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.
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.
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.
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.
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.
With the design completed, we choose an enclosure and all of the components. Here are the details of what we used:
- Barker and Williamson 2404TL 32 uH Airdux coil stock cut in half (3″ dia, 4 TPI)
- Array Solutions RF-15 15/20 kW RF Relays
- Balun Designs 1.5:1 Balun with eyelets
- V22ZA2P Varistors (MOVs), 0.1 uF Capacitors, 1N4001 Diodes make up the 12Vdc relay control circuits
- Outdoor NEMA Box Approx. 16″x12″x6.5″
- DX Engineering Saddle Clamps to fit our tower
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.
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.
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.
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.
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.
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.
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.
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.
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.
I recently wrote a blog article about the DX Alarm Clock software – here is Part 2 of the Series on the how I built the hardware for the DX Alarm Clock.
DX Alarm Clock Hardware Components
The DX Alarm Clock is based on a Raspberry Pi 3 computer and an Adafruit Pi-TFT Touch Screen Display. The list of components, along with links is below. Since I built the Raspberry Pi almost a year ago and technology is always advancing, some of the parts are no longer available or have better replacements available. I’ll provide information on what I used and a recommended replacement. Approximate prices are included.
Motherboard: Raspberry Pi 3 ($35) – includes a 1.2 GHz 64-bit quad-core ARM CPU, Build in WiFi, Ethernet, 4 USB Ports, an HDMI port and audio port (3.5″) and Bluetooth.
Case: Pimoroni PiBow Case for Raspberry Pi and Pi-TFT Display($20)
Portable Speaker: Any small portable/rechargeable speaker will do. Mine is a Kinivo, but it is no longer available. Any small speaker will do as long as it is Bluetooth or has a 3.5″ stereo connector.
Raspberry Pi Development Environment
After constructing the Raspberry Pi, case and TFT Display, the next step was to connect it to a monitor via the HDMI port, a mouse via one of the USB ports and to a Bluetooth keyboard. Then I loaded the Raspbian Operating System onto the Raspberry Pi via the micro SD card. I first copied the OS to the Micro SD card using a PC or Mac and then inserted the card into the Raspberry Pi and booted from it. You can find a good tutorial on how to do this at https://www.raspberrypi.org/learning/software-guide/quickstart/
Once Raspbian is installed, you will have a windows like GUI (Graphical User Interface) environment with a web browser, and a number of additional applications included.
This gave me a development environment that I could use to build and test the DX Alarm Clock software. I used the Python language to develop the software. I used the Python IDLE development environment, which is included in the Raspbian OS.
Interested in Raspberry Pi Amateur Radio Projects? See the article on a Raspberry Pi Satellite Rotator Interface.
We’ve made about 250 contacts with our Portable Satellite Station 2.0 and we have worked 106 grids which should be enough to earn a Satellite VUCC. The picture above shows the grids that we’ve worked via Satellites. We’ve learned a lot about satellite operation and had a great deal of fun in the process!
We’ve met all of our original goals for our 2.0 Station and we’ve used it portable at License Classes, Field Day, and other Amateur Radio Demonstrations. We’ve also shared presentations about our 2.0 Station with Amateur Radio Groups here in the New England area. The question that we get most often about the 2.0 Station is “What are your plans for the Portable Satellite Station 3.0”?
Well, here is the plan. We are working with a local group to secure and host an ISS Crew contact. The ARISS folks have published ground station requirements for these contacts. Here are the primary station requirements:
- Transceiver with 50–100 W output, 1 kHz tuning steps, and 21 memories capable of storing split frequencies
- Low-loss coax (such as 9913 or LMR-400)
- Mast-mounted receive pre-amplifier
- 14-element yagi antenna with switched circular polarity
- Antenna rotators for azimuth (0–360°) and elevation (0–180°), with an interface for computer control
- Computer running tracking software for antenna control (including flip mode operation)
Fortunately, our 2.0 Station meets or exceeds almost all of the primary station requirements with the exception of the antennas. The required antenna upgrades will shape the plans for our Portable Satellite Station 3.0.
