What is the range of a handheld vs an integrated DSC VHF?

[estarzinger]

Originally Posted by Dockhead

Gain is only one quality of antenna systems, and not the most important one.

So, what is the most important factor?

Let's assume the antenna's electrical length is appropriate to the vhf frequency.

I thought those were clearly the two top line factors (note we are talking here about vhf's, and not the full radio spectrum)

[Dockhead]

Originally Posted by estarzinger

So, what is the most important factor?

Let's assume the antenna is appropriate to the vhf frequency.

How well it's tuned with the feedline -- VSWR ratio.

See: VSWR

This determines how much of the signal is reflected back down the feedline and lost.

Efficiency.

This determines how much of the signal actually gets radiated from the antenna.

See: Antenna Basics

and:

Transmission Lines


"Gain" is just how much the radiation is concentrated in a particular direction. More is not necessarily better.

As you will see, it's not simple at all.

Also consider the fact that the condition of the cabling and connectors can make a huge difference in the amount of the signal which gets to the antenna, and to boot all of this is applied to not one, but to TWO antenna systems.

Then different radios have different sensitivity, different SNR, and other qualities.

And atmospheric conditions can make a huge difference.


The whole thing is complex enough that it would be really hard to predict anything meaningful.

A better way than an abstract calculator, is to actually test your own system on a regular basis, at different distances and with different correspondents. Then you get a real, practical experience about possible range under different conditions.

[estarzinger]

Originally Posted by Dockhead

VSWR ratio.

I would propose that we constrain ourselves to tuned VHF antenna - eg one that is the correct electrical length for VHF frequency. I am not proposing a calculator that can handle random length coat hanger wire antenna - only those specifically sold for and tuned to VHF.

I believe that would handle the antenna part of this effect


Efficiency

Have we not already addressed this in the power loss sub calculation? If specific brands and models of vhf antenna have significantly different efficiencies, they are surely published as a tech spec, and we just add that in the power loss calculation. But I was not aware that the common VHF antenna different that much in efficiency

transmission line

I am curious how big an effect this is in common VHF installations. It is discussed in HF installations, but I had never seen it discussed as a factor in VHF. You do understand that the wave lengths are quite different - right (on the order of 2m vs 35m I believe)?

We do know the cable length and might be able to calculate an estimate of this factor from that. But if not, we could include an (SWL) factor as an input (good, average, and poor).


Also consider the fact that the condition of the cabling and connectors can make a huge difference in the amount of the signal which gets to the antenna, and to boot all of this is applied to not one, but to TWO antenna systems.

yea, sure. I would start by assuming both systems were properly installed. You could then layer on top a 'good', 'average' and 'poor' factor if you wanted to.

Well, you dont want a calculator. You have made that clear. Fine. I happen to think something useful could be pretty easily done, because I have already seen something useful that is quite similar. And I don't like that when this question comes up the standard answer (radio line of sight formula) is just plain not right,.

........

[Jon Hacking]

Zinger, Dockhead is, unfortunately, correct. While something could be made, it probably wouldn't be that useful, which limits the enthusiasm to create it. There really are lots of variables to put in, & some of them simply aren't known - like propagation (atmospheric ducting) or insertion loss (I've been looking for a good VHF SWR meter for ages).

For instance, Ocelot has a reasonable VHF setup (I'm also a Ham). We usually have reliable boat/boat VHF coms out to ~30nm. But off the south coast of Mozambique we were regularly communicating with other cruising boats at 60-80nm, & some of those boats had pretty poor VHF installations. Remember, it takes 2 to tango, & the condition of both radio setups would have to go into the equations individually. I've received AIS fixes (which are just VHF) at 300nm, & friends have related stories of (salty) handheld VHF transmissions being received (by the corporate secretary) 1,000nm away.

Most of these can probably be hung on atmospheric ducting effects, which crop up here & there for poorly understood reasons. Sometimes they persist but more often they're pretty transitory. I can understand your frustration, but once you dig into it, you realize the complexity of the job. Leave out the difficult variables & calculations, & all you end up with is a "rule of thumb" calculator.

[estarzinger]

Yea, I know all that quite well . . . . and you guys are missing my point. SO let me try again.

I was NOT suggesting anyone try to create a complete 100% accurate calculator that encompasses all the possible physics and environmental factors to produce a 100% accurate calculation for every possible situation. Yes, I totally agree that is not feasible. It is not what I was suggesting.

The question I wanted to help answer was NOT "what precise range will I get with this specific equipment and this particular environment" . . . but rather "what sort of range can I generally expect in normal sort of conditions and if I change the primary user controllable elements how might I expect that general/ball park range to change."

my point/perspective is that right now when this question comes up we seem to have two answers to offer. Either Dock's "its too complex and we dont know" or the 'radio line of sight'. The first is not helpful and the second is not correct.

