At those times when there was no commercially made amateur radio equipment or antennas available hams were making all by themselves and the only instrument for antenna measurements and at those times was a homemade SWR meter.
There were also heavy tube type sweep generator based instruments but they were rarely used by hams.
Tuning and checking antennas then with simple instruments, sometimes using the cut and try or iterative approach, has created, what I call the “feeling of antennas”, that helped to avoid design and construction errors.
Decades passed and finally the technology advancement made it possible for hams to use both NEC and Numeric Electromagnetic Code based antenna modeling software designed at the Lawrence Livermore National Laboratory and also handy and reliable antenna analyzers.
Based on long engineering and amateur radio professionals’ experience these devices are known for their reliability and great quality and I we are going to describe you now all their important features and methods to make the use of the antenna analyzers most efficient and even pleasant.
Get to know “AA-55 Zoom”
It is a well-known axiom that the way to success for serious DXer and contester is a good antenna system.
No matter whether you bought the antenna or made it yourself, the reliable and convenient tool is required to check, tune and adjust it for your particular environment.
Such an instrument could be the RigExpert “AA-55 Zoom” antenna analyzer which is one of the best for amateur and professional use on the high frequencies up to 55 MHz. It is reliable, easy to use and precise.
This article explains all the functions of the “AA-55 Zoom” antenna analyzer and navigates through its menu.
Additionally, we are going through a real-life application by guiding you through the step-by- step process of using the AA-55 Zoom to create a homemade antenna and make the ¼ wavelength 50 Ohm symmetry stub for 50.2 MHz of coax with polyethylene dielectric.
We will tell you how to save the measurement results into the internal memory of “AA-55 Zoom” or at the custom RigExpert AntAcope2 software.
You will know how to optimize antenna performance. And finally – how to use AA-55 Zoom as a stable sweep signal generator.
AA-55 ZOOM – the DXCC Challenge Champion
There are many different models of RigExpert’s Antenna Analyzers that enable antenna and cable measurements. These analyzers have all the necessary options, such as measuring SWR, return loss, input resistance (R), input reactance (X), inductance (L), capacitance (C), and phase angle at a single frequency and SWR even on five frequencies simultaneously.
The “Cable tools” on these analyzers measure the velocity factor, cable length, cable loss, and allow for making of ¼ and ½ wavelength cable stubs and phasing lines.
The ZOOM option allows for more detailed viewing of the charts displayed on a large color TFT-LCD display. Measurement results can be saved in the internal memory for further processing or, if needed, using the AntScope2 software.
The key advantages of these Antenna Analyzers are their compact design, lightweight construction, and low power consumption.
For example, the AA-55 ZOOM only requires 2 AA-size batteries, which is a marked improvement over similar devices from other manufacturers that sometimes need up to 10 AA-size alkaline or rechargeable batteries to perform the same functions.
This feature enables amateurs to make measurements at the top of a tower or mast, eliminating the influence of the feeder.
This analyzer is designed for measuring SWR (standing wave ratio), return loss, cable loss, and other parameters of cable and antenna systems in the range of 60 kHz to 55 MHz. Its built-in ZOOM capability makes graphical measurements particularly effective. The following
tasks can be easily accomplished with this analyzer:
- Quickly checking an antenna
- Tuning an antenna to resonance;
- Comparing antenna characteristics before and after specific events (e.g., rain, hurricanes);
- Creating matching and phasing coaxial stubs and measuring their parameters;
- Testing cables, measuring cable loss and characteristic impedance;
- Measuring the capacitance or inductance of reactive loads.
To address the question of why the “AA-55 Zoom” is one of the best antenna analyzers for High Frequency DXers and contesters, let’s examine the ARRL (American Radio Relay League) DXCC Challenge Award, along with the accompanying DXCC Challenge Plaque.
This award is given for working and confirming at least 1,000 DXCC band-entities on any Amateur bands, from 160 through 6 meters (excluding 60 meters) after November 15, 1945.
Plaques can be endorsed using medallions in increments of 500 entities, with the total determining the Challenge standing.
The picture above shows the new design of the DXCC Challenge plaque while the legacy, more expensive design, is shown below.
Deleted entities do not count towards this award.
QSOs on the 160, 80, 40, 30, 20, 17, 15, 12, 10, and 6-meter bands qualify for this award.
Confirmations on bands with fewer than 100 entities are acceptable for credit towards this award, and paper certificates are also available.
It takes at least 10 years after receiving the basic Challenge-1000 plaque to reach the highest 3000 level.
