Long wire HF Antenna Length

[40 South]

Originally Posted by Wotname

More mundane detail, generally choose the mid frequency of the range of frequencies you expect to use.

I.E. you wont be using frequencies say above 18 MHz and unlikely to use any below 4MHz - at least not in Aussie waters. More likely to be using 4 & 8 and 12 & 16 MHz.

I total agree with this the likely frequencies. The problem here is the requirement for longer lengths of wire for these frequencies, hence the inverted "V" question.

So something to suit the 8 MHz would be the go for marine in Oz.

[haiqu]

Originally Posted by Wotname

More mundane detail, generally choose the mid frequency of the range of frequencies you expect to use.

I.E. you wont be using frequencies say above 18 MHz and unlikely to use any below 4MHz - at least not in Aussie waters. More likely to be using 4 & 8 and 12 & 16 MHz.

Disclaimer, I am currently out of touch with usual working AU frequencies and hopefully more up to speed folk will post accordingly.

OK, I guess that's my cue. 2182 is no longer monitored. 4125 and 6215 are the most usable frequencies for calling. The 40M ham band is also very useful.

I'd suggest mechanically tuning the wire for 7MHz and then using a tuner. This is a reasonable compromise for length on a yacht of around 35'. You can "extend" the active wire by winding a few turns around a piece of 3" PVC pipe before the connection to your radio. A ladder line from the backstay will provide the best impedance matching to that wire.

Rob
VK9VK/MM
MROCP

[btrayfors]

First, let's get the nomenclature right: a long-wire antenna means a wire antenna which is multiple wavelengths long! Backstay antennas are not long-wire antennas.

What we're talking about here are random-length end-fed wire antennas. Just about any length over 23' total (tuner to upper insulator of the backstay) will work, that is, will tune most frequencies from 2-30 mHz.

Longer lengths favor radiation on the lower bands, say under 8 mHz. Shorter lengths favor radiation on the upper bands, say 10 mHz and above.

A good compromise is somewhere in the 40-45' range.

It's not really useful to measure out a 1/4-wave length for a backstay antenna, because there are too many variables. One variable most folks don't think about is the electrical length @ HF frequencies vs. the physical length. These are not the same thing.

A backstay antenna -- no matter how you cut it -- is going to be a fairly good and versatile antenna when fitted with a modern tuner. But, it's not going to be a great antenna on any band.

For a great antenna you'd need something like a monoband center-fed vertical dipole antenna, but these are only practical on 20 meters and above because of the needed hoist. Single-band vertical antennas cut and tuned for 1/4-wavelength can be very good also.

Inverted-vee antennas are good high-radiation angle (short-range) antennas, but not worth much for long-distances.

Here's a table which compares various antennas on a sailboat: http://wdsg.com/gallery/main.php?g2_...geViewsIndex=1

Bill
WA6CCA

[40 South]

Thanks Bill

That was the sort of info I was after.

All the ham guys go into great detail.

So a wire of 40'-45' (I read somewhere 43'/13.1m was good), including the lead to the ATU would be a good working compromise. It would work well on a 15m mast with a length of spectra, or such, and an insulator to haul up towards the masthead with the lower end fed through a deck insulator to the ATU.

[Wotname]

Originally Posted by btrayfors

First, let's get the nomenclature right: a long-wire antenna means a wire antenna which is multiple wavelengths long! Backstay antennas are not long-wire antennas.

What we're talking about here are random-length end-fed wire antennas. Just about any length over 23' total (tuner to upper insulator of the backstay) will work, that is, will tune most frequencies from 2-30 mHz.

Longer lengths favor radiation on the lower bands, say under 8 mHz. Shorter lengths favor radiation on the upper bands, say 10 mHz and above.

A good compromise is somewhere in the 40-45' range.

It's not really useful to measure out a 1/4-wave length for a backstay antenna, because there are too many variables. One variable most folks don't think about is the electrical length @ HF frequencies vs. the physical length. These are not the same thing.

A backstay antenna -- no matter how you cut it -- is going to be a fairly good and versatile antenna when fitted with a modern tuner. But, it's not going to be a great antenna on any band.

