Moderated Discussion Areas
ContinuousWave: Whaler Performance
Range of VHF radios
|Author||Topic: Range of VHF radios|
posted 12-29-2001 09:49 PM ET (US)
My understanding is that VHF radios are suppose to have a "line-of-sight" range. I presume that this means a maximum of 5–10 miles on open water. Right?
Factors that affect range include the height and quality of the antenna, the number of watts used during transmission (1, 5, or 25 watts), obstacles on land, and weather conditions. The brand of the radio may also be an important factor. Is that correct?
My two 5-watt Shakespeare SE700 handheld radios have a transmission range of three miles (one handheld radio communicating to another, identical handheld radio). That's what I have experienced.
If I purchase a 25-watt, dash-mounted VHF radio and an 8' antenna, will I be able to transmit two or three times as far?
How far can you transmit?
posted 12-30-2001 12:25 AM ET (US)
Range at the VHF Marine Band is primarily a function of antenna heights above terrain.
The formula is approximately
Range (Miles) = 1.5 x SQRT_of_HEIGHT(Feet)
Compute the range between two stations by calculating their individual ranges and adding them.
For example, I am in my boat with antenna about 9 feet high. I want to listen to weather radio station KEC-63 with antenna 625 feet high.
My range is about 4.5 miles
I can hear KEC-63 from 42 miles away.
Power is generally not a factor at these ranges. One watt works as well as 25 watts if there is no interference.
posted 12-30-2001 12:29 AM ET (US)
Range is a function of line of sight,
antenna, and wattage. I deliberately
listed wattage last.
I have a 25 watt console mounted radio
Line of sight is kinda-sorta. I routinely
Antennas are important. Your handhelds have
I don't think there's a lot of difference
If you do get a new radio, get one that is
And, most submersible radios are DSC (Digital
posted 12-30-2001 10:36 AM ET (US)
I once worked with a ex-NASA engineer. He said that the telemetry on Apollo missions was approximately 1 Watt! Let's see height of moon,,,
posted 12-30-2001 10:58 AM ET (US)
And Apollo no doubt had a very high
gain antenna on each end.
posted 12-30-2001 11:07 AM ET (US)
I know much less than any of you about radios, but it seems to me that power (number of watts) is an important factor in determining the distance that a radio can transmit. I agree with you that power does not affect reception, only transmission.
I used an adaptor to connect my new submersible, handheld 5-watt Shakespeare SE700 to an 8' antenna that was mounted on the flybridge of a small yacht. The top of the antenna was 22' above the water line. We put a man in an 11' Whaler and had him head for a channel marker that was 3 miles away. Neither party noticed a significant difference in the quality of reception with the external antenna connected or not connected.
However, we hooked the same external antenna to the yacht's dash-mounted, 25-watt ICOM VHF radio. The man in the dinghy 3 miles away reported that he could hear us much more clearly when the 25-watt radio was used. On the yacht, we heard the dinghy's handheld equally well regardless of which radio we used.
So, from that experiment, i concluded that power was an important factor in determining the distance that a unit can transmit.
Does that make sense?
posted 12-30-2001 12:44 PM ET (US)
With that small sample size, you could also
conclude that Icom makes better radios than
Shake, or that the handheld was defective, or
VHF is FM. As long as there's "enough" power,
The higher gain antenna effectively gives
Finally, the SE700 is not submersible. It's
posted 12-30-2001 01:24 PM ET (US)
Okay. Thanks for the information.
posted 12-30-2001 01:59 PM ET (US)
At the distances normally encountered in Marine VHF Radio use (1-5 miles), the power (1-watt or 25-watt) generally would not make a significant difference in readability of the received signal, in the absence of interference.
Since marine channels are shared among many stations, there is often considerable on-channel interference. More power helps to override such signals.
The Frequency Modulation (FM) technique of tranmission enhances noise-suppresion and rejection of unwanted signals, as long as the desired signal is sufficiently stronger than the noise or interfering signal.
A drawback to the FM techniques is that the reability of the signal when its strength is marginal (compared to noise or interference) is much lower than it would be with Amplitude Modulation (AM) methods.
This is one reason FM is seldom used in weak-signal work; AM (actually SSSC or single sideband supressed carrier) is much preferred in those cases.
posted 12-31-2001 01:17 AM ET (US)
Thanks for explaining this to me, jimh and triblet.
posted 01-01-2002 09:03 PM ET (US)
Ok,we have line of sight,antenna gain,
height of antenna,power/wattage.
In open water from boat to boat 20 to 25
miles should be possible.Now what about
sea tow or coast gaurd,how far offshore
should you still be able to contact them?
I have done a radio check with seatow at
As far as cell phones they are almost
One more thing,has anyone noticed all
the rattle noise from the coaxial cable
shaking around in the fiberglass antennas?
posted 01-01-2002 09:19 PM ET (US)
The CG has 9 dB gain antennas on mountaintops.
There are coverage charts for the CG's VHF
These charts are about right or a touch
pessimistic if you have a 6 dB gain antenna,
quite optimistic if you have a handheld with
its standard antenna.
Yes, I've heard a rattle inside the antenna
posted 01-01-2002 10:15 PM ET (US)
This might help a bit.
Think of your transmitter as a light bulb and your receiver as an eyeball. Antennae are reflectors and/or telescopes.
In theory, if you don't have line-of sight to the receiver, it doesn't matter what power or antenna you have.
If you do have line of sight, and efficient enough reflectors and telescopes, it doesn't matter how far it is.
In more practical terms, how high your antenna is, the greater your range. The more power, the easier it is to communicate. Think of 25 miles, max, with your antenna 15' above the surface.
