Pushpit Rail Mounted VHF Antenna Suggestions

Mark Maulden · Oct 7, 2019

Find someone with an swr meter and test the current config? I would assume most yards could do this. Or a local ham radio guy. Contact some local ham clubs.

BigEasy · Oct 7, 2019

I had the local rigger swap out my coax cable, dockside, for a nominal fee. As Mark mentioned, an swr meter will indicate if there’s a problem with your present antenna & cable. Might only be a bad cable connector.....I purchased an inexpensive swr meter from amazon or eBay to test mine: they are simple to use. If you spend $$ for a push pit antenna & coax, you’re not going to get near the range of a mast mounted antenna. VHF signals are “line of sight” :therefore, you’re going to severely limit your transmitting range because of difference in antenna height.

Joe · Oct 8, 2019

Ward H said:
In the bay I just use my handheld VHF. I contemplating one or two trips going outside instead of the ICW, before the end of Oct.
I'm not sure if my nav to mast head antenna coax is good so I'm considering a pushpit mounted antenna with a fixed mount VHF radio with AIS and helm remote mic.

Any suggestions for pushpit mounted antenna that I can split for VHF and AIS?

Standard 8ft antenna with a deckmount bracket.... the antenna comes with 15 ft cable... just route it to your splitter... good to go. I have used this set up for years... will install mast mount in the future... but I've been saying that for 20 years. I regularly receive CG broadcasts from as far as 100 miles away... since their antennae are on towers...or tall buildings...or mountain tops.

Ward, if you're just going to get a vhf/ais radio(ais receiver only) you won't need anything else, unless you want to split for fm radio, and simple fm splitter is pretty cheap. If you decide to go with an AIS transponder... which will be separate piece of gear... you'll need a splitter, $200 or more... although there are some transponders than have built in splitters. If you go that way... the ais splitter will also have an fm socket.

dlochner · Oct 8, 2019

Ward, there is very little advantage to using a pushpin mounted antenna vs a handheld. VHF transmission is line of sight, antenna height is the key factor, a pushpit mounted antenna will be not be significantly higher than a handheld's antenna if you are standing up in the cockpit. There will be a slight advantage to the increased power, mostly that will affect the ability of the radio to push through any noise, but not increase distance.

The USCG's Rescue 21 system is designed to receive a 1 watt transmission from 20 miles off shore with the antenna at sea level. They should be able to hear you if you are in trouble.

As others have said, check the standing wave ratio, that measures the antenna and radio's efficiency.

Don S/V ILLusion · Oct 8, 2019

Anything is better than the standard ‘rubber duck’ stub antenna supplied with handhelds. You will notice a difference by substituting a real antenna regardless of height.

JohnShannon · Oct 8, 2019

Three issues with radio propagation, one is line of sight distance and the second is power. The handheld is likely 5W of power the pushpit is 25W from a fixed mount VHF. More power is better. The second issue is line of sight. This is related to the square root of the heights of the transmitter and the receiver. Taller is better. The coast guard has really tall antennas big ships have tall antennas and other pleasure craft not so much. If you want to be heard by everyone tall is important. Third item is antenna gain, as noted a rubber duck on a handheld doesn't have a lot of gain a normal VHF antenna is better at picking up small signals and more efficient at launching your VHF transmission.

Shakespeare makes a rail mount "emergency VHF antenna" that should do the trick and it will be better than the handheld, but not as good as the mast mount (assuming good cables)

Don S/V ILLusion · Oct 8, 2019

Ward H said:
My goal is to:
Have more than one radio on board. Handheld and preferably fixed mount.
Have a fixed mount with 25w of power. (5x handheld)
Have AIS displayed on Axiom CP.
Have more range than the handheld. I'm planning on coastal sailing, maybe 10 miles out max?

Right now I'm looking at the the SH GX6000 for it's AIS and NMEA2000 capabilities.

My issues with the current coax from the mast base to nav table is it is RG 8U. I cannot find PL259 connectors for the cable. The nav table end was tucked way down out of the way, not sure it was ever connected.
There was a rail mounted Shakespear Antenna that was connected to an old radio with bad mic. That antenna was fiberglass and disintegrating. I took it off and scrapped it as soon as I bought the boat and had a handful of splinters.

Going to Annapolis Friday and hopefully can find deals on what I want.

PL259s for RG8 are ubiquitous- I don’t understand why you cannot find them. The trick is to use good ones, not the knock-off junk likely to be found at a boat show.

Parenthetically, five times the power equates to a 3dB increase in signal strength- effectively indiscernible difference. You are better serves by increasing height than any other option.

BigEasy · Oct 8, 2019

Ward, the swr meter should give you the necessary info to analyze your rig. If you just replaced the antenna and cable two years ago, it’s not likely that is the source of the problem. On the other hand, cable connectors can be problematic, especially the crimp type. Amphenol soldered connectors are the standard for Ham operators. You need a high wattage soldering iron to solder them properly. There are several good videos on you tube showing how to make up the connectors. With the swr meter and the new radio that you intend to purchase, you should be able to troubleshoot the source(s) of your problem. Keep us posted.

Mark Maulden · Oct 8, 2019

You can also use an ohmmeter at the radio end. Use the lowest scale and measure between center pin and outer shell. If you read “0”, then most likely a connector is shorted. If you measure a few ohms, things are looking good. Since you can converse next door and not further, I’m suspecting a bad connector install...They reason for a few ohms is up the coax and through the antenna windings and back down the coax. Assuming the antenna has a loading coil at it’s base.
Don, 3dB is five times power? Last I heard, it’s half or double. Power being the key word...

JohnShannon · Oct 8, 2019

These guys have it as a little more 5x is 7dbm.

dBm - Wikipedia

en.wikipedia.org

Then you can play around with link budgets with this calculator and will see 7dbm gets you about 2x the range

https://www.pasternack.com/t-calculator-fspl.aspx

Which kind of makes sense 2x the range requires you to light up 4X the area so it is reasonable that that would take 4x the power.

Brian D · Oct 9, 2019

37dBm, not 7dBm.

0dBW = 30dBmW = 1 Watt ∴ 7dBW = 37dBmW = 5 Watts

JohnShannon · Oct 9, 2019

An increase of 7dbm is a factor of 5X in power.

Brian D · Oct 9, 2019

One more time...

0 dBW = 1 watt of power
30 dBmW = 1 watt of power

7 dbW = 5 watts of power
37 dBmW = 5 watts of power

7 dBW = 5 watts of power
7 dBmW = .005 watts of power

ggrizzard · Oct 9, 2019

Not to confuse the previous discussions on power, the following has nothing to do with bad connections or bad cables:
Most VHF radios have a selector for "High Power" and "Low Power" built in.
Since I don't know the model radio you were using for your test, I can't tell you how to switch the setting. If it's set on "Low", you could talk to your dock mate but not a distant station. Just sayin'...

JohnShannon · Oct 9, 2019

Brian D said:
One more time...

0 dBW = 1 watt of power
30 dBmW = 1 watt of power

7 dbW = 5 watts of power
37 dBmW = 5 watts of power

7 dBW = 5 watts of power
7 dBmW = .005 watts of power

What are you trying to express?

I see a 5X increase in power is a 7db increase, am I wrong