AIS Aerial Performance Comparisons

Summary

Taking the Collinear as the benchmark of 100%, the relative performances of the aerials are as follows

Antenna	Performance	Comments
Collinear	100%
Diamond F22	74%
Metz Manta-6	74%
Cushcraft Ringo Ranger 2	72%
Silva Marine VHF	47%
Slim Jim	74%
Garex Pre-amp		Awaiting testing

Relationship between message rate and range

As can be 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 propagation is favourable to "over the horizon" reception.

Mk 2 Collinear with Cushcraft Ringo Ranger II

The 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.

Mk 2 Collinear with Diamond F22

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 greatest.

Mk 2 Collinear with Metz Manta-6

Mk 2 Collinear with Ribbon Cable Slim Jim

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]

Mk 2 Collinear with Silva 1.2m Marine VHF Antenna

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.

Garex MP-3/AIS Pre-amp
Awaiting testing

How is it done ?

I'm 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).