NRX1 Datasheet, PDF (7/8 Pages) Radiometrix Ltd – Low cost VHF Narrow Band FM receiver

1/4-wave
whip
1/4-wave whip
Metal ground plane
50 Ω coax feed
(31-/44,-weqauvaellryasdpiaalceelde)ments
30-40deg.
50 Ω coax feed
Figure 6: Quarter wave antenna / ground plane configurations
Half-wave. There are two main variants of this antenna, both of which are very effective and are
recommended where long range and all-round coverage are required:
1. The half-wave dipole consists of two quarter-wave whips mounted in line vertically and fed in the
centre with coaxial cable. The bottom whip takes the place of the ground plane described previously.
A variant is available using a helical instead of a whip for the lower element, giving similar
performance with reduced overall length. This antenna is suitable for mounting on walls etc. but for
best results should be kept well clear of surrounding conductive objects and structures (ideally >1m
separation).
2. The end-fed half wave is the same length as the dipole but consists of a single rod or whip fed at the
bottom via a matching network. Mounting options are similar to those for the quarter-wave whip. A
ground plane is sometimes used but is not essential. The end-fed arrangement is often preferred
over the centre-fed dipole because it is easier to mount in the clear and above surrounding
obstructions.
Yagi. This antenna consists of two or more elements mounted parallel to each other on a central boom.
It is directional and exhibits gain but tends to be large and unwieldy – for these reasons the yagi is the
ideal choice for links over fixed paths where maximum range is desired.
For best range in UK fixed link applications use a half-wave antenna on the matching transmitter (e.g.
TX1, BiM1T) and a half-wave or Yagi on NRX1 receiver, both mounted as high as possible and clear of
obstructions.
Module mounting considerations
Good RF layout practice should be observed. If the connection between module and antenna is more
than about 20mm long use 50Ω microstrip line or coax or a combination of both. It is desirable (but not
essential) to fill all unused PCB area around the module with ground plane.
Variants and ordering information
The NRX1 receiver is manufactured in the following variants as standard:
NRX1-151.300-10 (151.300MHz Australian licence exempt frequency)
NRX1-169.4125-10 (169.4125 European licence exempt frequency -169MHz band)
NRX1-173.225-10 (for UK alarm applications on 173.225MHz)
NRX1-173.250-10 (for UK general applications on 173.250MHz)
Matching transmitter: TX1-xxx.xxx-10 (where xxx.xxx is the operating frequency)
Radiometrix Ltd.
NRX1 receiver data sheet
Page 7