DT81
7
Selection mode
Press the
MENU
button four times to access the Selection
Mode menu. This can be used to change the way services are
selected when scrolling with the rotary controller or when using
the
<
and
>
buttons on the remote control.
To change between ‘AUTO’ and ‘MANUAL’, turn the rotary
controller and press
SELECT
to confi rm the setting: the tuner
reverts to displaying the service name.
With the selection mode set to manual, the displayed service
name is selected by pressing the
SELECT
button on the tuner
or the
BAND
button on the remote control. When the selection
mode is set to auto, the displayed service is automatically
selected after 2.5 seconds.
TUNER BYPASS switch
The front panel Tuner Bypass switch is used to switch between
this tuner’s
AUDIO OUTPUT
and the audio output of an FM tuner
attached to the
FM TUNER INPUT
sockets. The digital output
continues to output the audio signal from the currently selected
digital service on the DT81.
A note on Programme types
The Programme Type (PT) label is the short description
displayed below the service name.
Two different PT labels are transmitted:
Static PT
and
Dynamic PT
. The static PT is the service ‘genre’ and does
not change. Radio 4’s static PT for example is ‘Current affairs’.
The dynamic PT refl ects the current programme’s content (for
example, for Radio 4 typical dynamic PTs include ‘Drama’,
‘News’, etc.).
When a service is selected, the dynamic PT is displayed; at
other times the static PT is shown. This means that Radio 4
will say ‘Current affairs’ while scrolling through services, then
may change to ‘Drama’ when that service is selected. The tuner
works this way because it cannot update dynamic PTs for a
multiplex to which it is not currently tuned.
Note also that, for secondary services, the tuner displays the
parent’s static PT, since a dynamic PT would not be relevant.
A note on Secondary services
Primary services can have one or more secondary services
attached to them. These tend to be temporary; sporting
events like football matches for example may be broadcast
as secondary services. Services that have secondary services
attached to them are indicated by a
>>
symbol. Turning the
rotary selector clockwise will then reveal these services. The
secondary services themselves are indicated by a
<<
symbol.
You need to select a main service in order to see if there
are secondary services attached. The BBC is currently not
distinguishing between primary and secondary services, to
work with tuners that do not support secondary services. The
effect of this is to make those services appear twice in the list,
once as primary and once as secondary.
Note that only primary services can be attached to a preset.
Dynamic label
This is a 128 character block of scrolling text used by most
broadcasters to display programme information (such as song
titles, useful phone numbers and website addresses).
Signal quality meter
The signal quality meter is a simple bargraph which gives a
quick visual guide to reception quality. Technically, it is an
inverse measure of the Viterbi error rate, with zero errors at
full scale (all segments are lit) and 300 errors/second (with
all segments off). When reception is marginal, the number of
segments displayed becomes a very sensitive function of the
received signal strength and can be used to optimize the aerial
position.
Engineering mode
The DT81 digital radio tuner has two modes – in addition
to
User Mode
(in which the unit powers up) it also offers
an
Engineering Mode
that allows you to view technical
information about the currently selected service.
To access Engineering Mode, press
SELECT
and preset
8
simultaneously. ‘ENGINEERING MODE’ is briefl y displayed. From
Engineering Mode you can return to User Mode by pressing
SELECT
and preset
8
simultaneously again.
Once in Engineering Mode, each of the eight preset buttons
shows different technical information:
Preset 1: Ensemble frequency
. This is the carrier frequency
of the currently selected ensemble.
Preset 2: Service data rate
. This is the data rate of the
current service in kilobits per second: the higher the number,
the better the sound quality.
Preset 3: Service start and end CU numbers
. The start
and end CU (Capacity Unit) numbers indicate the service’s
position within the ensemble.
Preset 4: Viterbi error/CRC failure count
. The Viterbi rate
indicates the amount of error correction that is going on. Audio
decoding normally works transparently with Viterbi rates up
to about 200; above this, audible degradation of the signal
may be noticeable. The CRC (Cyclic Redundancy Check) failure
count indicates the amount of uncorrected errors. Any fi gure
above zero may mean audio disruption.
Preset 5: Signal strength (AGC)
. A measure of raw RF
strength at the receiver front end.
Preset 6: Transmitter ID information
. This shows the IDs
(identities) of all the transmitters detected for the current
ensemble. DAB radio uses multiple transmitters for the same
signal and can add together for better results. If you turn the
rotor you can see how many transmitters are being picked up
and their respective fi eld strengths on a scale of 1 to 7.
Preset 7: Audio mode
. This shows that the selected
programme is being transmitted in Stereo, Joint Stereo or
Mono mode. (Joint stereo is an MPEG audio mode where the
data for one channel is sent along with data representing the
difference between the two channels. It allows a lower data rate
to be used, but is not as good quality as true stereo.)
Preset 8: Transmission mode
. This indicates which of four
possible methods of encoding/decoding transmissions is used
in the current service. This information may be useful to
engineers in diagnosing certain unusual problems.
