February 2021 Tech Night – Understanding and Using Propagation to Work The World
Anita, AB1QB, recently did a Tech Night Program on Radio Propagation 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 propagation and how to use it to facilitate contacts.
Anita, AB1QB provides a comprehensive overview of HF and VHF/UHF propagation and how to use it to Work the World. Topics include the many online tools to help one determine and measure propagation conditions. VHF+ modes such as Meteor Scatter, Tropo, EME, and Satellite paths are also covered.
EME II Tech Night – Station Construction and Operation
We recently did a second Tech Night Program on EME 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 build and operate an EME station for the 2m band.
January 2021 Tech Night – EME II: Station Construction and Operation
Our new 2m EME Antenna System has been performing very well. One area that we noticed that could use improvement was the alignment of our antennas as we move them in the Elevation plane. The problem is caused by the weight of the coax feedlines running from the antenna feed points to the power dividers on our H-Frame assembly. Our H-Frame assembly includes T-Braces to support the coax feedlines but the T-Braces tended to bend and distort the alignment of our antennas as the Elevation Rotator is moved.
Custom H-Frame Truss System
Matt at XX-Towers and Robert at M2 Antenna Systems helped us to come up with a very nice custom solution to solve these alignment problems. The solution consists of two additional truss cables on each of the H-Frame’s T-Brace assemblies. The truss cables are made from Phillystran Cable which is non-conductive and is adjusted via Turnbuckles that are anchored at the center of the H-Frame’s Vertical Risers. This approach minimizes any metal in locations that would affect the pattern of our antennas.
Cross Boom Extension
The first truss is mounted on a short custom extension on each end of our H-Frame’s Cross Boom and is run to an eye bolt in the center of each T-Brace Vertical Rod.
T-Brace Main Truss
These risers stabilize the tendency for the T-Brace Vertical Assembly to flex and move towards the center of the H-Frame when the full weight of the coax cables are bearing on them at various elevation angles. Careful adjustment of the combination of these new Truss Cables and the existing 45-degree T-Brace Horizontal Support Assemblies results in the rear of each antenna boom staying perfectly aligned as we rotate our antennas in elevation.
T-Brace Rear Truss
The other problem that our custom Truss Solution addresses is the tendency for the weight of the coax cables to bend the rear of the antenna booms down when the antennas are at 0-degrees in elevation. The bending is due to the weight of the coax cables on the T-brace being unsupported and bearing down on the rear of the antenna booms. This problem is solved by a second Phillystran truss cable that runs from the metal section of each Vertical Riser assembly to the junction between the rear of the bottom antenna booms and the associated junction of the Vertical T-Brace Assemblies.
We fastened the Phillystan cables directly to the junction point without the use of any metal hardware to ensure that the pattern of our antennas was not affected. These secondary Trusses now carry all of the weight of the coax cables on the T-brace as the antennas approach at 0-degrees in elevation and have eliminated the bending at the rear of our antenna booms.
With these modifications, our antennas remain perfectly aligned at any elevation angle. There is also noticeably less stress on the fiberglass sections of the Vertical Riser Assemblies since they are no longer carrying the load of the coax cables.
Software is a big part of most current EME stations. The JT65 Protocol, which was created by Joe Taylor, K1JT, has revolutionized EME operations. It has made it possible for modest single and two yagi stations to have lots of fun with EME.
Phase 1 of our 2m EME station software and hardware uses manual switching/selection of receive polarity. This Phase is about integrating all of the station components together and sorting out operational issues. After some experimentation, we have settled on a dual-decoder architecture for the First Phase of our 2m EME Station.
You can learn more about the Phase 1 EME hardware setup at our station here.
EME Software Environment
EME Station Block Diagram – Phase 1
The diagram above shows the current configuration of our 2m EME station. As explained in a previous article in this series, we are using a FUNCube Pro+ Dongle with the MAP65 application as our primary JT65b decoder and we are using our IC-9700 Transceiver along with WSJT-X as a secondary, averaging decoder. Using multiple decoders has proven to be a significant advantage. It is quite common for one of the two applications to decode a weak signal that the other does not.
We use two custom applications (WSJTBridge and Flex-Bridge) to capture the Moon Azimuth and Elevation data generated by the MAP65 application and use it to control the rotators for our EME Antenna Array.
