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
6m Yagi and 2m/70cm/23cm Satellite Antennas On A Tower
We will be hosting a Tech Night about Building and Operating a VHF+ Weak-Signal Station tonight, July 14th at 7 pm Eastern Time. The live, interactive video of our tech Night will be shared via a Zoom conference and all of our readers are welcome to join. I plan to cover the following topics during our session this evening:
Why do weak-signal work on 6 meters and above?
What can you work and what modes are used on these bands
How does propagation work at 50 Mhz and above and how can you measure it?
How does one operate using SSB, CW, and digital modes on these bands?
What equipment is needed and what are some possible ways that you can put together a VHF+ station?
Some demonstration of actual contacts
In addition to an overview of how to get on all of the bands above 50 MHz, we will focus on the 6 Meter (Magic) band. The session will include demonstrations of FT8 and Meteor Scatter contacts on 6 m. I will also briefly describe the 6 m station here at AB1OC-AB1QB and show how we use it to make contacts. A second Tech Night will cover stations and weak-signal operating on 2 m and above.
The Zoom information for our Tech Night Session follows. We suggest that you join early so that you have a chance to make sure that your computer, speakers, microphone, and camera are working.
Now that spring is here, we’ve continued work on our EME station project. The most recent project was to build complete the ground 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.
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
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:
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 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.
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.
We continued to test our Portable Satellite Station 4.0 as part of AMSAT’s 50th Anniversary Celebration WAS Activations. You can read about the activations and our station’s performance via the link above. Overall, we were pleased with how the portable setup performed. The weakest link was the downlink performance of our antenna system. We are working on some ideas to improve this element of our setup – more to come on this project…
There are many reasons to have an accurate time source in your station. Getting the best performance from WSJT-X modes like FT8 requires your computer clock to be synchronized to within a second for example. You can set your clocks accurately using NTP servers on the Internet. This is the most common way that most stations set their clocks.
What if you are portable and don’t have Internet access or what do you do if your Internet connection goes down? One way to solve these problems is to use a GPS controlled NTP time server in your station. We recently installed one from Leo Bodnar in our station.
This device is simple to install. It just requires an Ethernet connection to your network and a GPS antenna. The antenna is included with the unit. The antenna will need to be outdoors with a reasonably clear view of the sky.
GPS Satellite Lock Screen
After a minute or so after it is installed and powered up, the unit will synchronize to the visible GPS satellites in your location and report its coordinates. This indicates that you have a good GPS system lock and that the clock in the unit is accurate to within a microsecond.
NTP Summary Screen
The unit gets its IP either from DHCP or via a fixed IP address that you can program. Once the unit is set, you use its IP address as the NTP server in your software to set your clocks. You would set you NTP server in a program like Dimension 4 to accurately set your computer’s clock for example. You will want to disable your computer’s normal Internet clock setting function to avoid conflicts with Dimension 4. Once this is set up, your computer clock will be synchronized to the GPS system and will be very accurate and you will get the best performance from WSJT-X.
The performance of the 3.1 Station’s antennas is very good but the antenna system is a handful to transport. We are planning to install these antennas on a new tower at our QTH and use our Flex-6700 SDR-based Remote Operating Gateway with some upgrades to create a remotely controlled satellite station that can be operated via the Internet. The main components of the 4.0 Station will include:
Upgrade plans for our Transportable station include the addition of remote switchable polarity relays and a new Icom IC-9700 Transceiver when it becomes available.
Polarity Switch Installed in LEO Pack Antennas
The polarity switches have been installed on the M2 Antennas 436CP16 and 2MCP8A antennas in our M2 Antennas LEO Pack. We are using a DX Engineering EC-4 console to control LHCP or RHCP polarity selection on the antennas. We have been doing some testing with the upgraded LEO pack which includes the polarity switching capabilities and we are seeing a significant improvement in performance.
