The Pulsat LX2000 is an unusual design of antenna for reception of DTH (direct to
home) satellite signals. It includes a single-output LNB (Low Noise Block)
covering both low-band and high-band and horizontally and vertically polarized
transmission modes. It is intended to have lower visual impact than a
conventional dish antenna and can be mounted behind plastic materials for even
The LX2000's performance
can be measured, and the rest of the article covers this in some depth.
However, the design principles upon which it works can only be surmised. As an
engineer with some familiarity with audio techniques, the nearest I can come
to deducing how it works is by comparison with a ‘rifle microphone’ (shotgun mic). A rifle mic is directional in the same way that a satellite antenna needs to be. Both
design concepts need gain also. In the case of the rifle mic, delay is
introduced along the length of the tube such that signals from the required
direction all arrive in-phase and so add together, giving the gain. In the
case of the LX2000, I would guess that the tube contains dielectric material
which only passes-on the frequencies required, in the direction required. By
carefully designing the delay along the length of the tube, signals from the
wrong direction should cancel out and those from the required direction add
together. But that’s just a guess, and I’m not about to dismantle 200 bucks
worth of kit to find out!
The selection of receivers I use for satellite reception is shown in the
figure below. From top to bottom, they are the Amstrad-Fidelity SRX200, the Sakura
SR800ER, the Pace Prima, and the Nokia SAT780. I find the SRX200 easiest to
retune for experimental purposes such as this – the others are better in a
fixed domestic situation where remote control and greater program memory are
more important. The SRX200 also has a built-in frequency display rather than a
channel number, and this aids repeatability during the tests. The frequency
recorded differs from LNB to LNB due to internal offsets, so my results tables
include the frequencies noted for the transmissions selected.
Three different antennas were used: the LX2000 under test, a Sky MiniDish ™
and a full-size (2 foot) standard DTH dish. Each has its own LNB (described
later), and each was set up to give maximum reception. For the strongest
signal, the direction and elevation need to be correct, and the amount of
‘twist’ with respect to horizontal needs to be correct as well.
The MiniDish is about 40 cm across. It is fitted with a Grundig LNB, complete with built-in twist adjustment. Adjustment for maximum signal was straightforward – just setting the receiver to one of its preset channels and waving the dish around in the approximately right direction gives a TV image that can quickly be homed-in on. From the maximum signal direction, the strength trails off significantly when the LNB is displaced more than about one inch from the optimum setting.
From the table below, it is clear that, in my location in South-East England,
a MiniDish is only suitable for signals towards the upper end of the
frequency band. This is entirely respectable performance since the dish is
intended for use with SkyDigital ™ transmissions from a different satellite
As mentioned, the LX2000 has its own LNB already fixed to it, but the model of LNB is not shown on the casing.
Finding the satellite is just as easy as with the MiniDish. In fact, the
LX2000 is far less directional than conventional dish antennas. This is a
mixed blessing: it certainly eases initial setup, but may leave the device
more prone to unwanted signals. I would say that the tip of the antenna can
easily move 4 inches before the signal deteriorates significantly. Of course,
this helps when there is a lot of wind about, since the tube could deflect a
certain amount due to wind loading.
Standard 2-foot dish
I have both perforated dishes (as illustrated) and solid-back dishes available for my normal satellite reception. The dish used for the tests has a BZT brand LNB fitted, and results are perfect. For a weaker satellite (e.g., Hot-Bird), it is likely that the solid-back dish would perform better, but that is not the purpose of these tests.
For all the tests, a Work-mate workbench held the antennas. Elevation
adjustments were made using the crude but quick and highly effective use of a
car-jack under one corner of the workbench.
Reception strength using the LX2000 is likely to be marginal in most UK
locations. It seems to have a lower sensitivity than the MiniDish, so reception
of SkyDigital transmissions is likely to be more affected by rain-fade and to
not be possible in more northern areas of the UK and the rest of Europe.
- Graham Vine -