Marine radios

[dwman53]

Ran across an article about the latest radio features

http://www.paddling.net/guidelines/showArticle.html?609

[Lbeale]

Thank you - for this link and articles most informative. Amazing how these radios have developed over the years.

Les

[Gcosloy]

Does DSC capable radios allow you to automatically broadcast your position? i.e longitude/latitude If so could be a life saver! I won't go into details but over the last 6 years or so of kayaking I've made two Mayday calls, (well maybe one was a Pan Pan call.) In both instances I could not retrieve my position from my hand held GPS. Its a long story but I was too nervous to remember to press either the Find or MOB button on my Garmin 60CSX. The second episode I didn't have my GPS and was not able to give the CG location information that they could use to locate me. They tried to triangulate my VHF broadcast finally but by that time I found a bail out spot that was less than life threatening. Both instances were my bad-the first in attempting to rely on electronic gizmos that I barely new how to use properly, and the second having poor navigational skills that defied my ability to state my position unequivocally. But maybe DSC is designed for fools comme moi. I'm sure the CG spends more time and energy and perhaps with more failure and loss of life with examples like the above. Finally something close to idiot proof at an affordable price. Sure beats an EPIRG at $500 or more.

[EEL]

Does DSC capable radios allow you to automatically broadcast your position?

Gene:

Short answer. Yes. Long answer.

http://www.uscg.mil/acquisition/rescue21/benefits.asp

Very neat stuff.

Ed Lawson

[billvoss]

Does DSC capable radios allow you to automatically broadcast your position?

For a kayaking application you would want a DSC capable radio with a built-in GPS. There are also DSC radios without GPS, which would not be useful for a typical kayaking scenario.

For example, the original poster's article referenced the Standard Horizon HX851 (note, I own the prior HX850 model) which is described as having:

• Built-in 12 Channel GPS Receiver
• DSC functions include: Distress call with position, All ships, Urgency,

  Safety, Individual call, Position Request, Position Report and Group call

With the HX851 radio, you lift a plastic cover which is labeled "Distress" or "SOS" and press the button under it. The radio will then send an electronic SOS signal which includes both your GPS position information, and your MMSI number. So the coast guard will know who and where you are. For a coastal kayaker in New England, I would (and did) buy this radio before buying a PLB. (Though the following year I also bought a PLB).

The original article also referenced Standard Horizon HX471S which is described as having:

• DSC Distress call with NMEA GPS position input

The HX471S is a DSC radio. So it to is required to have a plastic cover labeled "Distress" or "SOS." If you lift that cover and press the button under it, the radio will send an electronic SOS signal which includes your MMSI number. So the coast guard will know who you are. However, it does NOT contain a built-in GPS. The phrase with NMEA GPS position input means if you connect a data wire between this radio and a GPS, then the radio will know where you are, and then it can include your position information in a distress signal. That is a reasonable option on a bigger boat, where the radio lives in a charging cradle that is wired into the ship's GPS system. It is not a useful option for a kayaker.

So yes, you can get the behavior you want, but you need a handheld DSC radio with built-in GPS.

[subaruguru]

Received the latest West Marine mailer touting all the new radios while reading an email from a fellow paddler annoyed that his new fancy GPScumRadio's antenna tickles his left nostril. Well!

I just finished replacing my 1/8 wavelength Miata's FM shorty antenna (16") with a "proper" old-school 1/4 wave (31.5" for NPR/college c. 90MHz), and will be comparing S/N ratios (probably cheating by just using the autoscan counts).

So naturally my brain cross-fired and I thought about calculating ideal antenna lengths for our VHF use (156-177 MHz). Simply:

1/2 wavelength: 72" (some say 5/8 wave can be better: 81"!)

1/4 wavelength: 36" (damned good)

1/8 wavelength: 18" (pretty ideal compromise for kayaks?)

1/16: 9" (yech...getting pretty weak, but has that old-school look!)

1/32 wave" 4.5" (probably what's used in the bulk of our modern choices...and pretty useless without unobtanium batteries?)

Manufacturers have to use HUGE battery power and thus fast drain-rates to overcome the poor signal strength capability of such short antennae.

Anybody successfully install a waterproof true 1/8" wave (18") telescoping antenna on their portable marine radio? Could be good for poking, pointing out seascape features, etc....

Or what about a flexible J-shaped 18" "hook" antenna that could, oh I dunno, hang around one's neck, solving both the attachment AND signal strength issues simultaneously?

Thoughts? Ideas? Pros and cons?

[EEL]

Manufacturers have to use HUGE battery power and thus fast drain-rates to overcome the poor signal strength capability of such short antennae.

Ern:

I have some thoughts on antenna length, but before saying more would like to know what you mean by this. Are you saying that if they used a more efficient antenna the radios could be designed for lower wattage output only which in turn would mean a smaller battery or at least enable the existing batteries to last longer?

