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RADIO WAVES: Frequency, Wavelength, and Physical Length

Amateur Radio Stations transmits voice, Morse codes, or packets, through radio waves.

Radio Communications

Radio Waves is a small portion of the Electromagnetic Waves spectrum.

Electromagnetic Spectrum [2]

Electromagnetic Waves or EM Waves are waves that are created as a result of vibrations between an electric field and a magnetic field. In other words, EM waves are composed of oscillating magnetic and electric fields. [1]

EM Waves are formed when electric field and magnetic field come into contact, thus its name.

EM Waves can be measure by its amplitude (height) and the wavelength (distance between the highest/lowest points of two consecutive waves)

Vertical Polarized Electromagnetic wave

EM waves travel with a constant velocity of 3.00 x 108 m/s in vacuum or space.

It is possible to calculate the wavelength of an EM wave or a Radio Wave given we know the frequency. Frequency is a number of cycles the waves in one second, cycles per second or Hertz (Hz).

Wavelength formula [3]


What is the wavelength of 145.0 MHz?

Using the formula above, v = 3.00 x 108 m/s and f = 145,000,000 Hz.

Wavelength is 3.00 x 108 m/s divided by 145,000,000 Hz.

Wavelength is 2.0689655172413793103448275862069 meters or 2 meters.

145 MHz has 2 meters of wavelength. This is why we call the 145 MHz Amateur VHF band as a 2 meter band.

The wavelength calculated above is based when the radio waves is travelling in a vacuum or space. This is the standard/reference measurement.

With enough energy, Radio Waves can travel in any medium – be it air, a solid material or vacuum. When the radio waves travels in a different medium, it travels relatively slower than of in vacuum. The term we use to indicate how much a material slows down the propagation of the radio wave is Velocity Factor, often written as VF.

Velocity factor Formula given the dielectric constant. [3]

Radio waves are intercepted by an antenna and converted it to electrical form into what we commonly called, Radio Frequency (RF) electrical signal. The RF signal is in electrical form and behaves as a wave similar to Radio Waves in space or atmosphere. RF signals can also be measured by its amplitude and wavelength similar to Radio Waves.

The velocity of the RF signal is much slower than that of Radio waves in vacuum. VF is less than 1.0. Because the wave is slower, the wavelength becomes shorter.

A radio wave of 2 meters in space is equivalent to 1.98 meters in a bare copper wire suspended in air, VF=0.99.

Wavelength_InCopperWireInAir= is 0.99 x 3.00 x 108 m/s = 1.98 meters.

Wavelength_Vacuum= is 1.0 x 3.00 x 108 m/s = 2 meters.

In antenna design, to tune in a certain wavelength or frequency, the actual physical conductor is trimmed according to its velocity factor, VF.

Where if we are to design a 145 MHz end-fed dipole antenna using a bare copper wire in air; the resulting actual physical length of the copper antenna is shorter by a factor of 0.99 which is the VF value. This shorter equivalent the wavelength in vacuum is what we called physical length.

Below is a visualization of the wavelength in vacuum and it’s equivalent physical length of the copper wire.

Wavelength vs Physical length

Another example for a common coaxial cable RG-58/U PE (Belden 9201), the VF is 0.66, the coax cable equivalent physical length for 145 MHz is 1.32 meters.

In Summary:

Radio waves is an electromagnetic waves composed of electric and magnetic waves.

Waves can me measured by amplitude and wavelength.

Waves travels in a vacuum at the speed of light 3.00 x 108 m/s. Given enough energy, it can travel through anything but relatively slower than in free space. The propagation delay manifested in a shorter equivalent physical measurement.

The physical length is dependent to its dielectric material. The physical length is used in antenna design, and transmission line calculations.

Reference Tables:

Properties of Coaxial Cable Dielectrics
(c = speed of light in a vacuum)
Dielectric TypeTime Delay
Solid Polyethylene (PE)1.540.659c
Foam Polyethylene (FE)1.270.800c
Foam Polystyrene (FS)1.120.910c
Air Space Polyethylene (ASP)1.15-1.210.840c-0.880c
Solid Teflon (ST)1.460.694c
Air Space Teflon (AST)1.13-1.200.850c – 0.900c
Cable VF and Loss [4]

Suggested Readings:


[1] https://economictimes.indiatimes.com/definition/electromagnetic-waves

[2] https://commons.wikimedia.org/wiki/File:Electromagnetic-Spectrum.svg

[3] Electronic Communication Systems, 2nd Edition, Blake

[4] https://febo.com/reference/cable_data.html

[5] Coaxial Cable Specifications

Half Wave Dipole Antenna

1/2 Wavelength Dipole Antenna Calculator

Speed of Light = 299,792,458 m/s = 300 = s

Frequency = Operating Frequency in MHz = fo

Velocity Factor (see text*) = constant for 50 ohms cable = 0.95

Results is in meter…..

