I’d like to invite our friends here on our Blog to visit us during Field Day on Saturday, June 26th, and Sunday, June 27th. We will be at Keyes Memorial Park in Milford, NH.
Testing Our Field Day Satellite Station
We will have a Tower up with a Triband Yagi and we’ll have our computer-controlled portable satellite station at Field Day.
6m LFA Antenna for Field Day
We’ll also have a new LFA Yagi for the 6m Band. We will be a 4A station with a total of 5 Transmitters on the air. Our stations will be equipped for SSB Phone, CW, and FT8/FT4 Digital modes.
We’ll also be doing training sessions on Satellite Operations, FT8 Digital on 6m, and Fox Hunting at 12:30 pm on Saturday, June 26th. If you have an HT, bring it and you can use it to hunt our foxes. We’ll also have HTs available for folks to use for Fox Hunting.
The Nashua Area Radio Society will be using our portable Satellite Station this year at Summer Field Day. A number of members got together recently to assemble and test our Computer-Controlled Portable Satellite Station for Field Day. Here are some pictures of our Field Day Satellite Station Test…
Several members of the Nashua Area Radio Society got together to set up and test our Portable Satellite Station for Field Day 2021. Our station is a computer-controlled one and enables us to work FM and Linear Satellites using phone mode and CW.
You can see how the portable station goes together in the article above. You can learn more about the design and construction of our Portable Sation from the series of articles that begins here. We hope to work some of our readers on the birds during Field Day this year!
We’ve been wanting to try a Loop Fed Array (LFA) Yagi on the 6m Band. The Nashua Area Radio Society’s 2021 Field Day operation presented us with a good opportunity to do this. We choose a lightweight 3-Element LFA Yagi from InnoVAntennas and used a fiberglass mast to get it up 25 ft (about 8 meters).
The LFA Yagi performed very well! You can read more about this antenna’s performance and our upgraded portable station via the link above.
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
We’ve been making good use of our Satellite Ground Station. Our existing 2MCP14 and 436CP30 antennas have enabled us to make over 2,000 satellite contacts; working 49 of the 50 U.S. States, 290+ Grid Squares, and 31 DXCCs. Our station is also an ARISS Ground Station which enables us to help Schools around the world talk to astronauts on the ISS.
The first step in the project was to unpack and carefully inventory all of the parts for each antenna. This included carefully presorting and marking each element as we did during the assembly of our EME antennas.
2MCP22 Completed Antenna
The new antennas are quite large and they took most of the available space in our workshop during assembly. Getting good results from any antenna is all about attention to the details. Small things like turning the boom sections to get a good alignment of the elements, using NOALOX on the boom sections and hardware to prevent corrosion and galling, carefully measuring and centering the elements, etc. are all good things to do.
2MCP22 Feedpoint Assembly including Polarity Switch Upgrade
The feedpoint system on these circular polarized antennas requires careful attention during assembly. It’s important to install drive element blocks, shorting bars, polarity switches, feedpoint splitters, and all phasing lines EXACTLY as shown in the antenna assembly manual. Failure to do these steps will likely results in SWR problems down the road.
436CP42UG Feedpoint Assembly
The images above show the feedpoint assemblies for both of our new antennas.
New Satellite Yagis Ready For Installation
A rough SWR measurement with the antennas on the ground was performed to check for assembly errors. It’s a good idea to use a 12V battery to test the antenna SWR’s in both RHCP and LHCP. These tests checked out fine and we are ready to begin installing the antennas on our Tower.
Old Antenna Takedown and Work Stand
Old Antenna Assembly Takedown Using Boom Lift
The next step in the installation was to take down our existing antennas. We rented a 50 ft Boom Lift for the project. The lift makes the work much easier and safer.
It’s important to fully test a complex antenna system like this on the ground prior to installation on a Tower. We have routinely found and corrected problems this way. This approach also enabled us to properly adjust our cross boom and antenna support trusses and balance the final assembly properly. All of the required adjustments are MUCH easier with the antennas on the ground.
We also run our rotators under computer control for at least one full day before installing the completed assembly on our Tower. We have consistently found and corrected problems with cabling and balance this way.
Antenna Mounting and Trussing
2MCP22 Boom Truss
The new antennas have very long booms (approximately 18 ft) and they have a tendency to sag. Add the ice and snow load that we experience here in New England and you end up with quite a bit of stress on the booms over time. Robert at M2 Antenna Systems came up with a custom truss assembly for our installation to address this problem. It’s important to minimize any metal in a setup like this to avoid distortion of the antenna patterns. The trusses use a solid fiberglass rod and small turnbuckles to support the ends of each antenna boom. There is much more weight on the rear of the booms due to the weight of the attached coax cables and polarity switches. For this reason, we located the truss anchor point for the rear of the boom such that it creates a sharper angle for the truss ropes at that end of the truss. This reduces the compression load on the rear of the boom and enables the truss to better carry the weight at the back of the antenna.
