FM broadcasting is a method of radio broadcasting using frequency modulation (FM) technology. Invented in 1933 by American engineer Edwin Armstrong, it is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. FM radio stations use the VHF frequencies. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. Usually 87.5 to 108.0 MHz is used. [Wikipedia, https://en.wikipedia.org/wiki/FM_broadcasting].
A personal FM transmitter is a low-power FM radio transmitter that broadcasts a signal from a portable audio device (such as an MP3 player) to a standard FM radio. Most of these transmitters plug into the device's headphone jack and then broadcast the signal over an FM broadcast band frequency, so that it can be picked up by any nearby radio. This allows portable audio devices to make use of the louder or better sound quality of a home audio system or car stereo without requiring a wired connection. They are often used in cars but may also be in fixed locations such as broadcasting from a computer sound card throughout a building.
Being low-powered, most transmitters typically have a short range of 100–300 feet (30–100 metres), depending on the quality of the receiver, obstructions and elevation. Typically they broadcast on any FM frequency from 87.5 to 108.0 MHz in most of the world. [Wikipedia, https://en.wikipedia.org/wiki/FM_transmitter_(personal_device)]
The Cache
This is a two stage multi cache placed in the Fernhill park. It used to live at Knockree along Wicklow Way, however, due to the low attendance of the area, it decided to relocate to a new place.
Fernhill is a former substantial family residence on 34 hectares of land at Stepaside. Fernhill Park and Gardens is Dublin’s newest Public Park, and forms an important component of the historic landscape on the fringe of Dublin City and an impressive example of a small estate dating back to around 1823. The former estate is a unique collection of heritage buildings, gardens, parkland, woodland and agricultural land. The elevated nature of the site, overlooking Dublin Bay on the threshold between the city and the Dublin mountains, lends a particular magic to the place. Fernhill is also home to a unique plant collection, made up of acid-loving plants such as Rhododendrons, Camelias and Magnolias, among others.
Opening hours: Fernhill is open on a full 7 day-a-week rota May/June 09:00 - 18:00 and July/August 09:00 - 21:00
Parking: New car park is open and there is parking for approximately 40 cars. Parking coordinates N 53° 15.600 W 006° 13.650
You will need a pen and an FM receiver. Most mobile phones have an FM radio receiver, however, some of them don’t, so you might need to verify if yours has it before attempting to find the cache. You will also need to use the headphones as antenna.
At stage one, you will find a medium sized container, which contains a black box. The small black box will help you find the second stage of the Secret Signal cache. It contains an FM transmitter which is powered by a 9V battery contained in the battery case on top of the box. To start the transmission, you need to toggle the on/off button on top of the battery case. As this is a low power transmission, the signal is very weak and you should keep the box very close to the antenna of your FM receiver. PLEASE, REMEMBER TO TURN OFF THE POWER AFTER YOU HEAR THE MESSAGE! Failing to do so will drain the battery. If you think the battery might be too weak, please report it to me. Do not try to change it.
During the broadcast you will hear four numbers A, B, C, D. The coordinates of the second stage are:
N 53 15.4(A)(B-8) W 6 13.5(C+2)(D-6)
The cache is placed in accordance with the Leave No Trace policy.