Handheld VHF antenna

[Chip Hindes]

Jeff:
On rereading my summary, one thing I didn't make clear is that, as long as you're in U.S. waters where a license is not required, you can operate any number of radios off any number of boats. Your dinghy is essentially just another boat, so it's fine to use your fixed radio on the big boat to talk to your handheld on the dinghy. It's only when you go ashore that it becomes a technically legal problem.

I gotta say as well, I have both observed many, many times and have also occasionally actually participated in, the illegal practice of using my handheld ashore. They're so blatant about it, I'm pretty sure not 20% of people who do this are aware it's illegal. Probably wouldn't stop them, even if they knew, but they probably wouldn't be quite so open about it.

We have a pair of the low power, no license required FRS radios for "legal" ship to shore, and these are cheap enough (<$30/pair) that you can add additional units for the kids, mother-in-law, dogs, cats, etcetera. You can pay a lot more for a "good" one, but if you pay $15, no big deal if you drop it overboard or run over it with the tow vehicle.

They work OK, though at 1/2 watt power the range is pretty limited. I've sometimes thought shouting might be more effective. GMRS radios have higher power, 1-5 watts, but they legally require a license.

[Moe]

We all value features differently, and to me, those extra bands on the HX471S are just fluff. What distinguishes it, perhaps enough to pry the premium price out of my wallet, is the DSC feature. I hoping it remembers the last coordinates from the GPS once disconnected. Anyone know?

And what I find better than RAM is RAM+ for the same reason as above, a DSC button on the remote. In heavy weather, where we're more likely to need it, the DSC button on the fixed unit is going to be in the cabin behind a closed companionway. I'd like to have one in the cockpit.

--
Moe

[Pouw Geuzebroek]

You lucky guys in US, we have to take an exam first and then pay 60 dollars for a license each year. All for the sake of trying to ban misusage, at least that's what they tell us, but that does not work ofcourse. Especially with DSC which has that very nice looking red distress button, which kits love to play with when you are busy doing other things.
Not a good idea Moe to have two of these buttons around, when you have small kids that is .

[Bill at BOATS 4 SAIL]

Hey Moe - In one of your previous posts, which I can't find now, I think you mentioned using an automobile radar detector on a boat. Would this indicate direction, distance, or ? - Thanks

[Moe]

Bill, the typical radar detector will only provide you with a strength of signal indication, a crude indicator of distance, but no direction. The antenna faces forward, and it relies on reflected signals to warn you of radar behind you (which aren't a real threat unless they come up behind and pace you).

My Valentine One has antennas front and back, and can give those directions. When it indicates radar to the side (same signal received on both antennas), it can't tell you which side.

All automotive dectectors cover X band (inland, coastal use) but do not cover lower frequency S band used offshore. However, it is possible, and I don't know for sure, but the harmonics from S band MIGHT trigger an alert on a higher frequency band.

--
Moe

[waternwaves]

I'll warn everyone now, this one may be a little dry for some peoples taste....

Moe,
I am having trouble finding references to US Racons for US offshore waters being S Band only, so maybe I am misreading my coast guard publications here.... but could you clarify the S-band reference..I thought they were all X, and some had S in addition.


Seems all my new marine equipment is X band, my
Furono 1623 operates on 9410 MHZ +/- 30 mhz


From the USCG tech page...


radar beacons
Racon Technical Characteristics
All racons used by the USCG are frequency agile type, designed to measure the frequency of every incoming radar pulse, and transmit an approximately 25 microsecond Morse-encoded response less than 700 nanoseconds later back to the radar on that frequency. The Morse-encoded response is encoded such that the length of one dash is equal to that of three dots, and the length of one dot equals that of one space. All racons operate over the frequency range 9300-9500 MHz marine radar band (X-band), and most additionally operate in the 2900-3100 MHz marine radar band (S-band). Racon range is approximately line-of-sight range, normally over 15 nautical miles, although actual range depends upon a number of factors, including mounting height, atmospheric conditions, and racon receiver sensitivity setting.

