OT Marine whip antenna
Pauline
This is all about marine VHF antennas..
I want to fit a whip to the wooden mast of my river cruiser, but
rather than pay £40 thought I would make one.
All the commercial designs just look like a whip, and no ground
plane!!.
My antenna theory tells me that at about 160 Meg a quater wave is
about 1foot 6 so the antenna would have two radials plus the whip. all
at this length.
Alternatively a 5/8 is about 3 foot but this still needs two radials
at 1 foot 6 as a counterpoise.
How do they do it without an apparant counterpoise?
TIA
Nick
Brian Reay
news:qptp405rivkb5bi1a...@4ax.com...
Chance are the commercial ones are 1/2 waves, which work OK without a ground
plane (I use a 1/2 wave on 2m on one of my cars as it largely fibre glass.)
They have a matching circuit at the base as the 1/2 is a high impedance
antenna.
1/4 wave ground planes normally have 4 radials, bent down at 45 degrees or
so to help with the impedance match (bringing it nearer to 50 ohms).
Not wishing to dampen your idea of DIY, don't forget the weather proofing as
you may need to rely on the antenna in an emergency.
--
73
Brian
G8OSN
www.g8osn.org.uk
www.amateurradiotraining.org.uk for FREE training material for all UK
amateur radio licences
www.phoenixradioclub.org.uk - a RADIO club specifically for those wishing
to learn more about amateur radio
Andrew Marshall
<Pau...@domain.com> writes
>This is all about marine VHF antennas..
>I want to fit a whip to the wooden mast of my river cruiser, but
>rather than pay £40 thought I would make one.
>All the commercial designs just look like a whip, and no ground
>plane!!.
>My antenna theory tells me that at about 160 Meg a quater wave is
>about 1foot 6 so the antenna would have two radials plus the whip. all
>at this length.
...and would also radiate at rather too high an angle for best surface-
to-surface communication, apart from the possible nuisance of the
projecting radials.
>Alternatively a 5/8 is about 3 foot but this still needs two radials
>at 1 foot 6 as a counterpoise.
Alternatively, you could perhaps use a single quarter-wave counterpoise,
dropping vertically downwards from the antenna base, or a quarter-wave
sleeve (tube) enclosing the descending coax feeder for that distance.
Mounting a sleeved antenna at its lowest point would need a good
quality, physically strong insulator capable of working efficiently at
160MHz, made of a material such as PTFE, as the lower end of the sleeve
would have a fair RF voltage on it. If the antenna was offset from the
mast, and a mounting bracket fitted at the base of the whip, the
insulator would not be needed - a small spacer ring to keep the coax
central as it emerges might be useful, though.
Other alternatives for a ground-plane/counterpoise-free ('free-space')
antenna would be a J-pole or a 'Slim Jim', scaled down from 145MHz to
156/160MHz; Google should turn up more info for you.
>How do they do it without an apparant counterpoise?
Usually by using an end-fed half-wave design, which will work reasonably
well without a ground plane or counterpoise; alternatively a coaxial
(sleeve) dipole, which is similar to the sleeve-plus-5/8-wave
arrangement, but with a quarter-wave top section.
Regards,
Andrew.
--
Andrew Marshall, M0MAA, G8BUR.
Unsolicited advertising matter unwelcome. Offenders may be blacklisted.
Geoff
news:c2iu0q$1t8lfg$1...@ID-140397.news.uni-berlin.de:
> Not wishing to dampen your idea of DIY, don't forget the weather
> proofing as you may need to rely on the antenna in an emergency.
It is also a good idea to carry a "rubber duck" or similar than can be
clipped to the pushpit in case of am emergency, like loosing the mast. Also
carry a marine band handheld.
If you are a licenced amateur, carry a broadbanded 2m radio too, which will
transmit on 156.800MHz.
Geoff
Pauline
Both the OM and I are licensed, and hold a licence for marine
operation.
I think I will experiment with the quater waves, or alternatively
watch ebay for a "bargain "!!!!.
73
all
Pauline
G7SPT
Mike @ www.lefkada-homes.com
>On Tue, 9 Mar 2004 19:24:27 +0000 (UTC), Geoff
><some...@nospam.demon.co.uk> wrote:
>
>>If you are a licenced amateur, carry a broadbanded 2m radio too, which will
>>transmit on 156.800MHz.
