Raising my antenna benefit / downfall questions

[intiractive]

hello everyone. i live exactly 5 miles from the ocean and intercoastal waterways in wilmington, nc. i have a uniden bearcat scanner that i have channel 16 on the marine band programmed in that i like to monitor during the summer due to high volume of boat traffic. i use a boat marine radio antenna 1/4 wave that is mounted to the side of my house above my window (maybe 10 feet off the ground).

i can hear all the base stations like the marinas, the docks, the bridge tender for the draw bridge, the coast guard etc, but 90% of the time i cannot hear vessel to vessel traffic. would there be any benefits of relocating the antenna to the top of the tree out my window (at about 30ft up in the air) with db loss for the extra coax?

the antenna only came with 10 feet of coax connected to it. can i get more coax and use a bnc to bnc barrel and connect them? i know that will be more db loss by doing that.

i have a 8 foot ground rod right outside my window that i put in, how should i connect the ground wire to the antenna?

thanks for any tips yall can give.

 

[kb0nly]

Higher is better, but also more gain is better. If your just running a 1/4w then no doubt you will have trouble hearing lower power or more distant stations, but still even with a 1/4w antenna more is better when it comes to height, even with a bit more coax loss.

As for splicing on, yes you could use a barrel and a jumper to add length, but your going to have to weatherproof the connection. Don't go with coax seal goop, get some rubber tape which most big box stores have in their electrical isle, usually called self amalgamating etc. You need to weatherproof with a couple layers of that and a couple layers of super 33 electrical tape as the rubber tape isn't UV resistant, it will last years and years and years if you take your time and do it right. We just discussed this on another thread recently.

 

[SCPD]

Once you get above obstructions, doubling the height will give you 3 dB gain. You could achieve the same result by going to a 5/8 wave(with a good ground plane). Also I'm assuming that you are using RG-58 which is pretty lossy at VHF(2.1 dB for 40ft @ 157MHz), RG-8 or RG-6 would be a much better choice.(Yes I know RG-6 is a 75 ohm coax but that only results in a 1.5:1 mismatch, more than offset by the lower loss.) As for the grounding, it should be bonded to the house service ground. As the 1/4 wave is not a DC grounded antenna the coax should be grounded so use a grounding block to make the splice instead of just a barrel connector.

 

[intiractive]

i would have no problem going to rg-6 as being that i work doing cable / sat tv and have plenty of it sitting around. forgive me for being new, but ive heard groundplane a few times, and i looked it up on wikipedia and google, but the complex terms mean nothing to me. i think it has to do something with the opposite side of the radiating transmission of the antenna? but im only doing RX and no TX, so does that still apply to me? i know its frustrating trying to explain this to a newbie... lol.

 

[SCPD]

Yes it still applies to rx. The ground plane is the radials sticking out around the bottom of the antenna or the metal body of the vehicle it is mounted on. Since you are in the business you are in I would cut off the RG-58 close to the antenna and use weather proof F connectors to couple on some RG-6.

 

[WA1ATA]

A rough rule of thumb is that your visual horizon in nautical miles is equal to the square root of your height in feet. The horizon for 157MHz VHF is another 15% or so.

The boats you are trying to hear also have a horizon distance, determined by the height of their antenna above water. If the sum of their horizon distance + your horizon distance is greater than the distance between you, then you have a good chance of hearing them.

The shore stations generally have antennas mounted much higher up than do small boats, so it is expected that you can hear them from further away. That is probably the reason you can hear them, but not boats.

The loss in the coax is negligible compared to the increase in radio horizon from putting the antenna at the top of a tree. I'm betting that getting a clear line-of-sight to the boats with antennas near water level will make much more difference than a couple of dB loss in coax, or a couple of dB from adding radials or going to a 5/8 wavelength antenna.

 

[intiractive]

Well i got off early from work and it wasnt the best conditions to work on it ( 96F, heat index 100F, UV=10 ),

but i did like yall said. shortened the rg-58 and connected it to rg-6. then i climbed to the top of the tree in my backyard till i got near the top and mounted my antenna up there.

then i connected to my ground rod outside my window for my ground plane, and hooked her up to the scanner and... wow. i hear at least 5 times more traffic than i used to.

ive already heard alot of vessel to vessel communications, and when i heard the 2 way convos, they were all crystal clear like they were sitting outside my house! thanks soooo much for the help guys. i hope one day i can become knowledgeable like all of you are.

 

[SCPD]

Glad you got it working