S-band racon antennas should be suitable for responding to radars using horizontal or vertical polarization. X-band racons should respond to radars using horizontal polarization. X-band antenna vertical divergence ranges from about 8 degrees for fixed installations, to 18 degrees for installation on buoys. S-band antenna vertical divergence is 22 degrees. Radiated power is 600 milliwatts. Receiver sensitivity is about -35 dbm.

Or am I misreading you for discussing older and higher power mobile shipboard radars, I.E the sperry, raytheon, furuno naval and weather radars ie..marine radars X-band 2-4 cm 8-16 GHz long-range precipitation radars C-band 4-7 cm 4-8 GHz long-range precipitation radars S-band 7-15 cm 2 to 4 Ghz

I think the SOLAS requirements for Shipping now are both X band and S band have to be on board the big guys..... I know at 300 tons....

2.3 All ships of 300 gross tonnage and upwards and passenger ships irrespective of size shall, in addition to meeting the requirements of paragraph 2.2, be fitted with:
2.3.1 an echo sounding device, or other electronic means, to measure and display the available depth of water;
2.3.2 a 9 GHz radar (xband), or other means to determine and display the range and bearing of radar transponders and of other surface craft, obstructions, buoys, shorelines and navigational marks to assist in navigation and in collision avoidance;

The S-Band requirement to carry is in addition.
and reads as follows

2.7 All ships of 3000 gross tonnage and upwards shall, in addition to meeting the requirements of paragraph 2.5, have:
2.7.1 a 3 GHz radar or where considered appropriate by the Administration a second 9 GHz radar, or other means to determine and display the range and bearing of other surface craft, obstructions, buoys, shorelines and navigational marks to assist in navigation and in collision avoidance, which are functionally independent of those referred to in paragraph 2.3.2; and



So if one could get a good omni feed antenna pointed at the X band detector that should cover all shipping traffic and fixed beacons. Realizing of course that the beacons will only respond when someone elses signal hits them... Thos beacons also have lights and horns tho for when we stray to close.

Thanks

|>[/url]

[Moe]

Darren,
This article, under Characteristics of Marine Radar

Marine radar comes in two flavors, X-band and S-band. Ships will typically carry both, while small vessels are limited to the smaller X-band units. X-band radar operates at a frequency of approximately 9.4 GHz (9400 MHz), with a wavelength of 3.2 cm, while S-band operates at approximately 3 GHz, with a longer wavelength of 10 cm. X-band radar offers greater resolution and detection of smaller targets, but is more susceptible to interference from rain and seas (sea clutter). S-band radar has longer range and less interference from rain and sea clutter, but has less sensitivity for small targets.

A ship will typically use her X-band unit near shore, due to its higher resolution and ability to detect smaller targets. In conversations with ships officers, nearly all indicated that in offshore waters they depend entirely on the S-band unit set to a 24-mile scale. The advantage of S-band in this situation is longer range, less interference from rain, and reduced interference from sea clutter (a factor of about 2, or -4 dB).

This is not good news for radar reflectors, however, since performance falls off as the square of wavelength. This means that, at least in theory, a given reflector will have an S-band return of only one tenth (-10 dB) compared to its X-band performance. In a situation where the return from the sea state is the limiting factor, part of this loss is made up by reduced sea clutter, but the effective return will still be reduced to one fourth (-6 dB) compared to X-band.

The bolding on that statement is mine. While it may not mean they turn the X band unit off, it indicates as a minimum, at least to me, that they may not be watching it. If that's the case, and it's still on, we're good with an X band detector. If not...

--
Moe

[waternwaves]

Moe, Thanks for the clarification, I thought you might be referring to heavies and not the racons also.

I was just presenting it for the comparison. Most S band radars are much higher power, tho CW for the older units....and the reflected signal is correspondingly increased....somewhat compensating for the decrease in resolution.

