As Field Day 2017 approaches, Dave, N1RF; Mike, K1WVO, Don, KC1CRK and I got together to assemble and test two of the Yagi’s that we are planning to use for Field Day this year.
New 6m Yagi
I’ve contributed a new 6m Yagi for Field Day this year – an M2 Antenna Systems 6M5XHP. This antenna has 5 elements on an 18 ft boom. This antenna is fairly lightweight for its size and performs great – perfect for Field Day.
Tuning the 6M Yagi
We installed it on two tower sections (20 ft) of so that we could properly adjust its tuning.
Final 6M Yagi Test on Tower
We found that we could adjust the antenna’s driven element and hairpin match for the best SWR performance with the tower tilted over and the antenna on its side. We got nearly the same SWR performance this way as we saw with the tower and antenna tilted up 20 ft off the ground.
Final 6M Yagi SWR
After several adjustments with the tower up and down, we finally came up with an SWR curve that looked good.
Installing the WRTC Tribander on the Test Tower
The club purchased a WRTC tower and Triband Yagi a little while back and this Field Day will be the first time that we’ve had a chance to use this combination. We found that the phasing system and feed point for the WRTC Tribander had been misplaced so we made a replacement for these parts and we wanted to test the WRTC Tribander’s performance with the new parts.
WRTC Tribander on the Tower
After a quick check of the WRTC Tribander’s SWR performance with the tower tilted over, we stood the tower up and measured its SWR performance on 10m, 15m, and 20m.
WRTC Tribander SWR on 20m
The antenna’s SWR performance with its new phasing lines and feed point looked great on all three bands!
We ended the day by disassembling the two Yagi’s and taking down the tower. With this project done, we’ll be working on a falling derrick system for our third tower for Field Day.
A big Thank You! to Dave, Mike, and Don for helping with this project. It was a lot of fun!
My main antenna is a full wave 40m delta loop which also matches well across 20m. While the match is good the pattern is not ideal for DX. EZNEC predicts numerous nodes and nulls and a high take off angle. I have been looking for a better 20m DX antenna while I wait to get a beam up.
At the Club’s (N1FD) recent VE session a Radio Wavz 20m Dipole was described as having good DX performance when mounted as a vertical. At $39 including a 1:1 choke balun, I decided to try it.
I shot a rope over a branch at 65′, attached and sealed the coax, and hauled the dipole up. The coax needs to come away from the vertical at roughly 45° to minimize the coupling to the lower antenna wire.
Figure 1 The Balun is hung at a right angle
A paracord is attached to Balun in the opposite direction from the coax to oppose the pull of the coax and is needed to keep the antenna wire vertical as shown in Figure 1.
I used a water bottle to weigh down the lower wire which allows the antenna to move with the tree to avoid damage during high winds. Figure-2 shows the Delta Loop and to its right the Vertical Dipole. It is difficult to see the Vertical, the green water bottle can be seen just below the center of the figure.
Figure-2 Delta Loop and Vertical Dipole (right)
After the initial installation, the first step was to measure the VSWR. This can be done using the radio’s VSWR meter or an antenna analyzer. If the antenna had to be brought down to adjust its length I wanted to do it before I secured the cables and finished the installation.
The antenna analyzer measured a <1.8:1 VSWR from 13.4 MHz to 14.35 MHz. A good match over 1 MHz of bandwidth is very good. The resonate point with a 1.2:1 VSWR was at 13.9 MHz. The antenna was long which is normal “out of the package” without any tuning. With a little shortening, the match was <1.5:1 across the entire 20m band and less than 1.2:1 at band center. This is better than EZNEC predicted. The VSWR measurement includes 100′ of LMR-400 which will improve the apparent match a little. I suspect most of the improvement is from the interaction with the angled coax. It is also possible the balun isn’t a perfect 1:1 as described by Radio Wavz. The antenna has a very good match across the full band and does not need a tuner.
The vertical dipole’s noise floor was S3 (-106 dBm 3 kHz BW) which is good. I had assumed it would be much higher because it was a vertical. It is only an S unit higher than the Delta loop which measured S2 (-111 dBm 3 kHz BW).
EZNEC shows a low 10-45 degree take off angle and no NVIS capability with the top of the vertical dipole at 65′ as seen in Figure 3.
Figure 3 EZNEC Analysis at 65′ height over poor ground
Based on EZNEC it should be better for DX than for local communications. In practice, this is the case.
For the first test, I tuned into the afternoon 20m Net. Most of the stations are within 400 miles of my QTH. The Delta Loop had a 10 dB to 20 dB SNR (signal to noise ratio) advantage at this range. An Agilent spectrum analyzer was used for these measurements. Tuning the band I found Vancouver BC, WA, OR, CA, and Ireland. Only Ireland could be heard with the Loop. I have never heard any 20m stations in the Pacific NW while using the loop.
The next test was to use the RBN (Reverse Beacon Network) to measure the antennas DX performance. For those unfamiliar with RBN, there are roughly 140 stations worldwide that are connected to CW Skimmers. Using CW you send a series of CQs and your call sign. If you are detected you are added to a Spot Collector which is accessible on a website or via telnet.
I transmitted on 14,037.5 when using the Loop and 14,038.5 when using the Vertical Dipole. By using two frequencies I could tell which antenna the Spot was reporting. Also, most of the RBN stations will not respond to a second call too soon after reporting the first intercept. With a quick QSY, I could transmit on the opposite antenna without waiting. Figure 3 is a sample of the RBN Spots.
Figure 3 RBN Spots
I plotted the distance to the Spots versus the reported SNR. This can be seen in Figure-4. The number of RBN nodes is limited and some of the nodes listed on the RBN website might not be available, especially during this weekends SSB contest. Also, the band conditions will impact the range and number of stations reached.
Figure-4 SNR versus Range
Note that where two data points (Red and Blue) are at the same range and therefore directly above each other both antennas were spotted by the same station. If the Spot could hear the Loop it always heard the Vertical Dipole but there were many times the Spot heard the Vertical Dipole and not the Loop.
KM3T is only 3.1 miles from my QTH. As seen in the RBN screen capture and on the plot the SNR with the Vertical is 55 dB and only 45 dB with the loop. The plot also shows an SNR=9 dB data point for the Vertical near the Y axis and no matching Blue data point for the Loop. This station was 70 miles away in MA. Both of these data points rely on ground waves and the Vertical Dipole has an advantage when compared with the Loop.
Overall beyond 1000 miles the Vertical Dipole clearly performs better than the Delta Loop and will definitely add DX to a log.
In summary when mounted high the vertical dipole retains the low take off angle of a 1/4 wave ground mounted vertical. It does not need ground radials and ground losses are reduced. It can be placed above obstructions such as a barn or house. It only needs one high support and it does not require a tuner.
It isn’t a hex beam or a yagi due to the impact of ground losses on the gain, but at $40, no tower required, it is a great antenna. It is very stealthy as well.
.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
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
I will explain these choices in more detail as our article series proceeds.
Portable Satellite Antenna 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.
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
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.
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
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
Levels and Compass for Tower Setup
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.
Weight Bags to Anchor Portable Tower
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
LEO Pack Satellite Antenna Parts
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.
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
2m Circularly Polarized Yagi Feed Point
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.
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:
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