Due to the 
range which should be examined by the VLQ it is clear
that the detectors have to be placed under very small angles
close to the beam pipe.
The spectrometer consists of
two identical modules one below and one above the beampipe.
To put the VLQ acceptance in the desired region it
is required to install the entire VLQ in a gap of approximately 50 cm
length between the iron yoke and a superconducting compensation solenoid for
beam optics in the existing H1 detector.
This puts severe constraints on the longitudinal extension of the spectrometer components. A tradeoff between the performance requirements of the different detectors yielded a total calorimeter length of 16 cm including the active volume as well as the readout electronics. From this limitation it is clear that no photomultipliers can be used for the readout since they would be too large. Thus photodiodes are chosen as active devices sensing the light output of the calorimeter. It is also clear that a very dense absorber has to be used to keep energy losses small. For this reason tungsten is used as absorber.
The photodiode readout requires low noise charge sensitive preamplifiers to measure the small charge generated by photons in the photodiodes. This demand is intensified by the high readout granularity required to obtain spatial resolution. Due to this the signal in single channels is lowered and noise behavior becomes more important.
The preamplifiers are developed as integrated circuits in the AMS
(Austria Micro Systems) 1.2 
CMOS process to satisfy the demand
for compactness.
The design goals concerning spatial and energy resolution are a spatial resolution of better than 1 mm for energies higher than 5 GeV. This is required to accomplish track cluster matching between tracker and calorimeter and to correct the energy scale at the edge of the calorimeter. The energy resolution should be at the level of 3-4 % at an energy of 30 GeV.