What aerials have people used for their VHF on the mast, I have been looking around and it seems there are few options. I am trying to keep down on length without losing efficiency and easy/tidy to mount to the mast. Any ideas would be great!!

Datawiz said...

eartH2Ocean said..
What aerials have people used for their VHF on the mast, I have been looking around and it seems there are few options. I am trying to keep down on length without losing efficiency and easy/tidy to mount to the mast. Any ideas would be great!!

Hi eartH2Ocean,
The reason there are few options for an aerial is because its physical characteristics are critical to its efficiency.
Aerial design is incredibly complex - best not to mess with it.
regards,
allan

I realize it is complex but you must have one that is why I am seeking other people's experiences to work out what is best to use

I had to replace my masthead antenna 2 years ago when at gold coast city marina. The guys there recomended a glomex masthead antenna which i installed. It was a stainless steel antenna 0.9 m.
I have had excellent reception receiving from 40 miles plus. I am on top of 15m mast

On our return trip from Lord Howe last year on Morning Bird we were getting reception on VHF more than 100 miles out.

Was talking with our local radio expert today and he said even with the optimum ariel, anything mounted in the same plane as it, such as nav light, wind transducer etc, will affect the ariel's efficiency.

If you have an ariel splitter to share it with an AM/FM radio it is possible or likely you will lose 5 to 10 % efficiency.

Technically speaking VHF range is determined by line of sight therefore the higher the ariel the better the range but I think sometimes atmospheric conditions may extend that but certainly not like HF radio skip.

Dammit, how do you spell ariel correctly. No matter how I spell it Google spell check underlines it red.

RiffRaff said..
I had to replace my masthead antenna 2 years ago when at gold coast city marina. The guys there recomended a glomex masthead antenna which i installed. It was a stainless steel antenna 0.9 m.
I have had excellent reception receiving from 40 miles plus. I am on top of 15m mast

I have the same. Excellent performance.

nswsailor said..
You can go as low as a 1/4 wave length which is about 450mm.

Have a look at the yachts around you and you will see that is the norm.

I agree with NSWsailor. 1/4 wave is a good compromise. I've designed lots of antennas for various radios, satellite and HF.

The antenna needs "capture" area and resonance at the frequency you want to use. By good luck (thanks to nature) a 1/4 wavelength antenna has an impedance of 50 ohms which is just right to connect directly to 50 ohm cable and then to a 50 ohm radio so its a good choice. And it works pretty well.

But increasing the antenna size increases the capture area and the signal will be better because doing that kind of focuses the signal. The next size up is a 1/2 wave. But its twice as long but its not 50 ohms any more. The next popular size up is 5/8 wave which works great on a mast because it aims your transmit radiation at the horizon and picks up received signal from the horizon with a much bigger capture area than the 1/4 wave. Its a so called "gain antenna".

I have a "Pacific Aerials P6001 VHF Stainless Antenna Mast Mount 1m" at the top of my mast. You can get them from BLA (Bob Littler Agencies). Works well.

SandS said..

Trek said..

nswsailor said..
You can go as low as a 1/4 wave length which is about 450mm.

Have a look at the yachts around you and you will see that is the norm.

I agree with NSWsailor. 1/4 wave is a good compromise. I've designed lots of antennas for various radios, satellite and HF.

The antenna needs "capture" area and resonance at the frequency you want to use. By good luck (thanks to nature) a 1/4 wavelength antenna has an impedance of 50 ohms which is just right to connect directly to 50 ohm cable and then to a 50 ohm radio so its a good choice. And it works pretty well.

But increasing the antenna size increases the capture area and the signal will be better because doing that kind of focuses the signal. The next size up is a 1/2 wave. But its twice as long but its not 50 ohms any more. The next popular size up is 5/8 wave which works great on a mast because it aims your transmit radiation at the horizon and picks up received signal from the horizon with a much bigger capture area than the 1/4 wave. Its a so called "gain antenna".

hey Trek , could you use the whole mast and spreaders as an Arial for VHF or if not, for 27meg ?

For 27MHz yes but for VHF probably not so good. Because the wavelength of VHF is short (ie metres) the benefit of being able to make the antenna a resonant length is high and the length of a much longer wire can loose much of the VHF signal any piece of it might capture. For 27MHz and other HF its possible to buy various kinds of ATU which is Antenna Tuning Unit and also automatic ones. They let you connect a 50 ohm radio onto one side and any kind of wire on the other. They then automatically work out how to make your piece of wire act like a proper aerial. Backstays on yachts are commonly used as antennas, I do that on Trek. The wavelength of 27MHz is close to 300/27 metres which is 11m. Thats a size close to what the height of lots of masts could be and as an antenna would work great. But you might irradiate yourself a bit sitting too close to it

Trek said..

