This antenna is 4 elements yagi built for the frequency 157.000 Mhz, in the Philippines most of the users of this frequency bands are Government Organizations, LGU’s, Civic Groups, Fire volunteers and the like. Although most of the requested antenna designs fall on the Amateur Band (144.000 Mhz to 146.000 Mhz) frequency. I decided to published the details of this antenna although not frequently requested. The details of the build is similar to building the 4 Elements Yagi for Amateur Frequency. Elements measurements and spacing are of course adjusted to resonate properly on the 157.000 Mhz band.
Antenna Center frequency 157.000 Mhz
Lowest usable band 152.000 Mhz
Highest usable band 160.000 Mhz
Antenna Gain: 9.52dBi
F/B ratio: 9.87dB
Beamwidth: 60° Vertical / 24° Horizontal
Manufacturer: Accuracy Agility Instrument
Working frequency: 137.5 MHz – 2700 MHz
Frequency stepping: 1 kHz
Display: 2.4″ TFT 320×240 (QVGA)
Build in battery: 2000 mAh
Power consumption: <1.5 W
Charging current: 400 mA[embed]https://youtu.be/3PI5P_fXs5g[/embed]
Charging port: USB
Automatic shutdown: set in range 5-60 min
Measured parameters: resistance (R), reactance (X), standing weve ratio (VSWR), S11
Resolution: 4 significant digits
Frequency accuracy: < +/- 3ppm
Antenna connector: SMA-K
Impedance: 0.1 - 1000 Ohm
Standing wave: 1.000 - 65
S11 (dB): od 0dB do -60dB
PCB: 54mm x 85.5mm x 11mm (excluding connectors and switches)
Measurement frequency: 50KHz ~ 300MHz (50KHz – 900MHz, with extended firmware enabled)
RF output: – 13 DBM (max. – 9 dbm)
Frequency accuracy: <0.5 ppm
Measurement range: 70dB (50kHz-300MHz), 50dB (300M-600MHz), 40dB (600M-900MHz) with extended firmware enabled;
Port SWR: < 1.1
Display: 2.8 inch TFT (320 x 240)
USB interface: USB type-C communication mode: CDC (serial)
Power supply: USB 5V 120mA, built-in 400mAh battery, maximum charging current 0.8A
Number of Scanning Points: 101 (Fixed)
Display Tracking: 4, Mark: 4, Settings Save: 5
Measuring S parameters, VSWR, phase, delay, Smith circle chart and it supports touchtones files which can be exported for various radio design and simulation software.
The package also includes a set of calibration kit SOL for (short, open and load) calibration, the calibration kit is not included on N1201SA but it is pre-calibrated at the factory. Calibration for N1201SA takes time to complete but it is just a snap on nanoVNA. The included calibration kit for the nanoVNA can also be used to calibrate the N1201SA so that’s a bonus point for the nanoVNA.
For the actual testing I’ve used an antenna a 3 element yagi for 2m designed for the amateur band as device under test (DUT). I conducted the test sweeping the frequency from 140 to 150Mhz, taking note of SWR response, S11 and impedance measurement on the exact center frequency.
Side by side the read out against each other is on point, the discrepancy is just because of the decimal point resolution from the two antenna analyzers 2 decimal digit resolution on nanoVNA and 3 decimal digit for N1201SA.
Feature wise and overall usefulness nanoVNA is much complete against the N1201SA. Read out is on point on both devices.
Actual test and comparison of the antenna analyzers
Note: Crap, I called the NanoVNA as N1201SA ha ha!, but anyway don’t be confused 🙂 enjoy!
If you’re a fan of satellite monitoring (hunting for birds) as they call it, you probably want a bigger antenna with lots of elements for good contacts. Long antennas are good for satellite contacts with low elevation angle now the downside of those antennas are the lengths and they are cumbersome to work with specially if you’re home brewing and the materials available are not light enough. Each element will add up to the weight and will easily become unwieldy for hand operations holding the antenna on one hand and on the other the radio unless you are muscular then that would be easy. For casual contacts and mobility a compact antenna will get you where you want to go and still hunt for satellite with high elevation passes if you’re a fan of long distance and low elevation then this may not be for you.