ISS Crew Contacts are conducted using 2m Simplex radios on the ISS. We choose the 14-element circularly polarized 2MCP14 yagi from M2 Antenna Systems to meet the ARISS requirements for 2m. Here are the specifications for this antenna:
The 2MCP14 antenna offers a good balance between gain (12.34 dBi) and boom length (10′-6″) and is near the size limit that is practical for use in our Portable Station. This antenna provides an additional 3.14 dBi of gain compared to the M2 Antenna Systems 2MCP8A yagi which we are currently using in the 2.0 Station.
While not required for an ARISS Crew Contact, we are also going to upgrade the 70cm yagi to a 30-element circularly polarized M2 Antenna Systems 436CP30 yagi. Here are the specifications for this antenna:
This antenna is a good match for the upgraded 2m yagi. The 436CP30 has a boom length of 9′-9″ and a gain of 15.50 dBi. This antenna will provide an additional 2.2 dBi of gain compared to the M2 Antenna Systems 436CP16 yagi which we are currently using in the 2.0 Station.
The new antennas will require some modifications to our portable antenna system arrangement. They will need to be mounted on a cross-boom near their centers. As a result, a non-conductive fiberglass cross boom will be required to avoid problems with pattern distortion.
We will be using an M2 Antenna Systems FGCB60 Cross Boom which has removable, non-conductive end sections made from fiberglass material. The removable ends will make it easier to transport the antenna system. We will also need to make a new mast which is 24″ longer than our current one in the 2.0 Station to create the needed ground clearance for the longer antennas.
We are also planning to use a larger Alfa Spid Az-El Rotator. This unit will handle the extra weight of the longer yagi antennas and cross boom assembly and is more precise than the Yaesu unit used on the 2.0 station.
The last piece of the 3.0 Station Antenna upgrade is to add switchable left-hand and right-hand circular polarity. This will be accomplished via M2 Antenna Systems PS-2M and PS-70CM switchable polarity feed point upgrades for the 3.0 yagis.
We have a DXEngineering EC-4 Control Box from a previous project and we can use it to control the relays in the Polarity Switches which will be part of the 3.0 Station antennas. The box will allow us to select any combination of left and right-hand circular polarization on the 3.0 Station uplink and downlink antennas.
We should have all of the parts here for the 3.0 upgrade by the end of the year. We’ll post more as the project proceeds. Other articles in the Portable Satellite Station series include:
- A Portable Satellite Station Part 1 – A Simple Station for AO-85
- A Portable Satellite Station Part 2 – 2.0 Station Goals and Antenna System
- A Portable Satellite Station Part 3 – Station Radio and Supporting Equipment
- A Portable Satellite Station Part 4 – 2.0 Station First Contacts!
- A Portable Satellite Station Part 6 – 3.0 Station Initial Contacts
- Plans for Upgrading Our 2.0 Station for ARISS Contacts
- Raspberry Pi Satellite Rotator Interface
- PTT Router for Satellite Station 3.0
You may also be interested in the satellite station at our home QTH. You can read more about that here.
We have a number of station upgrades planned for this fall. Our planned upgrades include:
- Enhancing our FlexRadio 6700 based Remote Operating Setup to include additional remote control client options, better networking via the Internet, and better integration with our microHAM system – you can read about this completed project here.
- Upgrading the second radio in Anita’s (AB1QB) operating position from the current Icom IC-7600 to a new an Icom IC-7610 SDR-Based Transceiver
- Adding a new Elecraft KPA1500 Solid State Amplifier to our station. The KPA1500 will be shared between the Icom IC-7610 and our FlexRadio 6700 based Remote Operating Gateway
We always begin our station projects by updating our station design documents.
Our Remote Operating enhancements will include:
- Updating our FlexRadio SmartSDR Software to V2 which provides operation of the radio over the Internet
- Using the SmartSDR CAT Cable features to create a direct interface between the FlexRadio 6700 and the microHAM Station Master Deluxe associated with the SDR
- The addition of a Maestro Control Console to our set of PC-based remote operating clients
The figure above shows an updated architecture for our Remote Operating Gateway which includes these enhancements. The planned Elecraft KPA1500 solid state amplifier will simplify the software associated with remotely controlling and monitoring the amplifier, tuner, and wattmeter components in our previous remote operating setup.