Out here in the northwest, I have been told Pilots will not escort a vessel without X band onboard. I dont know if East coast pilotage rules require the same.

I have always wondered about fishing vessels tho, since they are inbetween in size, and off of the west side vancouver island I have noticed none with only a single radar.

And I think you are right, If I am more than 25 miles offshore or from known hazards to navigation, I suspect most heavy traffic will be operating with the S-band. But most macs (I feel fairly comforatble with this) rarely operate 25 miles out... (though I am the first to admit, west side of vancouver island, or off the pacific coast of washington or Oregon, I feel much safer out a ways rather than inshore. ) . But I am reasonably sure that in those cases my detection signature could be greatly improved with one of the large inflateable reflectors, and live with the drag penalty. Does anyone know of a folding Davis type 3 plane sized for S-band... 60 cm or larger across???

I turn my radar on inshore when navigating at night or fog, but I have not been leaving it on for nights offshore relying only on the reflector or or holding minimum head sail....(for me, knockdown seems less likely if making minimum headway in head seas. (plus I only have 3 batteries.....lol)

I guess I worry about it since I am clutter on their screens....lol, But I think in any defined shipping channel and inshore , X band is now required by their insurers...

Lets see..... If I am going to be scraped upon someones bow......

the only way I can think to improve their vigilance is to install a 300 lb mine under the front bunk.... and I am not sure that is going to help me sleep. and if I get iht, it wont matter anyway.. (tho it would be more difficult to get into Canada I suppose)

But Moe, you bring up a great idea tho,,,

and S band transponder or beacon.....hmmm, maybe under 100 mw, .. might be viable. mounted directly in the horn of the antenna. I'll check the FCC regs for unlicensed emmissions limits in that band...

EDIT
on 2.9 to 3.26 ghz FCC
1) intermittant control signals.....nope 47CFR2.31
2) periodic transmissions .... maybe 5,000 microvolts @ 3m 47CFR2.31,
3)Automated vehicle systems nope 47CFR15.251
4) Any other..... 500 microvolt/m @3 m 47CFR15.209

Since it needs to be able to broadcast in all directions for oncoming vessels... periodic isnt going to work..... so number 2) is out.

a quick check of antennas that would function omnidirectionally, (damn small group of antennas...) Looks like a custom molded plastic double conical horn, with aluminum coating is cheapest.

But the power level at 500 microvolt @3 m.......... around a 360 degree radius, and needing 5 -10 degrees of vertical beam width. looking at about transmitter of about 20-40 mW cw.

[Duane Dunn, Allegro]

I think some of the DSC features besides the GPS distress location are the best reasons to get it.

Things like being able to call another station directly rather than having to hail them. Being able to command the radio on the other end to follow you to a working channel.

Coll stuff like that which you would actually end up using.

[Kevin]

I have a DSC radio with the calling features, but it's an early implementation I got new in the box for $100. It had been part of a raymarine bundle.

The problem is the calling function seems clumsy. I think it's going to need about 2 more generations before those features are implemented in a useful fashion.

[Moe]

The DSC non-emergency calling functions are MMSI to MMSI, which in the recreational world is fine, if you're only out with one other boat.

Unlike individuals, commercial entities can get a "group" MMSI typically used on a second VHF unit, so that all boats in a fleet can be directly called.

Groups of recreational fishermen in an area, who often go out together, have done this as well, if not legally, by applying for an individual MMSI that they all use on a backup VHF.

--
Moe

[Kevin]

Ok, it's illegal, but I never thought of how useful that group MMSI would be.

All academic to me now, since once you put in your ID number it can't be changed. At least now without knowing some secret handshake.

[Moe]

Icoms let you set the MMSI twice without having to send them back to the factory or to a service center.

Let me clarify that those who use a "group" MMSI, legal or otherwise, on one radio, still usually have a different radio with their individual MMSI in it.

It's not something you can switch back and forth freely.

--
Moe