436CP42UG Boom Truss
Installing a truss on the 70cm yagi is much trickier due to the tight pattern of this antenna. We minimized the added metal components by drilling the antenna boom to mount the truss plate directly to the boom via bolts.
We relocated the boom support plates on both antennas as far to the rear of the largest boom sections as possible to improve overall antenna balance. The clamps were also adjusted to change the orientation of the elements from vertical/horizontal to a 45-degree X arrangement. This maximizes the separation between the element tips and other metal components like the cross boom and truss plates.
Tubing Drill Guide
All of this required drilling some new holes in our antenna booms. We used a Tubing Drill Guide and C-clamps to perform the required drilling operations accurately.
Satellite Antenna Boom Assembly
The photo above shows the new antennas mounted on our cross boom. The modifications worked out great resulting in well supported and aligned antennas on the cross boom.
Balancing The Array
Cross Boom Counterweight and Trusses
It’s very important to properly balance any antenna assembly that is used with an elevation rotator. Failure to do this will usually result in the failure of your elevation rotator in a short period of time. We initially had some pretty major balance problems with our new antennas. This is due, in part, to the weight of coax cables that run from the antenna feed points along the L-Brace Assemblies. The added weight of the Polarity Switches near the rear of the booms was also a significant contributor to this problem.
We created a counterweight by replacing one of our cross boom truss tubes with a metal section of pipe about 4 ft long. The pipe acts as a counterweight to the weight of the coaxes, etc.
Wheel Weights Used for Balancing
Next, we added 4 1/2 pounds of weights to the front on the metal pipe. We used several layers of Wheel Weights built up in multiple layers to get the necessary counterweight. A heavy layer of electrical tape and some large cable ties were used to ensure that the weights say in place.
This got us close to a good balance but the boom of the 2MCP22 was still significantly out of balance. Matt at XX-Towers came up with a good solution to this problem. We added a few strips of wheel weights inside the very front of the boom of the 2MCP22 to finally get the antennas balanced. A combination of the adhesive tape on the weights and two small machine screws through the boom ensures that the weights remain in place and do not short the elements to the boom.
A final check and baseline of all of our antennas were made on the ground. Both RCHP and LHCP modes were checked and recorded for future reference.
432CP42UG Installed SWR
We found that some fine-tuning of the locations and routing of the phasing lines on our 436CP42UG improved the SWR curves. This is a common situation and it’s well worth the time to make small adjustments while carefully observing how they impact your SWR readings. The phasing cables are firmly secured to the antenna boom after the fine-tuning is complete.
New Antenna Installation and Integration on Tower
Upgraded Antennas Going On Tower
The next step in our project was to install the updated antenna assembly back on our Tower. We had to push the lower rotator and mast up about 4 ft to accommodate the larger antennas. We removed our 6M7JHVHD Yagi and temporarily fastened it to the side of our tower to make these steps easier. We also took the opportunity to work on our 6M7JHVHD Antenna to adjust the length of the Driven Element for better SWR performance in the FT8 and MSK144 section of the 6m band.
Satellite Tower Infrastructure and Accessories
There is quite a bit of feed line and control cabling involved in a complex antenna system such as ours. The next step in the project was to reconnect all of the cables and coax feedlines.
Control Cable Junction Box at the Base of VHF Tower
We use small junction boxes on our tower and a larger one at our tower base to make it easy to remove and reinstall all of the required control cables. Our approach was to hook up and test the rotators first to ensure that we did not have any new mechanical or balance problems. This step checked out fine. The stiffer chrome molly mast and its added length actually resulted in smoother operation of rotators than we saw during ground testing.
The final step was to work through the other control cables and feed line connections; testing each connection as we went. The Boom Lift makes this work much easier to do.
We took advantage of the availability of the Boom Lift and added some additional enhancements to our VHF Tower. Previously. changing the battery in our Weather Station involved climbing our main tower to 50 ft. We moved the weather station to the 30 ft level on our VHF tower to make this maintenance step easier.
Initial testing of our new antennas is showing some major improvements. The uplink power required to work LEO satellites has been reduced significantly. As an example, I have worked stations using the RS-44 Linear Satellite with just 0.4 watts of uplink power out of our Satellite IC-9700. The signal reports we’ve received have been excellent as well.
More About Our Ground Station
Here are links to some additional posts about our Satellite Ground Stations:
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.
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: