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