Pocket DAB Radio Sensitivity

The tests

There were two main tests to establish a general idea of how sensitive the digital radios were. A mobile test which determined how stable the signal was when used in a pocket on the move and a stationary test where the radios ability to pick up signals from DAB multiplexes were tested.

The radios tested are as follows:

The radios tested range from just above £30 (Goodmans GDPRDAB) up to £90 (Roberts Sports DAB 2) but can be found at varying prices via online and high store retailers. All the radios tested have a rechargeable battery (all except the Oxx and Roberts radios use the Micro USB standard connector) and support for DAB+ and the full Band III frequencies 5A-13F (the Pure Move 2500 also supports DMB-R and L-Band).

Update: Since this testing, the author has also obtained a Majority Petersfield Pocket DAB Radio, which has taken over the Goodmans GDPRDAB as the best selling radio on Amazon. Preliminary testing suggests this radio’s sensitivity is around the low-mid range of the radios previously tested. It struggled to find fringe multiplexes but did find the medium-strong ones. The signal out and about drops out for weak to medium strength signals, similar to the behaviour of the Goodmans and Azatom tested. Further testing suggests that the radio’s sensitivity is just below that of the Goodmans.

Second update: PURE has released an revision of its 2500 pocket radio, the 2520. The tuner sensitivity of the 2520 is exactly the same as its predecessor. The 2520 can be treated the same as the 2500 mentioned below in these tests.

Only two of the radios in the test have the voluntary Digital Radio Tick mark, designed to be awarded to radios which meet minimum standards set by the Department of Culture, Media and Sport in the UK and granted by Digital Radio UK — the Azatom and the Sony.

The author used a 1.2m headphone wire attached to Sennheiser MM 550-X headphones (the wireless functionality turned off at all times to prevent interference which would invalidate the tests). As mentioned, all telescopic aerials were contracted.

At the time of writing, the area the author lives in receives the following multiplexes:

Sadly, no minimuxes are broadcast in this area to test the experience of low powered transmissions with a pocket DAB radio.

These are not full-on scientific tests done in labs with sound proofing, micro multiplexes and laboratories. That is beyond the capability financially of the author! These are basic functionality tests to gather a general idea of the tuner sensitivity and stability of signals in real world scenarios where people would use a pocket DAB radio — in a pocket on the move or in a building for personal listening.

Mobile Tests

Two tests were performed to determine the sensitivity and stability of the pocket DAB radios using different signal strengths and surroundings.

The first test took place in a suburb in the authors home town. The route selected includes a open grass area, alleyways, paved residential areas and typical suburban roads — the things you would expect in a normal suburb. The radios were tuned to Jazz FM Stereo on the Sound Digital multiplex, broadcasting in DAB+, using equal error protection level 3A (the standard for UK digital radio) and Reed-Solomon error protection.

For both the suburban and urban tests, a stable signal was determined if a error free listening was attainable within a time frame of 1.5 seconds (the time it takes to make 2 paces at casual walking distance). For the suburban test, the radio was placed in a trouser pocket with the headphone socket aimed downward to ensure taller DAB radios were not given a height advantage that would skew the results. The headphone lead was allowed to string across and freely to ensure maximum signal reception. The results were as follows:

This proved quite a conclusive test. In normal reality, you would be handling your radio or have it in a coat pocket with the headphone signal further out which would improve reception a fair bit for those radios that rated 2% or more, but it does show how difficult all but one radio found handling and correcting errors on a medium strength signal. Whilst the Pure Move, which conclusively won this test, was capable of maintaining a signal for the vast majority of the route chosen, even it did have a few drop-outs.

A second test was performed in an urban setting, using a route that took in normal road arteries, open squares, closed alleyways and streets with clustered and large buildings. A typical urban setting. This time, all the radios were tuned to LBC on the Digital One multiplex which uses unequal error protection level 3 on a strong multiplex which is slightly weaker than the Sheffield multiplex but stronger than the BBC National DAB multiplex. A good all rounder. The test results were as follows:

Surprisingly, the Pure Move 2500 which blitzed the competition in the suburban medium signal test did not come out on top in this test. That honour goes to the Viewquest Blighty. In reality, those two radios and the Oxx Clip had virtually nothing between them. Unless you were paying attention, you wouldn’t notice a difference between them. At the other end of the spectrum, the Sony XDR-P1DBP struggled to maintain a signal for half the route.

No radio could attain perfect reception in either test, there were brief dropouts on the ones which scored highly.

