Coax cable for long run up mast

[Dockhead]

Originally Posted by S/V Illusion

You must be a new ham. Time to ‘hit the books’.

We’re not talking about audio level. We are discussing a power function which is entirely different. While you cannot hear a 1.5dB audio difference, a 1.5dB signal loss is equivalent to a 20% reduction in power output at the antenna and can be the difference in being intelligeable above the noise floor.

Parenthetically, marine VHF radio’s don’t have an AGC circuit or control.

The power function directly translates. He's right. And that's why we use dB for both.



20% is very unlikely to make the difference you say. 300% or 400% -- maybe.

[S/V Illusion]

Originally Posted by Dockhead

The power function directly translates. He's right. And that's why we use dB for both.



20% is very unlikely to make the difference you say. 300% or 400% -- maybe.

Actually, it doesn’t but the explanation is beyond what is appropriate on a boat forum. The internet is full of links which explain the distinction.

[Nicholson58]

Use the low impedance marine grade wire. You can shop it on line, Amazon. You will not regret having the longest range possible and best signal. You can make the ends if you are somewhat handy with a soldering iron or have the mast top end or perhaps both ends done by a pro if it makes you more comfortable.

Did you know you can place the radio in the cabin and operate it remotely if it is equipped with a RAM mic? The RAM at the binnacle has both mic and speaker and totally operates the radio.

[Wotname]

Originally Posted by S/V Illusion

.............

Parenthetically, marine VHF radio’s don’t have an AGC circuit or control.

Originally Posted by Wotname

I would be very very interested to know which marine VHF radio doesn't have an AGC circuit as I haven't seen one (yet).

Still waiting to hear about a marine VHF set without AGC???

[Dockhead]

Originally Posted by S/V Illusion

Actually, it doesn’t but the explanation is beyond what is appropriate on a boat forum. The internet is full of links which explain the distinction.

Sorry, but both sound and electromagnetic waves follow the inverse square law.

Now marine VHF is frequency modulated so there is the Capture Effect to consider, but this effect is determined by the intensity (in the physics sense) of the radiation at the receiving antenna. So the inverse square law washes out any +/- 20%. AlanR is right.

[Ericson38]

A cable run of 75' using RG 213 would have a loss of around 2.8dB at 150 MHz, knocking a 25 watt signal out of the radio down to 15 watts, just at the point where the masthead VHF antenna port connector screws into to the other end of the cable. If an RG58u cable were used, the loss would be over 6dB and the power would be about 8.5 watts (16.5 watts lost in the cable as heat). This difference is enough be either be understood, or not, depending on conditions, and receiving and demodulating a signal, or not.

[S/V Illusion]

Originally Posted by Wotname

Still waiting to hear about a marine VHF set without AGC???

Assumed you would do your own research. None have an AGC circuit as it isn’t relevant or useful for FM.

If there is a marine VHF which does, it’s a dual use radio for SSB or AM reception.

[S/V Illusion]

Originally Posted by Dockhead

Sorry, but both sound and electromagnetic waves follow the inverse square law.

Now marine VHF is frequency modulated so there is the Capture Effect to consider, but this effect is determined by the intensity (in the physics sense) of the radiation at the receiving antenna. So the inverse square law washes out any +/- 20%. AlanR is right.

The capture effect is a function of power, not audio, e.g., you can capture an FM receiver squelch with an unmodulated (no deviation) signal. Audio intensity field measurements are entirely different than RF signal strength loss expressed as dB.

Not sure why you want to debate this on a boating web site but suffice it to say the original intent here was to describe the effect of a 20+% loss of power due to coax loss which is both significant and easily detectable. Conversely, a 1.5 dB audio loss is not.

Bye

[Wotname]

Originally Posted by S/V Illusion

Assumed you would do your own research. None have an AGC circuit as it isn’t relevant or useful for FM.

If there is a marine VHF which does, it’s a dual use radio for SSB or AM reception.

Thanks.

Maybe it will become useful in the future!
https://patents.google.com/patent/US20030139157

[Dockhead]

Originally Posted by S/V Illusion

. . . suffice it to say the original intent here was to describe the effect of a 20+% loss of power due to coax loss which is both significant and easily detectable. Conversely, a 1.5 dB audio loss is not. . . .

Well, if you don't want to discuss it, that's fine. But 20% loss of power out of 25 watts is really meaningless and NOT detectable, for the same reason the same loss of sound power is meaningless and inaudible. Just like doubling the power (by illegally using my TM-D700 on the marine bands -- which I would never do of course ) to 50 watts is meaningless except in rare marginal cases.


I use my own radio set to low power,1 watt, 90% of the time.