It seems to me that it would not be very hard at all to create something better, which adds in accounting for (for example) cable loss, power output and antenna gain (which seem to me to be the main user controllable factors).

Would that produce a completely 100% correct range estimate - no of course not. But would it be better than what we have now to answer the question - yes, it seems to me that it would. And that it would not be hard to create.

Yes, of course it would be 'rule of thumb' calculator, rather than a precise physical calculation. But it would still help people set their expectations better and understand alternatives a bit better. You would frame it as for 'standard conditions' and tell the users that they might for instance get 150nm range in some less than normal environmental conditions.

It could be made more complex (I only mentioned factors that I remember being in the military calculator that I saw), but just a very simple calculator that took just a few of the more important factors into account (beyond LOS) would IMHO be a useful addition to the discussion.

But **** . . . I dont use marine radios anymore . . . . so forget it.

[btrayfors]

IMHO, trying to construct a simple calculator to yield VHF distance is a fools errand. In actual practice, no reliable estimate can be given (for all the reasons discussed above), beyond the basic "line-of-sight plus a little", given normal conditions.

In practical terms, the focus of attention on such calculations is virtually meaningless, whether you're talking HF or VHF. One sees discussions all the time to the effect that, "and I talked to a station 800 miles away". This is truly meaningless. I've talked to stations 10,000 miles away from my boat using a 2.5 watt portable SSB transceiver....and I have witnesses to prove it.

But, so what? This proves nothing.

From Morocco I regularly talked to stations in Portugal on VHF. This was using the tropospheric ducting conditions often present in the area. So what?

With my 5 watt VHF handheld, I can talk to the International Space Station. So what?

Bottom line: the focus in any radio installation needs to be on ensuring the best installation reasonably achievable thru choice of radio, means of powering it, coax, antenna, etc. Operating practice and knowledge of the operator are also important.

Beyond that it is what it is. Distance talk should be reserved for bragging or complaining over cocktails.

Bill
WA6CCA

[estarzinger]

Btw . . . http://www.atmel.com/images/atmel-91...ation-note.pdf

And http://oai.dtic.mil/oai/oai?verb=get...fier=ADA481899

Among others . . . So I would politely suggest that the Military at least does not agree with you guys that this is worthless.

[Reefmagnet]

As an aside, does anyone ever actually tune their VHF to reduce SWR?

Sent from my SGP521 using Cruisers Sailing Forum mobile app

[Jon Hacking]

Originally Posted by estarzinger

...Would that produce a completely 100% correct range estimate - no of course not. But would it be better than what we have now to answer the question - yes, it seems to me that it would. And that it would not be hard to create...

WE certainly use VHF - all the time. OK, how about this:

On our AIS page, we discuss range & I give the formula:

D=1.42*(√h) or D=√(2h), where D is Distance in miles and h is antenna height in feet above the water. Since we need the height of both the xmitting antenna & the receiving antenna, the formula becomes:
D=√(2h1)+√(2h2).

This assumes you're going boat-to-boat over open water & have the power & antenna gain to break through the squelch at the other end. This may not be true of a 2W AIS signal but should be true for most 25W base stations & older class-A AIS at ranges under 50nm. It also breaks down a bit when the CG puts their antenna at the top of Mt. Tam, as then the range becomes so big that power & receiver sensitivity considerations are dominant.

Rude & crude, but it's a pretty easy first cut. It gets much more complicated if you add signal strength (xmitter power, cabling losses, antenna gain) & receiver sensitivity (for each end). FWIW, I find that I get slightly better range than what this formula would predict, but I often don't know the height of the other guy's antenna.

[estarzinger]

Jon, That's just the radio line of sight formula. Which I am completely familiar with. It (for example) does not answer the very simple questions (1) what is the expected result if I push this low power button', or (2) what if I use a zero gain rubber duck antenna (as some racers consider doing, or (3) 'fixing' their coax connectors?

Bill, you are still completely missing my point. I agree with you. I don't care what sort of extreme range you get in some odd situation. as you say "Distance talk should be reserved for bragging or complaining over cocktails."

The useful question to answer is what likely effect in typical and normal conditions would be of typical and normal changes to the radio gear that sailors actually consider (like pushing the 1 watt button or using a o gain antenna or 'fixing' they connections).

If anything the question is NOT what is the maximum possible range but rather what is likely the minimum expected range. It is just that you amateur radio guys are all so caught up on the extreme range competition that you can't seem to think about it in any other way.

The Military on the other hand does in fact want to be able to understand the trade-offs of various radio configurations talking to their anti-tank missiles (just for instance). They want to understand if we change this (say the power level) factor what will be the likely operation effect to range. And they have found calculations useful to answer those sorts of questions.

[btrayfors]

Evans,

Well, I may be missing your point, but the truth is I don't find it relevant at all for the marine community. Why?

