AIS Aerial Performance Comparisons
Taking the Collinear as the benchmark of 100%, the relative
of the aerials are as follows
|Silva Marine VHF
seen the greater the message rate the greater the maximum
Also the Collinear
appears to perform even better at longer ranges particularly
favourable to "over the horizon" reception.
is plotted over a 9 day period. The aerials were alternated
6 minutes. The message rates have been smoothed (12 hour
average) to make the comparison
clearer. Click on the graph to see the unsmoothed graph.
Collinear received 39% more messages. During the
period of enhanced propagation, in the middle, the
performance of the Collinear was greatest.
The aerial was mechanically adjusted to 162Mhz, but not
adjusted to miminmum SWR as I do not have the necessary
The graph is taken over a 2 day period, the aerials being
every 6 minutes, simultaneously the message rate, number of
maximum range was plotted on the graph. Over the period the
received 35% more messages. It appeared from the graph that
Collinear message rate was showing the greatest improvement
Diamond the maximum range was disproportionatly better. In
the Collinear was even better at receiving messages when the
Collinear with Ribbon
The aerial was
made to the stated dimensions (within 1 mm). As RG213 is
3m of RG58 was
used to make the connection to the ribbon cable before being
(BNC to N-type) to the normal RG213 downlead. [Initial tests
hampered by a faulty connector]
As with most Marine VHF aerials designed for mast top
aerial came with 18m of downlead moulded into the base of the
This downlead was used.
How is it done ?
using a coaxial relay to
switch the aerials under control of the same PC running
plotting the graphs. It is synchronised to plot
message rate (1) or (2) on the graph as the aerial is
alternate message rate is
therefore recorded for a different aerial. The two aerials
at the same height about 10 feet apart, using the same
type and length
of downlead and feeding the same AIS receiver (SR162).