For a great antenna you'd need something like a monoband center-fed vertical dipole antenna, but these are only practical on 20 meters and above because of the needed hoist. Single-band vertical antennas cut and tuned for 1/4-wavelength can be very good also.

Inverted-vee antennas are good high-radiation angle (short-range) antennas, but not worth much for long-distances.

Here's a table which compares various antennas on a sailboat: MarineAntennaChoices2

Bill
WA6CCA

Nice table Bill and thanks for the correction in nomenclature. Some of us (or at least me), get lazy or forgetful some days.

[ka4wja]

I'd simply like to highlight Bill's excellent post here....as he gave you a simple, direct answer....and explained it concisely (something I often forget to do...)

Originally Posted by btrayfors

First, let's get the nomenclature right: a long-wire antenna means a wire antenna which is multiple wavelengths long! Backstay antennas are not long-wire antennas.

What we're talking about here are random-length end-fed wire antennas. Just about any length over 23' total (tuner to upper insulator of the backstay) will work, that is, will tune most frequencies from 2-30 mHz.

Longer lengths favor radiation on the lower bands, say under 8 mHz. Shorter lengths favor radiation on the upper bands, say 10 mHz and above.

A good compromise is somewhere in the 40-45' range.

It's not really useful to measure out a 1/4-wave length for a backstay antenna, because there are too many variables. One variable most folks don't think about is the electrical length @ HF frequencies vs. the physical length. These are not the same thing.

A backstay antenna -- no matter how you cut it -- is going to be a fairly good and versatile antenna when fitted with a modern tuner. But, it's not going to be a great antenna on any band.

For a great antenna you'd need something like a monoband center-fed vertical dipole antenna, but these are only practical on 20 meters and above because of the needed hoist. Single-band vertical antennas cut and tuned for 1/4-wavelength can be very good also.

Inverted-vee antennas are good high-radiation angle (short-range) antennas, but not worth much for long-distances.

Here's a table which compares various antennas on a sailboat: http://wdsg.com/gallery/main.php?g2_itemId=126&g2_imageViewsIndex=1

Bill
WA6CCA

EVERYONE here should thank Bill for this!!


Fair winds...

John
s/v Annie Laurie

[40 South]

Just had a walk around my marina and a few yachts (sailboats) have a wire antenna attached directly to the backstay with cable ties and/or tape from the deck insulator up.

Are there likely to be any TX or RF issues with this? I envisaged the wire to be hanging free from masthead to the deck insulator or other strong point near the deck with the tail to the insulator.

If the vessel had two independent backstays could two different lengths of wire be run up each backstay with a switch box to change over. Or run two lengths together up one backstay? The different lengths could be better suited to high and low bands.

[ka4wja]

Ted,
Not sure I understand what you are describing...
But in general, you'll run a wire (GTO-15) from the remote tuner output, up thru the deck (near the backstay), and connect it to the backstay just above the lower insulator (assuming you're using two backstay insulators)....

Originally Posted by 40 South

Just had a walk around my marina and a few yachts (sailboats) have a wire antenna attached directly to the backstay with cable ties and/or tape from the deck insulator up.

It's not a complicated set-up....
In years past, when the hulls were steel and/or when all the stays are grounded/bonded, it was standard-operating-practice to run this GTO-15 wire up from the thru-deck fitting to above the lower insulator, a few inches away from the backstay by using some "stand-off" insulators...this reduced/eliminated RF coupling to ground, and improved your signal....
HOWEVER, we now know that with fiberglass boats we can just remove the bonding/grounding wire from the backstay chainplate and run the GTO-15 directly against the backstay below the lower insulator, and NO ill effects are created....
(Further, Eric, a Cruiser's Forum member, who equipped the vessels at US Naval Academy Annapolis, has regularly written of NO ill effects noticed even if the GTO-15 is run along grounded stays/rails.....but I'd not recommend this...)
And, I have tested my set-up with the GTO-15 placed 4" - 6" away from my lower part of the backstay (below the lower insulator) and then cable-tied directly to it....no difference in antenna tuner "tuning", and no difference in performance noticed....
It has served me well for over 10 years, > 15,000 miles offshore, included two Atlantic crossings, etc.