We have been experimenting with Linrad as a front-end to MAP65 and WSJT-X. At present, we are using the NB/NR functions in MAP65 and in our IC-9700 as an alternative to Linrad. We expect the add Linrad into our setup when we add Adaptive Polarity capabilities in Phase 2.
EME Software Operating Environment (click for a larger view)
We use the DXLab Suite for logging and QSL’ing our contacts along with several web apps to find potential EME contacts and to determine the level of EME Degradation on any given day.
The screenshot above shows most of these apps running during a 2m EME operating session.
MAP65 Application – Primary Decoder and Operating Application
We are using MAP65 as our primary decoder. It also controls our IC-9700 Transceiver when transmitting JT65b messages. MAP65 used the I/Q data from our FUNCube Pro+ Dongle to detect and decode all of the signals in the 2m EME sub-band. A waterfall window displays all of the signals on the band as well as a zoomed-in view of the spectrum around the current QSO frequency. MAP65 also generates heading data for our rotators as well as estimates for the doppler shift between stations. The MAP65 application also provides windows that list all of the stations on the band as well as the messages that they are sending.
EME QSOs via MAP65
The screenshot above shows the main MAP65 window during a QSO with HB9Q. Round trip delay (DT) and signal strength information (dB) is shown for each message that is decoded. The MAP65 application along with a manual that explains how to set up and use the program for 2m EME can be downloaded here.
Moon Tracking and Rotator Control
Custom Rotator Control Apps (WSJT-Bridge and FlexBridge)
We developed an application we call FlexBridge some time back as part of our ongoing project to remote our Satellite Ground Station using our Flex-6700 based SDR Remote Operating Gateway. This application includes functionality to operate Az/El rotator controllers based upon UDP messages which contain tracking data. We wrote a second application that we call WSJT-Bridge which reads the Moon heading data that either MAP65 or WSJT-X and generates and sends UDP messages that enable FlexBridge to track the moon. The combination enables MAP65 to control tracking the moon in our setup.
Both of these applications are at an alpha stage and we will probably separate the rotator control functionality from FlexBridge and make it into a dedicated application.
Antennas On The Moon
One of the first steps in the integration process was to carefully calibrate our rotators to point precisely at the moon. We got the azimuth calibration close using the K1FO Beacon in CT. With this done, we made final adjustments visually until our antennas were centered on the moon on a clear night.
EME Tower Camera at Night
We recently installed an additional IP camera which gives us a view of our EME tower. This is a useful capability as it enables us to confirm the operation of our rotator from our shack.
WSJT-X – Secondary Decoder
We also run WSJT-X as a second decoder using the receive audio stream from our IC-9700 Transceiver. WSJT-X has some more advanced decoding functions and can average several sequences of JT65b 50-second transmissions to improve decoding sensitivity. It only works on one specific frequency at a time so we use it to complement the broadband decoding capability that MAP65 provides.
We can also transmit using WSJT-X which enables us to use its Echo Test functionality to confirm that we can receive our own signals off the moon.
The WSJT-X application along with a manual that explains how to set up and use the program for EME can be downloaded here.
Finding Contacts and Logging
Finding Contacts and Logging
We use the DXLab Suite for logging and QSL’ing our contacts. DXLab’s Commander application provides the interface between WSJT-X and our IC-9700 Transceiver. This enables the DXLab Suite to determine the current QSO frequency and mode for logging purposes.
MAP65 Software and DXKeeper’s Capture Window
We keep DXKeeper’s Capture Window open on the screen where we run MAP65 so we can easily transfer QSO information to our log as we make contacts.
We also use several web apps to find potential EME contacts and to get an estimate of the level of EME Degradation on any given day:
We are planning some enhancements to our H-Frame to enable better alignment of our antennas along with improved reliability and stability when rotator our antennas. We will cover these enhancements in the next article in this series.
