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10-08-2019, 20:32
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#31
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,759
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Re: DIY HF whip
Quote:
Originally Posted by GILow
My goodness, if that is what you use for an antenna I really suggest you don't go too far from shore.
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I have better.
Question was about inexpensive whip antennas for emergency use in the event of dismasting. i answered the question. They work not because they're good antennas but because QRP is a thing. With an M-802 and an auto tuner out of your 150 watts with a whip like that you maybe get 10 watts ERP. It works because QRP works. Well, sometimes.
The shortest transmitting antennas that work reasonably well are 1/4 wave, and there's no way around that. So you need 30 feet for the 8 Mhz frequencies that are overall the most reliable.
Now if you are on a dismasted sailboat trying to get out on HF your choices are these:
1) You can use a very large, very expensive self-supporting commercial antenna such as the Shakespeare 5310-R, which is $500 plus freight (and still not really long enough)
2) You can use a horizontal antenna, such as the lifelines, and get good ERP but a bad takeoff angle. This will actually work well up to around 100 miles or so using NVIS techniques at around 4 MHz
3) You can use a kite, balloon, drone, etc. to pull a wire
4) You can use an inexpensive or homemade antenna that is, electrically, too short.
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11-08-2019, 04:21
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#32
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Jammer
I have better.
Question was about inexpensive whip antennas for emergency use in the event of dismasting. i answered the question. They work not because they're good antennas but because QRP is a thing. With an M-802 and an auto tuner out of your 150 watts with a whip like that you maybe get 10 watts ERP. It works because QRP works. Well, sometimes.
The shortest transmitting antennas that work reasonably well are 1/4 wave, and there's no way around that. So you need 30 feet for the 8 Mhz frequencies that are overall the most reliable.
Now if you are on a dismasted sailboat trying to get out on HF your choices are these:
1) You can use a very large, very expensive self-supporting commercial antenna such as the Shakespeare 5310-R, which is $500 plus freight (and still not really long enough)
2) You can use a horizontal antenna, such as the lifelines, and get good ERP but a bad takeoff angle. This will actually work well up to around 100 miles or so using NVIS techniques at around 4 MHz
3) You can use a kite, balloon, drone, etc. to pull a wire
4) You can use an inexpensive or homemade antenna that is, electrically, too short.
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Fair enough, but really, it seems something like the squid pole suggested by E.P. is going to be a better option, because it is not "electrically too short". But I do now understand what you were suggesting, and I can see the logic in it.
__________________
Refitting… again.
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11-08-2019, 04:27
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#33
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Brian.D
OK @GILow, the math is simplistic enough for results. Might not be the best results, but results none the less.
We want to work in 1/4 wavelengths. Even multiples of 1/4 wavelengths is our enemy. So stay away from 2/4, 4/4, 6/4, 8/4, and so on. We know that 468 (150 in meters) is the number for 1/2 wavelengths. Therefore, 234 (75 in meters) is 1/4 wavelength.
With those numbers in mind, we see that at 23' (7.2m) the frequency at 1/4 wave is 10.17 MHz. That is a usable length because it will also work at 1/8 wave, or 5 MHz. So the tuner will tune the 40m band well.
So whatever frequency you want to use, it should be the lowest. If 7MHz is what you want, then 33' will tune nicely. However, you may have issues if you try 20m because 33' is very close to 1/2 wavelength on 20m.
The solution is to pick a frequency outside the band you want to operate on. So pick 6MHz or 8MHz or 9MHz and so on. This will allow your tuner to tune outside the ham bands. If you are dealing with Maritime frequencies you will want to think in the same plane. Some antenna lengths will work almost all bands but there will be some that the tuner will not like.
All this is based solely on my opinion. There may be others that will disagree with me. But it is all good.
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You've given me the mathematics that I really SHOULD have remembered from doing my HAM license about four years ago. Thank you.
And it is interesting to see how very well those numbers you have suggested tie in with the AT-130 manual that E.P. referenced.
My current thinking is to do a permanently mounted aluminium tube antenna based on your numbers, plus a squid pole, pre-prepared with wire, down below in a waterproof bag. I checked the layout at the stern today and I am reasonably confident my Aerogen 6 will not eat the aluminium pole for breakfast so all I need to be concerned about is a mast failure taking out the aft tower. If that happens, I'll have my E.P. squid fishing kit ready to go. All made easier because the AT-130 is mounted in the aft cabin, right where all these antennas terminate. And the AT-130 even has a wing nut on the output,so changing wires would be a breeze.
