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MEGA TEST -- HIGH-PERFORMANCE LNBS
INTRO
One of the simplest ways to improve the performance of your
satellite system is to upgrade the dish electronics. We've been looking at four
LNBs, for tweaking Astra and multi-satellite systems
COPY
Low noise block converters or LNBs have a
hard life; they operate around the clock, in extremes of temperature and
humidity, and although they generally have a very low failure rate they do not
last forever. Some fail as they get older, others suffer a drop in performance,
resulting in poor picture quality. Some were of questionable quality to begin
with, and swapping the original LNB for a newer type can have a significant
effect; older, less efficient receivers also work better with a less noisy
signal. Those living in borderline signal areas may benefit by fitting a
high-performance LNB, rather than increasing the size of their dish, and anyone
considering adapting their system for twin satellite operation will need an
extra LNB, preferably a high quality one as it's a demanding application.
One word of caution; if you are troubled
by an increase in sparklies, and your picture is getting steadily worse, don't
rush out and buy a new LNB just yet, it could be that the dish needs
re-aligning, or moisture has penetrated the connectors or the cable, it could
even be a fault in the receiver, so check all of these things first.
We've been comparing four single-band,
voltage-switched LNBs typically selling for between £50 and £100. They're all
suitable for upgrading small (60-80cm) fixed dish systems; they can also be
used on motorised or multi satellite systems but for maximum coverage and
flexibility many users prefer dual or triple-band models. They all have noise
figures, between 0.7 and 1.2dB. Don't be put off by the techno-jargon, the
noise figure is simply a way of expressing how much noise has been added to the
signal after it has passed through the LNB, so the lower the number the better.
The noise figure has a direct bearing on the quality of the picture and in
particular the amount of impulse noise, or sparklies.
The majority of LNBs supplied with budget
and mid-market Astra systems have noise figures between 1.5 and 2.0dB, though
they're getting better all the time, and 2.2 to 2.5dB was considered good not
so long ago. To give us some kind of benchmark to work with we've compared our
sample LNBs with a Marconi 'Blue Cap', with known performance. All of the LNBs
were tested using a modified 60cm offset metal dish, connected to a Pace IRD
and viewed on a Hitachi 'Opus' TV. Here's what we found.
MASPRO SCE-1
Definitely the odd one out, the
Japanese-made SCE-1 is short black cylinder 100mm long with a diameter of 63mm;
this is an unusual size and is not seen very often on small fixed dishes.
However, undaunted by the challenge we managed to locate a suitable bracket and
yes, it was worth the additional time and effort required to align the
unit. The quoted noise figure of 1.2dB
is born out by the better than average performance which was clear to see.
Checked against our reference blue cap, on a deliberately mis-aligned test-rig
the SCE-1 managed to reduce the number of sparklies on UK Gold, one of the
chosen Astra test channels, by well over 50%, the noise present in highly
saturated colours was also improved significantly. Overall a very good result
but in view of the unusual mounting requirements it probably wouldn't be
suitable for a dual-LNB installation as none of the extension arms we've seen
have a large enough mounting bracket.
Address: MASPRO UK Unit 6, Drury Way Industrial
Estate, Laxcon Close,
Neasden, London NW10 OTG
Tel: 081-451 6766
Verdict: (out of 5)
Performance ****
Ease of installation ***
Buying Satellite Rating
XX%
Throat dia: 63mm
Quoted noise figure: 1.2dB
MARCONI SOLO 1
The Solo is now Marconi's mainstay LNB
for Astra and other FSS (fixed satellite services) systems, since the famous
'blue cap' went out of production a few months ago. Incidentally, the first
blue caps rolled off the UK production line back in 1989, last year Marconi
received a coveted Queens Award for Industry for manufacturing LNBs. Solo 1 has
a 40mm throat and a conventionally shaped feedhorn, so it will directly replace
the commonest types of LNB, including, or course, the blue cap. The quoted noise figure for the Solo 1 is
'less than 1dB', a figure that was born out in our tests where it emerged as
the joint winner, along with the Protel (Continental) model. Against our
standard reference LNB the difference was clear to see, especially on UK Gold,
which on our mis-aligned antenna, was almost unwatchable, with a significant
number of sparklies; when replaced by
the Solo the sparkly count dropped to almost zero, with a noticeable
improvement in colour reproduction, especially in areas of high saturation.