You can read more about our EME station project via the links that follow:
The image above shows the equipment that is dedicated to EME and Satellite operations in our station. We built some shelves to make room for all of the equipment as well as to create some space to move our Satellite Ground Station 4.0 to this same area. The components in our 2m EME station include (left to right):
Unfortunately, the LinkRF Receiver and Sound Card to enable a full MAP65 Adaptive Polarity installation are not currently available. As a result, we’ve created a Phase I Architecture that uses an SDR Dongle and manual selection of Receive Polarity via a switch. We also added a receive splitter and a Transmit/Receive relay in front of an Icom IC-9700 Transceiver which is dedicated to our EME setup to enable both the MAP65 and one of either the WSJT10 or WSJT-X Software Decoders to operate simultaneously.
This approach has some significant advantages when conditions are poor as one of either MAP65 or WSJT10/WSJT-X will often decode a marginal signal when the other will not. More on this in the next article in this series which will explain the software we are using more.
Transceiver, SDR Receiver, and Sequencing
IC-9700 Transceiver and Sequencer
A combination of an Icom IC-9700 Transceiver and M2 Antennas S2 Sequencer handle the Transmit side of our EME Station including the associated sequencing of the preamplifiers and Transmit/Receive Switching which is part of our Antenna System. The IC-9700’s receiver is also used with the WSJT10 Decoder in our setup.
Reference Injection Board Installed in IC-9700 (Leo Bodnar Website)
We used a FUNcube Dongle Pro+ as a second Software Defined Radio (SDR) Receiver in our setup and as an I/Q source to drive the MAP65 Software. Good information on configuring the MAP65 software to work with this dongle can be found here.
EME Station RF Paths and Sequencing
The diagram above shows the RF Paths and associated sequencing in our Version 1 EME Station. A Manual Antenna Switch is used to select either Horizontal or Vertical polarity when in receive mode. The S2 Sequencer handles polarity selection during transmit. A splitter divides the Rx signal between the FUNcube Pro+ Dongle for MAP65 and a Transmit/Receive Switching Circuit in front of our IC-9700 Transceiver. The relay enables the IC-9700 to provide Transmit signals for both the MAP65 and WSJT10/WSJT-X Software applications. The IC-9700 drives a 1.2 Kw Amplifier during Transmit and the final Tx output is metered using a WaveNode WN-2 Wattmeter.
Completed T/R Relay Assembly
To enable both the receivers in our IC-9700 and the FUNcube Dongle to function simultaneously, we built a circuit using a CX800N DPDT RF Relay and a Mini-Circuits 2-Way RF Splitter. We also built a simple driver circuit for the relay using a Darlington Power Transistor and some protection diodes. The circuit enabled our S2 Sequencer to control the relay along with the rest of the sequencing required when changing our EME Station from Receive to Transmit and back.
Finally, we configured a 30mS transmit delay in our IC-9700 to ensure that the S2 Sequencer had some time to do its job as the station transitions from Receive to Transmit. This delay coupled with the Transmit delays built into the MAP65 and WSJT10 software ensures that we will not hot switch the MAP65 Preamp System on our tower. One must be very careful to ensure that RF power is not applied before the sequencer can complete its transition to the Transmit state or damage to the Preamplifiers and/or relays at the tower will occur.
Amplifier and Rotator Controls
EME and Satellite Ground Station Hardware Components
The Elevation Rotator from our Antenna System was added to the Green Heron RT-21 Az/El Rotator Controller previously installed in our shack and both the Azimuth and Elevation Rotators were roughly calibrated. Our EME station requires quite a few USB connections to our Windows 10 Computer so we added a powered USB hub to our setup. Chokes were added to the USB cables which run to our IC-9700 Transceiver and our FUNcube Dongle to minimize digital noise from getting into our receivers.
Our planned OM Power 2002+ Amplifier is not yet available so we temporarily moved our M2 Antennas 2M-1K2 Amplifier from our Terrestrial Weak Signal setup to our EME station. The 2M-1K2 can produce about 1KW of power on 2m when operating in JT65 mode and this should be enough power for our planned EME work until the OM Power Amplifier is available. Our S2 Sequencer also controls the keying of our Amplifier as part of the T/R changeover sequence in our EME station.
WaveNode WN-2 Wattmeter
We added a 2m high power sensor to the output of our Amplifier and connected it to a free port on one of the WaveNode WN-2 Wattmeters in our station to provide output and SWR monitoring of the Transmit output of our EME station.