1″ X 1″ Rectangular Aluminum tubing for the boom (cut to length)
3/8″ Aluminum tubing for antenna elements (cut to length)
2pc SO239 connector
#12 AWG Copper wire with insulation (12″for Gamma match)
5pcs Stainless steel nuts and bolts 30mm length 3mm diameter
6pcs Stainless steel nuts and bolts 30mm length 3mm diameter
1, Butterfly nut and 1 bolt 18mm length 3mm diameter
Aluminum plate 0.5mm thickness
Collapsible tube (shrinkable tubes)
4Nec2 data analysis
Antenna gain, beamwith and predicted pattern spit out by 4Nec2 antenna modelling software
Vector impedance analyzer frequency response data
This is the result of impedance analyzer testing for 2×3 elements cross yagi. Obtainable SWR is around 1.2:1 at the center frequency antenna reflection coefficient is at -23dB at VHF and -19dB at UHF. Pretty usable antenna, as you can see as well, the data spit out by 4Nec2 with regards to SWR on VHF side is close enough, I just directly cut the elements and assemble it with respect to the antenna measurement for the UHF side it was compensated with the use of gamma matching and correct length of the phasing harness. The capacitance of the gamma match when un-attached to the antenna assembly is around 10nf (0.01uf) and 20nf (0.02uf) respectively for UHF and the VHF side as measured using capacitance meter.
Actual testing of the antenna
This is actual testing of the antenna see the video around 2:30-2:38 I called out DV2JHA unfortunately we didn’t manage to confirm a successful QSO until the satellite signal started to fade out. Over all it’s a successful build.
This is the actual measurements of the cross yagi antenna I’ve used for satellite work, though the inline version of this yagi in which the VHF and UHF side are mounted inline but on the opposite side of the boom will also work for satellite communication. Inline version is here.
I have optimized this antenna for 145Mhz and 435Mhz painfully adjusting the exact length of the phasing harness to obtain lowest possible SWR/S11 curve on the antenna analyzer (measurements taken while actually holding the antenna). I just use 1/4λ length of the phasing harness, factoring the velocity factor of the coax for the actual length of the cable. VHF 145Mhz and UHF 435Mhz are complimentary harmonics frequency by design, actual length of the phasing harness are equal and using PL259 connector at both ends of the coaxial cable this connects to T-connector SO239. Patch cable is RG58 coax connector at the end is PL259 which will connect to the T-connector SO239, the opposite end of the RG58 coax is an SMA male connector which connect to my Vector Impedance Analyzer and also double as a patch cable for the radio which is about 65cm.
4Nec2 data shows beamwidth, expected pattern and predicted gain.
Antenna analyzer measurements and actual video footage
Measurements are taken while holding the antenna and the analyzer since we know that yagi interacts with the actual measurements if it’s too close to an object. This is to simulate the actual use case when using the antenna aiming it to the satellites.
Actual build, measure, cut and drill
These are some photos I took when building the antenna.
Initial testing of this antenna
I initially test this antenna using a phasing harness of 75ohms at 1/4λ x 3 for the actual length of the harness considering the velocity factor of the coax. The final use case testing, uses 1/4λ x velocity factor for the actual length of the phasing harness.
The fun part programming the radio before the hunt
Programming the radio with the satellite frequencies before the actual bird hunting. Since I work on a budget a Baofeng radio will suffice. I used a CIGNUS radio a rebranded radio that uses Baofeng internally ;). I encoded the frequency on the radio using CHIRP taking note of the CTCSS tone for each satellite and marking the channel name as name of the satellite and U for uplink D for downlink and A for arm to trigger some satellite timers before use.
Aside from programming the frequencies on your radio you also need a satellite tracker to predict the passes of the satellite you’re hunting. I uses Gpredict which works on both Windows and Linux machines, for Android you may use AmsatDroid Free version and tons of other satellites tracking apps on both Android and IOS.