Undoubtedly, the DXCC Challenge is a lifelong project.
The “AA-55 Zoom” can perform antenna measurements on all necessary amateur bands for both the DXCC Challenge and general/contest HF activities, making it an ideal instrument for checking and tuning antennas, stubs, traps, and other components for these 10 amateur bands.
As we approach the solar activity cycle maximum it is becoming possible to make QSOs on 12 and 10 meters using the simple homemade antennas, sometimes even indoor antennas.
The “AA-55 Zoom” will be very useful for these endeavors.
Hence, we call the “AA-55 Zoom” a “DXCC Challenge Champion”. Of course, if someone is interested in VHF/UHF, the more sophisticated analyzer is needed but for the goals we’ve been describing earlier the “AA-55 Zoom” is an ideal analyzer.
General Functions of “AA-55 Zoom”.
Now it’s time to know more about the functions and possibilities of “AA-55 Zoom” which allows to make measurements across the whole high frequency radio spectrum up to 55 MHz it can be used not only by amateurs but also by engineers and technicians working with antennas for the fixed, mobile, maritime, aeronautical and other radio services.
AA-55 ZOOM can be used for the following tasks:
Antenna SWR and impedance measurements
Tuning antennas to resonance
Matching antennas to the feed lines
Dealing with coaxial lines (making ¼ and ½ wavelength stubs, delay lines for phased arrays, etc) and measuring their parameters including cable loss and characteristic impedance
Measuring capacitance or inductance of reactive loads
Another useful feature of AA-55 ZOOM is the ability to be used as a stable sweep signal generator with, for example, 1 kHz span.
The shape of such signal is shown on the HDSDR screenshot picture below.
AA-55 ZOOM is easy to use through the main menu that shows up after the device is switched ON.
Scrolling down the menu one can find the following functions:
- Smith chart→ 2
- Frequency and range entry → 3
- SWR chart→ 4
- R,X chart→ 5
- SWR meter→7
- All params→ 8
- Setup→ F+1 (hold F key and press 1 on numeric pad)
- Calibrate→ F+2 (hold F key and press 2 on numeric pad)
- RL chart → F+4 (hold F key and press 4 on numeric pad)
- MultiSWR → F+7 (hold F key and press 7 on numeric pad)
- Tools → F+8 (hold F key and press 8 on numeric pad)
Each function can be reached both from menu and directly through the numeric pad buttons
Following is the example which explains how to check the SWR of the 14 MHz Yagi antenna:
- Press 3 on numeric pad and get the “Frequency and range entry window. Enter the central frequency and the measurement frequency range in kHz using the arrow and numeric pad buttons.
- When the band and range are defined, sequential keystrokes of keys 4 and OK on numeric pad start the band scanning procedure resulting in requested SWR curve.
- To ZOOM the scanning range in the horizontal plane use the “UP” and “Down” arrow keys. To ZOOM the vertical scale use the functional “F” key in combination with the “UP” and “Down” arrow keys.
When the SWR of the measured antenna is out of the needed range it needs to be tuned to resonance. By checking the antenna parameters it is easy to find out if trimming or lengthening of the elements is necessary.
Press 0 or 8 on numeric pad and get the “Data screen” or “Display all parameters”window.
The “X” or reactance parameter (+X – inductive or -X – capacitive) will be a guidance for the needed actions.
AA-55 Zoom can be used to check and tune multiband antennas.
The MultiSWR mode allows checking up to 5 different frequencies.
To enter this mode hold F key and press 7 on numeric pad.
Start with selecting needed frequencies by pressing the (Up) and (Down) cursor keys on numeric pad.
Then press the 3 (Frequency) on numeric pad key to enter a new value then press the (OK) key to start the continuous measurement.
The SWR value on five chosen frequencies will be displayed.
To stop the measurement press (OK) or (Cancel) on numeric pad.
The SWR on five different HF bands of a 50 MHz dipole antenna with the random piece of 50 Ohm coax is shown on a picture.
The next chapter will show how the AA-55 Zoom antenna analyzer was used to evaluate a multielement Yagi antenna for 50 MHz.
Using RigExpert АА-55 ZOOM to evaluate a real 50 MHz antenna.
There are many different antenna designs by different authors available but the ones by Martin Steyer DK7ZB have proven to be reliable and effective so the 6-Element-50-Ohm-Yagi with 6,00m-Boom, the Medium Bandwidth, High-Gain-Design with perfect Pattern and 9,46 dBd (11,61 dBi) gain design was chosen.
