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Antennas, Featured, General, Newsletter, Space

A Portable Satellite Station Part 2 – 2.0 Station Goals and Antenna System

February 22, 2017 Fred Kemmerer

.We came upon the M2 Antenna Systems booth while walking around the exhibit halls at Dayton last year. M2 had one of their LEO Pack satellite antenna systems on display there. This got us thinking about building a new, more capable version of our portable satellite station. The LEO Pack is a relatively lightweight circularly polarized antenna system for working satellites using the 2 m and 70 cm bands. It turns out that AMSAT members can purchase the LEO Pack at a discount. Starting with the LEO Pack in mind, I began to lay out some goals for a new, 2.0 Portable Satellite Station:

Capable of working all active Amateur LEO Satellites including those using linear transponders and digital modes
Be portable and manageable enough to be setup in an hour or less
Simple enough to operate so that HAMs who are new to satellites can make all types of satellite contacts with a relatively short learning curve
Utilize computer controlled antenna tracking to aim the antennas
Utilize computer control to manage radio VFOs to compensate for Doppler shift
Be easy to transport and store

Satellite Antena System Components

Satellite Antenna System - Computer Controlled Satellite Station via MacDoppler Software — Computer Controlled Satellite Station via MacDoppler Software

We decided to take a computer controlled approach for both antenna aiming and Transceiver VFO management. This was done to meet our goal of making the station simple to operate for new satellite operators. After some research on the available options, we choose MacDoppler from Dog Park Software Ltd. for this purpose. MacDoppler runs under Mac OS/X and works well on our MacBook Air laptop computer which is very portable.

This program also has broad support for many different rotator and transceiver platforms and is very easy to understand and use. Finally, the program features high-quality graphics which should make the station more interesting to folks with limited or no experience operating through Amateur Satellites.

With the satellite tracking software chosen, we made selections for the other major components in the 2.0 Portable Satellite Station as follows:

Glen Martin RT-424 4.5′ Roof Tower to mount all of the antenna system components for portable operation
M2 Antenna Systems LEO Pack Antennas and Hardware
Yaesu G-5500 AZ/EL Rotator
Green Heron RT-21 AZ/EL Rotator Controller
Advanced Receiver Research Low-Noise Preamplifiers for 2m and 70 cm
S3 Sequencers from M2 Antenna Systems for preamplifier control
LMR-400UF Coax for feed-lines
MacDoppler Satellite Tracking software from Dog Park Software
Icom IC-9100 Transceiver
WaveNode WN-2 Wattmeter

I will explain these choices in more detail as our article series proceeds.

Portable Satellite Antenna Tower

Satellite Antenna System - Glen Martin 4.5' Roof Tower — Glen Martin 4.5′ Roof Tower

Our solution to making the antenna system portable is built around a Glen Martin 4.5′ Roof Tower. This short tower is a high-quality piece made of extruded aluminum parts. The tower is very sturdy when assembled and is light in weight. We added a pair of extended “feet” to the tower which is fabricated from 36″ x 2″ x 1 /4″ strap steel. This gives the tower a firm base to sit on and allows us to use sandbags to weight it down (more on this later).

Our chosen Yaesu G-500 AZ/EL Rotator is a relatively inexpensive Azimuth/Elevation rotator which is suitable for light-weight satellite antennas such as those in the LEO Pack. This rotator can be installed as a single unit on the top of a tower or separated using a mast. We choose the latter approach as it is mechanically more robust and helps to keep the center of gravity for our portable antenna system low for improved stability.

Satellite Antenna System - Yaesu G-5500 Elevation Rotator — Yaesu G-5500 Elevation Rotator

Separating the Yaesu AZ/EL rotator requires a short mast and a thrust bearing to be used. The mast was made from a 1-3/4″ O.D. piece of EMT tubing from our local hardware store. The thrust bearing is a Yaesu GS-065 unit. Both of these pieces fit nicely in the Glen Martin Tower. The thrust bearing provides support for the LEO Pack and G-500 elevation rotator and greatly reduces stress on the azimuth rotator. We also added a Yaesu GA-300 Shock Absorber Mount to the azimuth rotator. This part provides shock isolation for and reduces strain on the azimuth rotator during the frequent starts and stops which occur during satellite tracking.