1. Because we're not going to "push the 1W" button unless there's a reason (like communicating with nearby boats) or using Channel 13 which automatically drops from 25W to 1W; and

2. Because most marine installations are what they are, bad connections and bad coax, and bad radios, and inexperienced operators and all.

Your question of "what's the minimum distance" is easy to answer, without any sort of table:

THE MINIMUM DISTANCE FOR VHF COMMUNICATION FROM A (COMPROMISED) VHF INSTALLATION IS ZERO.....ZIP....NADA.

BTW, little rubber-ducky type antennas on handhelds actually have a NEGATIVE gain, i.e., they are terrible. All very short end-fed antennas are the same.

A better question might be, What is the distance potential between marine VHF stations over water with a combined height of 100ft (two sailboats, each with the VHF antenna at 50ft above sea level) AND each with an ERP of 20 watts?

ERP is "effective radiated power" and is commonly used to describe the power of transmitted signals. It is always relative to a theoretical reference half-wave dipole antenna. ERP takes account of radio output power AND all losses and gains in the transmission line coax, connectors, meters, and antenna.

Here, again, the answer is pretty simple: it's line-of-sight plus a bit, perhaps 20%, under normal conditions. It is further augmented or reduced by magnitude of ERP and by the sensitivity of the two receivers and by factors amplifying or attenuating signals between the antenna and the transceiver.

Bill
WA6CCA

Originally Posted by estarzinger

Jon, That's just the radio line of sight formula. Which I am completely familiar with. It (for example) does not answer the very simple questions (1) what is the expected result if I push this low power button', or (2) what if I use a zero gain rubber duck antenna (as some racers consider doing, or (3) 'fixing' their coax connectors?

Bill, you are still completely missing my point. I agree with you. I don't care what sort of extreme range you get in some odd situation. as you say "Distance talk should be reserved for bragging or complaining over cocktails."

The useful question to answer is what likely effect in typical and normal conditions would be of typical and normal changes to the radio gear that sailors actually consider (like pushing the 1 watt button or using a o gain antenna or 'fixing' they connections).

If anything the question is NOT what is the maximum possible range but rather what is likely the minimum expected range. It is just that you amateur radio guys are all so caught up on the extreme range competition that you can't seem to think about it in any other way.

The Military on the other hand does in fact want to be able to understand the trade-offs of various radio configurations talking to their anti-tank missiles (just for instance). They want to understand if we change this (say the power level) factor what will be the likely operation effect to range. And they have found calculations useful to answer those sorts of questions.

[Ziggy]

Originally Posted by estarzinger

Jon, That's just the radio line of sight formula. Which I am completely familiar with. It (for example) does not answer the very simple questions (1) what is the expected result if I push this low power button', or (2) what if I use a zero gain rubber duck antenna (as some racers consider doing, or (3) 'fixing' their coax connectors?

Bill, you are still completely missing my point. I agree with you. I don't care what sort of extreme range you get in some odd situation. as you say "Distance talk should be reserved for bragging or complaining over cocktails."

The useful question to answer is what likely effect in typical and normal conditions would be of typical and normal changes to the radio gear that sailors actually consider (like pushing the 1 watt button or using a o gain antenna or 'fixing' they connections).

If anything the question is NOT what is the maximum possible range but rather what is likely the minimum expected range. It is just that you amateur radio guys are all so caught up on the extreme range competition that you can't seem to think about it in any other way.

The Military on the other hand does in fact want to be able to understand the trade-offs of various radio configurations talking to their anti-tank missiles (just for instance). They want to understand if we change this (say the power level) factor what will be the likely operation effect to range. And they have found calculations useful to answer those sorts of questions.

Evans,
What you're asking for is a link budget for a terrestrial VHF comm link. In order to calculate it, you need to know the receive station parameters, in addition to the transmitter. For example, you can trade transmit equivalent isotropic radiated power (EIRP) for receive antenna gain and receiver noise figure. That's why communicating with a Coast Guard station is different from communicating with a boater with a handheld radio with a rubber duckie antenna. If you really want to educate yourself, google "vhf link budget calculator" and you will find a few.

[estarzinger]

Originally Posted by Ziggy

Evans,
What you're asking for is a link budget for a terrestrial VHF comm link. google "vhf link budget calculator" and you will find a few.

YES, exactly. Thank you.

[Svanen]

Originally Posted by btrayfors

IMHO, every boat should have a quality fixed VHF radio installed, PERIOD. This is not a big investment in $$$, but certainly is a big investment in safety

As to EPIRBs, IMHO every boat venturing offshore should have a good EPIRB, preferably one with an internal GPS. Maybe in Indonesia they cost $1,000 but they cost much less these days in the U.S.

Everyone is entitled to their opinion; but I'm glad you're not in charge of enacting legal requirements.