So now we will procced making the homemade antenna is a four steps process.
Step 1. Choosing the design. There are many different European amateur antenna designers DK7ZB, G0KSC, YU7EF and others who design both short and long boom 50 MHz Yagi antennas of different configurations. When the preferred design has been chosen, we go to step 2.
Step 2. Use the antenna modeling software to check the chosen model and adopt it to the materials used in this homemade design. In this example the MMANA-GAL modeling software http://gal-ana.de/basicmm/en/ was used to do this job.
- the model based on original DK7ZB dimensions was made to check if patterns and input impedance correspond to the original antenna
- Initial dimensions for 12mm diameter elements are given by the author in table 1.
This is the starting point in building the own antenna.
- The next step is to use the antenna modeling software to check the chosen model and adopt it to the materials used in this own design.
- Telescopic elements were used instead of 12mm originals, so it was necessary to lengthen the elements using the MMANA “Edit→ Taper wire set” option. In this particular case the taper schedule is 16 > 12 > 8mm
- Calculation for the “tapered” design confirmed the correspondence of the following parameters R (Ohm), X (Ohm), SWR, Ga dBi and F/B dB between the original and “tapered” designs.
- Press “Plots → Detailed” buttons and the antenna patterns within the chosen bandwidth show up.
If calculated parameters satisfy the design objectives, mechanical design starts.
If resonant frequency is away from the calculated one, all element’s tips has to be iteratively changed equally at both ends. For instance, shortening all elements of the 6m Yagi antenna for 1cm or 0.33% will move SWR curve up approximately 160 KHz.
It is strongly recommended to carry out parameter recalculations after every iteration.
Table 2. The final calculated dimensions (Spacing from the rear and tapered element lengths).
Note: the length of the driven element includes the lengths of coaxial cable ends.
Step 3. Building and assembling the antenna. It is the “vanishing art” that requires both ingenuity and mechanical skill. It’s a great joy to see that the antenna made with your own hands works equally or better than the similar overpriced commercial ones.
Step 4. Measuring the antenna using the AA-55 ZOOM antenna analyzer.
The antenna was installed at the height of half wavelength (3 meters) for testing purposes. The results were encouraging with measured SWR of 1.13.
The results were encouraging and antenna was then erected to a height of 6 meters or 1 wavelength from the roof which acts as a “ground plane”, the SWR of 1.02 as measured by the AA-55 ZOOM analyzer and other parameters on the design frequency fully correspond both with
MMANA-GAL calculations and DK7ZB prototype characteristics.
Coaxial cable measurements using the RigExpert AA-55 ZOOM.
Coaxial cable measurements using the RigExpert AA-55 ZOOM.
Another important feature of the AA-55 Zoom is coaxial cable measurements. This option is mainly needed for those, who design and build their own antennas including the phased arrays.
The most common cases are making coax lines multiple to ¼ and ½ wavelength. The electrical length of the given line depends on cable’s velocity factor. For instance its 0.66 for polyethylene dielectric, 0.707 for teflon, and more then 0.8 for foam which is varied due to different manufacturing processes.
Now let’s make the ¼ wavelength 50 Ohm stub for 50.2 MHz of coax with polyethylene dielectric having 0.66 velocity factor which will be the basis for the symmetry stub for the 50 MHz antenna I’ve been talking earlier.
Firstly we need to make simple ¼ wavelength calculation:
- L¼=300/50.2/4*0.66 that equals 0.986 meters.
- Cut the peace of coax a bit longer then this value, connect it open-circuited at the far end to the AA-55 Zoom.
- Switch AA-55 Zoom to the “All parameters” by pressing the 8 button on numeric pad and OK button and get the resonant stub frequency.
- Cut small pieces from the far end of the coax until the X value is becoming +/- 0 (Zero) and/or the Phase is near 180 deg.
The simplified option to make ¼ and ½ stubs is through “Stub tuner” procedure described in Addendum 1 of the AA-55 Zoom manual.
To use this option go from Main Menu to Tools>Stub tuner and connect a cable with open or short far end and press OK to start.
The analyzer will immediately show resonant frequencies for both quarter wave and half wave stubs.
Remember: if adapters for different types of RF connectors are used, their length is added to the stub. This is most critical on high frequencies like 50 MHz.
Designing the quarter-wave coaxial braid stub to achieve symmetry in the 50 MHz Yagi antenna.