Control Cables and Coax

Satellite Antenna System - LMR-400UF Feed-lines and Antenna Connection Jumpers — LMR-400UF Feed-lines and Antenna Connection Jumpers

We decided to use LMR-400 UltraFlex coax throughout our antenna system. LMR-400UF coax provides a good balance between size, flexibility, and loss for our application. To keep feed-line losses reasonable, we choose to limit the total length of the coax from the transceiver output to the antenna feed point to 50′. This results in a loss of about 1.3 dB on the 70 cm band.

The result is that our planned IC-9100 Transceiver which has a maximum output of 75W on 70 cm will deliver a little more than 50W maximum at the feed point of the 70 cm yagi. This should be more than enough power to meet our station goals. Allowing a total of 15′ for antenna rotator loops and transceiver connections, we settled upon 35′ for the length of our coax feed-lines between the tower and the station control point.

Satellite Antenna System - Portable Tower Cable Connections and Base Straps — Portable Tower Cable Connections and Base Straps

We added some custom fabricated plates to the tower to act as a bulkhead for feed line and control cable connections and to mount our low-noise preamplifiers. The control connections for the rotators and preamps were made using 6-pin weatherpack connectors and rotator control cable from DX Engineering. The control cables are also 35′ long to match the length of our coax feed lines. This length should allow the tower and the control point to be separated by a reasonable distance in portable setups.

Satellite Antenna Preamp System

Satellite Antenna System - Low-Noise Preamplifiers from Advanced Receiver Research — Low-Noise Preamplifiers from Advanced Receiver Research

We added tower-mounted Low-Noise Preamplifiers from Advanced Receiver Research to improve the receive sensitivity and noise figure for our satellite antenna system. Two preamps are used – one each for the 2 m and one for 70 cm antennas. We decided to include the preamp control lead in our control cable to allow for control of the preamp switching via sequencers. This was done to provide an extra measure of protection for the preamps.

Miscellaneous Components

We added a compass and pair of bubble levels to the tower assembly. These additions make it easier to orient and level it during setup. This picture above also shows the Yaesu shock absorbing mount for the azimuth rotator.

Finally, we added a set of weight bags to securely anchor the tower when it is set up in a portable environment. These bags are filled with crushed stone and fasten to the legs of the Glen Martin tower with velcro straps.

Satellite Antenna Assembly and Test

With the tower and rotator elements complete, we turned our attention to the assembly of the M2 LEO Pack. The LEO pack consists of two circularly polarized yagis for the 2m and 70 cm bands.

The 2m Yagi is an M2 Systems 2MCP8A which has 8 elements (4 horizontal and 4 vertical) and provides 9.2 dBic of gain. The 70 cm Yagi is an M2 Systems 436CP16 with 16 elements (8 horizontal and 8 vertical) and provides 13.3 dBic of gain.

Both Yagi’s are meant to be rear mounted on an 8.5′ aluminum cross boom which is included in the LEO Pack. The picture above shows all of the parts for the two antennas before assembly.

Thanks to some help from Jamey, KC1ENX and Mike, KU1V, it took us about a 1/2 day to assemble and test the antennas and both produced the specified SWR performance when assembled and test in clear surroundings.

Satellite Antenna System - Assembled LEO Pack on Portable Tower — Assembled LEO Pack on Portable Tower

The picture above shows the assembled LEO pack on the portable tower. We attached a short 28″ piece of mast material to the cross boom as a counterweight to provide better overall balance. Also, we can minimize the strain on the elevation rotator this way. The antennas and the two outer sections of the mast can be easily removed to transport the antenna system.

Satellite Antenna Polarization

The LEO Pack yagis achieve circular polarization via a matching network. The matching network drives the vertical and horizontal sections of the antennas with a 90-degree phase shift. The phase shift (and a final 50-ohm match) is achieved using 1/4 wave delay lines made of coax cables. We configured our antennas for right-hand circular polarization.

The choice between right and left-hand circular polarization is not a critical one in our LEO satellite application. This is because most LEO satellites are not circularly polarized. The advantage of circular polarization in our application is the minimization of spin fading effects.

