EME contacts a while ago using the 2m antenna on our tower at about 112′. This experience created interest on my part in building a more capable EME station at some point in time. Well, the time has finally arrived.

EME Propagation

Understanding EME Propagation is a project in of itself. The following is a brief overview of some of the (mostly negative) effects involved.

The path loss for EME contacts varies by Band and is in excess of 250 dB on the 2m band. There are some significant “propagation” effects that further impair our ability to make EME contacts. These include:

  • Faraday Rotation – an effect that results in the polarity of signals being rotated by differing amounts as they pass through the ionosphere on their way to the moon and back
  • Libration Fading – fading caused by the addition of the multiple wavefronts that are reflected by the uneven surface of the moon
  • Path loss variations as the earth-to-moon distance vary – the moon’s orbit around the earth is somewhat elliptical in shape resulting in a distance variation of approximately 50,000 km during the moon’s monthly orbital cycle. This equates to about a 2 dB variation in total path loss. An average figure for the path loss for 2m EME might be in the range of 252 dB.
  • Transit Delays – at the speed of light, it takes between 2.4 and 2.7 seconds for our signals to travel from earth to the moon and back.
  • Noise – the signals returning from the moon are extremely weak and must compete with natural (and man-made) noise sources. The sun and the noise from other stars in our galaxy are significant factors for EME communications on the 2m band.
  • Doppler shifts – as the earth rotates, the total length of the path to the moon and back is constantly changing and this results in some frequency shift due to doppler effects. Doppler shift changes fairly slowly compared to the time it takes to complete a 2m EME QSO so it is not a major factor for the 2m band.
  • Moon’s size vs. Antenna Aperture – the moon is a small target (about 0.5 degrees) compared to the radiation pattern of most 2m antenna systems. This means that most of our transmitted power passes by the moon and continues into space.

Taking the moon’s size, average orbital distance, and average Libration Fading level into account, one can expect only about 6.5 % of the power that is directed toward the moon to be reflected back toward earth.

EME “Good Guys”

One might look at the challenges associated with making EME contacts and say “why bother”? EME contacts present one of the most challenging and technical forms of Amateur Radio communications. It is this challenge that fascinates most EME’ers including this one. Fortunately, there are some “good-guy” effects that help to put EME communications within reach of most Amateur Radio stations. These include:

  • WSJT-X and the JT65 Digital Protocol – In the early days of EME communications, one had to rely on CW mode to make contacts. All of the impairments outlined above made these contacts very challenging and the antennas and power levels required put EME communications out of the reach of most Amateurs. Along came Joe Taylor’s digital JT65 protocol which changed all of this. It is now possible to make 2m EME contacts with a single (albeit large) 2m yagi and 200W or so of input power. As a result of these innovations, many more Amateurs have built EME stations and are active on the 2m (and other) bands. Many DXpeditions are now also including EME communications in their operations.
  • Ground Gain Effects – a horizontally polarized antenna system will experience approximately 6 dB of additional gain when the antenna(s) are pointed approximately parallel to the ground. Ground gain effects made it possible for us to use our single 2m antenna to make our first 2m EME contacts.
  • MAP65 Adaptive Polarization – Fading resulting from polarity changes due to Faraday Rotation can cause a received signal to fade to nothing over the period of time needed to complete a 2m EME contact. These polarity “lock-out” effects can make contacts take a significant amount of time to complete. Fortunately, a version of the software which implements the JT65 protocol called MAP65 has been created that will automatically detect and adapt to the actual polarity of signals returning from the moon. More on how this is achieved follows below. MAP65 is most useful for making “random” EME contacts during contests. In these situations, a variety of signals will be present in a given band with different polarities, and the MAP65 software can adapt to each one’s polarity and decode as many simultaneous signals as possible.
  • Commercially Available Amplifiers for the VHF+ Bands – Modern, solid-state amplifiers have become much mor available for the 2m band (and other VHF and higher bands). This has made single-antenna EME on 2m and above much more practical for smaller stations with a single antenna or a small antenna array.

Our 2m EME Goals and Station Design

We began this project by making a list of goals for our 2m EME Station 2.0. Here is that list:

  • Operation using JT65 and QRA64 digital protocols and possibly CW on the 2m EME band
  • 80th percentile or better station (i.e. we want to be able to work 80% of the JT65 capable 2m EME stations out there)
  • Operation in EME contests and EME DX’ing; earn a 2m EME DXCC

We have come up with the following station design parameters to meet these goals:

  • An array of four cross-polarized antennas with an aggregate gain of approximately 23 dBi
  • A new 26′ Rohn 55G tower to support the antennas
  • A computer-controlled Azimuth/Elevation rotator system to allow us to track the moon
  • A legal limit input power of 1500W
  • A MAP65-capable SDR-based receive system that can support adaptive polarity
  • Low-noise, high-gain preamplifiers located at the antennas
  • A low-loss feedline system for both the transmit and receive sides of the system
  • Use of both the MAP65 and standard versions for WSJT-X for digital operations
  • Use of Linrad as a front-end to the receive side of our system
  • An Icom IC-9700 Transceiver and a W6PQL Legal Limit (1500w) 2m Power Amplifier for transmitting

Antennas

WA1NZP Antenna System (4 M2 XP32 X-Polarity Antenna Array)

WA1NPZ Antenna System (4 M2 Antennas XP32 X-Polarity Antenna Array)

It takes some fairly large antennas to create an 80th percentile EME station. We are planning a setup similar to Bob, WA1NPZ’s system shown above. We are going to put up a 26′ Rohn 55G tower for our EME antenna system. We will be using four M2 Antenna System XP28 Antennas mounted on an H-frame to create a 15′ x 15′ square array.

