JI1FGX/DU9 Amateur Radio Diary, Mindanao, Philippines, IOTA OC-130.
English. Japanese.



Yesterday's access.
Introduction. [Lily Diary.】
A diary of life in Mindanao.

   
25/07/13  IARU HF Contest
25/07/10 Software updates
25/07/08 DXV500ZS linear amplifier repair
25/07/07 CQ Machine Program
25/06/21 LoTW system upgrade
25/06/18 RG8 for 3.5MHz arrived
25/06/15  Time setting Ver0.5
25/06/14 Drone Habsan ZINO arrives
25/06/12 Philippine Independence Day
25/06/11 Algeria 7X2RF QSL card.
25/06/10 Translation API Program
25/06/09 DXCC150 award certificate arrived
25/06/08 AutoCWType_Ver1.4.1
25/06/07 Introducing the Shack
25/06/06 A portrait drawn by ChatGPT.
25/05/26 Windows full-width/half-width switching.
25/05/17 OK2ZAW BCD to 16 converter.
25/05/16 For 3.5MHz Zepp antenna.
Stepping motors
25/05/15 3.5MHz stepping motor design.
25/05/14 3.5MHz tuning coil installed.
25/05/11 3.5MHz antenna installation completed.
25/05/03 JTDX Autonomous Driving Program Ver0.4.3.
25/04/26 Drone Habsan ZINO.
25/04/25 Time setting Ver0.3.
25/04/24 AutoCWType_Ver1.3.
25/04/23 Preparing for FTDX3000 LCD repair.
25/04/22 Installation plan for 3.5MHz Zepp antenna.
25/04/21 AutoCWType_Ver1.1.
25/04/20 10,14MHz antenna installation completed.
25/04/19 JTDX Autonomous Driving Program Ver0.4.1.
25/04/19 14MHz antenna pole installed.
25/04/18 ThinkPad X390 repair completed.
25/04/17 Search is now possible.
25/04/15 Preparing the 10MHz dipole.
25/04/12 Hexbeam Part8.
25/04/06 My ThinkPad X390 is broken.
25/04/05. Time setting program.
25/03/31 JTDX Autonomous Driving Program.
25/03/30 Automatic log sending from CWType to Hamlog.
25/03/21 Hexbeam Part 7.
25/03/20 FreeDV Part 3 First QSO.
25/03/18 FreeDV Part 2 QSO in the shack.
25/03/16 Hexbeam Part 6.
25/03/15 Install FreeDV Part1.
25/03/09 Hexbeam Part5.
25/03/07 Hexbeam Part 4.
25/03/05 28MHz antenna modification
25/03/01 FTDX3000 is broken!
25/02/28 Pileup at 50MHz FT8.
25/02/28 DXV500ZS linear amplifier repair.
25/02/27 Tower pipe rebuilding plan.
25/02/26 Direction to Japan from Ozamiz.
25/02/26 28MHz is not available.
25/02/23 DXV500ZS linear amplifier repair.
25/02/22 Hexbeam Part 3
25/02/21 Hexbeam Part 2
25/02/18 28MHz antenna construction.
25/02/17 18,24MHz antenna height construction.
25/02/16 Z26NS Cosovo.
25/02/14 21MHz FT8
25/02/12 7,21MHz antenna repair.
25/02/08 Operating CW at 21MHz.
25/02/05 DXV500ZS linear amplifier failure.
25/01/19 Input Director.
25/01/14 Temporary license renewal.
28MHz antenna modification (2025/03/05) 
28MHz antenna installed on February 18th

7.21MHz dipole as a fan-out dipole antenna
A 28MHz element was installed, and the 28MHz element was inverted V to allow for element spacing.
However, I found out that if you place it next to the parent element (7, 21MHz) and leave a gap of about 10cm, there will be no effect.
It is attached to the 7.21MHz parent element with a 10cm corrugated insulator.
The length of the element was measured with a NanoVNA to be 2.30m, with the SWR settling at 28.110MHz.
Element length (one side): (300/28.110)/4*0.95=2.53I calculated it to be 100m, but it actually turned out to be much shorter.
I ordered the corrugated insulators from Japan on Amazon.
 
The 28MHz element was changed from an inverted V to a dipole.
The height above ground is now about 18m.

We received many calls from Europe, a place where no one had answered our calls before.
Maybe the increased ground clearance helped.
Measurement with NanoVNA
We had ChatGPT evaluate it.

Location and evaluation of each frequency

Marker 1: 28.080 MHz (for FT8)

  • Impedance: 54 + j1.31 Ω (almost pure resistance, very close to the ideal 50 Ω)
  • position: Smith chartNear the centerNearly ideal location
  • evaluation:
    →Excellent: The antenna radiates the energy from the transmitter with almost no waste.
    →Optimal tuning for FT8 operationis.

Marker 2: 28.590 MHz (SSB upper limit)

  • Impedance: 69.3 + j5.47 Ω (slightly high resistance and small inductance)
  • position: Smith chartupper right(Leaning slightly towards inductive)
  • evaluation:
    →Good: Although it is slightly off center, it is within the practical range and can be used without any problems.
    →SSB operation is also practical without an additional tuner.

Marker 3: 28.020 MHz (for CW)

  • Impedance：55 + j0.138 Ω (almost pure resistance component)
  • position: Smith chartVery close to the centerposition
  • evaluation:
    →Excellent: Fits almost perfectly in the center, with almost no energy loss.
    →Ideal for CW operation.

