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Old 11-09-2020, 20:29   #1
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B&G masthead VHF cable

Hi all,

I am looking for information about the B&G branded VHF masthead cable.

I recently noted one local boat that seemed to have exceptionally good AIS transmission. They remained visible on Marine Traffic up to 50% further than most of the other boats around here.

It turns out they are using "B&G V50 VHF with a standard B&G send/receive AIS module and standard B&G masthead cable ". Their mast is reasonably tall, at 22 meters, but there other boats with similar mast heights that do not perform remotely as well.

I know nothing about the B&G gear, other than it seems to work ok for people around here who have it, but I am most curious about their VHF cable. There are no specifications for the cable that I can find.

Is is similar to RG213? Something else?

Does anyone know?

Matt
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Old 12-09-2020, 04:21   #2
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Re: B&G masthead VHF cable

Looking at online IMages it just seems to be rg58/u. Nothing special.
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Old 12-09-2020, 04:34   #3
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Re: B&G masthead VHF cable

I can't think of a reason for their cable to be special. Probably, it costs more and is not the exact length you need for your installation. As a general rule, the thicker the better, and well-done (soldered, water tight) connections rule.
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Old 12-09-2020, 04:47   #4
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Re: B&G masthead VHF cable

The best cable? You need to get it exactly right, incl. brand name, range and model:

Brand: Times Microwave
Range: Ultraflex
Model: LMR-400

Times Microwave calls this LMR-400UF. There are hundreds selling LMR-400 and many even pop up when you add Ultraflex so make sure you get the genuine product.

Regular LMR-400 is too stiff for most installations. The thin version is LMR-240.
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Old 12-09-2020, 04:55   #5
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Re: B&G masthead VHF cable

Guys, this isn’t about what is best. I’m trying to figure out why their installation works so much better than all the other boats around here. Cable is one likely possibility, that’s all.
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Old 12-09-2020, 05:43   #6
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Re: B&G masthead VHF cable

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Originally Posted by GILow View Post
Guys, this isn’t about what is best. I’m trying to figure out why their installation works so much better than all the other boats around here. Cable is one likely possibility, that’s all.
Oh... so you don’t think that using “best” components is related to “better” performance? The only other factor is the quality of installation. When you get both right, performance is amazing.

You will never get similar results with for example RG58/U cable so I highly doubt that was used. Even when installed perfectly, with a mast that tall you can loose up to 75% of the transmission power before you get to the antenna. Most boats are lucky to get up to 50%.

For transmit, this isn’t even that much of an issue, because even 25% of 25W, say 6W at an antenna 22 meter up will perform good enough to get by. The problem is with receiving because they loose 75% of the received signal before it even gets to the receiver. In other words: they are thise who need others to relay to them because they can’t hear the other side. Happens all the time.

In my experience, in 90% of all cases the cause is the installation of RF connectors to the cable (sometimes a shorted cable stuck into a connector and fastened with duct tape) and 10% it is the antenna or cable.

In the case described by the OP, another factor may be the type of AIS transponder. If this is a class-A or a class-B+, it is much more powerful (both in signal strength and number of transmissions) than a class-B.
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Old 12-09-2020, 06:09   #7
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Re: B&G masthead VHF cable

There is very little difference between good quality RG 58 and Times Microwave LMR cable in terms of attenuation at VHF. What CAN make a difference is the quality of the RG 58 - it can vary widely between manufacturers.

Having said that, a +/-1 dB difference in characteristic attenuation for a given length is indiscernible so whatever difference in performance you may notice is the result of some factor other than the coax type.
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Old 12-09-2020, 06:27   #8
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Re: B&G masthead VHF cable

"...I’m trying to figure out why their installation works so much better than all the other boats around here. Cable is one likely possibility, that’s all."


Most likely their installation is brand new, and was done properly (correctly soldered connectors, etc.) Plastic-jacketed coaxial cable does not last forever in the sun and as soon as there is any sort of moisture allowed into the inside, attenuation begins to increase. Jacketing will erode and crack after years of exposure and improper sealing at the topside connection - all will allow moisture in - and the cable will be dying. I spent 30 years+ in the two-way radio business and installing antennas on towers & other structures was part of the job.



I just pulled out a piece of RG-8X (like LMR-240) that went to my radar mount 35' up - I had not done a sufficient tape-seal at the antenna (moving fast: "I'll fix that next week - oops!), and the cable was wet & the center conductor corroded all the way to the nav station - in less than a year! It looked good with the SWR meter, but the sweeper told the tale - it was lossy as h***. I replaced it with FSJ1-50 1/4" Superflex, and all is well now. (sealed it really good, too!).
Long term, it isn't so much the cable (though that makes a definite difference) it's the quality of the installation.


