Wireless Waffle - A whole spectrum of radio related rubbish
Freakquencies in Dhakasignal strength
Tuesday 23 October, 2012, 07:48 - Licensed
Posted by Administrator
Have you ever read the book 'Freakonomics'? It tries to demonstrate that sometimes cause and effect are far, far removed from each other. Rather like Sherlock Holmes adage:
When you have eliminated the impossible, whatever remains, however improbable, must be the truth.

Take a look at the list of FM frequencies for radio stations in Dhaka, Bangladesh. It may not seem odd at first, but look closely:

radio foorti logo88.0 MHz Radio Foorti
88.4 MHz Radio Aamar
88.8 MHz Bangladesh Betar (Traffic Channel)
89.2 MHz ABC Radio
89.6 MHz Radio Today
90.0 MHz Capital FM
dhaka fm logo90.4 MHz Dhaka FM
91.6 MHz Peoples Radio
92.4 MHz Radio Shadhin
97.6 MHz Bangladesh Betar
100.0 MHz BBC World Service
103.2 MHz Bangladesh Betar (Home Service)

Taken from a variety of sources such as: Asiawaves

Notice anything odd? What about the fact that there are 7 stations spread out every 400 kHz between 88.0 and 90.4, two more below 93 MHz and then the rest of the whole FM band up to 108 MHz contains only 3 more stations.

The 400 kHz spacing is sensible (see the previous Wireless Waffle article on the bandwidth required to transmit a stereo FM programme), but why are they crammed down at the bottom end of the band? Here's a quick Wireless Waffle quiz. See if you can get the right answer.

Is it because:
  1. Propagation at lower frequencies is better than at higher frequencies and thus the lower end of the FM band will yield marginally better coverage than the top of the band for the same power/antenna.
  2. Like many countries (including the UK which only had access to 88.0 to 97.6 for a long time), the bottom of the band was opened up for broadcasting first, and the upper frequencies have only recently become available.
  3. Buildings in Dhaka are built to a Government controlled specification which, ironically, has a resonant frequency at the top of the FM band, causing signals at this end of the band not to be able to penetrate inside them.
  4. The majority of cars in Dhaka are imported from Japan which has an odd FM broadcasting band that runs from 76 to 90 MHz and thus the radios in those cars don't extend much above 90 MHz.
  5. The transmitters used by FM stations in Dhaka are very old and work best at the lowest possible frequency, giving the highest output power and greatest efficiency.
So, which do you think it is?

banglatransmitterWell (a) is certainly true, though the difference in propagation is less than 20% between 88 and 108 MHz and is offset to some extent by the slightly better performance of receiving antennas at 108 compared to 88 MHz. As for (b), this is not true as the BBC service on 100 MHz has been on air for over 15 years and was one of the first FM stations in Dhaka. Answer (c) is a joke – have you seen the state of buildings in Dhaka?! Answer (d) could certainly be true as the Japanese FM band does run from 76 to 90 MHz. And finally (e) would be true of old transmitters were used, but most are modern and therefore don't suffer from this problem, which, as with (a) is pretty marginal anyhow.

dhakajamThe real reason that stations in Dhaka are clustered on frequencies around and below 90 MHz is (d). Think about it... when you listen to FM radio the most? Yes, perhaps you listen at home, especially on your alarm clock and in the morning, but most listening is done whilst in the car. There’s not much point being on a frequency that car radios can’t tune into and so there is the highest demand for frequencies on or below 90 MHz. Some older analogue radios will tune slightly above this so 90.4 MHz and thereabouts is not bad either. At the time of launch of the BBC service on 100 MHz there were very few cars (or FM radios for that matter) in Dhaka and so the issue didn't manifest itself.

Did you guess right? Would you have guessed that the choice of FM frequencies was driven by car imports if it hadn't been suggested to you? We doubt it! A case of 'Freakonomics' that is perhaps best labelled 'Freakquencies'.
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Eye in the Skysignal strength
Thursday 12 March, 2009, 09:00 - Licensed
Posted by Administrator
eye in the skyHave you ever tuned into your local radio station and heard the travel news being read out from the 'eye in the sky' - a presenter checking out the traffic from an aircraft high over the area concerned? Have you ever stopped to think how that is done? Well Wireless Waffle is here to help explain it all.

There is no denying that it would be very easy for any radio station to pretend to have a traffic plane or helicopter by playing sound effects in the background whilst the travel news was read out. However, there are some real benefits about doing it properly, not least it is possible to find out how the traffic is flowing as and when problems occur instead of waiting for listeners to phone in news (which can be unreliable) or for the local police or traffic department to let you know what's happening. But that doesn't mean that the aircraft in question can necessarily see all the problems in an area and in some cases, it is not possible to fly over certain areas due to airspace restrictions (for example, it would not make sense for a 'traffic plane' to be buzzing around a major airport, stopping commercial airliners from landing!)

