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Author Topic: Portable vs. Mobile  (Read 4713 times)
W7HDW
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« on: November 21, 2010, 05:09:16 PM »

I am getting back into Ham radio after a 20 year hiatus and still have my General license. I want a HF rig that I can use at home 70% of the time and on my boat 30%. I see there are portable and mobile rigs advertised. What would be the best bet for my situation?

When on the boat, the radio would be installed on my fully enclosed flybridge. My marine electrician says I have sufficient DC power for the radio. It would be on the boat from May through August.

I would plan to use the same antenna at home and on the boat, a Diamond BB7V Multiband Vertical Antenna or equivalent. I have antenna restrictions at home and can only use a vertical antenna without radials so this one works and, on the boat, the fact that it telescopes down to 5 feet and needs no added radial system seems like an easy choice. It would mount on my flybridge back railing on the boat and on my deck railing at home.

I would appreciate any feedback and advice.

Thanks.

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K0BG
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« Reply #1 on: November 22, 2010, 05:59:59 AM »

You're almost asking for the impossible.

The Diamond you mentioned is nothing more than a 50 ohm resistor with a radiator attached. Typically, it is from 25 to as much as 50 dB down from a properly installed 1/4 wave antenna. Considering the way it is made, I suspect it wouldn't last a season in a saltwater environment.

I have an Icom IC-706 installed on a 43 foot cat, out of Stuart, FL. It uses the starboard stay as a radiator, which is driven with an AH-4 ATU. The ground side is the outer starboard keel grounding plate. It's about as good as you can get on a composite hulled boat.

As for home, there are much better solutions than the Diamond. HyGain makes a loaded half wave which works fairly well, as long as you mount it just like they tell you to. You can't have any structure near it, or you just won't get it to tune up.
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W7HDW
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« Reply #2 on: November 24, 2010, 03:54:14 PM »

For home, what do you think about the Butternut HF6V with a decent radial system?
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W3LK
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« Reply #3 on: November 24, 2010, 06:59:27 PM »

For home, what do you think about the Butternut HF6V with a decent radial system?

That's what I use the majority of the time and I am very happy with the system. It's a better DX antenna than a local use antenna, though. I also have a multi-band dipole and switch between the two, as necessary.

The key is a GOOD radial field - I have 30, 40' radials.
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W7HDW
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« Reply #4 on: November 24, 2010, 09:15:20 PM »

Are all multiband verticals better DX antennas, or just the Butternut? I am interested in DX but there is also a 75 meter local net that I want to be able to access, too.

Also, what are the characteristics of the Butternut that make it a better DX than local antenna?

Thanks.
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W8JX
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« Reply #5 on: November 25, 2010, 06:59:00 AM »

Are all multiband verticals better DX antennas, or just the Butternut? I am interested in DX but there is also a 75 meter local net that I want to be able to access, too.


I have been using a Hustler 5 BTV  for about 20 years now and it is a bullet proof antenna and painless to setup. It uses traps and a big capacitive top hat on 80 and 40 meter bands. I find it works very well on 40 as I can work VK's with no problem and decent on 80 for a trapped vertical ( I have work europe many times with it in past) though it is narrow and only good for a 100khz or so with less than 2 to 1 swr on 80. It is not a fussy antenna about radial setup and while Butternuts can be good they can be fussy to tune (there is interaction between bands when tuning it) and are also picky about radials too.  Also I would stay away for Hustler 6 BTV because when they add 30 meter coverage to it they remove capacitive hat and performance on 40 and 80 suffers some.
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K5COV
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« Reply #6 on: November 25, 2010, 07:18:43 AM »

I think the key to any decent vertical antenna is a decent radial field in spite of the hype that tries to convince us otherwise. I LOVE my HF6V, but disconnect the radial field and it's still just half an antenna. Physics is physics.