Thanks again Brian, for your work and clear explanation.
__________________
Refitting… again.
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11-08-2019, 14:10
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#34
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Moderator
Join Date: Jan 2010
Location: Minnesota
Boat: Tartan 3800
Posts: 4,759
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Re: DIY HF whip
Quote:
Originally Posted by GILow
Fair enough, but really, it seems something like the squid pole suggested by E.P. is going to be a better option, because it is not "electrically too short". But I do now understand what you were suggesting, and I can see the logic in it.
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Well, your boat, your choices. There are a few things you might want to consider. The first is that a 6 meter pole (even if 7 meters electrically because the tuner is a full meter lower) is still electrically too short for reliable operation on the best bands (~40 meters), because....
Quote:
Originally Posted by El Pinguino
Have you read the manual by any chance? 6 metre squid pole with one metre tail to tuner = 7 metres....
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... the fact that the tuner can match the impedance doesn't mean that the antenna will radiate efficiently or that it will radiate in a useful pattern. So, your squid pole will work, but it still isn't long enough. Now, longer is better, so sure, a 6m squid pole will work better than a 2.5 meter stainless steel whip.
The catch is that any of the telescoping antennas have size/weight/cost/strength tradeoffs and they either have to be guyed or have an extremely secure socket base. For emergency use on land there are some good designs out there that fit in a large car and are designed so that you park one wheel of the car over the mount for ballast. You can get a full 43 feet that way. That works.
El Pinguino's experience -- that his fiberglass squid pole worked for a while then cracked -- is typical.
So the tradeoff you have make is whether you'll accept an electrically inferior antenna that has good physical integrity, or instead accept a physically inferior antenna that has somewhat better electrical performance. Now, if I were going to add a second HF antenna to a boat that could withstand a dismasting, on a budget, I'd use a whip, and install the mount and perhaps leave the whip below somewhere (or use it for the AIS antenna for a M-802). Because it can be properly, securely installed and will always work, even if you give up a few dB. And besides...
Quote:
Originally Posted by Salty Possum
Jim’s experience shows that an emergency backup antenna doesn’t require storing anything extra on the boat that you wouldn’t have on board anyway.
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... people in a dismasted boats build jury rigs. Well, whatever you use to hold up sails can also hold up a wire antenna. Or, again, you can use the lifelines and they'll sort of work, which may be all you need.
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11-08-2019, 14:25
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#35
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,178
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Re: DIY HF whip
Two points...
Its for an emergency
Both my squid pole and my moonraker suffered from fatigue at the taffrail at about the same time..... when the boat was overwintering in Stanley, F.I. where they were exposed to more wind in a few months than most boats will see in a lifetime.
The two squidpoles I have at the home QTH have been up for over ten years and both are doing just fine....
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11-08-2019, 14:57
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#36
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Jammer
...
So the tradeoff you have make is whether you'll accept an electrically inferior antenna that has good physical integrity, or instead accept a physically inferior antenna that has somewhat better electrical performance. Now, if I were going to add a second HF antenna to a boat that could withstand a dismasting, on a budget, I'd use a whip, and install the mount and perhaps leave the whip below somewhere ...
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I think your logic goes a bit wonky here. For a start, fatigue is not really an issue for the squid pole because it will be stored below. And once you have something stored below, it might as well be as good as it can be for the job. The telescoping property of the squid pole makes it as simple, or simpler, to store than the stainless steel whip.
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11-08-2019, 18:08
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#37
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,242
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Re: DIY HF whip
Thought bubble - Are you fitting a receive antenna to the 802 to enable it's full DSC functions?
If so, can this be pressed into service as an emergency Tx antenna should the need arise?
Note, I haven't thought this through - you can do that
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All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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11-08-2019, 18:29
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#38
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,135
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Re: DIY HF whip
Quote:
... people in a dismasted boats build jury rigs. Well, whatever you use to hold up sails can also hold up a wire antenna.
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Jammer, while this is sometimes true, in our case we lost mast, boom and spinnaker pole over the side. The bow pulpit was the highest point on the boat, so that's what we used.
If we had been further out (~75 miles SE of Cape Moreton) we might have needed to construct some sort of "mast" out of stuff from below decks and then try 20 meters rather than 40, but that wasn't required.
Matt, unless you go to Dyneema lifelines, they will be an adequate radiator for many instances, and the squid pole will be really pretty good... don't overspecify the situation!
Jim
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Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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11-08-2019, 19:38
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#39
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Jim Cate
Matt, unless you go to Dyneema lifelines, they will be an adequate radiator for many instances, and the squid pole will be really pretty good... don't overspecify the situation!