Capture effect sorts out which signal is heard, and the cases where there are two competing signals within +/- 20% of each other must be vanishingly rare. Because of the inverse square law, the usual difference between intensity at the antenna between two signals will be 10's, 100's, 1000's x.

[Ericson38]

When I 1st got my towing endorsement on my 100 Ton Masters License in Long Beach Ca in 1991, I decided that working for Vessel Assist (like Sea Tow on the East Coast) would be a fun way to use it. It was, and we went on a lot of calls, and used a lot of radio resources (no cell phones or GPS). So either line of sight VHF to the party, where we could talk directly to the other party, or relayed VHF calls via someone else (or the Coast Guard if there was no loss of life eminent), as well as RDF with voice count downs to get a proper bearing and mid trip updates. There is a big difference between transmitting at 5 watts and 25 watts, and there were plenty of times that the party that needed help would not start off transmitting at high power, until we made sure they were. I can't believe this discussion is ongoing this long. Five watt power is sufficient for many conditions, heights, antennas, ranges, and sea states. Most of our work was under duress (us and them), and great clear communications was needed 1st, then great equipment, then good enough boat handling to effect the rescue. There is a marked difference when someone scratchy on the channel switches up to 25 watts when they weren't before. Get the best cable, do the connections properly, install a quality 3sB whip antenna, and don't split the power down the cable with your AIS receiver. You need AIS reception out 5 miles or less, so an antenna on the stern pulpit will suffice. You need the range for voice comm, so top of mast for that one.

[Ericson38]

Human hearing is approximately Logarithmic. For something to sound twice as loud (in your head), the sound pressure level (SPL) has to be increased by 10dB (10 times).

[Dockhead]

Originally Posted by Ericson38

There is a big difference between transmitting at 5 watts and 25 watts, and there were plenty of times that the party that needed help would not start off transmitting at high power, until we made sure they were.. . .

Low power on most fixed mount marine VHF sets is 1 watt, not 5 watts. From 25 watts to 1 watt is 25x less. From 25 watts to 5 watts is 5x. Those are big enough differences to make a difference. But 1.5dB is just 1.2x, so you don't necessarily need the "best cable", and for sure avoid the foam core ones. Much more important are perfectly installed connectors, as few of them as possible (you can do without the disconnect at the base of the mast), and a really good antenna.

Originally Posted by Ericson38

. . . and don't split the power down the cable with your AIS receiver. You need AIS reception out 5 miles or less, so an antenna on the stern pulpit will suffice. You need the range for voice comm, so top of mast for that one.

I agree. But AIS antenna can also go on a spreader, which is where I have mine. Stern pulpit might be a little low -- 5 miles is not enough range -- decision point for most commercial ships is 10 miles out.

[Steve DAntonio]

This article might be helpful... https://stevedmarineconsulting.com/t...nd-connectors/

It's worth reducing loss to a minimum, even if that means using a bulkier cable, it could mean the difference between a mayday call getting through and not. I come across some horrendous coaxial runs and terminals/terminations/solder joints in my inspections, the vessel owner often reports the VHF works but when I asked about "distant" radio checks, I often get a blank look.

Agreed that LMR may be over kill for a 50 foot mast (plus the run to the radio), however, I like it and it is routinely used in commercial marine installations.

Also agree that soldering coax connectors takes practice to get it right, always check for shorts using an ohm meter before completing the connections to antenna and radio.

[Ericson38]

Originally Posted by Steve DAntonio

This article might be helpful... https://stevedmarineconsulting.com/t...nd-connectors/

It's worth reducing loss to a minimum, even if that means using a bulkier cable, it could mean the difference between a mayday call getting through and not. I come across some horrendous coaxial runs and terminals/terminations/solder joints in my inspections, the vessel owner often reports the VHF works but when I asked about "distant" radio checks, I often get a blank look.

Agreed that LMR may be over kill for a 50 foot mast (plus the run to the radio), however, I like it and it is routinely used in commercial marine installations.

Also agree that soldering coax connectors takes practice to get it right, always check for shorts using an ohm meter before completing the connections to antenna and radio.

Steve,

Great website. Also, what do you think of the current crop of internal or external AIS splitters ? The external ones I looked at a few years ago were really just that. As far as received power flow, they were connected to the VHF and AIS in such a way as to effectively split the received energy from the antenna to both receivers (AIS and VHF) equally, which means 1/2 gets to each one.

On the transmit characteristics, I wasn't sure how these combiners are arranged. A directional coupler could be used, so that full VHF power at 25 watts doesn't end up in the AIS receiver's front end, desensitizing it from receiving AIS packets at the same time. And vice versa, so that each time an AIS packet is transmitted by the Class B AIS, it does not overwhelm the VHF radio's front end, so that conversation can continue uninterrupted.