Aerials on a pole, another question.

[doug748]

I intend to put GPS, Navtex and AIS receiving aerials on a short pole at the pushpit.

Would these three interfere with each other in any way? I would like to keep things as tight as possible so I am thinking of a separation as little as 6 - 8in between each one.

Thanks.

 

[skip50]

I had a similar situation, these three aerials close together on the pushpit-never noticed a problem.

 

[pvb]

Receiving aerials won't interfere with each other.

 

[Pinnacle]

Don't know about the AIS aerial, but our GPS and Navtex units are this close together and seem to work fine;


View attachment 35188

 

[maby]

There will always be a small performance degradation, but I doubt it would be measurable without very sensitive laboratory instruments. The three operate on very different frequencies which will minimise any interaction.

 

[doug748]

Great.

Many thanks for the rapid responses!

 

[prv]

I intend to put GPS, Navtex and AIS receiving aerials on a short pole at the pushpit.

Would these three interfere with each other in any way?

From memory, GPS is microwave-ish frequencies, Navtex is a few hundred khz (relatively lowish frequency, though not actually LF), and AIS is of course VHF. So they should be well separated and unlikely to interfere, but RF is funny stuff...

Pete

 

[john_morris_uk]

Receiving aerials won't interfere with each other.

Assuming he's not going to run a Class B AIS transponder which does transmit. It shouldn't matter as the frequencies are all so far apart, but as someone else has said, RF is funny stuff... Just check its all operating properly when it's installed.

 

[pvb]

From memory, GPS is microwave-ish frequencies, Navtex is a few hundred khz (relatively lowish frequency, though not actually LF), and AIS is of course VHF. So they should be well separated and unlikely to interfere, but RF is funny stuff...

I can't envisage the mechanism by which purely receiving antennae might interfere with one another.

 

[maby]

I can't envisage the mechanism by which purely receiving antennae might interfere with one another.

Interfere - no, but they can interact. Carrying it to extremes, imagine putting up an AIS antenna (vhf) and completely surrounding it with Navtex antennae (lf) - they will shield it and reduce the sensitivity a lot. OK - nobody is going to do that, but look at any TV antenna - one dipole receiver and several reflectors and directors set out in a line to give you directivity - the presence of the unpowered and unconnected elements a few inches to feet away will influence the characteristics of the receiving element.

In the case that the OP is describing, I would be pretty sure that you could not detect the interaction without sensitive laboratory equipment - but there will be an interaction - impossible to predict what and certainly safe to ignore.

 

[pvb]

certainly safe to ignore.

That's what I thought.

 

[Chalker]

Maby has it perfectly

 

[Ex-SolentBoy]

No need to put GPS aerial there. Why bother.

They work perfectly well behind GRP. Put it inside near the GPS itself. Shorter cable run. No unsightly serial, out of the westher, less prone to damage etc.

 

[MM5AHO]

I can't envisage the mechanism by which purely receiving antennae might interfere with one another.

That's what Yagi said to Uda, when he said lets put this slightly longer element behind that dipole and see what happens.

But there's no risk to what the OP suggests

 

[skip50]

No need to put GPS aerial there. Why bother.

They work perfectly well behind GRP. Put it inside near the GPS itself. Shorter cable run. No unsightly serial, out of the westher, less prone to damage etc.

The same applies to Navtex aerials. I got fed up replacing my NASA Navtex aerial, due to water getting in, the previous owner had the same problem. Mounted it high up in the oilskin locker, totally protected from weather, completely out of sight in the locker-works just as well.

 

[maby]

The same applies to Navtex aerials. I got fed up replacing my NASA Navtex aerial, due to water getting in, the previous owner had the same problem. Mounted it high up in the oilskin locker, totally protected from weather, completely out of sight in the locker-works just as well.

True - Navtex works on such a low frequency that you would have to be a tall ship to get the antenna mounted anything like optimum. when you are talking about mounting it just a few feet above the waterline, you may as well mount it anywhere convenient. Do bear in mind that the frequency is so low that it will be very vulnerable to interference from electrical and electronic equipment - get it as far as possible from anything that consumes electricity!

 

[pvb]

That's what Yagi said to Uda, when he said lets put this slightly longer element behind that dipole and see what happens.

Ah, but technically that's the same antenna, rather than different receiving antennae.

 

[maby]

Ah, but technically that's the same antenna, rather than different receiving antennae.

Technically, yes, but the fact remains that it depends on the intended interaction between several completely disconnected bits of wire or rod. The same interactions can exist between adjacent antennae that are not intended to form part of a single antenna.

 

[doug748]

The same applies to Navtex aerials. I got fed up replacing my NASA Navtex aerial, due to water getting in, the previous owner had the same problem. Mounted it high up in the oilskin locker, totally protected from weather, completely out of sight in the locker-works just as well.

Sorry to bring this thread back from the dead but I am now considering bringing the Navtex aerial below decks, as suggested.

It would have to be around 2ft from the autopilot electronic brain box. Can anyone predict if this would cause a problem?
I don't want to site it and then have to move it mid season, as a lot of disruption would be involved and I would rather be sailing or drinking red wine.

I may even bring the GPS down as well; same question as above would apply really. Thanks

 

[st599]

GPS is receiving signals about the same power as a 60W bulb at a few hundred miles.

Any noise is bad. GPS has a negative SNR.