Amazing Power of Good Antennas

[El Rubio]

Originally Posted by s/v Jedi

Exactly, and this is the reason that you should not use RG8x or RG58 cable (or any equivalent) but step up to RG213/LMR400 type. With a limit of 25W you can not afford to throw half away like you seem to think. With higher output power you can compensate for losses in transmissions, but you only have 25W plus it does not help for receiving far away stations (except coast guard who use very high antennas and high output power).

I can simply check the 3dB difference by switching from 25W to 50W and find that the difference for long range communications is enormous. I can do this with one of my HAM radios.

For VHF cruisers nets I can relay for boats underway that nobody else even hears in the noise. This means that my antenna and cable is much better than theirs and this should be reason enough for anybody to do this. Every boat can install LMR400 size cable and the extra cost is marginal for such a primary safety device

So you're using your 2 meter transceiver opened up to transmit on VHF marine bands. Did you consider that you're breaking the law by transmitting higher power than is allowed by the FCC, also using a transceiver outside its designed frequency range? Following what I said previously, I don't think your 3dB power increase has much effect on other users, but you're running full power on a transmitter designed and tuned for the 2 meter amateur band. From what I've seen, this can create intermod and splatter which might be adding to the noise floor or interfering with other users. I'm not the radio police, but it did occur to me as you described your setup.

I believe your pwr increase produces a noticeable change, but enormous isn't a word I'd use to describe it. ( this is where someone is supposed to chime in with " that's what she said" ) I have done this, just not on marine frequencies.

Your relay example doesn't necessarily mean your antenna/feedline is superior, but sounds like maybe you were just between two stations which were closer to you than each other. A dB or two isn't enough to punch through the noise. I don't know the situation and it's likely affected by many things including the other station condition, antennas, and antenna height. Judging from your other posts here, it sounds like your rig would be in good working condition...except for the possible intermod when you transmit

This cable and acceptable loss thing is a bug of mine, as I'm sure anyone reading here is aware. Assuming 100' feedline, Lmr240 is rated at 3db loss.

The difference between LMR400 & 240 is 1.5dB, but 400 costs .30 per foot more.
RG213 & LMR240- 0.6 dB and about $1 per foot more than 240 for Belden 8267.

The .6-1.5dB difference is minuscule. There is really nothing to gain at these frequencies and lengths. $30- $100 isn't a lot, but why spend unnecessarily, and the 240 is very thin and easier to route. It can be an issue especially if you are running a second AIS antenna or spare VHF.

[s/v Jedi]

Originally Posted by El Rubio

So you're using your 2 meter transceiver opened up to transmit on VHF marine bands. Did you consider that you're breaking the law by transmitting higher power than is allowed by the FCC, also using a transceiver outside its designed frequency range? Following what I said previously, I don't think your 3dB power increase has much effect on other users, but you're running full power on a transmitter designed and tuned for the 2 meter amateur band. From what I've seen, this can create intermod and splatter which might be adding to the noise floor or interfering with other users. I'm not the radio police, but it did occur to me as you described your setup.

I believe your pwr increase produces a noticeable change, but enormous isn't a word I'd use to describe it. ( this is where someone is supposed to chime in with " that's what she said" ) I have done this, just not on marine frequencies.

Your relay example doesn't necessarily mean your antenna/feedline is superior, but sounds like maybe you were just between two stations which were closer to you than each other. A dB or two isn't enough to punch through the noise. I don't know the situation and it's likely affected by many things including the other station condition, antennas, and antenna height. Judging from your other posts here, it sounds like your rig would be in good working condition...except for the possible intermod when you transmit

This cable and acceptable loss thing is a bug of mine, as I'm sure anyone reading here is aware. Assuming 100' feedline, Lmr240 is rated at 3db loss.

The difference between LMR400 & 240 is 1.5dB, but 400 costs .30 per foot more.
RG213 & LMR240- 0.6 dB and about $1 per foot more than 240 for Belden 8267.

The .6-1.5dB difference is minuscule. There is really nothing to gain at these frequencies and lengths. $30- $100 isn't a lot, but why spend unnecessarily, and the 240 is very thin and easier to route. It can be an issue especially if you are running a second AIS antenna or spare VHF.

Sorry but you are not correct:

- For emergency traffic you can transmit with whatever you like at any frequency and power level. I do not use this for regular traffic. And yes, you sound exactly like the radio police.

- you give up 1.5dB of power level to save $.30/ft on cable? why would you put such a low price on safety for all aboard?

- 1.5dB on cable alone is not a small deal. It is a big deal and when you select connectors and installation methods the same way as the cable, you will be at a 3dB loss (half the power is lost) compared to a good install, which severely impacts your long range communications. You keep insisting that this doesn't matter, but that is not correct.

I believe you have LMR240 cable and now must persist that your (not so good according to us) choice is better because that is the way many act on the Internet.