Address: MARCONI ELECTRONICS LTD Elstree Way, Borehamwood
Herts WD6 1RX
Tel: 081-953 2030
Verdict: (out of 5)
Performance *****
Ease of installation *****
Buying Satellite Rating
95%
Throat dia: 40mm
Quoted noise figure: <1dB
PHILIPS
This LNB is manufactured by Philips in
their Crayfeld factory, it is also supplied to other companies, including
Channel Master and appears under a number of other guises. This particular
model is supplied as standard with Philip's RAST-256 package, which includes
the STU-802 tuner. Although operationally similar to most other FSS LNBs, it is
a slightly unusual design in that it uses a 'polyrod' lens, instead of a
conventional feedhorn. The polyrod lens, which was developed by Marconi, increases the efficiency of the antenna by ensuring that more of the
signal ends up inside the LNB. Another consequence of this design is a
significantly narrower throat, around 25mm, so it will not fit the majority of
dishes without a new or modified feed bracket, unless it's replacing a
similar-sized LNB. On some dishes this type of LNB may require a little more
effort during alignment, to get the best from it. The quoted noise figure for
this LNB is 1.2dB, which is not the lowest figure in this survey, but still
appreciably better than most standard LNBs. In our tests it performed well with
a marked reduction in sparklies, compared with the blue cap reference. Not,
perhaps such a dramatic improvement as the other models but still a worthwhile
increase in picture quality over most standard LNBs.
Address: PHILIPS CONSUMER ELECTRONICS, City House,
420-430 London Road, Croydon CR9 3QR.
Tel: 081-689 4444
Verdict: (out of 5)
Performance ***
Ease of installation ***
Buying Satellite Rating
85%
Throat dia: 25mm
Quoted noise figure: 1.2dB
PROTEL
A popular and widely-used LNB, badged
Protel but manufactured by Continental who also supply the LNBs used in a
number of packaged systems. Physically this is the smallest of the four LNBs
we've looked at, though the front-end is a familiar shape with a conventional
circular feedhorn that has a 40mm throat, so it will fit the majority of dishes
without any problems, as a direct replacement. The cast alloy box containing
the electronics is less than half the size of the Philips unit, and only
two-thirds as large as the Marconi Solo. In common with most other LNBs it has
electronic, dual probe, polarity switching, controlled by the receiver via the
LNB cable. In our evaluation tests this came out as the joint winner, with the
Marconi Solo, compared with the reference blue cap there was a substantial
reduction in sparklies on UK Gold, and a considerable improvement in colour
reproduction, particularly in highly saturated areas where noise and sparklies
are most prevalent.
Address: Protel Distribution Ltd., Communication House, 879
High Road Finchley, London N12 8QA.
Tel: 081-445 4441
Verdict: (out of 5)
Performance *****
Ease of installation *****
Buying Satellite Rating
95%
Throat dia: 40mm
Quoted noise figure: 0.7dB
VERDICT
All other things being equal the Protel
and Marconi LNBs would be our first choice on a fixed dish, dual-LNB system,
where low noise figures are essential in order to get the best from weaker
signals, from the satellites either side of Astra. If our results are anything
to go by both LNBs would do well as performance-boosters on 60cm dishes, in the
Midlands and Northern England, say, where it's normally preferable to use an 80cm dish. The Philips
and Maspro LNBs are both worthwhile upgrades, especially on older systems,
where the existing LNB is not giving its best, or the receiver is struggling,
however, be warned that neither of them use the most popular 40mm diameter
fitting so depending on the type of dish you have, the mounting bracket may
need to be changed or modified.
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© R.Maybury 1993 1908
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