We have been quite impressed with the performance of our Icom IC-7300’s radio’s receiver. As a result, we have decided to upgrade the second radio in Anita’s operating position to an Icom IC-7610. We expect that the IC-7610’s receiver performance will be as good as or better than the IC-7300.
The Icom IC-7610 also provides a very nice external display capability which will allow us to take the best advantage of the radio’s pan adapter. We believe that the IC-7610 will integrate easily into our microHAM system. It should be a “drop-in” replacement for our current IC-7600. We hope to see the IC-7610 shipping before the end of this year.
Our final upgrade will be to add an Elecraft KPA1500 Solid State Amplifier. This amplifier provides a full 1500 watts out on all bands 160m – 6m. The new amplifier will bring the Icom IC-7610 and our FlexRadio SDR-Based Remote Operating Gateway up to full legal limit power. This will be especially helpful on the 6m band where both the IC-7610’s and the FlexRadio 6700’s excellent receiver performance will help us to take the best advantage of the extra power for Meteor Scatter and other weak signal work on 6m.
Our microHAM Station Automation System can accommodate shared amplifiers. We will take advantage of this capability when we integrated the Elecraft KPA1500 into our station. The shared amplifier setup will also allow us to eliminate one of our bandpass filters. The KPA1500 amplifier integrates autotuner and wattmeter functions into the amplifier and provides a direct Ethernet interface for remote control and management. These enhancements should eliminate the need for several of the remote control server software applications that we are currently running on a PC in our shack. Also, we can manage all of these functions from a single client application on a remote client PC. These simplifications will make our remote operating gateway setup more reliable and easier to use.
We plan to share more on these projects in future posts here on our Blog. The FlexRadio Maestro and all of the other components that we need for Remote Operating Gateway enhancements have arrived. We will complete this part of our project in the very near future and post more here.
Also, it appears that the local control interface to the new Elecraft KPA1500 amplifier is nearly identical to that used by our current Elecraft KPA500 Amplifier. This means that we can begin our shared amplifier upgrades using the KPA500. We do not have a firm date for the IC-7610 to ship and that portion of our upgrade plans is likely to be our last step in the project.
Special thanks to Dave, K1DLM who has helped us with ideas for several aspects of this project.
Another new radio from Icom based on their SDR platform. This looks like a great radio for Satellite and EME use. We’re going put in a pre-order for this radio and will plan to include it in our Portable Satellite Station. I’ll post more here as details become available.
The Thirteen Colonies Special Event begins at 9 am Eastern Time (13:00 UTC) on Saturday, July 1st and ends on July 6th at midnight ET. The K2K NH team will have a full complement of top notch operators on all bands and modes again this year including a dedicated QRP station. We’ve also designed a new QSL card for this year’s special event (above).
Take some time during the event and work K2K New Hampshire for your own copy of our new K2K QSL and don’t forget to send for your certificate. If you work a station from all 13 Colonies, you certificate will indicate a “clean sweep”. There will be two bonus stations that you can work as well. Check out The Thirteen Colonies Special Event Site for all of the details on the event.
This event is a lot of fun for all involved and may well be the largest special event in the world. The QSO count for the event last year was 139,772 contacts in about 6 days! We hope to hear from you during the event and DX stations are especially welcome!
Fred, AB1OC (de K2K New Hampshire QRZ?)
Dave Merchant K1DLM, our Field Day chairman, is bringing some 21st Century radio and computer technology to our Field Day setup this year. There are several aspects to this new component of our Field Day plans including –
- Two Flex-6700 Software Define Radios running over a network for our new Digital and enhanced GOTA Stations
- An on-site WiFi Network to enable using the N1MM+ Logger in network mode for sharing of log information, station activity, real-time scores, and messages
- A central Score Board and Field Day Information Computer in our public information tent
We will again be holding our 2017 Field Day operation at the Hollis-Brookline High School in Hollis, NH. We are planning on using the upper baseball field area as our main operating location. We have decided to add a third tower this year and locate it on a soccer practice field which is situated several hundred feet away from our main operating area. All of our antennas and equipment will lie within the required 1000′ circle but the third tower would situate those operating at that location away from the rest of our group. Dave’s solution to this problem was to set up a network and operate two Software Defined Radios (SDRs) at the lower site remotely from our location on the upper field.