[JRM]

Let me toss in a data point here. I recently had my mast out, and replaced nearly everything. Except the antenna, which was a handy combo windex/antenna. I do a lot (well, did before I bought a project boat) of antenna experimentation at my ham station, so I have a MFJ antenna analyzer. The antenna toned out fine, so I reused it.

I did however, replace the coax with tinned RG-213, and I did away with the mast foot connectors. When I pulled the mast, I back-pulled a $7 snake from Harbor Freight with the coax. Then when the mast was restepped, it was a snap to just pull the long tail of 213 to the radio.

I double checked everything with the analyzer, and it's money. But the proof is in the pudding so to speak, and I am hearing "way" more traffic after than before. Quality coax and properly installed connectors make a big difference, even PL-259s...

I'm moving my AIS transponder over from the old boat, and it has its own antenna. I've been mulling over building a "patch panel" of sorts so that I can easily swap between radios and antennas. That way I can use the masthead antenna for AIS, but swap back out if I need the VHF range.

JRM

[El Rubio]

Originally Posted by s/v Jedi

Sorry but you are not correct:

- For emergency traffic you can transmit with whatever you like at any frequency and power level. I do not use this for regular traffic. And yes, you sound exactly like the radio police.

OK, your earlier post sounded like you used the amateur radio out of band to casually converse or relay non-emergency traffic. It's otherwise illegal and has a much higher likelihood of causing intermod and interference to others.

Originally Posted by s/v Jedi

- you give up 1.5dB of power level to save $.30/ft on cable? why would you put such a low price on safety for all aboard?

I wouldn't. 1.5dB is splitting hairs and not noticeable in regular operations.

Originally Posted by s/v Jedi

- 1.5dB on cable alone is not a small deal. It is a big deal and when you select connectors and installation methods the same way as the cable, you will be at a 3dB loss (half the power is lost) compared to a good install, which severely impacts your long range communications. You keep insisting that this doesn't matter, but that is not correct.

I don't see how you derive selecting connectors and especially installation methods out of what I said. A "good install" can be made with RG58 in the right situation.
You keep focusing on "3dB" which I believe is an acceptable overall loss. The 0.6-1.5 dB loss in comparison is what is miniscule and unoticeable. That is what doesn't matter in the real world. 3dB is noticeable, but minor and acceptable on the whole, just like the installation Dockhead described.
If the difference was 3dB or more, it may be worth it, but this is VHF and<100'.

Originally Posted by s/v Jedi

I believe you have LMR240 cable and now must persist that your (not so good according to us) choice is better because that is the way many act on the Internet.

I like 240 for the size. It's high quality, low loss for it's size, and relatively low priced. I think it's a great cable for mobile antennas & on most marine VHF installations. In reality, most marine installs will use closer to 50' and the losses around half of that which makes it even less significant. I didn't say it was better cable, but adequate for most marine VHF installations. Just like PL-259's are adequate. It's splitting hair.

[s/v Jedi]

Originally Posted by El Rubio

OK, your earlier post sounded like you used the amateur radio out of band to casually converse or relay non-emergency traffic. It's otherwise illegal and has a much higher likelihood of causing intermod and interference to others.

I wouldn't. 1.5dB is splitting hairs and not noticeable in regular operations.

I don't see how you derive selecting connectors and especially installation methods out of what I said. A "good install" can be made with RG58 in the right situation.
You keep focusing on "3dB" which I believe is an acceptable overall loss. The 0.6-1.5 dB loss in comparison is what is miniscule and unoticeable. That is what doesn't matter in the real world. 3dB is noticeable, but minor and acceptable on the whole, just like the installation Dockhead described.
If the difference was 3dB or more, it may be worth it, but this is VHF and<100'.

I like 240 for the size. It's high quality, low loss for it's size, and relatively low priced. I think it's a great cable for mobile antennas & on most marine VHF installations. In reality, most marine installs will use closer to 50' and the losses around half of that which makes it even less significant. I didn't say it was better cable, but adequate for most marine VHF installations. Just like PL-259's are adequate. It's splitting hair.

No, I think you are just insisting that your choice must be the right one. Just because you can do that, not because it is better.

[El Rubio]

Originally Posted by s/v Jedi

No, I think you are just insisting that your choice must be the right one. Just because you can do that, not because it is better.

Your Jedi mind reading powers are failing you. I'm not insisting my suggestion is the only way, but an economical, high quality, and adequate performance compromise. I posted my numbers and that's it. I didn't say it was better performance wise either. I said the compromise was minimal and basically undetectable during operation. I'm fine with you disagreeing, but don't try to decipher what you think is written between the lines.

[hellosailor]

JRM-
If you are pulling multiple cables...Consider putting a break at the base of the base, or wherever the AIS cable penetrates the hull as well. And then adding another run straight down to the keel, so that you can directly ground the coax if lightning looks likely.
Best way to encourage lightning to stay out of the radios, is to give it a straight short path right down and out. Or at least, install a PolyPhaser or similar device to encourage that, in the same location.

