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Old 31-01-2016, 14:54   #31
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Re: Standard Horizon VHF/AIS/GPS question

I recently installed the ram mic for our 2150. Works great, sounds good, and does what it needs to do. Install was fast and easy for the most part.
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Old 01-02-2016, 15:38   #32
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Re: Standard Horizon VHF/AIS/GPS question

Canibul,
Two important things here...

1) VHF radio range (and that of UHF cellular phones) is primarily based on the height of your antenna (as well as the condition of the antenna and your coaxial cable / connectors)....NOT on the "gains" of the antennas....


Please read this detailed thread....
VHF and AIS Radiowave Propagation and VHF and AIS Radio Range

Bottom line, assuming good cabling/connectors, a "3db" gain antenna at the masthead will ALWAYS have a longer range and better reliability than a "6db" gain antenna (or even a "9db" antenna), mounted 40' - 50' lower!!!
ALWAYS!!!

I've been hit by lightning myself, and I know what kind of a pain in the butt it is....and I understand your reticence to have only a masthead VHF antenna (and only one VHF radio??), but you can always have a rail-mounted VHF antenna (and a spare VHF radio, and/or VHF handheld with an external antenna pig-tail cable), and resolve your reticence about being left without VHF comms in the event of another lightning strike....

My advice:
Install a new 3' SS whip antenna on your masthead, using new coax / connectors (with properly installed connectors)....
And, if you feel the need, also install a rail-mounted VHF antenna (and keep a spare VHF radio, and/or VHF handheld with an external antenna pig-tail cable, on-board)....



2) As I have mentioned before, it is the RF isolation / RF separation between the external antenna and the internal antenna, of a "cellular booster", that allows them to work...

{I cannot stress highly enough that it is having adequate RF isolation that allows these things to work...
And, in large buildings or even in cars (with metal roofs), this isolation is obtainable....but on our fiberglass boats, it takes distance to make them work well....
The good news is that if follow the detailed advice and recommendations, these "boosters" DO work...
But, if you try to take short cuts / do not understand why these recommendations are so important, you can find yourself with a few hundred dollar frustration!!}

And, if I could figure out a way to politely impress this upon you, I know it will save you from that frustration / headache...but have not figured out how....yet...
So, I'm just going to let this all fly, and if you believe me that's great....if you don't, at least I tried...
Quote:
Originally Posted by Canibul View Post
Thanks for that feedback. I've been getting limited range, of course, with a short, metal whip VHF clamped to a handrail on the coachroof. If all the short metal antennas are 3 dB gain, that would help explain it. I've got a new metal whip for the mast head, and I also have a new Wilson marine antenna for their cell amp. I was planning to put them both on the mast head, but keep dragging my feet. I worry about another lightning strike. I also have an 8 ft. fiberglass VHF antenna, and thoughts of using that mounted to the corner of the hard top, and mounting the Wilson on a n aluminum pole 8 ft. above the deck, where I just removed a Air X wind generator. I believe the mast has been hit by lightning before the strike we went through. I'd much prefer to keep all the radios functional when it happens again.
Hopefully, this will help explain things...

A) Please understand that a "cellular booster" is just a full-duplex UHF repeater....and our cellular phones are just full-duplex UHF radios, that connect to the PSTN (Public Switched Telephone Network), rather than communicate with each other directly...

And, it is the RF Isolation / RF Separation that allows them to work.....the more isolation, the better!!


B) I personally have 35 - 40 years experience with VHF and UHF duplex repeaters (and radios), designing, installing, repairing, etc....and I can tell you with absolute certainty that the number one issue with "cellular boosters" is when they are installed without adequate RF Isolation...

And this is also why some of their antennas are supplied with very lossy coaxial cable, such as RG-58...which (depending on the exact RG-58, solid or foam, etc.) has 14db to 20db loss (per 100') at 900mhz, and 22db to 35db loss (per 100') at 1900mhz....

So, if you have 20' of RG-58 you'll have about 5db to 7db of loss (isolation) right there....and if you have another 20' of RG-58 on the internal antenna, you'll have another 5 - 7db....

{note that 100' of LMR-400uf has 4.7db of loss at 900mhz and 7db of loss at 1900mhz....so, if placing your external antenna at the masthead, using LMR-400uf for the entire run from the masthead cellular antenna down to the "cellular booster" itself (~ 75' is typical), will preserve approx. the same "loss" / "isolation" in the cabling....and keeping the internal antenna INSIDE the boat, as low down as possible, and most importantly as close to being directly below the masthead/external antenna....all should allow adequate RF separation / isolation for your "cellular booster"...
And, here on these high UHF frequencies, is where the excellent low loss of LMR-400uf cable is needed!!
http://www.timesmicrowave.com/calcul...mode=calculate
And, now you see why it is recommended by Digital, Wilson, Shakespeare, etc....for masthead cellular antennas!!}

The "cellular booster" manufacturers can supply you with their minimum isolation spec, but understand that they get some of this isolation from the loss in the cabling....
And, for those with sailboats (where we can place the external antenna 50' - 60' above the internal antenna, and therefore obtain a great deal of RF isolation) the added loss of all that small cabling can make the system less than stellar in its actual effectiveness...so, larger (lower loss) coaxial cable must be used....
BUT...
But, you must still make darn sure your antennas are adequately separated / RF isolated, from each other....
Again, keeping the internal antenna INSIDE the boat, as low down as possible, and most importantly as close to being directly below the masthead/external antenna....all should allow adequate RF separation / isolation for your "cellular booster"...


But, if you mount the external antenna just a few feet above the deck, and have the internal antenna nearby in the cabin (especially if it is only a few feet below the external antenna, and only separated by less than a dozen feet horizontally), there will be very little RF isolation / RF separation, and hence the system will not function well at all...and many times, won't work at all...




Again, I cannot stress highly enough that it is having adequate RF isolation that allows these things to work...
And, in large buildings or even in cars (with metal roofs), this isolation is obtainable....but on our fiberglass boats, it takes distance to make them work well....
The good news is that if follow the detailed advice and recommendations, these "boosters" DO work...but, if you try to take short cuts / do not understand why these recommendations are so important, you can find yourself with a few hundred dollar frustration!!


Sorry if it looks like I'm repeating myself....I'm just trying to make it absolutely clear that these things work, but in order to make them work well, you must understand the external to internal antennas must have adequate RF isolation from each other...



I hope this helps..

Fair winds...

John
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