Meter -> Inch = 1 meter = 39.3701 inches


λ =  s / fo

Vertical Monopole Element = (λ*0.5)*vf

Actual wavelength approximate rounding off to = 81.3990 or 81.4 inches

Substitute from the formula for 145.000 MHz

λ = s / fo (meters)
λ = 299,792,458 /145,000,000 = 2.0675 meters

λ =  = 2.0675 meters

Converting to inches by multiplying wavelength results to 39.3701

λ = 2.0675 x 39.3701 = 81.3990 inches


λ = 81.4 inches = L

vf = 0.95

Solving for one-half wavelength:

Radiating Element = (λ*0.5)*vf  = E

= (81.4 x 0.5) x 0.95 = 38.6645 inches                      

Divided by 2 elements for upper and lower elements

= 38.6645/2 = 19.3 inches

Gap between Radiating Element = λ / 200 = 0.407 inch = G

L = 81.4“

E = 19.3”

G = 0.407”

Note: important
Adjust To the lowest Standing Wave Ratio (SWR)

  • Add 5% to radiating element ->  = 20.265 inches
  • Check SWR, using SWR/Power Meter, tune to Operating Frequency (e.g. 145.00MHz)
  • Connect cable. Antenna -> SWR/Power Meter -> Radio
  • Set to SWR / Power to test
  • Hence: if SWR = 1-1.2, Power = Radio Power Output Set, if you set your radio power to 5 watts it should be 5 watts meter reading in the SWR/Power meter.
  • If the measurements of the cut elements are correct for the Operating Frequency, fixed and finalized antenna, else if the results reading is/are not meet the ideal reading, cut both elements.


  • Operating Frequency = 145.000 MHz
  • If the SWR is high and Power is low
  • Adjust radio frequency to either higher or lower frequency to read to the lowest SWR, take note the Frequency with the lowest SWR
  • Now, example the frequency with the lowest SWR is 146.000 MHz
  • New formula New Frequency divided by old Frequency multiple by original radiating element results.

                              = (146 / 145) x 20.265

= 20.125 inches

BY: Nicolas C. Medalla, DW7NCM

HRC – Tribu Amihan

Download: PDF File

Overview on Automatic Packet Reporting System – APRS


Bob Bruninga, a senior research engineer at the United States Naval Academy, implemented the earliest ancestor of APRS on an Apple II computer in 1982. This early version was used to map high frequency Navy position reports. The first use of APRS was in 1984, when Bruninga developed a more advanced version on a Commodore VIC-20 for reporting the position and status of horses in a 100-mile (160 km) endurance run.[3] [2]

During the next two years, Bruninga continued to develop the system, which he now called the Connectionless Emergency Traffic System (CETS). Following a series of Federal Emergency Management Agency (FEMA) exercises using CETS, the system was ported to the IBM Personal Computer. During the early 1990s, CETS (then known as the Automatic Position Reporting System) continued to evolve into its current form. [2]

As GPS technology became more widely available, “Position” was replaced with “Packet” to better describe the more generic capabilities of the system and to emphasize its uses beyond mere position reporting. [2]


The Automatic Packet Reporting System was designed to support rapid, reliable exchange of information for local, tactical real-time information, events or nets. The concept, which dates back to the mid 1980’s, is that all relevant information is transmitted immediately to everyone in the net and every station captures that information for consistent and standard display to all participants. Information was refreshed redundantly but at a decaying rate so that old information was updated less frequently than new info. Since the primary objective is consistent exchange of information between everyone, APRS established standard formats not only for the transmission of POSITION, STATUS, MESSAGES, and QUERIES, it also establishes guidelines for display so that users of different systems will still see the same consistent information displayed in a consistent manner (independent of the particular display or maping system in use). See the original APRS.TXT. The two images below should give you an idea of the kinds of information available to the mobile operator on his APRS radio. On the left is the Kenwood D710 radio showing the station list, and on the right is the attached GPS with map display showing the location of other APRS stations. [1]