Dave has enlisted Piece Fortin, K1FOP to be our IT Chairman for Field Day this year. Pierce has been instrumental, along with Dave, in the planning and testing of all of this new technology. Pierce and Dave have a great deal of networking and IT experience and knowledge and we could not have put together what is described here without them.
Dave K1DLM, Piece, Hamilton K1HMS, Mike Ryan K1WVO, Anita AB1QB, and I have gotten together multiple times to set up and test all of this new technology. I wanted to share some more about the equipment and the associated testing (which has been staged in the kitchen at our QTH – thank you, Anita!).
We began the testing process by setting up our 20m CW station.
This station uses an Elecraft K3S Transceiver, a K1EL WinKeyer and the N1MM+ Logger running on a Windows 10 Laptop PC. We used this station to get our basic N1MM+ setup including our Field Day CW keying macros right.
Next came our 40m SSB station. This setup uses an Icom IC-7300 Transceiver and allowed us to set up and test N1MM+ on the fly audio macro recording and playback. All three of our SSB stations will have on the fly recording and playback capability which will allow each of our SSB operators to record and use a custom set of audio macros.
Next came our Digital Station. This station uses one of the two remote Flex-6700 SDRs.
Dave, K1DLM put together a really nice package for the two Flex-6700 SDRs and associated equipment which will be located on the lower field. He used a rack system to mount the two SDRs, power supplies, a three-band Tri-plexor, a set of bandpass filters for 80m, 40m, 20m, 15m, and 10m and a 403A 8×2 networked antenna switch. This setup allows either of the two SDRs to share the tri-band yagi or the 40m and 80m Inverted-V antennas on the tower on the lower field and operate on any of the 5 available HF bands. Antenna and filter switching automatically track the frequencies of the two SDRs making the setup simple to use.
The Digital Station’s remote SDR will be operated using a SmartSDR client running on the Digital Station laptop PC. This station will have a second monitor to better accommodate all of the windows associated with it.
The main display associated with the Digital Station will run decoders for all PSK and RTTY modes. The ability to decode multiple PSK signals simultaneously and multiple RTTY decodes are available. The Digital station also acts as the N1MM+ master station in our Field Day setup for all of the other stations which use N1MM+.
Our Satellite Station 2.0 was also added to the test setup. It uses a MacBook Air laptop running MacDoppler to control the antenna rotators and the Icom IC-9100 Transceiver which are part of our Satellite Station. A Windows 10 Surface Pro computer is included which runs N1MM+ and provides logging and other network functionality for our Satellite Station.
We also tested our GOTA station which uses the second Flex-6700 SDR and a FlexRadio Maestro to provide a more conventional “buttons and knobs” interface for our GOTA operators to use. This station will also have a laptop PC running N1MM+ for logging.
We also build and tested a Scoreboard PC. This computer will be located in the Public Information tent at Field Day and will be connected to a large display. It will show our real-time score, QSOs being logged as they are made and other useful information about our Field Day operations. This computer will also continuously play videos from our Video Collection and will provide access to IP video cameras which monitor the tower and equipment on the lower field.
Our networked N1MM+ testbed contained at least one station of each type (CW, SSB, Digital, Satellite, and GOTA) that will be part of our Field Day setup this year. The Station Masters for the additional CW and SSB stations came by to test their setups using the test bed.
The networking system which Dave and Pierce built is central to all of the technology described here. All of the gear is mounted in a single rack which will be located on the upper field during Field Day. The setup includes a Firewall/DHCP server, a commercial grade outdoor WiFi access point, a 4G LTE modem for Internet access, an Ethernet Switch, and a UPS power supply.
