Header Image - Ham Radio Cebu, Inc.


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

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