The combined gain of the system will be approximately 23 dBi with a 3 dB beamwidth of 12.5°. The XP28 antennas are designed for stacking and have good Gain/Temperature (G/T) characteristics. G/T is a measure of the gain and noise performance of an antenna system. See VE7BQH’s tables for some interesting data on G/T for many commercially available EME and VHF+ antennas.

The antenna system will have separate feeds for the antenna array’s Horizontal (H) and Vertical (V) planes. The Horizontal elements will be oriented parallel to the ground to maximize ground gain when the H plane is used for transmitting (and receive). A pair of 4-port power combiners will be used to combine the H and V polarities of the four antennas into a pair of H and V feedline connections.

Plans call for a combination of the M2 Orion 2800G2 and MT3000A rotators to be used along with a Green Heron RT-21 Az/El Rotator Controller to provide computer-controlled tracking of the moon. A 22′ section of 3″ Chrome Molly mast material will allow the azimuth rotator to be located near the base of the tower where it can be easily serviced.

Tower Mounted Preamps and Polarity Switching

MAP65 Switching and Preamp Housing

MAP65 Switching and Preamp Housing

M2 Antenna Systems will be supplying a MAP65 Switching and Preamp System that will mount on the tower near the antennas. The MAP65 Housing provides switching and separate receive preamplifiers and feedlines for the H and V polarities of the antennas. Separate H and V receive coax connections bring the Horizontal and Vertical elements of the antennas back to the shack. A third coax connection is provided for Transmit. The transmit feedline can be routed to either the H or the V antenna polarity to help minimize Faraday Rotation related fading at the other end of the contact.

S2 Sequencer

S2 Sequencer

An M2 Antennas S2 Sequencer will provide Tx/Rx sequencing and H/V transmit polarity selection via the MAP65 Switching and Preamp System on the tower. The sequencer is essential to provide safe changeovers between receive and transmit and to protect the preamplifiers and the power amplifier during high power operation.

Feedline plans call for a run of 7/8″ Hardline Coax for transmit and a pair of LMR-400uF Coax cables for the H and V receive polarities.

MAP65 Capable Receive Chain

LinRF IQ+ Block Diagram

LinRF IQ+ Block Diagram

The signals returning from the moon in an EME system are very, very weak. Because of this, Noise and Dynamic Range performance are critical factors in an EME receive system. In addition, we will need a pair of high-performance, phase-coherent receivers to enable Adaptive Polarization via MAP65.

LinkRF IQ+ Dual Polarity Receive System

LinkRF IQ+ Dual Polarity Receive System

We are planning to use a LinkRF IQ+ Dual Channel Receive Converter in our EME system. The Link RF IQ+ features excellent noise and dynamic range performance and its phase-coherent design will support adaptive polarity via MAP65. The IQ+ separately converts both the H and V polarities of the antennas into two separate pairs of I/Q streams.

UADC4 High-Performance A/D Converter

UADC4 High-Performance 4-Channel A/D Converter

The four channels (two I/Q streams) from the LinkRF IQ+ must be digitized and fed to a Windows PC for decoding. The conventional way to do this is with a 4-channel, 24-bit soundcard. The available computer soundcards add a good bit of noise and therefore limit the overall dynamic range of an EME system. Alex, HB9DRI at LinkRF has come up with the UADC4 – a high-performance 4-channel ADC that is specially designed for software-defined radio. The UADC4 design is based on CERO- IF conversion and is optimized for EME use. The UADC4 should add about 10 – 15 dB of dynamic range improvement over a typical 24-bit PC Soundcard. Alex is currently taking pre-orders for the next run for UADC4 devices. You can contact him at info@linkrf.ch for more information.

Software

JT65 Software Block Diagram

JT65B Software Block Diagram

Our plans for JT65 software and related components for our EME station are shown above. We are planning on running a combination of Linrad and WSJT software on the same Windows PC to handle JT65B QSOs. There are two configurations that are applicable to our plans:

We are also planning to develop a simple Windows application that will read the Moon Tracking data that is generated by WSJT MAP65 and WSJT-X and use it to control the rotator system associated with our EME antennas. More on this to come in a future article.

Transmit System

2m Amplifier And Sequencers

M2 2M-1KW 2m Amplifier

A combination of an Icom IC-9700 Transceiver and an M2 2M-1K2 2m Amplifier will be used for the Transmit side of our system. The M2 2M-1K2 Amplifier can generate 900 – 1000W when transmitting in JT65B mode.

Well, that about covers it as far as our 2m EME goals and station design go. The plan is to break ground for the new EME tower later this week. We’ll continue to post more articles in this series as our project proceeds.

Here are some links to other articles in our series about our EME Station 2.0 project:

If you’d like to learn more about How To Get Started in EME, check out the Nashua Area Radio Society Teach Night on this topic. You can find the EME Tech Night here.

Fred, AB1OC

Working IC-9700 Shown In Tokyo

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Working IC-9700 On Display In Tokyo

Working IC-9700 On Display In Tokyo

The IC-9700 is a new VHF/UHF radio based on the Software Defined Radio (SDR) platform Icom uses in the IC-7300 and IC-7610.

It looks like this is going to be an excellent radio for Satellite, EME, and other weak-signal work on the 2 m, 70 cm, and 23 cm bands. The IC-9700 features a pan adapter display which will be very useful for working contacts through linear satellites.

Based upon previous new Transceivers releases by Icom, I would guess we are at least 8 months to a year away from when this radio will be offered for sale in the USA.

Here’s some video of the forthcoming  IC-9700 as well as other gear from Icom. The video also features other new products and updated Firmware capabilities from Icom. Enjoy!

Fred, AB1OC