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Technical details:
A vertically polarized quarter wavelength whip with groundplane and with a gain of 2 dBi and
an impedance of 50 Ω is normally used as a receiving antenna for the RX-C4. This is an omni
directional type. Sometimes a directional antenna is used in the case of a too little link margin or
in the case of interferers (see above). The supplied RG213 type cable has an attenuation of 3.5
dB per 100 meters.
Possible error sources and solutions:
Error: the antenna has been damaged.
Solution: replace the antenna.
Error: interference damages my data.
Solution: Make sure the antenna cable does not pick up unwanted RF signals by
separating it from power and data cables and/or see the paragraph on interferers above.
Error: the reception quality has degraded since the buoy frequency has been changed
considerably (more than 0.5 MHz).
Solution: Make sure the antenna has the correct length, see Appendix E.
A.5 Estimation of the transmission range
An estimation of the transmission range can be made with the gain and loss numbers of the
former paragraphs, but
only if the transmission range is noise (thus not interference)
limited!!
The maximum difference between the transmitted power ( +17 dBm) and the minimum
receiving power (-116 dBm) is 133 dB. Thus the sum of all following gains and losses:
1.
gain from the transmit antenna (+2 dB);
2.
path loss due to distance and terrain type (-50 up to -infinity dB);
3.
losses due to wave height (0 … -15 dB);
4.
losses from other obstacles (islands, ships close to the buoy, shadow from antenna
mounting structure, 0…-? dB);
5.
loss or gain from the height of the receiving antenna (-9 .. +8 dB);
6.
gain from the receiving antenna (+2 dB for the usual ground plane antenna up to + 8 dB
for a three element vertical dipole);
should be above -133 dB in order to guarantee reception.
Example 1:
a “normal setup” for 60 km over sea without obstacles will have an approximate loss of :
+ 2
dB
(transmit antenna, see A.2)
- 112
dB
(distance over sea water, see A3.1)
- 15
dB
(max. wave height 20 meters, see A.3.5)
- 0
dB
(no obstacles)
- 0
dB
(normal antenna height of 5 meters)
+ 2
dB
(gain of receiving antenna, see A.4)
which adds up to -123 dB which is 10 dB’s less than the maximum loss of -133 dB so that this
setup will guarantee reception under all circumstances but only if the transmission range is not
interference limited !!