Antenna Question

Razorbill RIBs · 06 March 2010, 09:30

Have been reading through old threads re Antenna's etc....still unsure of what to go for, so looking for some recommendations.

Okay, currently have an old pacific fibreglass pole type antenna, mounted on A frame, so gives great performance.....

However, we often go into sea caves etc and it is a PITA having to remove it before entering ones with low roofs (especially if it entails clambering over people to get to it).

Reception can be patchy here, so keen to keep as good perfomance as we currently have (if possible), but want a shorter /strong whippy type that will clear the roof and flex if it does make contact....

Recomendations please...Currently thinking Metz?

Dan

I guess one of the other issues with the pole is that IF someone forgot to take it down before tarilering under a garage forecourt, you might end up taking down one of the ancient plastic strip light covers with the arial, and end up having to foot the bill....

neil.mccrirrick · 06 March 2010, 11:13

Have a look at this:

http://www.shakespeare-marine.uk.com...ic.pdf#4187-HD

I use this bracket with a 396 - 1 attenna

The ratchet bracket means you can quickly ands easily lower the attenna so the height of the rib becomes the height of the A frame

Razorbill RIBs · 06 March 2010, 11:24

Thanks Neil....

Not discounting this, but it would still mean having to leave the helm and climb past the aft seatpods to reach the antenna to lower it....

Ideally, would like a high performance shorter whip type arial......any other suggestions greatly appreciated...

Dan

Channel Ribs · 06 March 2010, 12:21

Hi Dan, Metz are very very good antennae.

But for your purposes I would recommend a Pacific stainless steel 1m jobby:

http://www.pacificaerials.co.nz/Mari...elAntenna.aspx

I have used and fitted many of them and they always impress.

We recently changed the one on the RIB from one of these and the drop in reception is noticeable, so I will be switching back!

They are great value too at about 20 quid.

Razorbill RIBs · 06 March 2010, 15:55

Hi Martin....

do you stock the pacific items /could you recommend a good supplier?

The Metz was twice that cost IIRC? Do you know how the Pacific performs vs the Metz (in laymans terms...which is better and by how much?)

Thanks, D

Channel Ribs · 06 March 2010, 16:02

Quote:

Originally Posted by Dan Worth

The Metz was twice that cost IIRC? Do you know how the Pacific performs vs the Metz (in laymans terms...which is better and by how much?)

That is about right, the performance of the Metz is better but not twice as much. Where it does win over is with design life - very robust indeed.

Having said that I have never had cause to feel the Pacific 1m steel whip to be in any way inadequate.

In laymans terms: The Metz is something that will outlast your radio, while the Pacific is a lot of function for the price.

www.saltyjohn.co.uk has loads of technical stuff on the Metz, if you do get one I can recommend him.

Hightower · 07 March 2010, 12:38

Quote:

Originally Posted by Dan Worth

Ideally, would like a high performance shorter whip type arial......any other suggestions greatly appreciated...

Dan

Aerial length is everything! Obviously there are cheats out there like base loadings that will improve an antenna's lack of performance because of the shorter whip, but nothing will outperform an omnidirectional aerial of the same length as the wavelength your transmitting on.

I would guess that a 1 meter one as already stated is the minimum length you'd want for reliable performance. Perhaps you could mount it in a more forward position to make lowering it easier or mounting it on the side of the A frame like I've seen on other RIBs.

City Radio · 07 March 2010, 21:22

Quote:

Originally Posted by Hightower

Aerial length is everything! Obviously there are cheats out there like base loadings that will improve an antenna's lack of performance because of the shorter whip, but nothing will outperform an omnidirectional aerial of the same length as the wavelength your transmitting on.

I would guess that a 1 meter one as already stated is the minimum length you'd want for reliable performance. Perhaps you could mount it in a more forward position to make lowering it easier or mounting it on the side of the A frame like I've seen on other RIBs.

The size of any omnidirectional antenna is obtained by the following formulae:

300 divided by Frequency (Mhz) = Wavelength (Metres)

Therefore if you wish to make your own steel whip:
300 / 156Mhz = 1.92m Full wave
Half wave antenna would be 0.96M (96cm)
The antenna should be checked with a SWR (sine wave ratio) meter to ensure that the power from the radio is being dispersed by the antenna. It is ALWAYS worth checking the SWR of any radio setup -it will tell you how well your radio/antenna is operating and could save the power transistors of the radio from burning out!

Most marine antennae are halfwave and coil loaded to "electronically extend" the aerial.
The higher the antenna above ground/sea the better the range of transmission although in a RIB this is not always possible. That is why CoastGuard Stations have highly placed antenna stations around the coast linked to the main area station. If your audio is clear, most emergency calls should be picked up by the coastguard.

Most coil loaded whip antennae are suitable for a RIB; although with an anode in the sea water to act as a ground plane would make it perform better.

Ian M · 07 March 2010, 21:57

Quote:

Originally Posted by City Radio

The antenna should be checked with a SWR (sine wave ratio) meter

Sorry, at risk of being branded an anorak, SWR = standing wave ratio, normally measured as a VSWR (voltage SWR).

City Radio · 07 March 2010, 22:00

Yes your right, me getting mixed up with sine wave for AUDIO.

Channel Ribs · 08 March 2010, 08:42

Quote:

Originally Posted by City Radio

Most coil loaded whip antennae are suitable for a RIB; although with an anode in the sea water to act as a ground plane would make it perform better.

I have been aware of this in theory but never tried it nor know anyone who has, what kind of improvement would it yield?

Channel Ribs · 08 March 2010, 08:45

Quote:

Originally Posted by City Radio

Most coil loaded whip antennae are suitable for a RIB; although with an anode in the sea water to act as a ground plane would make it perform better.

I have been aware of this in theory but never tried it nor know anyone who has, what kind of improvement would it yield?

Edit: Hang on though, surely so long as your radio battery and engine battery share an negative you will get this effect regardless?

I need more tea!