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.
As you can tell, we are pretty active on Satellites so we decided to take our station up a level by upgrading our antennas. We choose the 2MCP22 and 436CP42UG antennas from M2 Antenna Systems with optional remote polarity switches. These are larger yagis with booms over 18+ ft in length. The upgrade required us to improve the mechanical aspects of our Satellite Antenna System as well.
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.
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.
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.
The images above show the feedpoint assemblies for both of our new antennas.
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
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.
We have a ground tower that we use for portable satellite operations. It was fitted with a longer mast to create clearance for our larger antennas. We lowered the existing antenna system onto the ground tower for disassembly, installation, and testing of our new antennas.
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
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.
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.
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.
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
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.
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.
Finally, we adjusted our Green Heron RT-21 Az/El Rotator Controller to slow down the ramps for the rotator. Final testing indicated the smooth operation of the rotator at slow speeds.
SWR Testing and Baseline
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.
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
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.
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.
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.
We also added an ADS-B antenna and feedline for the Raspberry Pi FlightAware tracker in our Shack. The parts that we used for the ADS-B antenna include:
- FlightAware 978 MHz ADS-B Antenna
- A pair of DX Engineering Genius Clamps and SS Hardware
- A 4 1/2 ft section of 1.5 in Aluminum Tubing
- Some LMR-400uF coax and Crimp-on N Connectors
You can view the statistics from our FlightAware Tracking station here. More on the FlightAware project to come in a future post.
Upgraded Antenna Performance
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:
- Portable Satellite Station Part 7 – Plans for a 4.0 Station
- Satellite Station 4.0 Part 1 – New Tower
- Satellite Station 4.0 Part 2 – Antennas
- Satellite Station 4.0 Part 3 – Antenna Integration and Testing
- Satellite Station 4.0 Part 4 – Tower Camera and J Mode Desensitization Filter
- Satellite Station 4.0 Part 5 – New IC-9700 Transceiver
- Satellite Station 4.0 Part 6 – Tower Finishing Touches
- Satellite Station 4.0 Part 7 – Flex SDR Satellite Transceiver
- Satellite Station 4.0 Part 8 – GPSDO Frequency Locking
- Satellite Station 4.0 Part 9 – Upgraded Simple Portable Station
- Satellite Station 4.0 Part 10 – Adding 23 cm To Our Satellite SDR
Fred, do you have any need for pre-amps on your satellite system? Any recommendations?
I do use preamps on my satellite systems. Even with short feedlines, the good ones often improve the system noise factor of a satellite system over the radio alone. In the past, I’ve used RF switch units from Advanced Receiver Research very successfully. Unfortunately, ARR no longer provides these. I’ve also heard some good things about SSB Electronics RF switched preamps. You can still use the lower power RF switch preamps from ARR if they are combined with external relays and sequencing (see the recent 6m article here on our block for an example of this approach), but this is not a cost-efficient approach at the power levels typically used with satellites. I link to use preamps in satellite applications that are coax powered as most modern satellite capable radios handle the power and sequencing of this type of preamp directly from the radio.