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Old 17-02-2012, 19:16   #16
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

This is great to have detailed distillated (?) information all in one place. I don't have a backstay, and the nearest rigging to the pilothouse where the radio is, is a running backstay, so that might be out. A hoisted inverted vee might work on some bands. Maybe a hoisted random wire with the automatic tuner will work OK. Any masthead wiring is a real chore. I remember an end fed coax inverted vee with coils to block RF from the tuner or transmitter. Some of the older hams are gone now, and their knowledge is gone too. SSB is still good to have on board as a long range communication tool. I guess I'll become an experimenter later this year.
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Old 17-02-2012, 19:31   #17
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Originally Posted by kaimusailing View Post
This is great to have detailed distillated (?) information all in one place. I don't have a backstay, and the nearest rigging to the pilothouse where the radio is, is a running backstay, so that might be out. A hoisted inverted vee might work on some bands. Maybe a hoisted random wire with the automatic tuner will work OK. Any masthead wiring is a real chore. I remember an end fed coax inverted vee with coils to block RF from the tuner or transmitter. Some of the older hams are gone now, and their knowledge is gone too. SSB is still good to have on board as a long range communication tool. I guess I'll become an experimenter later this year.

btrayfors, Bill WA6CCA, is probably the most experienced on this subject, so if he revisits this thread, that would be one of your "older hams" that ISN'T gone, so get his input, he is a published author on this subject.

If he doesn't return to this thread, I'll be the young (59) guy ham, that will be building my inverted vee trapped dipole again this Spring and would be happy to share pictures, coil and cap values (do you have an L/C bridge/meter? If not I'll spec for you wire gauge, amount of turns, and diameter.), and element lengths with you.
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Old 18-02-2012, 08:15   #18
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Thanks DO,
I will be looking for your new rig when you do it.
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Old 19-02-2012, 10:56   #19
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Originally Posted by btrayfors View Post
Anyone interested in building a "marinized" vertical dipole antenna can find construction details here: Marine Antennas

These antennas, by the way, are very robust. Mine survived several major hurricanes with winds in the marina over 100 knots in Tortola. The vertical dipole can be used easily at anchor, at dockside, and underway on long tacks. To get it out of the way for tacking, just undo the lower end and move it back into the shrouds and tie it there, where it will still work but with some detuning.
Bill,
Finally got a chance to look at the construction details of your dipoles. I LOVE the use of the lifeline material...very robust indeed. I have all the nicropress tools and fittings already. In fact the company that makes the center insulators is right here in San Diego where I have my boat! I think I'll build a couple of these for fun and give them a try. BTW, another plus is that I think the lifeline wires will coil up more nicely than the regular stranded OR solid copper wire hams normally use. Great job!

73 de K6LSD
Marty
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Old 19-02-2012, 13:08   #20
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Bill,
Finally got a chance to look at the construction details of your dipoles. I LOVE the use of the lifeline material...very robust indeed. I have all the nicropress tools and fittings already. In fact the company that makes the center insulators is right here in San Diego where I have my boat! I think I'll build a couple of these for fun and give them a try. BTW, another plus is that I think the lifeline wires will coil up more nicely than the regular stranded OR solid copper wire hams normally use. Great job!

73 de K6LSD
Marty
Hi, Marty...

Glad you like the design. It's evolved over the years. I first built one to try in the Virgin Islands. It was constructed of AWG14 stranded bare copper wire...what was then in common use for antennas. It lasted barely two weeks in the harsh marine environment!

I've just made up two more for customers. Couple of hints:

1. Make one for 20m first, since that will fit nicely on your boat and it's the band which is most open for DX these days. From San Diego, you should easily reach to the East Coast and westward well into the Pacific and Asia.

2. Vertical dipoles tend to be a bit shorter than their horizontal cousins. But, be careful not to cut it too short. I generally cut them according to the formula (468/freq in mHz)...or maybe just a bit shorter....then trim them on the boat.

3. Use 1/8" s/s insulated lifeline, and 1/8" Nicopress sleeves. Strip back exactly 4.5" of insulation from the two ends which are to fit into the center insulator. Drill out the holes in the center insulator with a 5/32" bit to facilitate easy passage of the bare s/s wire.

NOTE: the pic on my website shows one side of the Nicopress sleeve with an insulated section, the other bare. I've found it's better to use 1/8" sleeves and use bare s/s thru both sides of the Nicopress sleeve. Makes a smaller and a stronger connection.

4. Now, thread the bare s/s wire through a Nicopress sleeve, pass it thru one of the holes in the Budwig center insulator, and bend it back on itself. I've found it easiest to pass the end back thru the Nicopress sleeve before trying to insert the copper stub from the insulator. Once you've got that, you can manipulate the loop so as to allow the copper stub to be pushed into the center of the Nicopress sleeve. Pull everything up tight and press on the sleeve.