Satellite Antenna Rotator Controls

Green Heron RT-21 AZ/EL Rotator Controller

The final step in the construction of our antenna system was to add the rotator controller and test the computer aiming system. We have had very good results using Green Heron Engineering rotator controllers in our home station so we selected their RT-21 AZ/EL rotator controller for this application. The RT-21 AZ/EL rotator controller is really two rotator controllers in a single box. The rotator control parameters can be independently adjusted. The available settings include such as minimum and maximum rotator speed, ramp, offset, over travel, and others.

Satellite Antenna System - Rotator Test Using MacDoppler — Rotator Test Using MacDoppler

The RT-21 AZ/EL Rotator Controller connects to our computer via a pair of USB cables. We run Green Heron’s GH Tracker software on our MacBook Air laptop to manage the computer side of the rotator controller and to provide a UDP protocol interface to the MacDoppler tracking software. The picture above shows the test setup used to verify the computer controlled antenna pointing system.

Configuration and System Test

Mixed OS/X and Windows Software Environment

One challenge associated with selecting a Mac OS/X platform for computer control is what to do about the inevitable need to run Windows software as part of the system. In addition to the GH Tracker software, the WaveNode WN-2 Wattmeter and digital modem software for satellite/ISS APRS and other applications require a Windows run-time environment.

To solve this problem, we use a virtual machine environment implemented using VMware Fusion and Windows 10 64-bit on our MacBook Air Laptop along with Mac OS/X. Using the Unity feature of VMware Fusion allows us to run windows apps such as GH Tracker as if they were native Mac OS/X apps. The picture above shows an example of this.

Rotator Controller and Software Configuration

With the antennas removed from the cross boom, we tested the operation of the computer controlled tracking system. The Yaesu G-5500 AZ/EL Rotator have some limits as to its pointing accuracy and backlash performance. Setting up the combination of the RT-21 AZ/EL rotator controller, GH Tracker, and MacDoppler required experimentation to achieve smooth overall operation.

We finally settled on a strategy of “lead the duck” tracking. The idea here is to set up the rotators so that they over-travel by a degree or two. Also, we couple this with a relatively wide 2-3 degree tracking resolution. This maximizes the overall accuracy of the pointing system. Also, we minimize the tendency towards the constant start-stop operation of the rotators during satellite tracking. Our current configuration for all of the elements involved in the tracking system is shown above.

Next Steps

We can now move onto the next step in our project – the construction of a computer controlled transceiver system. We will cover this element in the next part in this series. Other articles in the series include:

You may also be interested in the satellite station at our home QTH. You can read more about that here.

Fred, AB1OC

Activities, Antennas, Featured, General, Newsletter, Space, Station Equipment

A Portable Satellite Station Part 1 – A Simple Station for AO-85

February 20, 2017 Fred Kemmerer

Our club has quite a few members who are interested in space communications. We decided to build a simple portable satellite station last year for our 2016 Field Day operation to learn about satellite communications and to create something new for folks to work with during 2016 Field Day.

Our 1.0 Portable Satellite Station was a relatively simple setup built around an HT, an Elk 2m/70cm satellite antenna, and some gear to improve the receive performance and transmit power output of the HT. All of the gear was mounted on a board to make it easy to transport and it is powered by a LIPO rechargeable battery. The gear in our 1.0 station is made up of the following:

A Kenwood TH-72A Full Duplex 2m/70cm HT
A Heil headset with a boom microphone to make using the HT easier
A pair of 2m and 70cm Low-Noise RF switched preamps from Advanced Receiver Research
A Mirage BD-35 2m/70cm amplifier (this amp produces about 25 – 35W out when driven by the HT)
A Diamond SX-400 Watt Meter and an MFJ Dummy Load for testing and monitoring
A RigRunner DC distribution block with voltage and current monitoring and a 4S4P A123 LIPO Battery Pack
An Elk 2M/440L5 Dual-Band Log-periodic Antenna

Improved Portable Satellite Station Antenna Support — Improved Satellite Antenna Support

Our first contacts with our 1.0 station were made using the Elk Antenna hand-held. Later, we created a “plumber’s special” setup with a camera tripod to make pointing the antenna easier. Note the angle meter from a local hardware store which measures the elevation angle of the antenna.

