Radio wave experts - Radar reflector on whip aerial

superheat6k

superheat6k

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I have just installed a tubular Radar reflector onto the VHF whip aerial, about 1/3 from the base where the section is still quite thick.

Will mounting the reflector here affect the VHF transmission or reception in any way.

UNADJUSTEDNONRAW_thumb_2d1e.jpg
 
It looks very pretty but these reflectors are notoriously ineffective and will be even more so when mounted vertically, unlike the Blipper type which is designed to be mounted thus.
 
Also putting an amount of foil around your antenna could detune the antenna, not really a receive issue but certainly reducing transmit power
 
It's unlikely to have a significant effect on the VHF aerial in either receive or transmit.
Assumng that the VHF aerial is just a simple whip, which I'd expect it to be. If it's a dipole and the reflector is across the centre, it could be a bit more interesting.
The reflector is much shorter than a wavelength and much too close to do much to the aerial's field.
The aerial won't improve the performance of the reflector, might give a blind spot.
 
That will have minimal impact on the VHF - but also I am afraid that type of reflector is of minimal use too.
 
bedouin said:
That will have minimal impact on the VHF - but also I am afraid that type of reflector is of minimal use too.
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Those things are better than nothing, if your radar can't see them, maybe you need a better radar?
They tick the box of carrying a permanent radar reflector, which is usually the object of the game.
 
superheat6k said:
I have just installed a tubular Radar reflector onto the VHF whip aerial, about 1/3 from the base where the section is still quite thick.

Will mounting the reflector here affect the VHF transmission or reception in any way.

UNADJUSTEDNONRAW_thumb_2d1e.jpg
Click to expand...

Even if the risk of that tubular reflector affecting vhf performance was very low, it is a risk I would not want to take. Also, given the well documented evidence of the very poor performance of that type of reflector, I would not fit that type at all. But that is just my view. :)

Www.solocoastalsailing.co.uk
 
lw395 said:
Those things are better than nothing, if your radar can't see them, maybe you need a better radar?
They tick the box of carrying a permanent radar reflector, which is usually the object of the game.
Click to expand...
The point of those is not for your own radar to see them but for other vessels - and all the tests show that that type have a minimal impact on your RCS. That particular design has a maximum RCS of about 1m2 whereas 10m2 is the recommended minimum
 
bedouin said:
The point of those is not for your own radar to see them but for other vessels - and all the tests show that that type have a minimal impact on your RCS. That particular design has a maximum RCS of about 1m2 whereas 10m2 is the recommended minimum
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Read your Skolnik and tell me that 1m2 is not a useful RCS in real life.
 
Indeed I appreciate the effect is likely marginal , but it is the sole legal requirement for a boat of my size under SOLAS regulations. I am now compliant, although I appreciate a vast majority are not.

However, is my effort to achieve legal compliance (that most don't bother with BTW) compromising the real value of the VHF radio as a key safety device (NB a VHF Radio is NOT required by SOLAS as I understand it) ?
 
That type of VHF antenna is designed to work with no external ground plane so definitely not a simple dipole. The components usually a coil and tuning capacitor and various radiating elements are housed in the grp tube. So much would depend on the location or the radar reflector in relation to the internal components. So IMHO almost certainly going to detune the antenna resulting in much less RF power going out. Now of course you may never notice the difference but it might just make a difference one day at extreme range so I would not mount the radar reflector on the antenna. ol'will (plus I think people who see it will think you a fool)
 
I think I'd be just as concerned about the strain on the antenna. Simply not designed to carry something like that. Your bigger risk is breaking the antenna.

The small tube reflectors are only any good for scrutineering purposes. Unless you are entering a race where they are required and you want bare minimum, then no point. IIRC the rules say 'where practicable' but if you're going to the trouble for your own safety you might as well use a real one. Doubt any private vessel has ever been prosecuted for lack of reflector.

You can get that type with a deck mount which you could put on the other side of coach roof. If you can get the 4" one in that style, even better. You can also get the Echomax as a deck mount.

Johnalison suggested they should be horizontal but vertical is the correct orientation.
 
MikeCC said:
I think I'd be just as concerned about the strain on the antenna. Simply not designed to carry something like that. Your bigger risk is breaking the antenna.

The small tube reflectors are only any good for scrutineering purposes. Unless you are entering a race where they are required and you want bare minimum, then no point. IIRC the rules say 'where practicable' but if you're going to the trouble for your own safety you might as well use a real one. Doubt any private vessel has ever been prosecuted for lack of reflector.

You can get that type with a deck mount which you could put on the other side of coach roof. If you can get the 4" one in that style, even better. You can also get the Echomax as a deck mount.

Johnalison suggested they should be horizontal but vertical is the correct orientation.
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The ones I have seen have the elements disposed in line with the tube and will have no reflecting apices when vertical as with the octagonal type. I'll have another look when I see one in case here are other designs.
 
superheat6k said:
Indeed I appreciate the effect is likely marginal , but it is the sole legal requirement for a boat of my size under SOLAS regulations. I am now compliant, although I appreciate a vast majority are not.

However, is my effort to achieve legal compliance (that most don't bother with BTW) compromising the real value of the VHF radio as a key safety device (NB a VHF Radio is NOT required by SOLAS as I understand it) ?
Click to expand...

All vessels must also have available an illustrated table of the life saving signals given by ships aircraft and persons in distress. http://solasv.mcga.gov.uk/mca docs/lifesaving sigs.pdf
MCA advice is that this should be prominently displayed in the wheelhouse.
 
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lw395 said:
Dipoles don't generally have ground planes anywhere near them.
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Yes you are right. My senior's moment again. 1/4 wave antenna should be substituted for dipole. However in fact the tube may contain a dipole with the lower 1/4 wave length piece in lieu of ground plane connection or as a ground plane.
So to be honest I don't know what is inside the tube. ol'will
 
That type of antenna is usually a 5/8 wavelength whip. These are either stub tuned or coil tuned at the base. It is not advisable to hang any metal from them as it will affect the tuning. This can have the effect of a greater SWR causing power to be reflected back into the transmitter, if its too high it could lead to damage of the final transmit stages of the VHF.
Would I do it ? No is the answer as it will affect transmit / receive to a greater or lesser extent and it may just make the difference between being heard or not in the case of an emergency.
 
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