The upper and lower fields at our Field Day site are separated by several hundred feet. A thick line of trees between the two locations raised concerns about connecting the upper and lower sites using WiFi. Pierce came up with a great solution to this problem – we will be using MoCA Data Modems and RG6 Quad Shield 75 ohm Coax Cable to provide a 10 Mbps data link between the two sites. We tested the MoCA link using a much longer run of coax cable then we will need to use at Field Day and confirmed full 10 Mbps throughput.
Our networked N1MM+ setup will allow any station in our setup to send messages to everyone who is operating at Field Day. We can use this capability for important communications like “lunch is ready!” or “I need help from Pierce (our IT chairman) on the 40m SSB station”, or “The 6m band is wide open!”.
Our GOTA and Digital stations will be located together in the same tent and will provide our Field Day 2017 visitors to see and use 21st-century Amateur Radio technology to make contacts. We are expecting young people who participated in our High-Altitude Balloon project and from other local schools where we have done Amateur Radio activities to attend. In additional to being a learning opportunity for all of us in the Nashua Area Radio Society, we hope that the state of the art technology that we are using will generate interest among our visitors. If you are local to the Nashua, NH USA area, come pay us a visit during 2017 Field Day. We’d enjoy providing a tour for you and your family along with a chance to Get On The Air. Hope to see you at Field Day!
Every so often, I drive Fred’s truck into work and people ask me what that big antenna on the back of the truck is for. I explain to them that it is for Ham Radio. But the reply is usually, why ham radio – isn’t that outdated technology? We have cell phones and IM, etc…what do we need Ham Radio for? So I thought I would put down my thoughts as a relatively new Ham about why I enjoy spending so much of my time with Ham Radio.
The number one reason we still need Ham Radio along with all the other technology we now have is for public service. When there is a disaster and cell phones, television, etc are all not working, Ham Radio operators provide the critical communication.
Ham Radio operators help locally to keep hospitals and first responders in contact with each other to help those affected by the disaster.
Hams also use our ability to communicate around the world on HF bands to help family members around the world to get in touch with loved ones affected by a disaster.
Ham Radio operators have been on the scene helping in every disaster from the earthquakes in Nepal to the recent flooding in California.
Technology and the Maker Movement
I only became a Ham 5 years ago but many of my fellow Ham Radio operators got their license when they were in their early teens and used what they learned to launch their careers. Many have had very successful careers in STEM fields, all launched by their interest in Ham Radio at a young age. As technology advances, so does the technology used in our hobby. We even have a nobel laureate, Joe Taylor K1JT who is a ham. Joe has developed weak signal digital communication modes that let us communicate by bouncing signals off the moon!
As technology has advanced, so has the use of it in Ham Radio. Most Ham Radio operators have one or more computers in their shack. Many also have a software designed radio (SDR), where much of the radio functionality is implemented using Software, we use sound cards to run digital modes, which are a lot like texting over the radio, and we use the internet extensively as part of operating. We can also make contacts through satellites orbiting the earth and even the International Space Station.
Most hams love do-it-yourself technical projects, including building a station, home brewing an antenna, building a radio or other station component. In my day job, I am a program manager for software development projects, but its been a while since I have built anything. As a Ham I taught myself how to code in Python and about the Raspberry Pi and I built the DX Alarm Clock.
One of the coolest things about being an amateur radio operator is that you can communicate with other hams all over the world. Ham Radio is an international community where we all have something in common to talk about – our stations and why we enjoy ham radio. The QSL card above is from a memorable QSO with Mal, VK6LC, from Western Australia, who was the last contact that I needed for a Worked All Zones award. I must have talked to him for 1/2 hour about his town in Australia and his pet kangaroos!
I have learned much about geography from being on the air and trying to contact as many countries as I can. There are 339 DX Entities, which are countries or other geographical entities and I have learned where each one is in order to understand where propagation will allow me make a contact. I have learned a great deal about world geography. Through exchanging QSL cards often get to see photos from so many areas of the world.