It is well known that the dipole is a symmetrical antenna. Connecting the unsymmetrical coaxial feedline directly to it will result in a distorted pattern and vertically polarized noise pickup
Therefore some measures must be taken to make the entire system (antenna plus feedline) symmetrical in order to optimize antenna performance.
There are various solutions employed by amateurs to achieve symmetry in HF and 50 MHz setups. These include creating a coaxial choke by winding up to 10 turns the coaxial cable near the Yagi feed point or using multiple Amidon ferrite core rings on the coax. Both of these solutions are effective but can lead to a significant imbalance in weight on the boom.
In light of this, I decided to explore the well-known VHF quarter-wave coaxial braid stub as an alternative approach.
Assuming the reflection coefficient of the polyethylene outer coax jacket is 0.66, the length of the stub can be calculated using the formula mentioned above: Lst = 300 / 50.2 /4 *0.66 = 0.986 m.
Making the stub.
- Cut the piece of coax at least 10cm longer then the calculated in accordance with the
formula:
L=300/50.2/4*K
where K is a reflection coefficient that equals:
- 0.66 for polyethylene,
- 0.707 for teflon
- 0.85 +/- for foam
Prepare the antenna end of the coaxial cable as follows:
- remove at least 4 cm of the UV-resistant black PVC outer coax jacket
- unweave 3+ cm of the coax braid and twist it for soldering into the brass terminal later
- remove the inner coax dielectric and prepare the inner conductor for soldering into the brass terminal
- ensure that both leads, including the terminals, are not longer than 3 cm. REMEMBER: the length of the leads is included in the calculated driven element length
- crimp and solder the terminals.
Preparing the extra braid as follows:
- cut the 1.5m piece of an old 50 or 75 Ohm coax with an outer diameter equal or larger than the main feedline (preferably;
- remove the UV-resistant black PVC outer coax jacket;
- carefully pull off the braid from the inner coax dielectric, trying not to deform it. The tube thus created will become the quarter-wave stub after it is pulled over the UV-resistant black PVC outer coax jacket.
Assuming the reflection coefficient of the polyethylene outer coax jacket is 0.66, the the length of the stub can be calculated using the formula mentioned above: Lst = 300 / 50.2 / 0.66 * 4 * 0.66 = 0.986 m.
Final adjustments and hints:
- wrap a thick teflon tape around the main coax near the antenna terminals since the quarter-wave coaxial braid stub is at the high voltage potential at that point. Good RF insulation is needed to avoid RF arcs. Secure it with the 0.2mm X 20mm teflon plumbing tape;
- wrap up the antenna end of the braid inwards to avoid the accidental contact between the tiny braid wires and the center conductor or the main coax braid;
- pull the stub braid over the UV-resistant black PVC outer coax jacket. Tightly wrap the 0.2mm X 20mm teflon plumming tape over the stub braid. Then tightly wrap the black electric PVC tape over the Teflon plumbing tape. If these wrappings are done correctly, the stub braid will be fixed and won’t move;
- pull 1 meter of the black UV-resistant black heat-shrinkable
tubing of the suitable diameter over the stub and heat it with a fan. The stub is now ready for tuning and assembling; - carefully cut the coax to have a length of 1.02-1.05 meters, leaving the extra length for RF connector connection;
- remove the UV-resistant black PVC outer coax jacket and join the main and stub braids together at 0.986m point for soldering to the connector’s body;
- cut the inner dielectric and inner conductor for soldering to the central pin of the RF connector.
RF Connectors and Their Use with the Quarter-Wave Coaxial Braid Stub:
According to DK7ZB-Macth for Yagi article, in order to suppress common-mode current, a simple solution is to ground the outer shield at a distance of λ/4 at the peak of the current. Therefore, in addition to the quarter-wave coaxial braid stub, connecting the body of the RF connector soldered at a distance of λ/4 should eliminate common-mode current completely.
There are several methods to attach the RF connector to the boom, and two of them are shown. Both methods require an easy-to-build mounting Aluminum plate.
Method 1. Solder the stub directly to the SO-239 or other female connector which is mounted on the mounting plate using stainless screws or rivets. It is important to ensure a careful sealing of both the SO-239 and PL-259 connectors to prevent water leakage.
Method 2. This method is considered the best due to its electrical and mechanical advantages. Solder the stub into the sealed CP-50-163 female connector. These high-quality silver plated RF connectors were manufactured across the former Soviet Union and are still available.