✅3. Overall Evaluation and Conclusion

  • Distribution of the entire Smith chartLooking at28.02MHz to 28.59MHzThere is no significant deviation within the range.
    All frequencies are ideally located near the center.
  • Impedance biasAlthough there is a small inductive (upward) shift,
    No additional matching requiredAnd it can be sent efficiently.
 

Evaluation of 28MHz dipole antenna

1. VSWR (Voltage Standing Wave Ratio) Evaluation

  • Marker 1 (28.080 MHz / for FT8)
    • VSWR: 1.084→ Very good (almost 1:1 with little waste)
  • Marker 2 (28.590 MHz / SSB upper limit)
    • VSWR: 1.403→ Good (below 1.5, so within practical range)
  • Marker 3 (for 28.020 MHz / CW)
    • VSWR: 1.100→ Very good

conclusion:

  • 28MHz bandFT8, CW, SSBAll in all, VSWR is good.
    There is no need to worry about the rig's (radio's) protection circuit being activated.
  • Even with SSB upper limit of 28.59MHz1.5 or lessTherefore, it can be operated without a tuner.

2. Impedance assessment

  • Marker 1 (28.080 MHz):54 + j1.31 Ω(Excellent, close to the ideal value of 50 Ω)
  • Marker 2 (28.590 MHz):69.3 + j5.47 Ω(A little high, but still within acceptable limits)
  • Marker 3 (28.020 MHz):55 + j138 mΩ(Almost ideal value)

conclusion:

  • Close to 50 Ω at all frequencies,Since the transmission efficiency is high, stable transmission is possible without loss.

3. Return Loss Evaluation

  • Marker 1 (28.080 MHz):-27.913 dB(Very small reflection = efficiency over 99%)
  • Marker 2 (28.590 MHz):-15.512 dB(Reflection approx. 3.5% = within practical range)
  • Marker 3 (28.020 MHz):-26.470 dB(Efficiency over 99%)

conclusion:

  • All points are sufficientLow reflectioncan be confirmed,
    The transmission output is transmitted to the antenna with almost no waste.
  • **28.59 MHz (SSB upper limit)** is also within the practical range, so you can use it without worry.

.
 21MHz dipole antenna
Measured with NanoVNA
No readjustment was required even after adding the 28MHz antenna.
However, the lowest SWR point is 20.930MHz, so the coil needs to be adjusted.
If I'm feeling well tomorrow I'll try adjusting the coil.


3.Smith Chart Evaluation
  • trajectoryis relatively close to the center of the circle (50Ω), but allcapacitiveI'm stopping by.
  • Target FrequencyTo bring it to the center, useIncrease the coil slightly to increase inductivityIt is necessary.
 
21MHz dipole

1.SWR (VSWR) Rating

  • Best point (Marker 1)At 20.930 MHzSWR=1.195
    • The matching is quite good, but it is a little slower than the target frequency.Lower limit of the bandI'm stopping by.
  • Marker 2At 21.290 MHzSWR=1.700
    • Although it is close to the center of the band, the SWR is slightly elevated.
  • Marker 3At 21.020 MHzSWR=1.258
    • Although it is near the lower end of the band, the SWR is good.

→The lowest SWR point is at 20.930 MHz and needs to be shifted to 21.000 MHz or higher..

2.Impedance assessment

  • Marker 1 (20.930 MHz):45.2 - j6.94 Ω
    • The resistance is almost 50 Ω,Slightly capacitive (−j6.94)is.
  • Marker 2 (21.290 MHz):34 - j15.2 Ω
    • Low resistance and high capacitanceThis is a trend.
  • Marker 3 (21.020 MHz):46.6 - j10.6 Ω
    • Although the resistance is close to 50 Ω,capacitiveis.

→Possibility of improving matching by making the impedance slightly inductiveThere is.
 7MHz dipole


7MHz Dipole Antenna Rating:

①Checking the resonance frequency

  • Marker 1 (7.04 MHz),Marker 2 (7.02 MHz),Marker 3 (7.18 MHz)Measured at.
  • resonance pointis approximately7.02MHzIt is located nearby, but the SWR is1.566does not match perfectly.

②Impedance Characteristics

  • The ideal impedance is50 ohmsHowever, the measurement results are as follows:Slightly higherIt is available in.
    • Marker 1:74.3 + j13 Ω(Some inductive components)
    • Marker 2:77.2 + j9.8 Ω(It's a little off from the ideal, but it's close.)
    • Marker 3:62 + j35.9 Ω(Capacitive reactance is large)
  • Coil inductanceis slightly larger, suggesting that the resonance is leaning towards the lower frequency side.

③SWR (voltage standing wave ratio)

  • Marker 1:1.566(7.04 MHz)
  • Marker 2:1.586(7.02 MHz)
  • Marker 3:1.951(7.18MHz)
  • Around 1.5teethToleranceBut a little moreImpedance MatchingThere is room for improvement.
 
 Smith Chart Evaluation
  • On the Smith chart, all the measurement pointsAbove the resistive componentLocated inInductive componentis strongly expressed.
  • Resonance point7.05MHzTo align to a nearby area:
    • Reduce the number of coil turns by 1 to 2 turns
    • Extend the element slightly(Fine-tune in 1cm increments)
bonus
When I work outside during the day, my feet get burned and hurt when I wear sandals.
Only the rubber part of the sandals is not sunburned, but the toes and the top of the foot are well sunburned.
March 01, 2024   March 07, 2025