(Yes, there are some guys who will still advise using stand-offs, and I don't criticize them....but, on fiberglass boats, in reality it is not necessary...)

Have a look at some photos of my set-up....both with and without the padded covers over the turnbuckle, etc...








Now, the actual connection of the tinned-copper GTO-15 wire to the SS backstay wire IS important, and should be well waterproofed, etc.
Bill and others may have some photos/examples of "how-to" do this, and more time that I do this morning...

Sorry, I gotta' go...


Opps, forgot this point...

Originally Posted by 40 South

If the vessel had two independent backstays could two different lengths of wire be run up each backstay with a switch box to change over. Or run two lengths together up one backstay? The different lengths could be better suited to high and low bands.

Do NOT over think things....just use the length that makes sense...
(Note that I also have twin backstays...)
In your case, with a mast of 15m (~49'), keeping the top insulator a few feet (50cm - 100cm) away from the masthead and a foot or so away from the other backstay, you'd end up with a backstay antenna no longer than about 50'...and you may just measure and decide on the "normal" / "typical" 45' length overall....


To sum-up:
a) As I wrote above, it is not a complicated thing...No matter what ramblings you read....
b) Re-read Bill's post...
c) For your boat (with a 15m tall mast), just use a backstay antenna length of 40' - 45'....




Fair winds..

John
s/v Annie Laurie

[John Drake]

Just to quickly add: not all tuners tune all lengths of random wires. Over 30 ft, you should be OK with any tuner...BUT....check the specs on the specific tuner to see what the minimum length of random wire it will tune. There can be significant differences.

[Goudurix]

Chossing a good starting and/or optimal "random end-fed sloping wire antenna depends on:
- you want long range (thousands of miles) or short range communication
- the frequencies you want to use
- the matching range of your tuner
- avoiding lengths around a 1/2 wave for any target frequency.

Frequencies:
- what is the highest frequency you want to use : avoid a total wire length (from top of wire until the antenna connection on the ATU) longer than 0.625 wavelength. At about 0.6 WL your wire antenna should give you some gain it is at the so-called "Double extended Zep antenna length (look up in the ARRL antenna handbook if you want some more background). Having a longer wire produces mainly radiation lobes shooting up to the sky and only good for shorter range communication.
- what is the lowest frequency you want to use with good efficiency => do not make the wire shorter than about 60% of a quarter WL or you will get increasing efficiency loss
- avoid lengths that are close to a 1/2 WL for any target frequency giving very high impedance at the antenna feedpoint and probably making it impossible for the ATU to match that impedance

An example:
- you mainly target DX HAM frequencies 40m-20m-17m-15m bands. The typical 40-45 feet isolated backstay antenna is really too long for a good long range radiation pattern at 15m HAM band were the maximal (but also optimal length at 0.625 WL) is about 30 ft.
- at 45 ft it is a 1/2 WL for 11 Mhz so not a problem for our target frequencies
- at 40m it is 129% of a 1/4 WL this is OK
- even at the 80m HAM band it is 66% of a 1/4 WL so still some acceptable efficiency to be expected
- at 45 ft it is 0.625 WL for 13.8 Mhz hence probably not good anymore even for a good radiation pattern on 20m HAM band
- for these given target frequencies a wire antenna length of about 9 metres (30 ft) is optimal ( my SGC230 tuner even tunes all marine SSB a,nd HAM frequencies from 2.1 Mhz - 30 Mhz with this length)

This is off course the theoretical side - seawter being the ideal RF grund and take-off platfrom for long range DX, even suboptimal wire atenna lengths will give results.

This is about optimising the wire length before deciding to cut up your backstay.

Jan

[Goudurix]

Oops I was typing really too fast hence sloppy typing;..sorry.

[continuouswave]

Originally Posted by Goudurix

...At about 0.6 WL your wire antenna should give you some gain it is at the so-called "Double extended Zep antenna length...