Guys, you know when you're talking db losses and what's "normal" or "acceptable"...like the former Federal Reserve chairman used to say "A couple of billion here, a couple of billion there, sooner or later you're talking real money."

And since all marine VHFs are FM radios and the FM capture effect applies to all transmissions from them...If I'm trying to call a restaurant to reserve their last dock and their last steak for dinner and a tie-up tonight, and they read me just ONE DB more than they read you, I'm going to capture the flag, walk right over your call, and that last slip and last steak are mine. Right?

So one db here, one db there...it doesn't pay to get anal about it, but if you can add a few db of gains here and there, sooner or later it is real money. 3db loss probably won't kill anyone, unless that was your distress call not capturing the flag.

[Dockhead]

An additional data point.

I was just outside of Cherbourg harbor yesterday, and called Solent Coast Guard, 60 miles away, for a radio check. The answer was "you are weak, but readable". I told my shipmate -- you see, all the great range I was experiencing last summer really was just tropospheric ducting or something like that, after all.

Then I noticed that the radio was set on low power -- 1 watt. Its normal setting these days -- I forgot to switch it over.

What it means is that with a good antenna and a 25 watt marine VHF radio, you have comms over a huge area -- thousands of square miles. It means that there is no place in the English Channel -- a very large body of water -- where I can't talk to someone's or another's coast guard by VHF.

[colemj]

I heard you all the way in Guatemala! Good thing you weren't on 25W - we would have to get earplugs!

Mark

[transmitterdan]

Originally Posted by Dockhead

What it means is that with a good antenna and a 25 watt marine VHF radio, you have comms over a huge area -- thousands of square miles. It means that there is no place in the English Channel -- a very large body of water -- where I can't talk to someone's or another's coast guard by VHF.

Not so fast there Grasshopper<g>. More power does not equate to more coverage area. When you hit the radio horizon the path attenuation increases like a rocket. This is why some of us have argued that 1-2dB loss in the installation does not reduce coverage area significantly. You have basically proven the point some of us were ridiculed for advancing. Your attenuation was 14dB and you still got through.

More power does allow you to overcome more noise. But that's not the same thing as more coverage area.

[goboatingnow]

But 60 miles to a CG tower is not at all unusual in my experience, any good Vhf install will achieve that

Dave

[El Rubio]

Originally Posted by goboatingnow

But 60 miles to a CG tower is not at all unusual in my experience, any good Vhf install will achieve that

Dave

I think this is Dockhead's point, properly installed components perform well.

[transmitterdan]

I agree that a good install will reach a CG tower that is 75M above the earth. But a bad install with 10dB of attenuation can do that too especially considering the CG are talking back to you with way more than 25W. But no amount of install prowess can overcome the curvature of the earth. Only ducting can do that but ducting is not reliable.

And please don't jump me as if I am promoting "bad" installs. I'm not saying we should do things badly. Badly done installs are often unreliable or intermittent which is exactly what you don't want. Well made connectors are more reliable. Good quality coax is more reliable. But adding a bunch of weight aloft and clogging up the mast with fat coax cables is not necessary to have a "good enough" install.

Perhaps this thread should be titled The Amazing Power of VHF FM Radio. It truly is amazing.

[Goudurix]

Reciprocity, guys.

A 3dB gain in power by replacing the RG58 with a better coax doubles your power at the antenna.

But the same goes for your reception hence advantage at weak signal reception.

And off course this is all less important and critical when talking to 75m high CG stations.

I optimized my system with a better coax (hell those who've read the read on soldering PL-259's will now I should still optimize the plug up the mast ) and I know I can rely on my system.

And I have my yaesu FT897 at hand as a spare in case the marine VHF fails or extra power and a better receiver are needed....

Jan

[transmitterdan]

Originally Posted by Goudurix

Reciprocity, guys.

A 3dB gain in power by replacing the RG58 with a better coax doubles your power at the antenna.

But the same goes for your reception hence advantage at weak signal reception.

Jan

Yes, your math is right but more power doesn't normally translate into longer distances. Dockhead's report shows that even a 14dB reduction in transmit power still provided great coverage distance. VHF FM systems with 25W transmitters are naturally limited by the curvature of the earth. To communicate past the line of sight requires a massive power increase (way more than 3dB) or a higher antenna. In 99.9% of cases in open water, line of sight can be reached with even 6dB less than 25W. For open water comms the 1-2dB of power gained by big fat coax is wasted and the extra weight and space in the mast is not necessary. One might make a limited case for inland boats that communicate through vegetation that a couple dB more signal helps. But even then the benefit is marginal because inland comms are normally over shorter distances.

This and other threads have debated the effects of a 1dB insertion loss from an AIS splitter. 1dB loss is not significant compared to 14dB in line of sight VHF over open water. It is much more important that connections are well made, water is kept out and the cable and connectors are high quality and the right impedance. Also, receiver sensitivity can be a significant factor but most good radios are sensitive enough.