Supporting Station Infrastructure
VHF+ Antenna Switching Console
We had some work to do to configure the antenna, grounding, and DC power infrastructure in our station. We redid the manual switching in our VHF/UHF Antenna Switching consoles to accommodate our new EME Antenna System as well as to prepare for our Satellite Station to be moved into our shack in the near future. The console on the right provides Grounding of the Transmit and Receive sides of our EME Antenna System as well as the selection of the Antenna’s Horizontal or Vertical polarity for decoding.
We also expanded our station grounding system to provide a ground point directly behind all of our EME equipment. Our DC power system was also expanded to accommodate our EME equipment.
GPS NTP Server
Our station already has a GPS Controlled NTP Time Server installed and we’ll use it to ensure that the clock on the PC which will run the MAP65 and WSJT10 software will have very accurate clocks for JT65 decoding.
EME Tower CAM
We already have cameras that cover our Main and Satellite Towers. We’ve added a third camera to allow us to view our EME Tower’s operation from our shack. This ensures that we can visually confirm the operation of our antennas and detect any problems should they occur.
All of the new EME equipment has to be integrated and tested with the software components which provide digital operation, tracking of the moon, logging, and other functions in our station. The software setup as well as our initial experience with operating our new EME station will be covered in the next article in this series.
You can read more about our EME station project via the links that follow:
After a year’s worth of planning and 10 months of construction, we have our new 2m EME Antenna System installed on our EME Tower and working! This stage of our project took about a week and included a lot of help from Matt and Andrew at XX Towers.
Antenna Ground Test
The first step was to arrange the four 2MXP28 Yagis that we built on saw horses near our EME Tower and check each antenna’s vertical and horizontal SWR. Performing SWR measurements with the antennas close to the ground like this does not produce very accurate measurements. Doing this does allow one to spot potential problems if some of the measured SWR fail to show a resonance or are wildly different than the other antennas in the group. All of our antennas checked out as expected.
50 Ft Boom Lift, H-Frame Cross Boom Assembly On The Ground
We also rented a 50-ft Boom Lift and set it up near our EME Tower. A tool like this is almost essential to safely assemble and adjust a large, complex antenna system involving an H-Frame. It also speeds up the assembly and adjustment process considerably.
Elevation Rotator and H-Frame
Elevation Rotator Installation on Mast
The first step was to install the MT-3000A Elevation Rotator on the mast. We pre-installed the control cable for the elevation rotator before installing it on the tower. This enabled us to get it temporarily hooked up to the Rotator Controller in our shack so that we could adjust the elevation of the H-Frame and Antennas as we installed them.
With the H-Frame in place, we installed the upper 2MXP28 Yagi Antennas next. The image above shows the rigging of the boom trusses which was done on the Tower.
Lower Antenna Installation and Adjustments
Next came the lower 2MXP28 Yagis. We spent considerable time leveling and aligning all of the Antennas and H-Frame components at this stage.
Feedlines, Electronics, and Balancing
T-Braces and Feedlines
The T-Brace assemblies and Antenna Phasing Lines were installed next. Each Antenna requires two LMR-400 Phasing Lines and these coax cables add considerable weight to the backs of the Antennas. The T-Braces support these cables and help to align the Antennas on the H-Frame.
We replaced the Vertical H-Frame Boom Truss Pipe with a heavy section of Mast Pipe to act as a counter-weight and balance the final H-Frame and Antenna assembly. This step is critical to ensuring a long life for the Elevation Rotator’s drive system and chain.
Phasing Lines, Power Dividers, and Feedline Connections on Crossboom
The Rotator Loop contains the following cables and Coax Feedline connections from the H-Frame/Antenna assembly:
Vertical and Horizontal Rx Feedlines
Elevation Rotator Control Cable
MAP65 Housing Control Cable
All of these cables are bundled and securely fastened to the H-Frame Cross Boom and to the Tower. Andrew is a master at this sort of rigging!
Control Cable Connections at Tower Base
I took some time to finalize the Control Cable connections at the base of our tower. Time was spent with a voltmeter doing checks to ensure that everything was connected correctly and working. This effort resulted in the discovery and correction of some wiring errors and a faulty relay in the MAP65 housing. Had I not done these steps, we would have surely destroyed the Preamps in the MAP65 Housing when we transmitted for the first time.