Achievement – DXing and Contesting
DXing and Contesting provide a sense of achievement and exciting opportunity for competition. Many Hams work toward operating awards. You can get an operating award for contacting all 50 states, contacting 100 or more countries, contacting Islands, cities in Japan, countries in Asia, or anything else you can imagine. Each of these operating awards provides a sense of accomplishment and helps to build skills. Contesting builds skills through competition among Hams to see who can make the most contacts with the most places in 24 or 48 hours. Contesting also improves our operating skills and teaches us to copy callsigns and additional data accurately.
Teaching Licensing Classes – Passing it On
Recently I have joined a team of club members who teach license classes to others who want to get licensed or upgrade their existing Amateur Radio licenses. Teaching provides a way to improve my presentation skills and also helps me to really understand the material that we teach about Amateur Radio. It is always a thrill at the end of the class to see so many people earn their licenses or upgrades.
There are so many interesting aspects of Ham Radio which is what makes is such a great hobby. Getting your license can open up a world of possibilities. Upgrading to a new license class provides more opportunities to communicate over longer distances. Ham Radio clubs, including our local club, the Nashua Area Radio Club, provide many resources to help you get your first license, upgrade to a new license class, and learn about the many aspects of our hobby.
Anita and I like to take advantage of the mild fall weather to do antenna projects at our QTH. We have completed two such projects this fall – the installation of a Two-Element Phased Receive System and a rebuild of the control cable interconnect system at the base of our tower.
Our first project was the installation of a DXEngineering NCC-1 Receive Antenna System. This system uses two receive-only active vertical antennas to create a steerable receive antenna system. The combination can work on any band from 160m up to 10m. We set ours up for operation on the 80m and 160m bands.
The NCC-1 System can be used to peak or null a specific incoming signal. It can also be applied to a noise source to null it out. The direction that it peaks or nulls in is determined by changing the phase relationship between the two Active Antenna Elements via the NCC-1 Controller.
The first step in the project was to open the NCC-1 Control Unit to install a set of 80m and 160m bandpass filter boards. These filters prevent strong out-of-band signals (such as local AM radio stations) from overloading the NCC-1. The internal switches were also set to configure the NCC-1 to provide power from an external source to the receive antenna elements through the connecting coax cables.
The next step in the project was to select a suitable location for installing the Receive Antenna Elements. We choose a spot on a ridge which allowed the two Antenna Elements to be separated by 135 ft (for operation on 160m/80m) and which provided a favorable orientation toward both Europe and Japan. The antenna elements use active circuitry to provide uniform phase performance between each element’s 8 1/2 foot whip antenna and the rest of the system. The antenna elements should be separated by a 1/2 wavelength or more on the lowest band of operation from any towers or transmit antennas to enable the best possible noise rejection performance.
The two Antenna Elements were assembled and installed on 5 ft rods which were driven into the ground. To ensure a good ground for the elements and to improve their sensitivity, we opted to install 4 radials on each antenna (the black wires coming from the bottom of the unit in the picture above). The Antenna Elements are powered through 75-ohm flooded coax cables which connect them to the NCC-1 Control Unit in our shack. The coax cable connections in our setup are quite long – the longer coax of the pair being approximately 500 ft. The use of flooded coax cable allows the cables to be run underground or buried. Should the outer jacket become nicked, the flooding glue inside the cable will seal the damage and keep water out of the cable.
It is also important to isolate the connecting coax cables from picking up strong signals from nearby AM Radio stations, etc. To help with this, we installed Receive RF Chokes in each of the two coax cables which connect the Antenna Elements to the NCC-1. These chokes need to be installed on ground rods near the Antenna Elements for best performance.
We ran the coax cables underground inside cable conduits for a good portion of the run between the antenna elements and our shack. The conduits were installed in our yard when we built our tower a few years back so getting the coax cables to our shack was relatively easy.
The last step in the outdoor part of this project was to install a pair of 75-ohm coax surge protectors near the entry to our shack. An additional ground rod was driven for this purpose and was bonded to the rest of our station’s ground system. We routed both of the 75-ohm coax cables from the two Antenna Elements through surge protectors and into our shack. Alpha-Delta makes the copper ground rod bracket shown in the picture for mounting the surge protectors on the ground rod.
The installation work in our shack began with the construction of a larger shelf to hold all of our antenna control equipment and to make space for the NCC-1. The two incoming coax cables from the Antenna Elements were connected to the NCC-1.