You are confused about the Extended Double Zepp antenna. You won't have a "double extended Zepp" antenna. The "extended" modifier refers to extension beyond 0.5-Wavelength. The "zepp" refers to an end-feed 0.5-Wavelength antenna with a high-impedance, fed with a balanced feed line of 0.25-Wavelength. I believe the "Zepp" came from its use in airships or zeppelins, where there could be no "ground" reference.

The antenna being described here has none of these characteristics. It is a sloping vertical of various wavelength depending on frequency. It is being fed by a single wire feed line and the hull or some other conductor in contact with the sea is used as a ground.

In vertical antennas the electrical height of the vertical radiator is often chosen to be around 0.625-Wavelength for two reasons:

--this is the tallest vertical in which the major lobe of radiation is still at a very low elevation angle; any taller and the main lobe begins to break up into smaller lobes at higher angle of elevation.

--the impedance is usually in the range of 100-Ohms resistive with some reactance, which is not too hard to match to a 50-Ohm transmission line.

Such an antenna is not an Extended Double Zepp. An Extended Double Zepp is a center fed horizontal flat-top antenna of overall length of 1.25-Wavelength. The antenna suggested here for use as a backstay antenna is a sloping vertical being fed against the seawater as ground.

de K8SS

[Goudurix]

Yeah yeah Continuouswave,

you are right, I mistakenly used "Double extended Zep length" it is off course "extended Zepp length", 0.625xWavelength is indeed the length used for an "extended Zepp" antenna. But I said "DEZ antenna length" not "antenna"!
Our ships are waterships not airships

Here we are not talking about an antenna "several wavelengths long".

If you model a vertical dipole (or doublet) 2x0.625 WL long, or a groundplane with the vertical radiator 0.625 WL long and 2 or 4 elevated 1/4 WL radials, you will see the same effect: concentration in a strong low-angle radiation lobe. Make the radiator than 0.625 WL and you will see strong lobes developing at high take-off angles, hence less suited for long range DX.
A similar result is to be expected for a sloping end-fed wire antenna with a good ground system.

My advice is based on this: do not make the wire or insulated backstay (inclu. the GTO15 wire) longer than 0.625 WL for the highest frequency you want to use for long-rnage DX.
Try not to make it shorter than 0.15 WL for the lowest frequency you want to use.

Jan
ON3ZTT

[nhschneider]

I hope I can take advantage of your expertise in an area that continuously confuses me.

I'm in the process of re-rigging the main mast on my ketch. A friend of mine suggested eliminating the backstay insulators altogether and just run a 12AWG wire in a 5/16" dacron rope with the rope core removed. He says it works great for him.

I have a few questions, though:

Do I measure the 12AWG wire from the tuner?

If I were to make it 30' long, I could run it straight up my mizzen mast - would this be better?

Should I just bite the bullet and pay the US$1,000 for the insulators?

Thanks for your help.

Fair winds and calm seas.

[Goudurix]

Hi nhschneider,

Since for both an insulated backstay or wire antenna ("alternate backstay antenna) you need the automatic tuner and a way to bring down a wire or GTO-15 through the deck towards the antenna lug of the tuner, you have nothing to lose trying out hte cheaper solution first you will only need the stretch of AWG12 wire and2 or 3 cheap HAM isolators at $ 0,50 a piece.

What does matter is to have the wire run a bit away from other stays, shrouds etc as your antenna wire will couple into those and distort radiation pattern however on a sailing boat this is unavoidable...

For a trial setup there is no need to run the wire inside a dacron rope.

30 feet should do well (30 feet from top of the wire at the top isolator until the antenna tuner's antenna connection lug). This should give you good to very good operation 7 Mhz - 22 Mhz losing some efficiency lower than 7 Mhz.

Another low(er) cost experiment/solution is to use a 7m fishing rod, run the wore alongside the rod, and install this at the aft pulpit. This will probably give you about 7,3-8 meters of total antenna length, I would rather go for about 7,3 m to avoid 1/2 wavelength on 18 Mhz HAM band. I guess this is a good solution to get a bit farther away from the standing rigging but not a very sturdy one so I would go for the 30 ft wire antenna from the mizzen if it doesn't interfere with the mizzen boom off course.

Jan