5. Some goop on the ends of the sleeve might be a good idea to keep water out, then cover them with adhesive heat shrink, tape, etc.

6. If you have an antenna analyzer handy, that will make tuning the dipole much easier, because what is necessary is to form temporary loops at the ends of the dipole, hoist it using a spare or dedicated halyard, tie the lower end off near the lifelines or toerail between the mast and the forestay, and see where it's resonant. It you cut it to formula, it will be resonant WAY lower than the intended frequency, so considerable trimming will be necessary.

7. Bit by bit, trim equal amounts off each end of the dipole, reform the temporary loops, and measure the resultant resonance. For 20m, you'll probably wind up with about 31.5 or 32' overall length. Take your time doing this...you really don't want to mess up by inadvertently cutting the legs too short!

8. The length of the coax, and it's orientation also play a role in getting SWR down near 1:1. If you're planning to install a "black box" under the gooseneck, like mine, you will have a relatively short coax lead in on the antenna, and a permanent coax from the "black box" to the rig. For trimming purposes before you build the box, just use a length of coax which approximates the total run you'll have when permanently installed.

9. For coax to the antenna, use RG8X. RG-213, 214, LMR400, etc. are too heavy. Try to bring the coax back to the mast or shrouds as high as possible, so as to be as perpendicular to the dipole as is conveniently possible. It doesn't have to be perfectly perpendicular, but try to do it as well as you can. I use a spare spinnaker car on a track on the forward side of my mast.

Let me know how it goes. Maybe I'll work you on 20m :-)

Bill
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Old 20-02-2012, 05:31   #21
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Ahoy Capn Bill,
Thank you for all the information on your site. How tall is your mast? I will be fooling around with an ICOM M800 with antenna tuner later this year. I retired from doing broadcast engineering all over the Baltimore/Washington/Annapolis area for CEI in Newington. I'm not a ham though.
Thanks again,
Andy S.
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Old 20-02-2012, 05:54   #22
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Originally Posted by kaimusailing View Post
Ahoy Capn Bill,
Thank you for all the information on your site. How tall is your mast? I will be fooling around with an ICOM M800 with antenna tuner later this year. I retired from doing broadcast engineering all over the Baltimore/Washington/Annapolis area for CEI in Newington. I'm not a ham though.
Thanks again,
Andy S.
Hey, Andy...

My mast is 64.5' above the water, including a 3db VHF antenna. Just make it under the ICW bridges!

Hey, with your background there's no excuse for not having a ham ticket. They're very easy to get these days...no code requirement. That M800 will work fine on the ham bands :-)

Cheers,

Bill
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Old 21-02-2012, 01:36   #23
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Re: @ Bill: Do you want an HF antenna that performs 20~40 db better than a back stay?

Hi Bill I have to admit I still have 3 vertical dipoles(20m-17m -15m) lying around in the boat....unused.... sorry Bill

My experience so far is that it was impossible to tune them to SWR <= 1:1.5 by trimming the wires. I seem to have a lot of detuning from the (ungrounded) rigging. Especially when rigging those V dipoles between the mast and the forestay. It is slightly better when rigging them between mast and backstay but this is really impractical.
A vertical dipole freestanding over salt water should give an impedance close to 40-50 Ohms no? So it must be the rigging.

I have a 1:1 current balun in each of them, though maybe on a sailing boat with all the rigging it makes no sense to try and avoid common ground currents on the coax.

I thought of modeling them in EZNEC to find out the expected impedances at feedpoint but it will be next to impossible to model the rigging and get a decent result I guess.
Maybe an antenna analyser: is this correct I should use a electrical 1/2 wave of coax feedline to be able to measure at the coax and transceiver? ... that would mean 3 different coax lengths to measure out all 3 of them...

Maybe I should learn to live with 1:2 VSWR's....that's not that bad but my Yaesu FT897 doesn't have an onboard atu.

Jan
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Old 21-02-2012, 03:11   #24
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

20 m vertical dipole in Eznec, above seawater:

5.14m per leg
lower leg 1.5m above seawater
Z = 86 + j0.6 Ohms (about reasonance)
50 Ohm SWR = 1.72
(but no rigging included so freestanding vertical dipole...)

Vertical elevation plot: 6.35 dBi at 7° = ideal for DX

This explains my SWR. In fact I should use 75 Ohm coax....

or use a hairpin match which is not really handy in a sailboat situation...