>
>As Brian will tell you, it would be illegal to use such a radio on
>156.800 MHz. Equipment used on that frequency has to be type approved
>for the purpose.
>
The guy with his thumb on the PTT needs
a VHF marine operators licence too !
--
Mike @ www.lefkada-homes.com
Dick G0XAY
Procom!) at a price you can afford!
Dick G0XAY
Geoff
news:8hcs40ddannd7hvfl...@4ax.com:
> On Tue, 9 Mar 2004 19:24:27 +0000 (UTC), Geoff
> <some...@nospam.demon.co.uk> wrote:
>
>>If you are a licenced amateur, carry a broadbanded 2m radio too, which
>>will transmit on 156.800MHz.
>
> As Brian will tell you, it would be illegal to use such a radio on
> 156.800 MHz. Equipment used on that frequency has to be type approved
> for the purpose.
I doubt that Brian would tell me so, Walt.
Obviously you are not aware of the SOLAS regulations - these permit !
anybody! to use !any! communications equipment in case of risk or danger to
a vessel at sea or to life (at sea).
The Safety Of Life At Sea international regulations, to which the UK
subscribes, override any other requirements, and of course, the WT Acts do
not apply.
I just knew that somebody would come up and say something like "type
approval is required".
Geoff
Geoff
news:cggs40pqhmuah53fp...@4ax.com:
> Thanks for all your help.
>
> Both the OM and I are licensed, and hold a licence for marine
> operation.
>
> I think I will experiment with the quater waves, or alternatively
> watch ebay for a "bargain "!!!!.
If your vessel has an aluminium mast, a quarter wave will do, fed against
the "ground of the mast. You might have to adjust the length for the best
match.
If you have a sailing vessel, then keep the aerial as high as possible,
masthead is normal, but use a low gain aerial. If the boat is heeling, a
higher gain aerial will squirt all the power into the sky and sea.
If it is a power vessel, then a higher gain aerial is suitable as power
boats shouldn't heel much - but do allow for trim.
On my sailing yacht, I have a dual band 2m/70cm aerial masthead mounted
about 1 metre from a 1/2 wave for 156/162MHz. The heeling effect is
noticeable on 70cm.
Geoff
Geoff
news:l2is40dpm48ptipfs...@4ax.com:
No he doesn't - under normal circumstances a marine VHF may be operated
under the supervision of an appropriately licenced operator. In case of a
defined emergency, anybody can use the radio, unsupervised.
Geoff
Geoff
> On Tue, 9 Mar 2004 23:16:00 +0000 (UTC), Geoff
> <some...@nospam.demon.co.uk> wrote:
>
>>Obviously you are not aware of the SOLAS regulations - these permit !
>>anybody! to use !any! communications equipment in case of risk or
>>danger to a vessel at sea or to life (at sea).
>
> But they would have to install it before they could use it. It would
> be illegal to install transmitting equipment without the necessary
> licence. So how do you get around that one?
>
The licence required to install marine radio equipment is relevant to the
vessel and does not require any qualification on the part of the owner. The
licence costs £15.00 (IIRC) and is issued by the RLC on the completion of
the appropriate paperwork.
Geoff 2, Walt 0
:-)
Geoff
Andy Cowley
> But they would have to install it before they could use it. It would
> be illegal to install transmitting equipment without the necessary
> licence. So how do you get around that one?
>
> 73 de G3NYY
>
Take your broadbanded VX5R out of your pocket, perhaps??
Not quite awake yet, eh, Walt?
vy 73
Andy, M1EBV
Andy Cowley
> On Wed, 10 Mar 2004 13:55:31 GMT, Andy Cowley <andy....@uwe.ac.uk>
> wrote:
>
>
>>Take your broadbanded VX5R out of your pocket, perhaps??
>
>
> What on earth is a VX5R? Some kind of scanner or CB rig?
