Link XP L2102/L2104 Receiver Instruction Manual Issue 1 - October 2003 Page 28 of 48
Link Research Ltd. 23/24 Watford Metro Centre, Dwight Road, Watford, Hertfordshire, WD18 9XA, England. Tel: +44 (0) 1923 200 900
Registered in London No. 2074604
Web:
www.linkres.co.uk Fax: +44 (0) 1923 241 357
L2102 & L2104 Receiver
Instruction Manual
Besides the characteristic impedance, cables are measured on the losses they incur as the
signal passes along them. Therefore the lower the cable losses, the greater the cable
length that can be used. To get the best performance from the Link receivers, only low
loss cables must be used. Whilst these are more expensive than lossy cable, the
performance gain is worth the extra cost.
Low loss cables generally have a foam dielectric whereas more lossy cables have a solid
dielectric. Also low loss cables usually have more copper in their conductors than lossy
cables.
The cable from the down convertor to the receiver is the most critical in terms of loss
because this is normally required to be 10s of metres long. The maximum loss that can be
tolerated on this cable length is 43dB. To find out what this equates to in the real world,
look up the attenuation per 10 metres at 900MHz in the manufacture’s data tables.
Dividing this figure into 43dB will give the maximum cable length in 10s of metres.
2.2.4 Cable
types
Ideally the receive antenna should be mounted directly on the down convertor (see figure
31). Where this is not possible, the shortest length of cable should be used to minimise the
losses. A low loss heliax such as Andrew type LDF450 should be used. This is a ½” thick
cable using foam dielectric and solid copper outer. Other similar low loss thick cable can
be used.
For the cable between the down convertor and the receiver, a low loss foam dielectric such
as Comscope RG59 or RG11 should be used. Using these cables will allow a 200 metre run
with RG59 and 300 metres with RG11.
Where the output from the receiver is SDI and cable lengths of greater than 5 metres are to
be used a line driver will be required to equalise the signal on the cable. This will allow
cable lengths of up to 300 metres to be used. A suitable line driver is the AGA video type
D5DA as shown in the illustration below.
Figure 34 – AJA video line driver type D5DA
Only use cables whose electrical characteristics and type numbers are known. Other
cables may give poor performance at best.