Stationary Tests

The author conducted a number of tests with solely the headphone wire for an antenna, headphones to listen to the audio for any dropouts and a full autoscan was performed to determine the number of services each radio could receive. The tests were done in both an indoor urban setting in the middle of the authors home town and an indoor suburban setting at the edge of the authors home town. The results were as follows:

The Pure Move 2500 wins across the board when it comes to finding stations and maintaining a stable signal without unrecoverable signal errors causing dropouts. The Viewquest Blighty and Oxx Clip also do reasonably well. Although from my experience, the Oxx can end up picking up less stations in a scan than its nearest competitors, it is better at maintaining a signal. Worth noting the hybrid pocket and portable DAB radios did less well, particularly the Sony XDR-P1DBP. It is worth noting that if telescopic aerials were allowed in this test, the Sony would do well and pick up as much as the Roberts did with only the headphone lead as an antenna. However, such an arrangement in a public setting may not be practical or desirable.

One thing to note with the manual tuning setting (not tested in this test) on the Azatom is that there is a bug on weak-medium signals. The radio will tune to the multiplex for a brief moment before showing no signal. Sadly, as the firmware is locked and cannot be upgraded, this bug can only be fixed with a newer revision release.

Recovery Tests

Tests were also made to determine how quickly the radios could maintain a signal to quickly decode an audio stream or in the event of losing signal lock, how long the radios take to start decoding the audio stream.

The Goodmans and Oxx radios are able to maintain a signal lock indefinitely (ie. they do not attempt to retune as all the other radios do) until you change station but still takes a little time to recover (see below) when it regains a useful signal. The Roberts will not attempt to retune for just over 20 seconds. Most radios wait a few seconds to quickly recover before retuning.

The Azatom and Pure take less than two seconds to recover and start decoding an audio stream. Whilst the Azatom is fast at decoding — slightly faster than the Pure, it is let down with losing signal lock so quickly which may explain its lower scores in both the suburban and urban tests. The Roberts radio time is higher because there were a few occasions where it was taking many seconds to recover to a position to regain a signal and decode whilst at other times, it took around 3–4 seconds — still higher than the average radio on test.

A word about antenna performance

The other critical component of a digital radio set-up is the antenna. Whilst a few of the radios on test have a miniature telescopic antenna, this shouldn’t be extended whilst being used in a pocket (unless you’d like it to break instantly). All the radios on test use the headphone lead to pick up radio signals. The majority of radios on test supply their own in-ear headphones with cable lengths between 1m and 1.2m. A few do not to keep costs down, namely the Azatom and Goodmans whilst the Sony is designed as a portable radio first with pocket radio capability included so also does not contain headphones.

From use of various headphones, I have found the sweet spot for cable length when used out and about is 1.5m. The 1.2m cables provided with the Pure and Oxx work just as well but did introduce the odd dropout which didn’t occur with headphones using a 1.5m lead. The shorter 1m cables were slightly worse in reception quality. The optimum length for an antenna wishing to receive DAB(+) in the UK at half a wavelength is between 77.3cm (block 7D) and 65.5cm (block 12D) — which a 1.5m cable can roughly reach untangled if the radio is placed within a coat or trouser pocket with the rest of the cable looping back up into the pocket where the radio is contained.

The price of the headphones did not matter in terms of reception — a £6.99 pair of Intempo headphones from Home Bargains kept up or even surpassed slightly the reception of DAB signals from a £250 pair of Sennheiser headphones used in these tests — both use a 1.5m cable. There is virtually no difference in reception whether the headphones split the cable in two to each speaker or whether the wire went to one speaker then over the headphone band to the other or in terms of the thickness of the plastic protecting the cable. Obviously, cables work better as an antenna when untangled.

Whilst the sound quality of the Intempo headphones will be trampled upon by the Sennheiser ones, for low bitrate DAB listening, sound quality is not a primary focus of concern as opposed to radio reception.

In terms of which pocket to place the radio, that will be down to personal preference and which direction the signals are coming from for best reception — something only the user can experiment and decide upon. The other issue with picking up reception using a headphone lead is you — but there isn’t much you can do about that — the main factor for signal strength as demonstrated in the aforementioned ERA Technology study for Ofcom is the position of the headphone cable.

Where problems did occur were with headphones using 3m cables, notably the cheapest Sennheiser on-ear headphones. Even when tidying up the cable so as to make it a shorter length for convenience, losses were apparent and the signal strength was degraded considerably to the point of consistent dropouts which would not occur with 1.2–1.5m headphones.

And for those who travel on public transport, for best signal reception, be as high up as possible (top deck of a bus is best), sit in a window seat or stand next to a window and have as much of the wire exposed to the window as possible in a vertical position to match the polarisation of the broadcasts. The metal framework of buses and trains causes signal loss as it works as a faraday cage. Also worth nothing that LED lights and signs used within buses and the electrical components of vehicles can create RF interference, so much so as to wipe out radio reception, particularly for DAB, up to several metres away, affecting people in cars, people walking along the pavement and in buildings close to the road.