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You know me Jim, always over-thinking things.
But yeah, the squid pole really looks the goods for this one. And given the kind of reception I get from the EP Home QTH I really would be silly to ignore his advice.
I will probably add the aluminium pole option, just because:
a) I like options.
b) It will look kinda salty.
c) I am planning to get into the HAM stuff in a big way when I get aboard, and playing around with antennas seems as good a way as any to pass the time in HAM land.
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11-08-2019, 19:42
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#40
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Wotname
Thought bubble - Are you fitting a receive antenna to the 802 to enable it's full DSC functions?
I probably should I guess...
I still haven't got around to feeding it some GPS data, so there's a bit to do to finish the installation.
If so, can this be pressed into service as an emergency Tx antenna should the need arise?
Note, I haven't thought this through - you can do that
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Jammer suggested the DSC receive antenna as well, but given I would be looking to add something VERY small, I think it would be best left alone. Also, the ATU and the radio CPU are a long way apart on the boat, so I'd be adding some horrible coax duplication.
I think the squid pole is going to be the best option, it will work really well with the boat layout, and the layout of the radio components in the boat itself. (Radio head unit in the saloon, CPU in the midships cabin and the ATU in the aft cabin.)
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11-08-2019, 20:23
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#41
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Registered User
Join Date: Jan 2019
Location: Oceanside Ca
Boat: Lancer 27PS
Posts: 617
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Re: DIY HF whip
I know you know this but... remember that the length of the feed from the antenna tuner is part of the total length of the antenna. This was mention before about the 6 meter squid pole. Just want to make sure you are overthinking this. LOL
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12-08-2019, 00:47
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#42
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Quote:
Originally Posted by Brian.D
I know you know this but... remember that the length of the feed from the antenna tuner is part of the total length of the antenna. This was mention before about the 6 meter squid pole. Just want to make sure you are overthinking this. LOL
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I do know, but no harm in checking and good for anyone else that reads this thread looking for the same answers.
I’ve managed to get the ATU very close to the antenna base, at the cost of making it a bit of a feature of the aft cabin. But I don’t use the aft cabin anyway, so it kinda doesn’t matter.
At one point I got worried about giving myself an electric shock because of the exposed wing nut on the ATU output. Then it slowly dawned on me that I would need arms that were 26 feet long to reach the microphone from the aft cabin.
I will have to consider any guests though. Probably not all that likely to be stuffing around with the radio if guests are sleeping anyway, the ATU makes a lot of noise when it is tuning.
On a side note, my son is currently studying antenna theory for his year 12 physics. I am no help to him at all.
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12-08-2019, 20:32
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#43
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Registered User
Join Date: Jan 2019
Location: Oceanside Ca
Boat: Lancer 27PS
Posts: 617
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Re: DIY HF whip
Dang nabit, @GILow, now you got me thinking of adding a vertical at home. Right now I am using 106.5' (32.5 meter) wire antenna. Now I want to try a 23' (7.2 meter) vertical. Can't get a squid pole but we can get carbon fiber fishing poles up to 7.2 meters. I just attach some 22awg wire, run it down to a tuner, and use a DIY KISS counterpoise. It should work. My wire antenna uses a 4:1 UNUN and my DIY KISS counterpoise.
Well, off to the drawing board. LOL
Goodonya Mate.
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13-08-2019, 01:06
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#44
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Registered User
Join Date: Sep 2008
Location: On the boat, somewhere in Australia.
Boat: Swanson 42 & Kelly Peterson 44
Posts: 9,112
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Re: DIY HF whip
Brian, I get it. I love to tinker too. I really am looking forward to moving aboard and playing with radio some more.
Good luck with the antenna. I feel I should know what to expect from the change of setup, but, alas, all that theory has escaped from my brain. I will revisit it when I am on the boat because I will finally have time.
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13-08-2019, 01:34
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#45
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,178
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Re: DIY HF whip
So... where to you plan to get in trouble? Long way off shore use the squidpole as a vertical.
Closer to home then angle the base and strap the tip down and get a bit of NVIS https://en.wikipedia.org/wiki/Near_v...idence_skywave
Scroll down to pic M-9
NVIS Army FM 24-18 | KV5R.COM
I can't find a pic just now but that is why army APCs etc would have their whips 'strapped down'....
Or you could just get seriously serious.... https://www.spiderbeam.com/product_i...5488a8cad2f22b
Not only a means of communication but also a place to rig an emergency rig....
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