Red sky at night. . .
posted 01-01-2002 11:56 PM ET (US)
Well put, JB.
Except that: VHF is only kinda line-of-sight.
Other frequency ranges are more or less
posted 01-04-2002 10:40 PM ET (US)
This is an interesting topic, and something that has confused me a bit.
Where my house in WI is, I am at the top of a hill that seems to be about 300 feet above and .5 miles from the bay in Ephraim WI (those that were at my house for the Door County Rendezvous party this summer know what I am describing). This house is also about 5 miles to the south of the water at Sister Bay.
On the top of my roof, I mounted one of those metal Shakespere whips that rag boaters stick on the top of their lightning rods...er...masts - about 3 feet. It hooks to a VHF I have in my garage ( for any FCC people out there, I am not operating a land based transmitting station without a liscense. This is just a hypothetical essay, and I would never intentionally violate any rules or laws).
Now, I am unable to contact or receive transmissions from Ephraim harbor, but I am able to do both to vessles and land stations in Sister Bay, or points farther. Would I be right in assuming that I may be shooting my transmission over the top of vessles that are nearer to me because of the steeper angle down to them over a shorter distance? Or is there some other force at work here?
posted 01-04-2002 11:13 PM ET (US)
You should be able to "work" stations in the nearby harbor. Perhaps you are shadowed by something intervening.
It is also possible to have some rather deep nulls in the antenna pattern at higher angles away from the horizon. Your antenna could have such a null exactly at the angle needed to receive signals from the harbor. This might be mirrored by similar nulls in the antennas of boats in the harbor, doubling the effect.
In television broadcast antennas, which are typically mounted 1000 feet above terrain, special attention must be paid to providing some radiation at sharp downward angles in order that receivers in the vicinity of the antenna (0-3 miles) will be able to get decent reception.
In some settings, where the antenna is located on a hill top, it is not unusual to incorporate "beam tilt" to angle the signal downward from the horizon to put more energy into where most of the receivers are located, instead of sending it all at the distant horizon.
The higher the "gain" of the antenna, the smaller the lobe of its radiation. This is why I do not favor high-gain antennas on boats; the rolling and pitching of the boat causes the antenna to aim its radiation all over the place. The wider the beam the less fading you will experience in these situations.
posted 01-05-2002 01:29 AM ET (US)
What antenna do you recommend for the Whaler, Jim?
posted 01-05-2002 09:22 AM ET (US)
I like the shorter fiberglass whips, about 4-5 feet long. I see these on most Coast Guard boats, too. They're more expensive than the longer 9-foot antennas!
One of these mounted on an extension mast would be great.
But not to mistlead you--I have the typical cheapo 9-foot whip on both my boats at the moment!
posted 01-06-2002 03:18 PM ET (US)
On my former 18 Outrage I used one of those rag boater Shakespear 3' loaded stainless whips connected to a Standard Nova Plus (not made anymore) with great success. That antenna allowed me to deploy the suntop without physical interference from the antenna. Most of my boating with the 18 Outrage was never more than 6 to 10 miles off shore. The typical range limit of ship to ship communications was between 15 and 20 miles apart.
posted 01-06-2002 03:58 PM ET (US)
Ok guys-- I know absolutely nothing about the engineering aspects of my VHF radios. Explain to me how my base unit Apelco (older) receives communications on Sunday mornings from Tampa/St. Pete when I'm on Merritt Island/KSC??? It has a button for International-does this improve reception. Or, does the fact that the antenna I've mounted on the roof help some. Sunday morning receptions seem quite good from the Gulf area- is this some sort of religious reception.?? I seem to be receiving VHF from 150 miles away. ???? Thanks David
posted 01-07-2002 12:16 AM ET (US)
You are probably hearing the Coast Guard stations. They often use a "trunked" radio system, and if they want they can transmit simultaneoulsy on transmitters located all over the place.
Up here in the Great Lakes it is not uncommon for me to hear "Coast Guard Group Detroit" making broadcast announcments on Channel-22A when I am 250 miles due north of them--the signal is getting retransmitted on practically every CG station on the lakes.
The Canadians recently cut back their staffing of radio watch standers so when I call Canadian Coast Guard in Wiarton (on Georgian Bay) I am actually talking to a guy in the western part of Lake Superior--everthing relayed on dedicated land lines from the receivers/transmitters at Wiarton up to the north and west about 300 miles.
posted 01-07-2002 12:18 AM ET (US)
The "Interenational" button changes the
frequencies associated with the various
channels a bit, and makes some duplex
channels half-duplex and vice-versa. It
should not affect range.
Having the antenna on the roof should help.
And who are you hearing? If it's the CG,
And is it EVERY Sunday?
posted 01-07-2002 07:30 AM ET (US)
You are correct it is often the Coast Gaurd. Sometimes SeaTow or other emergency operations. 6 months ago I listened in on a heart attack emergency in Tampa Bay. The antenna is relatively short, maybe 4 ft in length and made out of steel with a bulb at its bottom. It sticks up from the fascia (sp,?) of the house. Less then half the length of the antenna on the boat. You guys are correct -- come to think about it -- I don't remember listening in on fishing banter. Thanks for the info. David
posted 01-07-2002 07:58 AM ET (US)
No, it is not every Sunday.
posted 01-14-2002 05:30 PM ET (US)
Outrageman: It's time for both of us to pickup our trusty West Marine catalog and do some reading. I know they discuss the benefits of and reasons not to use various "Gain" antennae for certain applications. I'll see if I can find the time to read that page again. It's been a few years. I hope your house does not heal like a sailboat, which is why an antenna designed for a sailboat would give less than optimal performance.
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.