Antenna switching and control in our station is handled by a microHAM System. Each radio has a dedicated microHAM Station Master Deluxe Antenna Controller which can be used to select separate transmit and receive antenna for the associated radio. The microHAM system allows our new Receive Antenna System to be shared between the 5 radios in our station.
The first step in integrating the Receive Antenna System was to connect the output of the NCC-1 to the Antenna Switching Matrix outside our shack. We added a low-noise pre-amp (shown in the upper left of the picture above) to increase the sensitivity of the Antenna System. The blue device in the picture is a 75-ohm to 50-ohm matching transformer which matches the NCC-1’s 75-ohm output to our 50-ohm radios. The other two pre-amps and transformers in the picture are part of our previously installed 8-Circle Receive Antenna System.
The Antenna Elements must be protected from overload and damage from strong nearly RF fields from our transmit antennas. In a single radio station, this can be handled via a simple sequencer unit associated with one’s radio. In a multi-op station such as ours, it is possible for a different radio than the one which is using the Receive Antenna System to be transmitting on a band which would damage the Receive Antenna System. To solve this problem, we built a multi-radio sequencer using one of the microHAM control boxes in our station. The 062 Relay Unit shown above has one relay associated with each of the five radios in our station. The power to the Receive Antenna System is routed through all 5 of these relays. When any radio transmits on a band that could damage the Antenna Elements, the associated relay is automatically opened 25 mS before the radio is allowed to key up which ensures that the system’s Antenna Elements are safely powered down and grounded.
With all of the coax and control connections complete, I was able to update the microHam system design information for our station and add the new receive antenna system to our setup. You can find more about the programming of our microHam system here.
So how well does the system work? To test it, we adjusted the NCC-1 to peak and then null a weak CW signal on 80m. This is done by first adjusting the Balance and Attenuator controls on the NCC-1 so that the incoming signal is heard at the same level by both Antenna Elements. Next, the B Phase switch is set to Rev to cause the system to operate in a signal null’ing configuration and the Phase control is adjusted to maximize the nulling effect on the target signal. One can go back and forth a few times between the Balance and Phase controls to get the best possible null. Finally, the incoming signal is peaked by setting the B Phase switch to Norm.
The picture above shows the display of the target CW signal on the radio using the NCC-1 Antenna System. If you look closely at the lower display in the figure (null’ed signal) you can still see the faint CW trace on the pan adapter. The difference between the peak and the null is about 3 S-units or 18 dB.
The NCC-1 can also be used to reduce (null out) background noise. The picture above shows the result of doing this for an incoming SSB signal on 75m. The system display at the top shows an S5 SSB signal in the presence of S4 – S5 noise (the lower display in the picture). Note how clean the noise floor for the received SSB signal becomes when the unit is set to null the noise source which comes from a different direction than the received SSB signal.
We are very pleased with the performance of our new Receive Antenna System. It should make a great tool for DX’ing on the low-bands. It is a good complement to our 8-circle steerable receive system which we use for contesting on 160m and 80m.
Our other antenna project was a maintenance one. We have quite a number of control leads going to our tower. When we built our station, we placed surge protectors at the base of our tower and routed all of our control leads through exposed connections on these units. Over time, we found that surge protection was not necessary and we also became concerned about the effects that sunlight and weather were having on the exposed connections. To clean all of this up, we installed two DXEngineering Interconnect Enclosures on our tower and moved all the control cable connections inside them.
We began with a pair of enclosures from DXEngineering and we mounted screw terminal barrier strips on the aluminum mounting plates in each enclosure. The aluminum plates are grounded via copper strap material to our tower.
The picture above shows one of the interconnection boxes. This one is used to connect our two SteppIR DB36 Yagi Antennas and some of the supporting equipment. The barrier strips form a convenient set of test points for troubleshooting any problems with our equipment on the tower. There are almost 100 control leads passing through the two enclosures and this arrangement keeps everything organized and protected from the weather.
With all of our antenna projects complete, we are looking forward to a fun winter of contesting and low-band DX’ing.