So in a setup without antenna tuner at the transceiver, and when using 50 Ohm coax, the better option would be to turn down the TX ppower a bit and live with the 1:1,7 VSWR.
The optimal vertical radiation plot with low take-off angle at 7° will compensate that royally....

On a(very) rainy day I will try to model including all the rigging....

Jan
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Old 21-02-2012, 03:23   #25
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Bringing the base of the vertical dipole higher than the 1.5m above sea level, eg 3 m for the 20m V-dipole improves the Impedance (lower) and brings down the SWR to 1:1.5.

Off course some minor lobes pointing up to the sky apear.

What is your opinion on this Bill?

Jan
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Old 21-02-2012, 06:23   #26
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

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Originally Posted by btrayfors View Post

Vertical antennas rigged at the stern of a sailboat can exhibit pretty good low angle performance as well. Not as good as the vertical dipole, but very respectable. So, too, can the traditional backstay antennas on certain bands, though not on others. Performance of these antennas depends very much on the configuration of the individual boat and, of course, on the care taken with the installation.



Bill
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Bill I have modeled a simple system: a 7.2m vertical antenna pole at 0.5 m from the right side of a 3.5m wide transom.
For 14.225 Mhz: 2 1/4 wave radials. Port radial: first bit is 3m wire along transom, then remainder running to the front. SB radial 0.5m wire to port side of trnasom then remainder to the front.
I have done the same for 7.1 MMhz, 18.30 Mhz and 21.250 Mhz bt each time with 2 1/4 wave long radials.
With this I simulate a simple radial ground system. I would'nt know how to model an extra short stretch of copper foil to an underwater bronze...

The vertical elevation plots are really nearly as good as for a vertical dipole, although no sharp nulls at the center so the flat donut seems to be "filled flat" in its normal center hole.(trying to explain visually...)

7.1 Mhz: + 4.4 dBi at 10° (miniaml gain, but good low TA angle)
14.225 Mhz: + 5.3 dBi at 8° (I modeled + 6.35 dBi for vertical dipole)
18.30 Mhz: + 6.0 dBi at 7°
21.25 Mhz: + 6.44 dBi at 7°

That doesn't look bad at all but off course a very rough approach and excluding ground losses and tuner losses that are not there for the vertical dipole.

Jan
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Old 21-02-2012, 07:28   #27
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Quote:
Originally Posted by btrayfors View Post

Vertical antennas rigged at the stern of a sailboat can exhibit pretty good low angle performance as well. Not as good as the vertical dipole, but very respectable. So, too, can the traditional backstay antennas on certain bands, though not on others. Performance of these antennas depends very much on the configuration of the individual boat and, of course, on the care taken with the installation.



Bill
WA6CCA
Bill I have modeled a simple system: a 7.2m vertical antenna pole at 0.5 m from the right side of a 3.5m wide transom.
For 14.225 Mhz: 2 1/4 wave radials. Port radial: first bit is 3m wire along transom, then remainder running to the front. SB radial 0.5m wire to port side of trnasom then remainder to the front.
I have done the same for 7.1 MMhz, 18.30 Mhz and 21.250 Mhz bt each time with 2 1/4 wave long radials.
With this I simulate a simple radial ground system. I would'nt know how to model an extra short stretch of copper foil to an underwater bronze...

The vertical elevation plots are really nearly as good as for a vertical dipole, although no sharp nulls at the center so the flat donut seems to be "filled flat" in its normal center hole.(trying to explain visually...)

7.1 Mhz: + 4.4 dBi at 10° (miniaml gain, but good low TA angle)
14.225 Mhz: + 5.3 dBi at 8° (I modeled + 6.35 dBi for vertical dipole)
18.30 Mhz: + 6.0 dBi at 7°
21.25 Mhz: + 6.44 dBi at 7°

That doesn't look bad at all but off course a very rough approach and excluding ground losses and tuner losses that are not there for the vertical dipole.

Jan
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Old 21-02-2012, 09:48   #28
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Re: @ Bill: Do you want an HF antenna that performs 20~40 db better than a back stay?

Hi, Jan...

Sorry you've been having difficulties. I've never experienced the same, and I've been trimming dipoles on all kinds of sailboats for over 30 years!

First, no, you don't need the balun. I learned a long time ago that on a sailboat these are both unnecessary and they create a weak point by adding weight and windage.

Next, you do NOT need a 1/4 wave coax length. In fact, that could cause some problems. Random length is good, though very occasionally some trimming is needed.

The trimming process itself is laborious if you don't have an antenna analyzer. Most of the VD's I've put up were done the old-fashioned way, by trimming the length of both legs back inch-by-inch and watching the SWR go down as the resonance moved up towards the desired frequency.