APRS is not a vehicle tracking system. It is a two-way tactical real-time digital communications system between all assets in a network sharing information about everything going on in the local area. On ham radio, this means if something is happening now, or there is information that could be valuable to you, then it should show up on your APRS radio in your mobile. See typical oversights and hear my talk on the 3 Oct 08 Rain Report See also some original APRSdos views and concepts overlooked in some new programs. [1]

APRS Internet System (APRS-IS): Like most other Ham radio systems, APRS has been fully integrated with the internet beginning with the efforts of Steve Dimse and the Sproul Brothers in 1997. Currently there are many web pages for live viewing of APRS activity such as APRS.FI, or FINDU.COM. [1]

APRS also supports global callsign-to-callsign messaging, bulletins, objects email and Voice because every local area is seen by the Internet System (APRS-IS)! APRS should enable local and global amateur radio operator contact at anytime-anywhere and using any device. See the APRS Messaging/Contact Initiative. [1]

APRS SPEC! . APRS continuously evolves. There have been several initiatives that have drastically improved APRS network performance and useability for users. The original APRS spec was updated in 2004 with the APRS1.1 addendum and since then with the APRS1.2 updates. [1]

Sample APRS VHF frequencies [2]

There is NO known assigned frequency for APRS by the NTC in the Philippines.

APRS in the Philippines

AFAIK, there is not too much APRS activity in the Philippines. Most of the stations are DMR and Echolink beacons through APRS-IS.

Here is an image capture from APRS.FI website.[3]

APRS stations in the Visayas Regions [3]
APRS stations in Luzon Regions [3]
APRS stations in Mindanao Regions [3]

RF-to-RF and RF-to-IS: There is an active APRS SatGate and Igate in District 6 by DU6DKL. Experimental APRS Stations are currently made, as of writing, in Cebu.

DV7HAA spearheaded the APRS System development in Cebu as his amateur project for 2020. Together with the DX7CBU-Ham Radio Cebu, Inc. members, slowly the APRS system in Cebu is making progress, with the specific motivation to aid Disaster Resiliency in Communications.

The project has a facebook group APRS-PH. As of the moment the APRS frequency is at 145.825MHz, same as to ARISS.


[1]Automatic Packet Reporting System, Bob Bruninga, WB4APR , http://www.aprs.org/

[2]Automatic Packet Reporting System, From Wikipedia, the free encyclopedia, https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System .

[3] www.APRS.fi

Radio Etiquette

Get familiar with the etiquette of two-way radio communication. Learn walkie talkie lingo. To make radio communication go more smoothly, over the years certain rules, or etiquette, have been established. Below we have outlined the basic etiquette a radio user should understand. It will help improve your overall experience when using your radio!

Basic Radio Etiquette Rules

  • The international radio language is English, except in cases where you are licensed to speak in some other language.
  • When using a two-way radio you cannot speak and listen at the same time, as you can with a phone.
  • Don’t interrupt if you hear other people talking.  Wait until their conversation is finished unless it is an emergency. If it is an emergency, inform the other parties that you have an urgent emergency message (see “Emergency Calls” below).
  • Do not respond if you aren’t sure the call is for you.  Wait until you hear your call sign to respond.
  • Never transmit sensitive, confidential, financial or military information.  Unless you are certain your conversations are secured with the proper level of encryption for the level of sensitivity, assume your conversations can be heard by others.
  • Perform radio checks to ensure your radio is in good working condition.
    • Ensure the battery is charged and the power is on.
    • Keep the volume high enough to be able to hear calls.
    • Regularly make radio checks to make sure everything is working and that you are still in range to receive signals.
  • Memorize call signs and locations of persons and radio stations you communicate with regularly.
    • In radio communication, you are not called by your name. Everybody has their own unique call sign. 
  • Think before you speak.
    • Decide what you are going say and to whom it is meant for.
    • Make your conversations as concise, precise, and clear as possible.
    • Avoid long and complicated sentences. If your message is long, divide it into separate shorter messages.
    • Do not use abbreviations unless they are well understood by your group.