The fun part really start when you begin the hunt and successfully received a very readable reception on your radio coupled with your homebrew antenna. If you’re not familiar with the actual satellite operations listen first until you feel comfortable pressing the PTT on your radio. Satellite resource hog are always frown upon so be courteous every time. Have fun!, and if you feel this will help someone feel free to share, thanks again!
Stacking two antennas – and effects of feed line to a properly tuned antenna
Stacking antenna is done to achieve additional gain ideally a 3dB additional gain is targeted but may not be achievable in real world due to losses introduced by additional cables, you need to make sure that the phasing harness is of the same length and construction. If your cable is not the same length then the signal from those won’t reach the antennas at the same time. The differences may be small but it is enough to create phasing problems, when your signal get to the antenna at two different times they don’t result in a much stronger signal in fact in extreme cases if the signal are exactly 180° degrees out of phase they would cancel each other and you’ll get nothing.
Basic Stacking Requirements
1. Two antenna’s with similar characteristics in terms of
Gain: 8.89 dBi
Center Frequency: 145Mhz
Matching: Gamma Match (Tuning stub)
Impedance: 50 ohms
Beamwidth: 84° vertical 58°horizontal
Front/Back ratio: 11dB
SWR: 1:1 @ center frequency
2. Phasing harness – must be of the same length Velocity Factor of coaxial cable accounted for, use two basically identical cables. If the cable types are different, or if the connectors are different, you can have the same phasing problems.
3. Tune the antenna to the lowest possible VSWR match, identically the same response is ideal but a slight mismatch or mis-alignment is acceptable but not much. Your antenna analyzer can help you check this before stacking.
Tuning two stacked Yagi Antenna
A properly matched single antenna, combined with a similar antenna to achieve stacking gain will perform much better than a single antenna, however care must be taken to achieve a good stacking practice. The result of a combined antenna when tested with a good antenna analyzer will result in very little deviation in its Center Frequency , VSWR curve, S11 curve, and Impedance even if different lengths of feed lines are used to test the antenna system.
Improving on the design of my 15 Element Yagi Antenna for 2.4Ghz Wifi band, now with a much cleaner pattern no side lobes and higher front to back ratio at 24.8 dB. This antenna is pretty much usable from to 2340 Mhz to 2460 Mhz with less than 2:1 SWR this is centered at 2420Mhz with 1:1 SWR and about -30dB S11 antenna reflection coefficient.
Im still using the same materials to build the antenna
1. 12mm x 8mm uPvc moulding (Boom)
2. #12AWg solid wire for elements
3. Measuring tool / precision cutter
4. 1 SMA female connector
5. Coaxial cable suitable for SMA connector
6. Sandpaper or file tool for removing rough edges of the elements
Building it is pretty straight forward just cut and paste (lol) bend the driven element and feed it with a 50 ohm coaxial cable rated for WiFi frequency, and check the SWR of the antenna.
Here’s the finished antenna side by side with my previous build.
SWR testing video of 15 Element 2.4Ghz yagi antenna
Actual receive analysis and link performance of the yagi antenna
Build your own 2m/70cm 3 Elements VHF by 5 Elements UHF Yagi antenna with excellent gain for both VHF and UHF operation. This antenna is designed for amateur band frequency for both VHF (2m) and UHF (70cm). The antenna has good reflection coefficient and VSWR ratio @ 1.2:1 at center frequency and 1.7:1 at band edge.