Ed Lawson

[bob budd]

On something like a cell phone, the participants continuously train for optimal output power to maintain communications. This is usually called "battery management". For a VHF radio I don't believe there is a similar conversation going on, though there could be. Most likely the antenna length has been optimized for duration and quality of service and modifying the antenna would not save battery life, especially if there is no feedback as discussed above. However, a different antenna might extend your range, though it might also interact with the measures taken to optimize duration and quality of service.

As an example, the optimal antenna length for AM reception (dating myself here) is a size that is impractical for mounting in an automobile. Instead, components such as rod antennae are installed to improve reception. In fact, a better antenna can overdrive the receiver and reduce performance. Because FM reception happens at ~100x the frequency of AM reception the optimal antenna is ~.01x (~1/100x) the size and thus practical for mounting in an automobile, one reason why FM reception is demonstrably better in most autommobiles.

[subaruguru]

Ern:

I have some thoughts on antenna length, but before saying more would like to know what you mean by this. Are you saying that if they used a more efficient antenna the radios could be designed for lower wattage output only which in turn would mean a smaller battery or at least enable the existing batteries to last longer?

Ed Lawson

Hi Ed,

That's my hypothesis. An antenna is really a transducer of sorts. Or maybe think of pushing a fluid through a pipe: the smaller the orifice the higher the pressure needed to move a given amount.

When I was a kid I learned that it wasn't so much the power of my ham radio transmitter that was important as it was using as long an antenna as possible that was tweaked to match band wavelength (in this case I recall c. 80 ft being correct for high efficiency, as I didn't have a 160 ft yard).

Hi Bob,

Interesting premise re battery management, but I believe that ergonomics (VERY short antenna) is a given primary design constraint, and that the balancing act becomes battery type (cost) vs. power output, and thus drain cycles.

However I think the "overdrive" issue you mention is a red herring for portable marine VHF, as saturation (signal overload) and possible resultant audio clipping is not a critical issue. As kayakers don't we struggle more with antenna placement (keeping it as high off the water as possible to help with earth's curvature) while using an incredibly inefficient antenna both for reception AND especially transmitting? I don't think intelligibility is compromised by overload as often as by poor signal to noise ratio, and the latter can be greatly improved with a longer antenna.

Because reception requires little power, battery issues are less critical, but in transmitting we're really trying to push a signal through a small hole, using as much power as possible for only meager success. It occurs to me that a limiting factor too is overheating via too-fast battery drainage. A friend of mine flies RC gliders using tiny super-high RPM motors that drain a battery pack in in 90sec, getting both REALLY hot. Can't have that in a small radio either....

Again my antenna thoughts are based on classic RF theory and NOT state of the art product designs. Hence my post-hibernation queries....

Nice to hear from ya.

[EEL]

The short antennas supplied on handheld radios of all types are known as a rubber ducky and jokingly referred to as a dummy load by hams because they are not efficient by any means.

However, it is not simply a short antenna in terms of its electrical as opposed to physical length as this article shows.

http://en.wikipedia.org/wiki/Rubber_ducky_antenna

All things considered they are a better antenna, by far, for the intended use than a physical 1/4 or 1/2 WL vertical attached to a handheld.

Been there, done that. Not going back.

It is true a rubber ducky is about 6db down from a good 1/2 WL antenna which in turn means for the same field strength it needs to be driven with four times as much power which in turns means more current and faster discharge of the battery. However a 1/2 WL (physical and electrical) antenna for marine VHF use is way too big to be practical for a handheld used by a kayaker.

Ed Lawson

[subaruguru]

The short antennas supplied on handheld radios of all types are known as a rubber ducky and jokingly referred to as a dummy load by hams because they are not efficient by any means.

However, it is not simply a short antenna in terms of its electrical as opposed to physical length as this article shows.

http://en.wikipedia.org/wiki/Rubber_ducky_antenna

All things considered they are a better antenna, by far, for the intended use than a physical 1/4 or 1/2 WL vertical attached to a handheld.

Been there, done that. Not going back.

It is true a rubber ducky is about 6db down from a good 1/2 WL antenna which in turn means for the same field strength it needs to be driven with four times as much power which in turns means more current and faster discharge of the battery. However a 1/2 WL (physical and electrical) antenna for marine VHF use is way too big to be practical for a handheld used by a kayaker.

Ed Lawson

I know, I know. It's just a whatever-length aided by a tuned coil. I used to have to build them to trim long ham antennas as a kid too. Basically a box of coils and switches so that one could use a fixed-length antenna for different wavelengths, "tuning" its electrical length easily. Beats getting on a ladder in the winter or in a storm!

I just noticed that the Standard Horizon I have has an exposed 7" flex-whip...probably extended 2-3 inches into the body, totaling about 9.5", or a 1/8 WL. Is it then "goosed" with a coil or some other means? Dunno.

To cut to the chase: I simply wonder if using a true 1/4 WV (19") would significantly improve reach, and therefore reduce battery usage too?