>
>
No.
http://www.yaesu.co.uk/amateur/vhf/vx5r/vx5r.htm
or even better
http://www.yaesu.co.uk/marine/radio/hx260e/hx260e.htm
neither of these need to be "installed". Just press the
tit and go.
vy 73
Andy, M1EBV
Geoff
> On Wed, 10 Mar 2004 13:15:39 +0000 (UTC), Geoff
> <some...@nospam.demon.co.uk> wrote:
>
>>The licence required to install marine radio equipment is relevant to
>>the vessel and does not require any qualification on the part of the
>>owner. The licence costs £15.00 (IIRC) and is issued by the RLC on the
>>completion of the appropriate paperwork.
>>
>>Geoff 2, Walt 0
>
> And do the people that you were exhorting to use equipment on 156.8
> MHz hold such a licxence?
As people are not ships, they are not required to be licenced. As I was
only referring to the use of "modified amateur" radio equipment in
specific circumstances, that is a situation that is causing risk or
danger to a vessel or to life, catagorically, neither a licence nor type
approval of the equipment is needed.
You may be aware that this has happened in a number of occasions, most
notably when amateurs took over the distress working of ships when
Cullercotes (was it?) radio (a shore station) failed during the east
coast floods in 1953.
Of course, you will remember the amateurs who were hauled off to court by
the PMG because their MOPA top-band transmitter were not type approved.
The SOLAS regulations are issued and managed by the IMO, part of the UNO
and the UK is a signatory to these regulation.
Geoff 4 Walt 0 (including a penalty awarded for sheer stupidity).
:-)
Geoff
Andy Cowley
> Geoff 4 Walt 0 (including a penalty awarded for sheer stupidity).
>
Walt should have been sent off in the first half. ;-)
vy 73
Andy, M1EBV
Geoff
> On Wed, 10 Mar 2004 17:17:35 +0000 (UTC), Geoff
> <some...@nospam.demon.co.uk> wrote:
>
>>> And do the people that you were exhorting to use equipment on 156.8
>>> MHz hold such a licence?
>>
>>As people are not ships, they are not required to be licenced. As I
>>was only referring to the use of "modified amateur" radio equipment in
>>specific circumstances, that is a situation that is causing risk or
>>danger to a vessel or to life, catagorically, neither a licence nor
>>type approval of the equipment is needed.
>
> Oh, I see. So you are recommending that when an emergency presents
> itself, the people concerned should immediately sit down and modify
> their amateur radio equipment to facilitate operation of the marine
> emergency frequency?
No, I am not and have never said that. What I said, and will say again,
is that it is not illegal to use any radio equipment for distress
working. "Any" includes amateur equipment working outside the amateur
bands. It would also apply to some of the professional synthesized radio
equipment that I see from time (and I don't necessarily mean a Pye
MX294).
A prudent skipper of a small craft will carry backup equipment for use
in an emergency. I (on my boat) carry an Icom M12 and an international
channels marine handheld, plus the Seavoice RT6500 VHF marine radio
fitted. However I realise that in an emergency the RT6500 may fail and
that after a while the batteries in the h/h might/will fail. In that
case, my amateur equipment will serve, even though the performance will
probably be less than that of a dedicated radio.
Of course, "compulsory fit" vessels do carry backups, and backups to the
backups, but my boat is not required to do so, and would probably sink
under the weight of the equipment required to be fitted to a 300 tonner.
Now, you will say that it must be a dire circumstance when all these
systems fail, but when you read the reports of such disasters, it is
often the case that equipment fails or is otherwise unavailable.
>>You may be aware that this has happened in a number of occasions, most
>>notably when amateurs took over the distress working of ships when
>>Cullercotes (was it?) radio (a shore station) failed during the east
>>coast floods in 1953.
>
> Things have moved on a bit in 51 years, Geoff. That's over half a
> century, you know. You'll be quoting the sinking of the Titanic as an
> example next.
Well, the "sinking of the Titanic" was the trigger of the initial SOLAS
regs, but I guess that you knew that, otherwise you wouldn't have
mentioned it.
As the IMO say on their web page, the SOLAS regs are a "living document"
being formally revised every four years and can be updated between
times. So there is a good chance that the SOLAS regs are somewhat more
cognesent of todays practices than you are Walt.
This is getting to be a bit of a whitewash:
Geoff 6 Walt 0
:-)
Geoff
Geoff
news:Xns94A8C98186...@158.152.254.254:
> Geoff 6 Walt 0
Final Score then Walt :-)
Geoff
Pauline
Thanks Dick
have sent you an Email
Pauline
g7spt