ais/vhf next to radar

[Javelin]

Has anyone had experience of placing the ais/vhf antenna next to or near the radar dome such as on a radar arch.
I was wondering if there's any bad interference either way.

So the balance is I guess based on potential interference whilst on a odd occasion the radar and ais transponder are on at the same time.
Given that the radar is usually only on in v/poor vis and the transponder is on when approaching shipping lanes otherwise its just on receive.

against the additional £200 + required for a decent quality vhf splitter

 

[knuterikt]

Has anyone had experience of placing the ais/vhf antenna next to or near the radar dome such as on a radar arch.
I was wondering if there's any bad interference either way.

So the balance is I guess based on potential interference whilst on a odd occasion the radar and ais transponder are on at the same time.
Given that the radar is usually only on in v/poor vis and the transponder is on when approaching shipping lanes otherwise its just on receive.

against the additional £200 + required for a decent quality vhf splitter

If you can install the antenna so it is above the radar dome it will be outside the radar beam.
Works fine for us. GPS for AIS and plotter beside the AIS transceiver antenna.

 

[RAI]

Probably not a problem. Do keep the AIS GPS and VHF antennas as far away from the radar scanner as you can. If possible, higher than the radar's vertical beam width.

 

[jerrytug]

Has anyone had experience of placing the ais/vhf antenna next to or near the radar dome such as on a radar arch.
I was wondering if there's any bad interference either way.

So the balance is I guess based on potential interference whilst on a odd occasion the radar and ais transponder are on at the same time.
Given that the radar is usually only on in v/poor vis and the transponder is on when approaching shipping lanes otherwise its just on receive.

against the additional £200 + required for a decent quality vhf splitter

I don't see how there could be interference at radio frequencies, given that the AIS operates around 150 mega Hertz, and the radar, around 10 giga Hertz, a huge difference.

 

[MM5AHO]

I don't see how there could be interference at radio frequencies, given that the AIS operates around 150 mega Hertz, and the radar, around 10 giga Hertz, a huge difference.

There can be interference. While the frequencies you quoted are the intended transmit frequencies, there are possibly unintended transmissions on other frequencies. In addition, a strong transmit output (like Radar is, in pulses), can induce re-radiated emissions at other frequencies from all manner of other items, such as connections, metal items and more (known as "rusty nail effect"). [When I transmit on 3.7 MHz, my compass illumination light comes on. It should only "receive" 12V DC, but is quite bright, even though it doesn't have much of an antenna!]
Further, a strong signal on another frequency, into a receiver can overwhelm the receiver, even though it was tuned to a quite different frequency that the one it suffered. ("front end overload".)
So despite the differences in intended frequencies, items using totally different bands can interfere with each other.

 

[Javelin]

Thanks for the replies thus far.
Presumably the short length of ss tube supporting the other sensors and vhf, will cause a blind spot on the radar ?
Given the mast must create a blind spot fwd, would it be beneficial to align the upright of any bracket to be in line with the mast?

 

[BelleSerene]

Thanks for the replies thus far.
Presumably the short length of ss tube supporting the other sensors and vhf, will cause a blind spot on the radar ?
Given the mast must create a blind spot fwd, would it be beneficial to align the upright of any bracket to be in line with the mast?

As others say, it's probably fine directly above the radome - but why not stick the antenna right up the mast, be done with the problem and get much better VHF range into the bargain?!

 

[Javelin]

why not stick the antenna right up the mast, be done with the problem and get much better VHF range into the bargain

I'd have to run a new cable, - keel stepped mast - pain in the .......
You really need to keep vhf antennas at least 4' apart, otherwise you can get signal snatch and directional issues.

The "above the radome" looks to be the best move.

 

[RAI]

Thanks for the replies thus far.
Presumably the short length of ss tube supporting the other sensors and vhf, will cause a blind spot on the radar ?
Given the mast must create a blind spot fwd, would it be beneficial to align the upright of any bracket to be in line with the mast?

Small diameter SS vertical tube is not likely to block the radar much, the scanner antenna is wider.

 

[jbweston]

There can be interference. While the frequencies you quoted are the intended transmit frequencies, there are possibly unintended transmissions on other frequencies. In addition, a strong transmit output (like Radar is, in pulses), can induce re-radiated emissions at other frequencies from all manner of other items, such as connections, metal items and more (known as "rusty nail effect"). [When I transmit on 3.7 MHz, my compass illumination light comes on. It should only "receive" 12V DC, but is quite bright, even though it doesn't have much of an antenna!]
Further, a strong signal on another frequency, into a receiver can overwhelm the receiver, even though it was tuned to a quite different frequency that the one it suffered. ("front end overload".)
So despite the differences in intended frequencies, items using totally different bands can interfere with each other.

About 25 to 30 years ago, my office was on the first floor of a building in central Loughboriough, right over the road by a set of traffic lights. In those days we used Philips desktop mini-cassette dictation machines. These were mains-powered. Whenever a Council dustcart went past using his two-way radio (the antenna of which was on his cab outside my window a few feet from my desk) his voice would come over loud and clear through the speaker of my dictation machine. The machine had no radio receiver. It must have been that the old two way radios transmitted with enough power to affect the internals of my equipment.

Technolgy has come on a long way since then, but I can well imagine that all sorts of peculiar interference is still possible.