AlfaSpid Az-El Rotator
We are also planning to move the upgraded LEO pack antennas to the current 3.1 Tower to take advantage of the AlfaSpid Rotator which is installed there.
Icom IC-7900 Transceiver
The other major upgrade planned for the 2.2 Station is the new Icom IC-9700 Transceiver when it becomes available. This radio will utilize Icom’s SDR platform and includes a Pan Adapter/Waterfall display which will be a very useful addition for operation with Linear Transponder Satellites.
Upgraded Portable 1.2 Station
We really enjoy mountain topping and activating grid squares so we are planning upgrades to our 1.2 Station for this purpose.
Our 1.2 Portable Satellite Station on Mt. Kearsarge
The 1.2 Station utilizes computer control to enable operation with linear transponder satellites and will use solar/battery power along with a 100w/70w Icom IC-910H Satellite Transceiver.
A pair of 90W foldable solar panels, an MPPT solar charger, and a pair of LiPo 4S4P A123 batteries provide plenty of power to run the IC-910H Transceiver and the associated computer. The portable station also includes a pair of ARR preamps.
Portable Satellite Antenna System
The antenna system we’ll be using is an Elk Portable Log Periodic 2m/70cm yagi on a camera tripod. A combination of a compass and an angle finder gauge helps us to correctly point the antenna.
As you can probably tell, all of these upgrades are in progress and are at various stages of completion. We will post updates here on our Blog as we continue to make progress. Here are links to some of these posts:
Quite a few Nashua Area Radio Society members have been working on a display to get young people and potential new Hams interested in Amateur Radio. Our display will be part of the New England Amateur Radio Convention in Boxboro, MA on September 8th and 9th. We are also planning a similar display for NEAR-Fest at Deerfield Fairgrounds, NH later in the fall. You can see more about our planned display and the associated hands-on activities via the following link.
I want to share some information about an Amateur Radio event that we will be doing at the Boxboro, MA Ham Radio Convention in September. Our display and hands-on activities provide an introduction to Amateur Radio for young people and include information and a chance to try Amateur Radio activities such as:
You can read more about our plans for the event via the link above.
Morse Trainer Kit
We’ve been working with Steve Elliot, K1EL to develop an inexpensive kit building project to include as part of our displays. We will be including a new kit building activity in as part of our display. Builders can purchase the Morse Trainer Kit shown above for $20 and build it at the show. We will provide soldering equipment and kit building mentors to help builders complete their kit. The package includes batteries and a printed manual. We will have these kits available for walk-up purchase at the show on both Saturday and Sunday.
I am also planning to provide forum presentation on the following topics on Saturday at Boxboro:
Creating Successful Youth Outreach Projects
Portable Satellite Station Design, Operation, and Planning for an upcoming ISS Crew Contact
STEM Learning for Young People via High Altitude Balloons Carrying Amateur Radio
The Amatuer Radio gear on the International Space Station (ISS) supports digital and SSTV modes as well as FM voice communications. The astronauts onboard periodically fire up the SSTV system and transmit images to commemorate milestones in space travel. We recently received a set of 12 images from such an event which commemorated Cosmonautics Day. You can read more about how this is done and view the images via the link below.
We installed a 75m loop for SSB operation on our tower when we built it. The loop is full size and is diamond shaped so that our lower SteppIR DB36 yagi can rotate inside of it. The loop is fed at the bottom corner about 20 ft up from the ground. It works great for SSB operation on 75m but we have often wished we could use it across the entire 80m band. This goal led to a project to create a matching system for the antenna. The idea was to use a set of loading coils in series at the feed point create a good match in all segments of the 80m band.
EZ-NEC Model for 75m Loop
The first step in the design of our 80m matching system was to build a model of our current loop using EZ-NEC. The model was then used to determine the correct values of a set of series loading inductors to match different segments of the 80m band.