Testing Our New Antenna System
Vertical Polarity Tx SWR at Shack
A series of SWR measurements were taken before sealing the coax cable connections on the tower. SWR measurements were checked and recorded for future reference at the following points in the feedline system:
At the ends of the phasing lines associated with each antenna
At the output of the two Power Dividers on the tower
At the shack entry ground block
Measurements were taken separately for both the Vertical and Horizontal elements of the final Antenna System. The image above shows a typical SWR measurement for our final Antenna System.
I did many final checks and adjustments while the Boom Lift was still here. These steps included:
Checking the oil level in the elevation rotator
Re-lubing the elevation rotator chain
Adjusting the limit switch stops on the Elevation Rotator to allow enough over-travel for future adjustments and maintenance
Checking all hardware for tightness
Sealing all coax cable connectors with Coax Wrap and Electrical Tape
Making some final adjustments to align the four 2MXP28 Antennas with each other and the H-Frame
We also spent some time identifying and inventorying all of the parts. M2 supplied upgraded aluminum saddle clamps for our H-Frame. These parts improve the clamping action between the components and also reduce stresses on the fiberglass and other tube parts.
Truss Cable Parts Prep
We spent some time preparing the parts for the Phillystran Truss cables for the Main Cross Boom and Vertical Risers. Prep included a drop of oil on each of the clamp threads and some NOALOX Antioxidant Compound on the turnbuckle threads. We also added stainless steel jam nuts to the turnbuckles to lock them in place after installation.
With this done, we assembled the Main Cross Boom, Vertical Risers, and T-Brace sections. This helped us to get all of the parts and hardware in the correct locations and to become familiar with how all of the parts fit together. We used a generous coat of NOALOX on all of the metal to metal tubing joints to facilitate the assembly and to prevent corrosion from forming at the joints of the metal tube sections. This sort of corrosion can cause increased noise levels after the array is installed outdoors for some time.
Main Crossboom Assembly
Cross Boom Truss Assembly
Next, the 3″ Main Cross Boom and its support Trusses were assembled. We carefully measured the assembly and marked the center as well as the locations of the Vertical Risers on the Main Cross Boom using a sharpie pen. these measurements will make the final assembly of the H-Frame on our Tower much easier.
Cross Boom Truss Details
The Phillystran Truss Cables and associated hardware were assembled and adjusted next.
Vertical Riser Assembly
Vertical Riser Mock-up
We decided to Mock-up a section of the Vertical Riser center tubes and the associated Vertical Riser Truss supports on the Main Cross Boom. This allowed us to confirm that the final horizontal spacing of the Risers was correct and to get the clamps associated with this part of the H-Frame assembly properly oriented and squared.
Fiberglass Tubing Reinforcements
Reinforcement Bushing Design
The Vertical Risers use fiberglass tubes at each end to provide a non-conductive mast for mounting the Antennas and their Truss Supports. The Antennas we are using are large and will need to be tightly clamped to ensure that they stay aligned and in place. The Antenna and associated Truss U-clamps put a great deal of stress on the fiberglass tubes and they can become distorted or damaged over time.
To prevent this, we decided to make a custom set of reinforcement bushings from polycarbonate plastic. Bushings were designed to reinforce all of the points on the fiberglass tubes of both Vertical Risers where U-Clamps will be used. You can see the full set of specifications for the bushings here.
W2SW Custom Reinforcement Bushings
Spencer, W2SW, owner, and founder of AntennaSys, Inc. made a beautiful set of custom bushings for us. Spencer has an amazing machine shop at his home and the parts turned out great and fitted precisely.
Reinforcement Bushing Installation
The reinforcement bushings were installed at the correct depth in each of the Fiberglass Tubes and are pinned in place using small stainless steel machine screws.
One consequence of installing the reinforcement bushings is that water can accumulate in the fiberglass tubes if they are in a horizontal position for a period of time. If such accumulated water freezes, it could cause damage to the tubes. This problem is easily solved by drilling a series of small 1/8-inch drain holes in the tubes on the bottom side when they are horizontal.
Assembled Vertical Riser
The final step was to assemble all of the parts associated with both Vertical Risers. The risers were marked to indicate the location of each Antenna Boom and Truss Clamp and the clamps were installed. The Phillystran Truss Cables were installed in the Eye Bolts on the Vertical Risers.