SandS said..

Trek said..

nswsailor said..
You can go as low as a 1/4 wave length which is about 450mm.

Have a look at the yachts around you and you will see that is the norm.

I agree with NSWsailor. 1/4 wave is a good compromise. I've designed lots of antennas for various radios, satellite and HF.

The antenna needs "capture" area and resonance at the frequency you want to use. By good luck (thanks to nature) a 1/4 wavelength antenna has an impedance of 50 ohms which is just right to connect directly to 50 ohm cable and then to a 50 ohm radio so its a good choice. And it works pretty well.

But increasing the antenna size increases the capture area and the signal will be better because doing that kind of focuses the signal. The next size up is a 1/2 wave. But its twice as long but its not 50 ohms any more. The next popular size up is 5/8 wave which works great on a mast because it aims your transmit radiation at the horizon and picks up received signal from the horizon with a much bigger capture area than the 1/4 wave. Its a so called "gain antenna".

hey Trek , could you use the whole mast and spreaders as an Arial for VHF or if not, for 27meg ?

For 27MHz yes but for VHF probably not so good. Because the wavelength of VHF is short (ie metres) the benefit of being able to make the antenna a resonant length is high and the length of a much longer wire can loose much of the VHF signal any piece of it might capture. For 27MHz and other HF its possible to buy various kinds of ATU which is Antenna Tuning Unit and also automatic ones. They let you connect a 50 ohm radio onto one side and any kind of wire on the other. They then automatically work out how to make your piece of wire act like a proper aerial. Backstays on yachts are commonly used as antennas, I do that on Trek. The wavelength of 27MHz is close to 300/27 metres which is 11m. Thats a size close to what the height of lots of masts could be and as an antenna would work great. But you might irradiate yourself a bit sitting too close to it

Thanks Trek , so good to have all you guys on here with expertise in these areas !!!

So would it be right to say that for 27 mhz would the ATU negate the need for insulators ?

Trek said..

SandS said..

Trek said..

SandS said..

Trek said..

nswsailor said..
You can go as low as a 1/4 wave length which is about 450mm.

Have a look at the yachts around you and you will see that is the norm.

I agree with NSWsailor. 1/4 wave is a good compromise. I've designed lots of antennas for various radios, satellite and HF.

The antenna needs "capture" area and resonance at the frequency you want to use. By good luck (thanks to nature) a 1/4 wavelength antenna has an impedance of 50 ohms which is just right to connect directly to 50 ohm cable and then to a 50 ohm radio so its a good choice. And it works pretty well.

But increasing the antenna size increases the capture area and the signal will be better because doing that kind of focuses the signal. The next size up is a 1/2 wave. But its twice as long but its not 50 ohms any more. The next popular size up is 5/8 wave which works great on a mast because it aims your transmit radiation at the horizon and picks up received signal from the horizon with a much bigger capture area than the 1/4 wave. Its a so called "gain antenna".

hey Trek , could you use the whole mast and spreaders as an Arial for VHF or if not, for 27meg ?

For 27MHz yes but for VHF probably not so good. Because the wavelength of VHF is short (ie metres) the benefit of being able to make the antenna a resonant length is high and the length of a much longer wire can loose much of the VHF signal any piece of it might capture. For 27MHz and other HF its possible to buy various kinds of ATU which is Antenna Tuning Unit and also automatic ones. They let you connect a 50 ohm radio onto one side and any kind of wire on the other. They then automatically work out how to make your piece of wire act like a proper aerial. Backstays on yachts are commonly used as antennas, I do that on Trek. The wavelength of 27MHz is close to 300/27 metres which is 11m. Thats a size close to what the height of lots of masts could be and as an antenna would work great. But you might irradiate yourself a bit sitting too close to it

Thanks Trek , so good to have all you guys on here with expertise in these areas !!!

So would it be right to say that for 27 mhz would the ATU negate the need for insulators ?

On the assumption the mast was metal and the base of it well insulated from the seawater (which would hard to do in damp conditions because of salty topsides) it probably would work. Depends on the brand of ATU. An exact wavelength at 27.88MHz is 299.7/27.88 metres which is 10.75 metres. (Where 299.7 is the speed of light). If your mast happened to be exactly that and the stays were insulated it would work great. Like Crusoes 1m antenna which Im guessing is a 1/2 wavelength so has more captrue area than a 1/4 wave, but is at VHF instead so its much shorter. If the stays werent insulated they probably would effectively increase the apparent size of the mast and it probably would still work, but not as good, because it wouldnt be the exact 1/2 wavelength any more.

interesting , thanks Trek , those atu sound like handy things . but for laypersons like me , stock proven sticks are the go i recon .

cheers .