Matching System Design Analysis
We also considered how likely different segments of the 80m band were to be used by profiling historical spotting data from DXSummit. All of this analysis led to the creation of a final design which is captured in the spreadsheet shown above. The final design requires our current 75m loop to be shortened a bit to work well at the very top of the 80m band.
Modeled Loading Coil Inductance Values
A set of 5 different inductor pairs can be used in series with the loop’s feed point to create a good match across the entire 80m band. The modeled values for the series matching inductors is shown above.
Matching System Modeled SWR
Our microHAM control system can easily implement the switching of the various inductance values based upon the frequency that a radio using the antenna is tuned to. Result modeled SWR for the final 80m loop and match combination is shown above. The design should achieve an SWR < 1.5:1 across the entire 80m band except for the very top where the SWR remains < 2:1. Also, the design optimizes the system’s SWR in the important CW DX, SSB DX, and Digital windows on the 80m band.
Layout of Components in Enclosure
With the design completed, we choose an enclosure and all of the components. Here are the details of what we used:
The first step in the construction was to layout all of the components in the enclosure. Attention was paid to keeping the two series inductors at right angles to avoid coupling and to keep RF connections as short as possible. The relays were arranged to keep the leads connecting to the coils of roughly equal length. Finally, the control circuitry was kept as far removed from the RF leads as possible.
Enclosure Mounting Ears and Clamps
The matching system attaches to a tower leg via saddle clamps. We fabricated a set of mounting ears and spacer blocks to position the enclosure far enough away from the tower so that the antenna connections do not interact with the tower.
80m Matching System Construction
A summary of the completed matching system construction is shown above.The design uses a set of four double-pole double-throw relays to switch in different coil taps which selects the loading inductance provided by the matching system.
We did a set of calculations and found that our relays would be subjected to a worst case peak-peak voltage of about 2.1 KVp-p at the coil tap points.
The relays are arranged such that two sets of contacts have to be traversed to select any given coil tap. The relays we are using have a third pole which we are not using. We disassembled each relay and removed the internal contact wiring for the center pole which improves both the coil to contact voltage rating and the isolation values of the relays.
These steps combine to improve the voltage rating of the system. This is an important design element given that the match will operate at legal limit power.
Completed RF Deck
The completed RF deck and control circuitry is shown above. The enclosure we choose came with a removable plastic plate that made mounting and wiring all of the components simple.
Loading Coil Mounting and Taps
The loading inductors are mounted using nylon hardware with the ends connected to the two antenna terminals on the sides of the enclosure. The coils use movable tap clips to allow us to fine-tune the match once the system is installed with the antenna on our tower. The initial clip locations are set to create the inductance values modeled during the design phase.
Relay Control Circuit Connections
The relay control leads use twisted pair wiring to minimize RF pickup. The control leads are routed away from the RF connections to minimize potential RF coupling.
Relay Control Circuit Details
The control circuits for each relay use a combination of a Diode, a Varistor (MOV) and a filter capacitor in parallel to avoid relay coil switching interference and to suppress control line noise.
1.5 to 1 Matching Balun
The matching system is designed to operate at 75-ohms which is pretty close to the resonant impedance of our 75m loop. The current antenna uses a 1.5:1 Balun to match the loop to our 50-ohm coax feedline. We disassembled an identical matching balun (actually a 75-ohm balun plus a 1.5:1 unun) and used it without its enclosure to create a final 50-ohm match.
MicroHAM Setup to Control 80m Matching System
The final step in the construction of our matching system was to program our microHAM antenna switching system to properly configure the relays in our matching system. This was quite simple to do using microHAM’s frequency dependent antenna control capabilities. The microHAM system automatically operates the appropriate relays to create the best possible match as the radio which is using the matching system is tuned across the 80m band.
Unfortunately, we are in the middle of winter here in New England so I will have to wait for warmer weather to install our new matching system on the tower and make the final adjustments. I am planning another article here when the final integration steps are done to cover the performance of the completed project.