Testing vhf

[rszobel]

I remember reading somewhere that there is a way to perform a test on a VHF where you can transmit a test and it is then transmitted back to you. Can anyone tell me how to do this as I can't remember where I read about it and just installed a new radio.

[vkmaynard]

http://m.seatow.com/automated-radio-checks

[opie]

I use the Seatow automated radio check on channel 27 in my area.

However, I have had thoughts about how to check for distance. I mean, a normal radio check can be from a service or a vessel 200 yards away and that does not give a good indication of your antenna function. I can get such a signal without even hooking up my antenna. So what would be the etiquette for asking the furthest vessel to do your radio check? I have not done it, but I was thinking something like this, "This is the Marin in Blank inlet looking for a radio check from a distant vessel to check my antenna." My thought would be that a vessel within a few miles would not answer but a good-natured vessel 10 to 20 miles away would. With my mast antenna up I hear the coast guard side of various conversations from Charleston or Morehead City (maybe 80 or more miles) but never hear the vessel side of the conversation. Don't know how may watts the CG uses compared to the 25 watts max of my Furuno VHF.

[Tomfoolery]

With my mast antenna up I hear the coast guard side of various conversations from Charleston or Morehead City (maybe 80 or more miles) but never hear the vessel side of the conversation. Don't know how may watts the CG uses compared to the 25 watts max of my Furuno VHF.

It's likely you're hearing a USCG repeater, or atmospheric skip, or some such thing, unless the CG's antenna is something like 4000 ft above the water. In that case, you won't hear the other vessel if it's beyond something like 15 miles (sailboat mast top antenna to sailboat mast top antenna). Maybe 16 miles if the other boat has a 60 ft antenna height.

VHF being line-of-sight, more power doesn't help much unless the antenna is high enough to 'see' further, where the exponential decay of the signal with distance from the antenna starts to matter. I would also think they use a highly directional antenna, with a very flat donut pattern, as signal transmitted up/down is wasted, giving a higher effective power (gain). Unless talking to aircraft, but I'm guessing they use something else to do that even though aircraft use VHF frequencies too. But I don't know that.

[Russ]

With my mast antenna up I hear the coast guard side of various conversations from Charleston or Morehead City (maybe 80 or more miles) but never hear the vessel side of the conversation. Don't know how may watts the CG uses compared to the 25 watts max of my Furuno VHF.

Coast Guard uses the same 25 watts. The difference is altitude. They mount their antennas up high on land based towers with quality coax running to them. Since the tower is stationary (doesn't rock) they can also use high gain (8db narrow beam) antennas. All 25 watts makes it to the top of that tower and gets some gain from the antenna. Same principle of why lighthouses are on top of hills. Aren't we glad they have quality installations.
So the CG has a greater range than the boat they are talking to with their deck mounted antenna.

Lesson here is that height matters with VHF. It's likely the boat they are talking to is blasting their 25 watts into the sea or at the sky or can't get over swells to reach you but can to the high CG tower. It's also possible that the boat is further away.

Also, since you can hear the GC, they can probably hear you. On a good day I've been able to pick up CG Montauk, NY from Manasquan, NJ which is about 150 miles. Powerboat friends could not.

Still want to mount that VHF antenna low on your deck?

[mastreb]

Keep in mind that VHF is "near line of sight"--it is bent weakly by the atmosphere and so it extends to the "radio horizon" which is about 20% farther out than the optical horizon. Also, VHF is easily ducted in thermal refractive gradients. Here in So call you can often see Catalina on the horizon as a mirage because of thermal refractive gradients, and during those times you can also easily pick up Avalon harbor master.

A few weeks ago we had a situation where a boat that had run its keel aground in south San Diego Bay sent a distress call that was responded to by Avalon Harbor master over 100nm away.

When I was in the Navy do no electronic warfare radio spectrum surveillance in the UHF range, we would occasionally receive high powered transmitters over 600 miles away.

So radio range is a very complicated thing, and should be considered in terms of minimums expected, not maximum possible.

By the way, my mast carrier mounted -6Db antenna can raise Avalon from Newport, so it does everything I need it to do. I thing that's more because their receiver is atop the hill, but it works just fine for my needs.

[rszobel]

I tried to locate channel for sea tow check in my area and there isn't one. Stafford virginia on Potomac river. Does anyone know of another automated radio check I could try??

[vkmaynard]

FYI

Our Icom M-422 radio has receive problems for the last two seasons+. We purchased a new Shakespeare 5400 XP antenna with no improvement. A friend help us check the SWR and TX power. New antenna worked great but super weak receive. The automated radio check was so weak that we could not hear the announcements and barely the echoed message.

Bottom line: Icom said they've been replacing bad filters under warranty. They are so swamped that the repair will be 2-3 weeks.

Victor

[mastreb]

I tried the SeaTow automated check on 27 in Newport Beach--no response.

[Catigale]

We routinely hear Coast Guard station Brooklyn in Albany NY, 130 miles. Up river. Has to be a repeater up river of course.

[mrron_tx]

Hi All: Newbie here I am looking for information on mast mounted vhf antennas ,and info on wether to run coax inside or outside mast etc etc. I'm in East Texas and will get out to Galveston Bay and the Gulf before tooooo long. Right now I'm just on local lakes. Thanks for any help.

[davidbourne]

Hi All: Newbie here I am looking for information on mast mounted vhf antennas ,and info on wether to run coax inside or outside mast etc etc.

Hey and welcome to the Forum,

I just did an "advanced search", which you can find in the top right of any forum page. I found this, which is just one of many posts regarding the subject.

http://www.macgregorsailors.com/forum/v ... na#p237532

When you search, it can help to search just in the titles on the first round. That's an option under the advanced tools farther down the page. Either way you do it, you will find a lot of great info here. Seek and ye shall find.

I'm also interested in this same project on an M. I hope to get to it this Spring. Let us know what you learn.

Cheers, DB

EDIT: Don't miss the post by RussMT. If you can use his method, it will be a lot easier than the "foam boring" method.
http://macgregorsailors.com/forum/viewt ... a&start=45

[mrron_tx]

Thanks !!!! That was great info.... I haven't got time to read all of the post right now....but will later today. Thanks again. Ron

[vkmaynard]

Icom repaired our radio no cost . Defective filter.

Definitely check out your radios.

Victor

[davidbourne]

Icom repaired our radio no cost .

I'm glad to hear that Victor. One way conversations are just not as fun.

I'll always keep a spare mobile on board, too. I have an attachment that lets me plug into the better antenna if I need to.