As we did with the Antenna Truss Cables, we will wait to install the turnbuckles until the Vertical Risers are installed on the tower and balanced. This will likely change the length of the Phillystran Truss cables.
Elevation Rotator and MAP65 EME Preamp System Test
The next major component in our new EME station is the assembly of the Elevation Rotator. This step also involves pre-assembly and testing of the MAP65 Pre-amp Housing, Antenna Power Dividers, Transmit/Receive Sequencer, and the Rotator Controller. Here are the components involved in this part of our project:
We choose the MT-3000A Elevation Rotator for its heavy-duty construction. This will be important to handle the weight of our EME antenna array as well as the winter conditions that we encounter here in New England.
Elevation Rotator Assembly
MT-3000A Elevation Rotator Parts
The first step was to inventory all of the parts for the MT-3000A Elevation Rotator and carefully read the MT-3000A manual from M2 Antennas.
Assembled MT-3000A Elevation Rotator
Assembly of the MT-3000A is pretty straight forward. It uses a chain-drive system to produce a very strong, high-torque elevation rotator system. It’s important to fill the gear-box with the supplied gear oil and to lube the chain with the proper lubricant prior to testing and installing the rotator. Spray style chain lubricants for motorcycle chains work well in this application.
RT-21 Configuration of the MT-3000A Elevation Rotator
The MT-3000A is a pulse-counter style rotator with 0.1-degree positioning resolution. It required a custom setup in the Green Heron RT-21 Az/El which was easily accomplished with Green Heron Engineering’s setup utility. One must determine the correct Divide Ratio setting by experimentation. When the correct value is found, a rotation of 90 degrees on the controller will result in exactly 90 degrees of actual movement by the MT-3000A. This calibration was much easier to do with the MT-3000A in our shop than it would have been once the unit was installed on our tower. We also set up the RT-21 Az/El Controller to allow for 5 degrees of rotation beyond the 0 and 90-degree points.
After some testing, I decided to use the 42Vdc tap setting in the RT-21 Elevation Controller with our MT-3000A. The specifications for the MT-3000A allow for up to 42 Vdc to be used to run its motor. To be safe, we set the Max Speed setting in the RT-21 Az/El to “8” which resulted in a maximum of 40 Vdc measured with a voltmeter at the output of the controller.
Assembly and Integration of MAP65 Housing and Cross Boom
Elevation Rotator and MAP65 Preamp Housing Assembly
A control cable for the MAP65 EME Preamp Housing was made up and connected to the terminal strip on the housing.
EME Sequencer Testing
The S2 EME Sequencer from M2 Antennas is designed to control the MAP65 Housing but its internal jumpers must be properly set to do this. We spent some time with the manual for the S2 Sequencer and for the MAP65 Housing carefully setting the S2 Sequencer’s jumpers and verifying proper voltages at both the output of the S2 Sequencer and the terminal strip in the MAP65 housing with a voltmeter. The manuals for the S2 EME Sequencer and the MAP65 EME Preamp Housing were clear on these steps.
Mounting Power Dividers
Power Divider Mounting Bracket
The next step in this part of our project was to mount the M2 Antennas 4-Port Power Dividers that are used to connect the MAP65 Pre-Amp housing to the four 2MXP28 Antennas. Two power dividers are required as each antenna has a separate feed point connection for their horizontal and vertical polarities. We made up some custom mounting brackets for the power dividers from 1-1/4″ aluminum angle material.
The final step was to make up LMR-400 coax cables to connect the MAP65 Preamp Housing to the Power Dividers. We used right-angle male N connectors to make the connections to the 4-Port power drivers to avoid sharp bends in the cables.
We also made up three additional LMR-400uF coax cables to connect the MAP65 Preamp Housing to the coax Tx and Rx feedlines that are installed on our tower. It’s important to keep the H-Pol and V-Pol cables as close to identical in length as possible to minimize and phase differences between the associated receive feedline systems.
The next step in our project will be the final assembly and preparation of the H-frame which will be used to mount our four 2MXP28 Antennas. You can read more about our EME station project via the links that follow:
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 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.
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 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
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
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
We also pre-assembled things like the Mast Clamp and the Boom Truss Clamp during the parts inventory process.
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.
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 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
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
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.
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
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
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.
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
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:
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