Antenna Specs from 4Nec2
VHF Gain: 7.25dBi @ 145Mhz
Beamwidth: 114° degrees
Front to Back Ratio: 14.1dB
Expected Pattern VHF
UHF Gain: 10dBi @ 440Mhz
Beamwidth: 60° degrees
Front to Back Ratio: 14.4dB
Expected Pattern UHF
Building Video 3 Elements by 5 Elements 2m/70cm Dual band Yagi including Tuning
Material list for 3×5 Elements Dualband Yagi
1. 1″ X 0.5″ Rectangular Aluminum tubing for the boom
2. 3/8″ Aluminum tubing for antenna elements
3. 1cm Outside diameter antenna tubing for elements holder
4. 2pc SO239 connector
5. Pop rivets / Rivet tool
6. #12 AWG Copper wire with insulation (12″for Gamma match)
7. Soldering iron
8. 10pcs Stainless steel nuts and bolts 20mm length 3mm diameter
9. 1pc, Butterfly nut and 1 bolt 18mm length 3mm diameter
10. Aluminum plate 0.5mm thickness
11. 4 X 2″ Aluminum tube for bracket
12. Collapsible tube (shrinkable tubes)
QYT KT8900 has good form factor that fits in the palm of your hand. It’s a dual band radio 2m/70cm that supports dual frequency monitoring has an acceptable receiver capability for the price, good audio performance (loud and crispy). Supports FM radio broadcast listening moreover it has a built in repeater function that will work in combination of another QYT KT8900 or pair it with QYT KT8900D by just enabling the function on the menu system and adding a repeater interface cable which can be built easily with spare LAN cable, RJ45 connectors and crimping tool.
If it’s not for the faulty heat sinking then probably this radio will work longer than expected rather than giving up the magic smoke of the RF finals too soon.
Preparing the RF finals removal and replacement
Disassembling the radio to replace the broken RF finals reveals that the screw holding the heat sink is loose just secured by a piece of copper strip inserted to the metal spacer to float the heat sink above the RF finals.
Replacing the RF finals is moderately easy provided you have the right tools a hot air rework station, solder flux, a pair of tweezers. The radio board backside reveals a slightly bigger heat sink which probably is intended to absorbed the heat more effectively by coupling it on the radio chassis, but without using a heat sink compound this also is not too effective to properly address the heat issue.
Time to replace the RF finals, apply the solder flux on the chip, heat the board just enough for the solder to melt at the bottom of the RF finals, remember that this is also attached to a copper heat sink below so heating it will take a little longer before you can see that a solder is flowing on the side of the finals. Once removed successfully replaced the finals with a new one. Good news for people living in the Philippines, the RF finals is now available by visiting your favorite electronics store in Gonzalo Puyat street in Sta. Cruz Manila price varies depending on the stores.
Preparing the fan modification on the radio chassis
Attaching the fan on the radio chassis requires a bit of drilling and tapping to hold the fan securely at the back of the chassis. For QYT KT8900 you can see at the back of the chassis that they somewhat prepared a fan mounting holes, but they didn’t pushed through with the plan. On later versions of this radio a fan is now attached to help in cooling the radio.
Drilling the fan mounting hole with a drill step bit.
Preparing the screws holder by tapping a thread.
Putting it back together.
Finally the finished modification applied to the radio.
The final look and successful cooling fan modification.
QTY KT8900 and QYT KT8900D chinese radios and variants have a built in repeater function that works out of the box without additional modification on the radio. You just need to enable the repeater function (cross band repeater VHF/UHF or UHF/VHF) via the menu system. Connect the two radios via the mic port using the cable shown here and enable the repeater function on the radio. The radios will work in the repeater mode cross band and will re-transmit your audio either on the VHF or UHF and vice versa.
The repeater interface will work on the variants of these radios in either combination of at least 2 KT8900 RX/TX,
2 KT8900D RX/TX or 1 KT8900 and 1 KT900D and of course Baofeng Tech radios. The configuration is done on individual radios by setting the REP-M (Repeater transponder function on both radio). Once a matched Carrier, CTCSS/DCS, TONE or DTMF is received in either of the radios it will re-transmit the audio on the other radio and vice versa.
Build the cable
Do it yourself using RJ45 modular connector and a piece of LAN UTP cable
Finished Cross Band X-Band repeater interface
Let’s see how it works
Testing video of working repeater system
1. Easy deployment for field work to extend portable radio range with acceptable results
2. Will fit easily in a go box
3. Inexpensive but it works
1. Recommended for light usage as QYT Radios tend to heat up easily
2. Use the upgraded version of QYT the KT8900D for more stability
3. Suitable only for Cross Band configuration
3. KT 8900 heats up like a barbecue grill if it didn’t burn your finals at least bring a hotdog to grill …