FM radio transmitters and smartphones with FM radio receivers maybe a low-cost, high-quality audio system for public protests

1. Introduction

Civil rights movements (“grassroots”) focusing, for example, on ecological justice,  racial justice, or economic justice have usually little budget available to organize public protests. Visual messages, eg posters and banners, and audible messages are key elements at public protests. While I am presenting tutorials to create visuals elsewhere [1], I want to propose here using FM radio transmitters and personal smartphones (with build-in FM receivers) as a low-cost, high-quality audio system to broadcast public speeches to large crowds.

2. The Basic Idea

The basic idea is that a public speaker uses a microphone which is connected to a low-energy FM radio transmitter operating in the standard FM (VHF Band II) wave spectrum between 87.5 to 108 MHz  [2]. Individual protesters use their smartphones with built-in FM radio receivers in combination with personal headphones (or portable loudspeakers) to listen.

Note: The used FM radio frequency, effective radiated power (ERP), permission to broadcast, and (optional) permission to broadcast the planned contents may have to agreed in advance with national competent authorities.

4. Example: How to get permissions from National Competent Authorities in Sweden

In the following I describe my experiences with the National Competent Authorities in Sweden (Post- och telestyrelsen (PTS, [4]), Myndigheten för press, radio och tv (MPRT, [5]), which finally granted permission to operate an FM radio station named “Wilmar Igl Biosphere Protection – FM Radio” at a public square (Forumtorget) in Uppsala.  First, permission to broadcast  media content has to be received from MPRT, second, permission to technically operate an FM radio transmitter has to be obtained from PTS:

4.1 Tutorial

  1. Apply for permission to broadcast content from MPRT agency (“Anmälan om tillfälligt sändningstillstand”, takes about 1 week)
    1. Online Form (Note: Add specific location and dates of operation of  FM transmitter!)
    2. Application Template [PDF]
  2. Apply for permission to broadcast FM radio signals from PTS agency (“Ansökan om att använda radiosändare för ljudrundradio eller TV”)
    1. Online Form (Note: Add specific location and dates of operation of  FM transmitter!)
    2. Application Template [PDF]
  3. Apply for permission for public protest from police (“Allmän sammankomst”) [OPTIONAL]
    1. Application Info
    2. Application Templates (see example)
  4. Buy FM transmitter based on the permitted specifications (esp. signal strength) [RETEKESS] [AMAZON]

4.2 My personal document history of applications and permissions

  1.   Application for Permission to operate a FM radio transmitter (Link: [8], not [9]!]:
    1. Application 1: 20200315_PTS_Ansökan_Dnr20-2187.pdf
    2. Application 2 (updated with a specific location): 20200519_PTS_Ansökan_Dnr20-5898.pdf
  2. Assessment by MPRT on requirement for permission by MPRT :
  3. Application for Permission to broadcast planned contents via an FM radio transmitter (Link: [11])
  4. Permission by MPRT granting a temporary broadcasting  permit:
    1. 20200625_MPRT_Beslut_Dnr20-02638.pdf
    2. 20200625_MPRT_Register_Dnr20-02638.pdf
  5. Permission by PTS granting permission to operate an FM transmitter:
  6. (Optional) Application for permission for a public protest from the police:
    Application Info

5. FM Radio transmitter models

After getting permission to operate an FM radio transmitter and broadcast the planned contents, I had to decide on what FM radio transmitter model to use (ie buy). While I initially had focused on portable (light-weight, battery-based power supply, long lasting), low-energy FM transmitters used by tourist guides with 0.6Watt (ERP) and a range of up to 300 meters, PTS granted me permission to operate a FM radio transmitter up to 3Watt (!), which is an ERP performanc level more typical for stationary FM radio transmitters (eg drive-in cinemas, drive-in churches).

After some research, I settled on models by the manufacturer RETEKESS [12, 13, 14], however, have not bought or tested the following models, which seem most suitable after discussion with RETEKESS sales support:

  • Retekess TR506 Portable FM Transmitter Long Range [15]  (up to 400m in open range)
  • Retekess TR501 FM Transmitter 1W 6W Radio Station [16] (up t0 2km in open range, needs external 12V power supply)
  • Retekess TR507 Bluetooth FM Transmitter [17] (up t0 2km in open range, needs external 12V power supply)

Note: Selected RETEKESS FM radio transmitters are also available at the AMAZON.DE website.

A review of FM transmitters with LCD display is published elsewhere [18].

Update 2020-09-08:
I used the Retekess TR506 FM transmitter in a suburban area with terraced houses and the signal on smartphone with FM receiver and headset was good to very good up to 180m, when it broke.

6. Major learnings

Public authorities can be really slow, ie requiring 3.5 months (2020-03-15/2015-05-15 to 2020-06-29) to issue such simple permits. After I had not heard back from PTS after my initial application, I contacted them to find out what was wrong, and it seemed that they just put my application aside because it was a bit unusual and they did not know how to handle my application. After PTS recommended to submit a  second application, there were delays because information that the PTS required was not asked in their application form (eg exact dates and times) and no tools were given to select available frequencies and determine signal strength and height of antenna, which required additional interaction. However, after the initial delay the officers at  PTS were helpful and reached out via email or phone to ask the missing information (eg exact dates) or did the calculations for me to select an available FM radio frequency, signal strength and antenna height, which required some physics (thanks!). Overall, after the initial reminder I felt the agencies handled my application in a timely and professional manner, but their systems could be made more user-friendly.

However, consider the criticism against the Swedish state-funded public service system of radio and television broadcasting (see also blog by Aron Flam on Public Service vs Public Service [6] and confiscation of his bok [7]), this raises concerns about “soft power” control to suppress freedom of speech regarding opinions which may politically not convenient. Considering that this was obviously a individually motivated action to take part in a  vital discussion in society regarding climate actions, I wonder, why the authorities did not handle an application trying to push climate action with higher priority in this climate emergency.  Additionally, I find it not quite plausible why the permission to broadcast the planned contents by MPRT were required considering the limited broadcasting range on a small public square in Uppsala, for a few hours, on specific days. At the same time no broadcasting permission is required, for example, for a drive-in cinema.







[6] Flam, A. (2020-06-02). Public service vs Public service [Podcast]. Dekonstruktiv Kritik [Serie].

[7] Arpi, (2020-06-17). En svensk tiger at upp hans bok. Svenska Dagbladet, Link: [JPG]

[8] PTS (2020-07-04). Ansökan om att använda radiosändare för ljudrundradio och TV,

[9] PTS (2020-07-04). Ansökan om att använda radiosändare för trådlös mikrofon eller hörseltekniska hjälpmedel,
Note: The application is not relevant, because it concerns frequencies between 174  and 1805 MHz, which are outside the FM radio spectrum and cannot be received with standard FM radio receivers.


[11] MPRT (2020-07-04). Tillfälliga sändningar,










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