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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What is Amateur Radio Worth?signal strength
Thursday 27 September, 2012, 18:26 - Amateur Radio, Spectrum Management
Posted by Administrator
About 18 months ago, the Wireless Waffle team wrote a paper on the topic of what radio amateurs in the UK might have to pay if spectrum pricing was applied to the spectrum they use. The paper was offered to the RSGB and to Practical Wireless as material that could be used for an article in their prestigious magazines.

xe0yl sexy radio hamThe RSGB indicated that it was not the sort of article they normally published as it didn't have antennas in it or any pictures of people standing on a mountain or remote desert island. Practical Wireless never responded as they were too busy assessing the merits of the latest amateur radio gizmo to come from Latin America (see right) and the whole thing got shoved to the bottom of the 'to do' pile and forgotten about. At least I think that was what the RSGB and PW said, the old memory is a bit hazy on the subject.

Whilst the material contained in the paper is now around a year old, it still makes for interesting reading and it is almost certain that Wireless Waffle readers will find it worth the time to study. Rather than think what to do with it next, it has been uploaded to the web-site and is now available for anyone to download and read.

So, for your reading pleasure, we present 'The Duffer's Guide to Spectrum Pricing. Pour yourself a beer, turn on your VHF radio, and have a read. Then, if you are a radio ham, realise how lucky you are to be able to afford that beer you just poured yourself!
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Is 5 better than 2.4 (GHz)?signal strength
Thursday 9 August, 2012, 15:13 - Radio Randomness, Spectrum Management
Posted by Administrator
wi five logoAlthough the standard for WiFi at 5 GHz has been around for a long time, most manufacturers have focused upon producing equipment for the 2.4 GHz band. The reason for this is a simple one - it's cheaper! The higher you go in frequency, the more difficult, and therefore expensive, it becomes to transmit and receive radio signals. As a result, home routers, laptops, smart phones and other devices have almost exclusively been equipped to use the 2.4 GHz band for their WiFi connection.

Previous Wireless Waffle articles have discussed how to select the best WiFi channels in the 2.4 GHz band, and other techniques, to maximise coverage and signal quality, however we have not looked at the 5 GHz band. Recently, there seem to be a slew of articles which are claiming that using 5 GHz will produce better range and more reliable connections compared to 2.4 GHz. The logic of these articles seems to go '5 is a bigger number than 2.4 - in fact it is more than double - so it must be at least twice as good'. This, sad to say, is not the case. Here are the real facts:
  • Signals at 5 GHz only travel HALF as far as those on 2.4 GHz as higher frequencies have poorer coverage than lower ones.
  • Signals at 5 GHz will struggle almost TWICE AS HARD to get through walls than signals at 2.4 GHz due to their poorer propagation characteristics.
  • 5 GHz WiFi equipment is subject to exactly the same POWER RESTRICTIONS as that for 2.4 GHz, so there is no inherent advantage in terms of the technology itself.
  • The use of some of the 5 GHz channels is subject to the requirement to STOP TRANSMITTING if a nearby radar is detected. No such restriction applies at 2.4 GHz.
  • 5 GHz equipment will be (slightly) more POWER HUNGRY than its 2.4 GHz counterparts, increasing battery drain especially in mobile devices.
  • 5 GHz receivers are likely to be LESS SENSITIVE than 2.4 GHz receivers because of the increased difficulty of making low noise devices at higher frequencies.
  • The 5 GHz band consists of up to 25 (territory dependent) independent channels which can be used without interfering with each other meaning there is much GREATER CAPACITY for more networks, whereas the 2.4 GHz band has 13 channels of which only 3 can be used independently.
  • The 2.4 GHz band is also used for Bluetooth, microwave ovens, wireless cameras and many other applications meaning it can be subject to a lot of background interference. The 5 GHz band is MUCH CLEANER, though the band is not exclusive to WiFi systems.
  • There are still fewer 5 GHz devices around than 2.4 GHz once and hence it is likely to be LESS SUSCEPTIBLE TO SNOOPING.
As coverage is determined both by signal strength and by the amount of interference, it is therefore possible that people in particularly densely populated areas where there are lots of 2.4 GHz users around might find that the 5 GHz band provides a more reliable connection and may even provide greater coverage. In most cases, however, the 2.4 GHz band has many advantages and the claims being made that 5 GHz is somehow 'twice as good' are just plain wrong.

For a home network, in a small house or apartment, using 5 GHz may offer some advantages given the lower interference it will suffer from other devices, but in large family homes a 5 GHz WiFi router is unlikely to be able to outperform the coverage and range that a 2.4 GHz router achieves.

five is betterWhere the 5 GHz band may come into its own is when the not-quite-yet-finalised IEEE 802.11ac standard is adopted. This works in the 5 GHz bands and uses the greater capacity of the band to deliver connection speeds of up to 1 Gbps. For streaming media around, this has clear advantages. As a wireless distribution for a home internet connection, however, there is unlikely to be any improvement noticeable using 802.11ac than with the existing 802.11n standard which can already offer connections of over 100 Mbps - much faster than most home internet connections!
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Gareth Emery feat. Christina Novelli - Concrete Angelssignal strength
Wednesday 4 July, 2012, 21:40 - Chart Predictions
Posted by Administrator
Another random pop prediction from the Wireless Waffle team. This time it's Southampton's very own Gareth Emery who has teamed up with the daughter of television chef Jean-Christophe Novelli to cook up a delightful tune called 'Concrete Angels'.



It seems unlikely that this will ever truly make the charts (not least it was released 5 months ago and is yet to challenge the chart countdown). But here at WW we thought that the clever use of the lights in tower blocks to represent electronic volume meters was pretty suave. Definitely a late night tune, headphones on, lights out, eyes closed. Or is that just us?
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