I could imagine some kind of waterproof "extender" that could pull out and extend the existing 7" to 16" (+ 2.5" in the base)? Or an upside-down "J" that could loop GENTLY around one's neck? Ok ok....

I'm discussing this very topic with the clowns on an auto site who are comparing cute stubby antennae. I just killed an hour comparing sensitivity vs antenna length using FM (88-108...not too far from our 146MHz) and an efficient and reproducible capture ratio used by the seek function of an auto receiver. Worked nicely:

Antenna Length (in) ..... Stations "captured" cleanly

0" ... 3 stations

1" ... 13 (anything's better than nothing!)

2" ... 13

3" ... 14

5.5" ... 21 (starting to get somewhere)

8" (1/16 WL)... 24

16" (1/8 WL).... 29 (nice compromise for a fixed car antenna)

24" ... 34 (this increase was a bit unexpected)

31.5" (1/4 WL) ... 37 (nice old-school telescoping whip for an auto)

41" (whip max) ... 37 (as expected, no improvement over 1/4WL yet)

63" (1/2 WL) ... wish I had one on hand....

You said "Been there. Done that." You've tried an 19" 1/4WL antenna on a marine VHF? What'd you find? I understand the not insignificant ergonomic hurdles, but I'm very curious about performance improvement.

[EEL]

You said "Been there. Done that." You've tried an 19" 1/4WL antenna on a marine VHF?.

I have used a telescoping antenna as a 1/2 WL end fed antennas on two meter ham band handheld which is around 147MHz which compares well to the 155MHz of the marine band. It enabled me to have better communication with a base station and with distant repeaters than a stock rubber ducky in special operating situations. However, that is a big antenna for normal use. Too big actually. In theory, I doubt there would be a sufficiently greater advantage to using a physical 1/4 WL antenna compared to a rubber ducky to matter much and have never used one, but until you measure with a field strength meter you don't know. I think as bad as they are, a good rubber ducky is not that bad as a practical matter. Of course there are some stock ones are poor. Still, I routinely talk to friends using a stock two meter 5W handheld via repeaters that are well over 20 miles away. Reception is never a problem. I can hear repeaters over 75 miles away.

Ed Lawson

[subaruguru]

Hi Ed, (et al?)

Yeah, 1/2 WL is out of the question, and as I remember just doable for 2m portable ham, but I was too young to drive back then!

Couldn't remember the efficiency diff between 1/4 and 1/2WL monopoles, but a google popped up the following, suggesting best performance of a coil-based monopole of a way too longish 5/8WL:

http://www.smeter.net/antennas/bottom-loading.php

Another site referred to bent monopoles, like a "meander antenna" that I suppose are more compact, but I'm still intrigued by the possibility of adding a 1/4 WL to our marine VHF to see if transmitting "reach" is dramatically improved.

Are our SH and iComm units 1w max or really pushing 5w? That would be damned-quick battery drain....

G'night, and thanks for the trip down memory lane.

[leong]

Hi Ed, (et al?)

Yeah, 1/2 WL is out of the question, and as I remember just doable for 2m portable ham, but I was too young to drive back then!

Couldn't remember the efficiency diff between 1/4 and 1/2WL monopoles, but a google popped up the following, suggesting best performance of a coil-based monopole of a way too longish 5/8WL:

http://www.smeter.net/antennas/bottom-loading.php

Another site referred to bent monopoles, like a "meander antenna" that I suppose are more compact, but I'm still intrigued by the possibility of adding a 1/4 WL to our marine VHF to see if transmitting "reach" is dramatically improved.

Are our SH and iComm units 1w max or really pushing 5w? That would be damned-quick battery drain....

G'night, and thanks for the trip down memory lane.

In my experience it seems that line-of-sight clearance and antenna height in a kayak is a bigger problem than path loss limitations due to antenna efficiency. I’d take a “rubber ducky” elevated to 10-feet over a better antenna at water level any day. Balloons or kites anyone?

[Pintail]

<Balloons or kites anyone?>

Yes, Royal Air Force pilots "downed" in World War II were issued not only with an inflatable raft, but also a kite to carry aloft...the aerial (antenna) for their R/T!

[PeterB]

<Balloons or kites anyone?>

Yes, Royal Air Force pilots "downed" in World War II were issued not only with an inflatable raft, but also a kite to carry aloft...the aerial (antenna) for their R/T!

"per ardua ad astra"

[subaruguru]

In my experience it seems that line-of-sight clearance and antenna height in a kayak is a bigger problem than path loss limitations due to antenna efficiency. I’d take a “rubber ducky” elevated to 10-feet over a better antenna at water level any day. Balloons or kites anyone?

Indeed. I commandeered a salvage telephone pole from my street as a kid and asked my Dad to help me re-erect it in the back yard to get my ham antenna up another 20 ft.

Still liking the telecoping marine 19-incher idea, but a 75" boon collapsible boom would be MUCH better!

Let's build it, Leon!