The connector is mounted to the mounting plate using a special nut and spring washer
Method 3. This method is similar to method 2 but utilizes a large sealed female N-connector instead. The design of the mounting plate depends on specifications provided by the connector manufacturer.
The assembles mounting plate with female stub connector is attached the boom using the stainless hose clamp of the appropriate size.
Saving the measurement results.
Finally, when antenna is assembled tuned and installed, it is advisable to save the results.
AA-55 Zoom allows this. To save, for instance, the SWR chart, press “6” and then “OK” on the numeric pad and type the name of your project.
- You can type figures from the numeric pad directly by pressing the number and the “Right Arrow” key successively, to return press “Left Arrow” key.
- To insert letters use “Up Arrow” and “Down Arrow” keys.
- Press “OK” when done.
You can recall the saved project by pressing 4 (SWR chart) on numeric pad or choose the corresponding menu item, then press 9 (load), select a saved data and press OK. The saved SWR chart will show up on display.
The data from AA-55 Zoom can also be saved using the custom RigExpert’s AntScope2 software.
For that connect AA-55 Zoom analyzer to the PC USB port. Make sure the analyzer is turned on.
Run AntScope2 under Windows. The program will automatically detect the analyzer type and display it in the pop-up window. You can pick up the needed one if several analyzers are connected to USB ports of your PC.
Enter start and stop frequencies in the Frequency window. You can click Center, Range button and enter center frequency and measurement range instead of limits.
Next click Single to perform the scan. Any further scans will be added to the Measurements list and stay on display to perform comparison easily. They can be saved or removed at any time later.
You can freely zoom the chart by pressing + and – keys or scrolling the mouse wheel.
To change vertical zoom just hold the Ctrl key and press + and – keys or scroll the mouse wheel. You can pan/zoom chart using the cursor moving keys.
Using RigExpert “AA-55 Zoom” as a stable sweep signal generator.
There is another undocumented neat feature of the AA-55 Zoom which can be used as a stable +10 dBm sweep signal generator to check receiver and low power transmitter stages.
This option is useful especially in the Field Days to check the working ability of receivers, LNAs, power amplifiers when specialized signal generators are not available.
The ability to use the antenna analyzer as a signal generator was firstly found to be useful several years ago by using the MFJ-259B SWR Analyzer to evaluate the country side.
Raspberry PI4 WEBSDR http://194.44.134.212:8901/ Despite of severe frequency drift MFJ-259B non-precision signal source was handy to check the performance of both receivers and antenna performance at the remote village site.
AA-55 Zoom performance as a signal source is far superior. Firstly, because its frequency is stable as a rock with absolutely no drift
Secondly, because the fixed +10 dBm signal level can be attenuated by using the calibrated step attenuators to approximate the receiver sensitivity.
To use the AA-55 Zoom as a signal generator we need to set the minimum sweep of 1 kHz.
To do this:
- press the “3” button (fq.range) on the numeric pad;
- select the Central frequency in kHz, say 50.314;
- select the sweep range in kHz, +/- 00 001;
- press “OK” button when done;
- go to Main menu → SWR chart;
- press “OK” button;
- press “OK” and “F” buttons together and AA-55 Zoom starts to transmit the stable +10dBm 1 kHz sweep signal continuously;
- to stop transmitting press “OK” or “Cancel” buttons.
We can see how the 1 kHz +10dBm sweep signal looks like on the air.
The resonant 50 MHz outdoor dipole was connected to the output of the AA-55 Zoom. SWR on the transmit frequency is 1.32 which is quite acceptable.
The receiving site which is 6 km away, is equipped with 6 element Yagi antenna, that has been described in Part 4 of this series, Elecraft K3 transceiver with SPF5189Z receive LNA.
AA-55 Zoom 1 kHz +10dBm clean sweep signal was easily detected on the FT8 waterfall of JTDX software.
Conclusion
The RigExpert’s AA-55 Zoom antenna analyzer is a reliable, multifunctional, convenient and economic device for serious DX-er and contester looking for create the optimized antenna system.
The very important advantages of this antenna analyzers is its compact design, small weight and low power consumption (only two AA -type alcaline batteries needed). This allows the amateur to make measurements at the top of the tower or mast, make coaxial stubs and phasing lines and even be used as a stable signal generator.
AA-55 Zoom allows making measurements across the whole high frequency radio spectrum from 0.06 to 55 MHz so it can be used not only by amateurs but also by engineers and technicians working with antennas for the fixed, mobile, maritime, aeronautical and other radio services.