AO-85 (Fox-1A) U/V Mode FM Cube Satellite

This setup worked great for making FM contacts through AO-85 (Fox-1A), a U/V mode FM EasySat. We used the 1.0 station on multiple occasions including Field Day 2016 and several of our club members used it to make their first satellite contacts. The Full-Duplex HT allowed us to hear our own signal coming back from the satellite which was an important tool to help with aiming the antenna properly. The ELK Dual-Band antenna is also a good choice because it uses a single feed point and a single polarization for both the 2m and 70cm bands.

Portable Satellite Station Team Operating Approach — 1.0 Station Team Operating Approach

We used the team operating approach outlined above. This worked especially well for new folks who had not made a satellite contact before as it enabled each of the three team members involved in making the contact to focus on a specific part of the contact. We used orange plastic tent stakes to make AOS, Time of Closest Approach, and EOS to mark headings for each satellite pass. Small flashlights used at the stakes made them glow for night-time passes.

We certainly had a lot of fun with our 1.0 Satellite Station and I expect that we’ll continue to use it. As we gained a little experience with AO-85, we decided that we wanted to build a more capable Portable Satellite Station which we could use to operate with linear transponder satellites and which included a tracking system and better antennas. I know from experience with our home satellite station that DX contacts are possible using higher altitude linear transponder satellites like FO-29.

We would also like to be able to use APRS and other digital modes through satellites as well as receive SSTV pictures from space.

These goals have become the basis for building our Portable Satellite Station 2.0. More on the new station in Part 2 of this series. Other articles in the series include:

You may also be interested in the satellite station at our home QTH. You can read more about that here.

73,

Fred (AB1OC)

Antennas, Featured, General, Homebrewing, Newsletter

Moxons in the Attic (Part 3)

December 18, 2016 Ed Deichler

Well, another month has gone by on my two-band attic Moxon antenna project. If you recall from last month, I was left with a perplexing matching problem with the 15M antenna while the 17M one works fine. I had to figure out how to come up with a way to chase down what was causing the problem. I guess this just proves that there is no such thing as a simple, straightforward antenna project.

So, with a can of suds as brain fuel, I sat down to methodically list what to do and rule out possible causes. As a starting point, I connected a 1:1 balun to the 15M and a no-balun, connection to the 17M beam. This time, I decided to do all measurements from the shack so that losses from the shack coax would be taken into account. SWR checks on each antenna were consistent with earlier measurements, namely an SWR <2:1 on 17 and 15 meters using the 17M Moxon while rising to 4.4:1 – 6.0:1 across the band when switched to the 15M beam.

Ameritron RCS-4 Antenna Switch — Ameritron RCS-4 Remote Antenna Switch

The next step was to rule out any leakage inside the RCS-4 remote switch. I decided to try this step because I was suspicious of the current design of the RCS-4. I had used one for about 20 years in good ol’ NH weather without a problem. The new unit, however, felt light. The relays in the remote unit were too quiet for my liking, and an AC power pack replaced the internal power supply from the old unit. I moved the 17M connection to the last position on the switch so that it was on a separate relay from the 15M antenna and measured. No change. I then disconnected the 15M antenna from the switch, leaving it open, and measured. Again, no change. I connected a jumper across the 15M connector to short the antenna elements together and measured both bands on the 17M antenna. As observed earlier, the 17M beam works fine on both bands, indicating the 17M Moxon does not see the 15M one.

OK, so now what? It was clear the 15M beam was being influenced by the 17M one. I decided to check the phasing between the two beams wherein the center and shield sides of the coax were connected to the respective sides of each beam. The casual observer will recall a demonstration by Dale, AF1T of what happens when stacked beams are fed in-phase or out-of-phase. However, since I’m operating on two different bands, why do I want to do this? The answer: electromagnetic behavior is complicated; just ask J. C. Maxwell.

To do this, I connected a center insulator that has an integrated PL-259 connector to the 15M beam. I had used this connector in the past and it was already marked for the shield and center conductor sides. I checked the balun connections that I had removed from the 15M beam, found the shield side on the first try, and marked it. I installed the balun on the 17M beam which now represented the opposite of the previous antenna connections. My rationale for doing this was that a direct, non-balun connection showed a good match on 17M.