4 Golden Rules of Radio Communication

1. Clarity: Your voice should be clear. Speak a little slower than normal. Speak in a normal tone, do not shout.
2.  Simplicity

Keep your message simple enough for intended listeners to understand.
3. Brevity: Be precise and to the point.
4. Security: Do not transmit confidential information unless you know the proper security technology is in place. Remember, frequencies are shared, you do not have exclusive use of the frequency.

Speaking the Language

General Terms Meaning
Radio/Signal Check What is my signal strength?  Can you hear me?
Go Ahead  You are ready to receive the transmission.
Stand-by You acknowledge the other party, but I am unable to respond immediately.
Roger or QSL Message received and understood.
Negative Same as “No”.
Affirmative   Same as “Yes”.  Avoid “yup” or “nope” as they are difficult to hear.
Say Again Re-transmit your message
Over Your message is finished.
Out All conversation is finished, the channel is clear for others to use.
Break, Break, Break You are interrupting in the middle of communication because you have an emergency.
Read you loud & clear   Response to “Radio Check”. Means your transmission signal is good. Also, use “Read you 5-by-5“.
Come in You are asking the other party to acknowledge they hear you.
Copy You understand what was said.
Wilco Means “I will comply”.
Repeat Used before you repeat something. ex: “I require 9-5, repeat 9-5, gallons of diesel fuel. Over”
Marine & Aviation  
Sécurité Safety call. Alert to some safety warning. Repeat 3 times. Has priority over routine calls.
Pan-Pan Urgent call. Help needed.  Repeat 3 times. Has priority over safety calls.
MayDay Distress call. Repeat 3 times, and again following each transmission. Has priority over all other calls.
  See our section  Using VHF Marine Radios  for more information.
Q-Codes (ICAO) See our  Q-Code Aviation Guide  for a list of all Q-codes used in aviation.
CB & Ham Radio  
10-Codes See 10-Code Communication Guide  for a list of all 10-codes.
Q-Codes See Q-Code Communication Guide  for a list of all Q-codes.

These terms can be combined such as “Roger Wilco” means “I understand and will comply”, or “Over and Out” means “I’ve finished talking and I’m signing off”.

Making a Call

Follow these easy steps to make a call.

  1. First, listen to ensure the channel is clear for you.
  2. Press the PTT (Push-To-Talk) button.
  3. After 2 seconds:
    • Say “recipient’s call sign”  twice
    • Followed by   “THIS IS”   and “your call sign“.
  4. Once the person replies, convey your message.

Here’s a typical radio conversation:

            You: “4 Foxtrot 7 Mike Hotel Zulu(4F7MHZ), 4 Foxtrot 7 Mike Hotel Zulu(4F7MHZ), This is Delta Whiskey 7 November Charlie Mike(DW7NCM), Come in, Over”   (4F7MHZ is their call sign, DW7NCM is your call sign)
  Recipient ” Delta Whiskey 7 November Charlie Mike, This is 4 Foxtrot 7 Mike Hotel Zulu, Go Ahead, Over”
  You: Say your message and then say:  “Over”
  Recipient: “Roger Wilco, Over”
  You: “This is Delta Whiskey 7 November Charlie Mike, Over and Out”

Did you notice how at the beginning and end of the transmission you pronounce your call sign?  Because there can sometimes be many people listening on the frequency, pronouncing your call sign, and the call sign of the party you are calling, lets everyone know who the transmission is for. Communicating this way might feel a little odd at first, but you’ll soon get used to it. With practice, it will start to feel natural.

Emergency Calls

   If you have an emergency message and need to interrupt others’ conversations:

  • Wait and listen until you hear “Over”.
  • Press PTT and say “BREAK, BREAK, BREAK, your call sign, I have an emergency message for (recipient’s call sign), Do you copy, Over”.

Memorize the Phonetic Alphabet

  • It is almost certain you will have to use it in your conversations.
  • You will often be required to spell a certain word or name in your radio conversations to make sure you are understood.
  • Using the phonetic equivalents instead of letters will make sure letters such as ‘F’ are not misinterpreted as ‘S’, ‘T’ as ‘C, or ‘M’ as ‘N’.

Following is a list showing the international phonetics used for the alphabet:

             – ALPHA H – HOTEL O – OSCAR V – VICTOR

Download links:

Jpeg file: Radio Etiquette

PDF file: Radio Etiquette

Reference: https://quality2wayradios.com/