What happens, therefore, is that there is someone on the ground who collates traffic information in the normal way (eg through listeners or the police) and then relays this information to the man in the aircraft. The plane (or chopper) can then visit some of the travel hotspots and see what is happening and if, along the way, they see other problems that haven't been reported, they can update the person on the ground. This means that, in general, travel news from an aircraft is more accurate and up-to-date than travel news from a regular travel studio.

From the technology perspective, there is lots of radio used (hence the Wireless Waffle interest). For starters, the pilot will be communicating with various air traffic controllers on the VHF aeronautical band (117.975 to 137.000 MHz).

in flight serviceNext, there is a need for the person on the ground, including the presenter in the radio studio, to be able to communicate with the presenter in the aircraft - the 'uplink'. Typically this is done via a simple VHF or UHF PMR frequency (in the UK try listening around 141.000 to 141.500 MHz and 455.000 to 455.500 MHz). As well as passing travel news to the airborne presenter, this frequency is also often used as the 'cue', providing a live feed of the station on which the travel news is to be broadcast so that the airborne presented knows when to start reading the news.

Finally there is a the link from the airborne presenter to the ground - the 'downlink'. This is usually (but not always) a slightly higher quality link than the uplink as the audio is going to be broadcast. In the UK, these links are usually at UHF (try between 467.250 and 469.900 MHz). As they are transmitted from the aircraft, despite being low power, they can often be heard over a wide area.

If the aircraft is providing travel news for a wide area, more than one up and/or downlink might be used for the different areas, depending on whether or not frequencies which can be used over a wide area are available.

In some countries, the presenter uplink and downlink are also in the aeronautical VHF band (this is the case, for example, in Malta), and the frequencies use do vary significantly between countries. If you are in an area where the local radion station has a travel plane or helicopter, why not have a tune around and see what you can find and post a comment to let us all know.
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Easy Listeningsignal strength
Tuesday 17 February, 2009, 20:38 - Licensed
Posted by Administrator
My couple of previous posts concerning reception of BBC World Service English language programmes on short-wave in Europe led me to wondering whether there wasn't a more elegant solution to the problem of identifying which frequencies to tune to at any given time of the day.

As it happens, every 6 months, the majority of international broadcasters get together and sit down to negotiate and co-ordinate their HF frequency usage for the coming 6 months at a conference known as the High Frequency Co-ordination Conference. The resulting plans (know as the Winter and Summer seasons) are published on the web. So with a little ingenuity and a few spare hours, Wireless Waffle proudly presents:

* The 'find a frequency in a given language, for a particular broadcaster (or both) analysis tool' *
(catchy name isn't it?!)

It works like this: You can select broadcasts in a particular language, or by a particular broadcaster in which case you will be presented with a list of transmissions currently on-air (or on-air at a time you select) today for that broadcaster together with a map of the world showing where those frequencies are being transmitted from. Using this list you can try tuning to those transmitters most local to you (or for fun those more distant) to see what you can hear.

Alternatively you can select a broadcaster AND a language in which case you will receive a list of all frequencies and times for that broadcaster in that language for today, highlighting those which are currently on-air with a map showing where those frequencies which are on-air are being broadcast from. It sounds more complicated than it is - go and try it!

short wave info

To help, regions in daylight and darkness are also shown. Generally speaking if you are in an area of darkness, look for stations also in darkness which are transmitting on low frequencies (say 10 MHz - 10000 kHz - or less). If you are in an area of daylight, look for frequencies also in daylight (over 10 MHz or so).

Happy listening.
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World Service English (Take II)signal strength
Saturday 27 December, 2008, 08:29 - Licensed
Posted by Administrator
bbcworldserviceFurther to last month's comments on receiving BBC World Service English in Europe, we've been testing out some of the frequencies that were suggested from the Wireless Waffle HQ in southern Great Britain. At all times checked, at least one BBC English frequency was available and at some times, several were audible. The list below gives the times checked and the frequencies that were audible. A simple rating system has been employed with one * representing poor reception, ** representing reasonable reception and *** representing a nice strong signal.

Reception will change from day-to-day and month-to-month so this list may not remain accurate indefinitely but it shows what can be achieved with a little effort. This list will be updated from time-to-time so check back occasionally if you're missing your Lily Bolero!

07:00 - 08:00 GMT
7255kHz***
9650kHz**
11760kHz**
08:00 - 09:00 GMT
11760kHz**
15400kHz**
09:00 - 10:00 GMT
11760kHz**
15400kHz**
17640kHz**
10:00 - 11:00 GMT
11760kHz** (though annoying co-channel China CNR-1)
11:00 - 12:00 GMT
11760kHz**
15310kHz**
17830kHz*
12:00 - 13:00 GMT
11760kHz**
15310kHz**
17830kHz*
13:00 - 14:00 GMT
11760kHz**
15310kHz**
17640kHz*
14:00 - 15:00 GMT
11760kHz**
17830kHz*
15:00 - 16:00 GMT
12095kHz**
15105kHz**
15400kHz**
17830kHz**
16:00 - 17:00 GMT
12095kHz**
15400kHz**
18:00 - 19:00 GMT
5875kHz**
19:00 - 20:00 GMT
5875kHz**

This information was last updated on 7 January 2009.
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