Measurements from the shack on the 15M beam now showed an average SWR of ~3.3:1 across the band, better than before but not great. Measurements on the 17M beam when tuned to 15M, however, were clearly worse with an average SWR of 4:1. Measurements on 17M were also degraded with the SWR above 2:1. Clearly, the antennas were not happy with this arrangement. I decided to disconnect the 15M beam from the RCS-4 switch based on the noticeable change observed on the 17M beam, and remembering that the 17M beam did work before on 15 meters. When I tuned the 17M beam across 15 meters, the SWR jumped to 8:1. I was now suspicious of what effect the balun was having on antenna behavior. Why should the performance be significantly worse with a balun when compared to the simple split feed of the center insulator?

I pulled the insulator and the balun off the antennas to check the connections again. I was surprised to find that the center insulator showed an open-circuit for the center conductor side. Even more surprising was the fact that the balun showed the same thing, meaning NO CONNECTION to one side of each antenna. I looked at the lugs for each device where the center conductor was and noticed that they were loose. Furthermore, the PVC plastic around each lug had been melted from my efforts to remove old wire and solder from the lugs. Murphy, you struck again!

In desperation, I took a hacksaw to the top of the center insulator connector to check the center wire inside. I found it to be intact so I then removed the eye-bolt and replaced the lug with a new one. The connection to the PL-259 center conductor now worked. I could re-use the “topless” insulator since it would be in the attic and not exposed to rain. I scrutinized the same lug on the balun and figured the melted PVC plastic, as in the case of the center insulator, must have formed an insulation between the lug and the eye-bolt to the balun center conductor. I scrounged around the junk box and found another PL-259-equipped center insulator I could use.

I trudged back up to the attic and reinstalled the center insulators on each beam and scrambled back to the shack to measure things. This time, SWR for the 17M Moxon was flat across the 17M band vice over 2:1 before. Performance on 15 meters for the 17M beam was now down to 2.2:1 which was certainly better than 8:1. The 15M Moxon, however, still showed slightly greater than 3:1, indicating some interaction was still going on, or still a mismatch. Now what?

As I pondered what could be happening, I remembered something about RF chokes around the coax jacket to prevent common-mode interference. I recalled my education about rejecting common-mode interference from a presentation by Chuck, W1HIS, aka, Doctor “Ferrite”. Chuck is the de facto High Priest of Common-Mode Exorcism to prevent RF from entering the shack via feed lines and anything else that comes into the shack. (By day, Chuck is an MIT professor emeritus. The Dr. Ferrite title has been bestowed upon him for his prolific use of ferrite chokes throughout his house. He hates RF noise.)

Admonishing my transgression, I grabbed a couple of ferrite cores from my junk box and scurried up to the attic. I wrapped as many turns as possible of the RG-8X coax line from the shack until there was no more slack on the attic floor. I also wrapped a few turns of the coax from the 15M Moxon around a core. Sadly, there was no change when I checked each beam from the shack. Well, at least I was relieved that I did not appear to have RF sneaking back into the shack and playing tricks on me.

OK, what next? As I pondered what to do it occurred to me that the antennas were fed in-phase wherein the shield side of each antenna was the same. The logical next step was to feed them out-of-phase. I removed the center insulator for the 17M Moxon and reversed the leads so that the coax center conductor was now under the shield side of the 15M Moxon. A sweep of the 17 and 15-meter bands while feeding the 17M Moxon showed an SWR under 2:1 for each band. Switching to the 15M Moxon and sweeping the band still showed the perplexing behavior of SWR greater than 3:1. I did a sweep of several MHz above and below the 15-meter band to determine if the 15M Moxon might be resonant elsewhere but it was not.

Well, at this point it looks like I can operate two bands with the 17M Moxon so it is not a total loss. I am back to where I started in terms of performance of the antennas except the flaky balun is gone for 15 meters. I checked how the EZNEC pattern looks when operating at 21 MHz with the 17M antenna and it does not look much different from 18 MHz. On the bright side, I can always use the tuner in the K3 to make the 15M Moxon play right for the band, giving me some flexibility if I can hear a station better on one antenna than the other. Like I said, the electromagnetic behavior is a complicated phenomenon.

Ed, K2TE

Nashua Area Radio Society

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