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Old 12-09-2020, 06:33   #9
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Re: B&G masthead VHF cable

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Originally Posted by S/V Illusion View Post
There is very little difference between good quality RG 58 and Times Microwave LMR cable in terms of attenuation at VHF. What CAN make a difference is the quality of the RG 58 - it can vary widely between manufacturers.

Having said that, a +/-1 dB difference in characteristic attenuation for a given length is indiscernible so whatever difference in performance you may notice is the result of some factor other than the coax type.
That is an illusion

Here are the facts, for 100’ (30 meters) of cable the cable loss for RG58 at VHF frequency is 7.1dB. The same cable in LMR400 is 1.5dB. That is huge, not “very little”.

To make this simple: with LMR400 you get 75% of your signal to the antenna while, with RG58, you only get 20% of the signal to the antenna. That is almost 4 times as much with LMR400. That is a lot more.

I think that may be you were thinking of RG8 instead of RG58. RG8 has an attenuation of 1.7dB which is very close to the 1.5dB of LMR400UF, but that cable is a pain to install. Many use RG213 which sits at 2.6dB.
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Old 12-09-2020, 06:52   #10
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Re: B&G masthead VHF cable

S/V Jedi:



"...Here are the facts, for 100’ (30 meters) of cable the cable loss for RG58 at VHF frequency is 7.1dB. The same cable in LMR400 is 1.5dB. That is huge, not “very little”."


I suspect he was referring to LMR195, which would be the same physical size as RG-58, and which would have a loss of 4.4 dB for 100' at 150 MHz.
I might note that "RG-58" covers a LOT of very different cables - Belden says theirs has about the same loss at 150 MHz as the LMR, while specs for other brands range from 5 dB up to 8 or even 9 dB (probably cabling designed for ethernet use). Ancor's RG-58C/U "Marine" coax seems to be spec'd at about 5.2 dB/100', so not a lot higher.

The big difference, of course, is the center dielectric - solid polyethylene or foam -- foam is much lower loss, but more difficult to keep from center-conductor migration problems (in a tight bend subjected to solar heating, the center conductor will move off center, causing impedance issues).


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Old 12-09-2020, 07:28   #11
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Re: B&G masthead VHF cable

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Originally Posted by s/v Jedi View Post
That is an illusion

Here are the facts, for 100’ (30 meters) of cable the cable loss for RG58 at VHF frequency is 7.1dB. The same cable in LMR400 is 1.5dB. That is huge, not “very little”.

To make this simple: with LMR400 you get 75% of your signal to the antenna while, with RG58, you only get 20% of the signal to the antenna. That is almost 4 times as much with LMR400. That is a lot more.

I think that may be you were thinking of RG8 instead of RG58. RG8 has an attenuation of 1.7dB which is very close to the 1.5dB of LMR400UF, but that cable is a pain to install. Many use RG213 which sits at 2.6dB.
Nonsense. Let’s be objective about the difference -

Good quality (e.g.Belden) RG 58 cable has a characteristic attenuation of 4.7dB ( not 7) compared with good quality RG 213 or TM 400 which have a loss of approx. 3 dB - the difference is trivial.
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Old 12-09-2020, 09:05   #12
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Re: B&G masthead VHF cable

It may not be the cable, but the antenna. Keeping the cable as short as possible also helps.
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Old 12-09-2020, 09:08   #13
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Re: B&G masthead VHF cable

I think that you may find this interesting.

https://www.westmarine.com/WestAdvis...-a-VHF-Antenna
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Old 12-09-2020, 09:38   #14
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Re: B&G masthead VHF cable

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Originally Posted by S/V Illusion View Post
Nonsense. Let’s be objective about the difference -

Good quality (e.g.Belden) RG 58 cable has a characteristic attenuation of 4.7dB ( not 7) compared with good quality RG 213 or TM 400 which have a loss of approx. 3 dB - the difference is trivial.
Show your source for those numbers. Any RG213 is 2.6 and lmr400 is 1.5.
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Old 12-09-2020, 10:04   #15
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Re: B&G masthead VHF cable

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Originally Posted by Stewie12 View Post
It may not be the cable, but the antenna. Keeping the cable as short as possible also helps.
I wou L d question if any other vessel using this brand enjoys superior performance as well. I would also be curious what other antennas are on that masthead, are there parasitics
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