Actually, technically, SWR and resonance are not the same thing. However, for this purpose what you want is to trim the antenna for lowest SWR at the radio. While the rigging and adjacent vessels and structures in a marina will affect readings somewhat, it should still be possible to achieve a low SWR at the intended operating frequency....say, 1:1.3 or less. I generally get down to 1:1.2 or less.

Note also that SWR on a sailboat will change due to proximity to other boats and obstructions, rain/sleet/snow, detuning from rigging, etc., etc. For that reason, it's a good idea to have some sort of tuner to use if needed...either one built into the rig or a separate one. I use a tiny Kenwood AT-130 for final trimming when needed with my marine rig (FT-600). My ham rig on the boat (FT-900AT) has its own internal tuner and nothing more is needed. In fact, I rarely use the tuner(s) at all.

73,

Bill
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Quote:
Originally Posted by Goudurix View Post
Hi Bill I have to admit I still have 3 vertical dipoles(20m-17m -15m) lying around in the boat....unused.... sorry Bill

My experience so far is that it was impossible to tune them to SWR <= 1:1.5 by trimming the wires. I seem to have a lot of detuning from the (ungrounded) rigging. Especially when rigging those V dipoles between the mast and the forestay. It is slightly better when rigging them between mast and backstay but this is really impractical.
A vertical dipole freestanding over salt water should give an impedance close to 40-50 Ohms no? So it must be the rigging.

I have a 1:1 current balun in each of them, though maybe on a sailing boat with all the rigging it makes no sense to try and avoid common ground currents on the coax.

I thought of modeling them in EZNEC to find out the expected impedances at feedpoint but it will be next to impossible to model the rigging and get a decent result I guess.
Maybe an antenna analyser: is this correct I should use a electrical 1/2 wave of coax feedline to be able to measure at the coax and transceiver? ... that would mean 3 different coax lengths to measure out all 3 of them...

Maybe I should learn to live with 1:2 VSWR's....that's not that bad but my Yaesu FT897 doesn't have an onboard atu.

Jan
ON3ZTT
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Old 21-02-2012, 09:55   #29
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay?

Jan,

Interesting figures. And, basically, they confirm what I've seen and most knowledgeable hams have reported, i.e., vertical whips on the stern have a pretty low takeoff angle and can be quite effective for DX.

As you say, though, there are some losses from the tuner, ground system and, of course, from the design itself (essentially an end-fed random-length vertical wire), especially compared to the vertical dipole which has none of these losses.

The vertical whip has the advantage over a traditional backstay in that it has a pretty good radiation pattern all round the horizon, whereas the backstay (essentially an end-fed random length sloping wire antenna) is somewhat directional. However, the backstay will likely be more effective on the lower bands because of it's length advantage.

73,

Bill
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Quote:
Originally Posted by Goudurix View Post
Bill I have modeled a simple system: a 7.2m vertical antenna pole at 0.5 m from the right side of a 3.5m wide transom.
For 14.225 Mhz: 2 1/4 wave radials. Port radial: first bit is 3m wire along transom, then remainder running to the front. SB radial 0.5m wire to port side of trnasom then remainder to the front.
I have done the same for 7.1 MMhz, 18.30 Mhz and 21.250 Mhz bt each time with 2 1/4 wave long radials.
With this I simulate a simple radial ground system. I would'nt know how to model an extra short stretch of copper foil to an underwater bronze...

The vertical elevation plots are really nearly as good as for a vertical dipole, although no sharp nulls at the center so the flat donut seems to be "filled flat" in its normal center hole.(trying to explain visually...)

7.1 Mhz: + 4.4 dBi at 10° (miniaml gain, but good low TA angle)
14.225 Mhz: + 5.3 dBi at 8° (I modeled + 6.35 dBi for vertical dipole)
18.30 Mhz: + 6.0 dBi at 7°
21.25 Mhz: + 6.44 dBi at 7°

That doesn't look bad at all but off course a very rough approach and excluding ground losses and tuner losses that are not there for the vertical dipole.

Jan
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Old 22-02-2012, 04:14   #30
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Re: Do you want an HF antenna that performs 20~40 db better than a back stay ?

Yes Bill...the never-ending quest for the optimal all-band antenna on a sailing boat...

I would expect even a vertical 'random length' end-fed antenna will have directionality because of the effect or the nearby backstay, mast, stays, etc.

I would very much like to try and model my own sloping "alternate backstay" antenna "Copyright B.Trayfors " to really find out about the expected radiation patterns... but I'm novice at Eznec.
Modeling the mast, stays and my 1/4 wave radials etc. is feasable, but what about the pushpit, lifelines, toerail who are in fact grounded since they are linked to the copper tape to an underwater bronze....

I wish our good old friend Greg was around to help me there....

Jan
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