Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

and about 1.3 meters when measuring on 700 MHz. This distance in the chamber
used is only about one meter. This will also increase the uncertainty of the
measurements.
The probes are designed to send frequencies down to 700 MHz and do not work
very well for lower frequencies. Since the measurements are done relatively this
should not affect the results.
All these possible error contributions give a pretty big uncertainty for the absolute
value in the measurements. However the different prototypes that have been
measured could be compared to each other with a rather high precision.
5.2 Testing with DVB-T receiver
Since DVB-H is supposed to be sent with the same base stations as DVB-T and
on the same channels one can draw the conclusion that DVB-H will be sent with
the same power as DVB-T. If DVB-H becomes successful the plan is to build
more transmitters to get better coverage. The present DVB-T base stations
transmit with 50 000 Watt ERP.
From the antenna point of view it is the same thing to receive a DVB-H signal as
a DVB-T signal. A difference between the two signals is that the DVB-H signal is
harder coded with MPE-FEC than the DVB-T signal. A DVB-H receiver will
therefore need lower received signal strength to have good reception. In other
words, if our antennas can receive and show a DVB-T signal they will also be
able to receive and show DVB-H signals.
A relevant test for the built antennas is therefore to try and receive digital TV with
them in different environments. This was done with a laptop and a DVB-T box
that was connected to the computer through a USB 2.0 port. The DVB-T box
antenna connection is matched to 75Ω and all the antennas built are matched to
50Ω. The tested antennas will need somewhat higher signal strength together with
the DVB-T box than they will with a future DVB-H receiver since this will be
matched to 50Ω.
At the moment there are five different channels transmitted in Skåne at 482, 506,
634, 794 and 818 MHz. The tests were done on 482 and 506 MHz because these
are the only channels that transmit programs free of charges.
To get an idea of how strong the DVB-T signal is the constructed dipole antenna
was connected to a spectrum analyzer and the signal strength of the different
channels were measured. Inside Perlos laboratory no signal could be found. To get
a signal the window had to be opened, and then signal strength of around –80dBm
70