I have a 30' Cape Dory and don't trust the stay antenna idea, though it is more than likely a perfectly safe idea. Just me. I use an inverted V peaked by a spare main halyard fed by balanced line and work all bands with it. I also have an Outbacker Perth Plus on the stern rail that in spite of the limitations it has (SHORT vertical, jumper to change bands, needs a VERY good ground) works amazingly well for something to throw up on the stern rail or the bumper of my Jeep at the marina. I've been very pleased with it especially since you can likely get it up high in the fly bridge. Key is GOOD GROUND plane. I worked Scotland on 20m SSB with my IC-7000 and my Perth Plus temporarily clamped to a friend's 53' Hatteras fly bridge. Same day checked in to the local 160m net 300 miles away net without a problem.  
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K0BG
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« Reply #7 on: November 25, 2010, 08:35:23 AM »

I'm always amused when folks use a DX contact(s) as a ratings score for their antenna. If the band conditions are right, a few microwatts of ERP is about all it takes to talk half way around the world, as any QRP operator can attest to. The Outbacker is a good example. On 40 meters, even over a decent ground plane, it isn't much more than 2% efficient, and we already have a DX reference for it posted below. Part of the issue with any antenna is the fact 95% of the time, folks don't have another antenna to compare it to. When they do, it is quite common to compare a vertical with a dipole or beam. That's comparing apples and oranges.

Another way to look at this is perhaps the lowly HF mobile antenna. We have a height limitation when we use one mobile-in-motion. All considering, on average, an HF mobile antenna will have an 80 meter efficiency of about 2%, albeit 5% can be achieved if you do everything correctly. On 10 meters, 80% is about all you can hope for even with a full 1/4 wave due to ground loss issues. Yet, making DX contacts isn't all that difficult.

So the question is, why is the ability to make a DX contact with some specific antenna so important to average joe ham?
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W3LK
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« Reply #8 on: November 25, 2010, 05:33:17 PM »

Are all multiband verticals better DX antennas, or just the Butternut? I am interested in DX but there is also a 75 meter local net that I want to be able to access, too.

Also, what are the characteristics of the Butternut that make it a better DX than local antenna?

Thanks.


A typical vertical (just about any brand) installed over a proper radial field has a low takeoff angle. Low takeoff angles are better for longer distance (over 1,000 miles). Dipoles can and do work better under 1k than verticals do. It was common for me to not be able to talk across town in Baltimore on 80m on the vertical.

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W8JX
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« Reply #9 on: November 25, 2010, 07:40:39 PM »


A typical vertical (just about any brand) installed over a proper radial field has a low takeoff angle. Low takeoff angles are better for longer distance (over 1,000 miles). Dipoles can and do work better under 1k than verticals do. It was common for me to not be able to talk across town in Baltimore on 80m on the vertical.


While in "theory" this is true what happens in actual application can vary. Optimum distan with a good vertical depends on band, sun spots and time of day. I have used my vertical extensively on 40 and a fair amount on 20 digi. On 40 during day when band is short it works well from about 150 to 800 miles or so and is strongest it seems in 300 to 500 mile range getting me 9+10 to 20 reports many times running about 800 watts. As far as ground wave it works out to about 50 miles or so here (I am on high ground too) and if there is a hole it is in the 50 to 125 mile range as I have had few contacts in that range on 40. At night and early morning west coast give me 59+ to 10 or so and 59+ in VK land. On 20 I see it more as between vertical and band it is usually at least 300 miles or better with it. Also being ground mounted it seems losses are a bit higher on 20 and above than on 40 and below. 
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K0BG
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« Reply #10 on: November 26, 2010, 06:39:35 AM »

One very common mistake about 1/4 wave verticals is the notion that they have a low takeoff angle. They really don't. The point of maximum power is typically about 27°. The energy radiated below this angle is directly dependent on the ground plane losses. As the losses are reduced, the pattern starts to look more like a donut, rather than a pointy lobe, but the point of maximum power doesn't change much. This fact is why proper mounting of an HF mobile antenna is so important.
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W8JX
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« Reply #11 on: November 26, 2010, 07:28:42 AM »

Very true Alan. Compared to a dipole though it does have a much lower "average" radiation angle. As you increase size of it (say 5/8 wave) you lower the angle of lobe peak and also increase its strength as you "squash" the donut. Adding elements (such as in a collinear array) further "squashs" the donut  and lowers lobe peak angle and increases field strength while doing it too. It is not very practical to make a 5/8 wave on 40 and below but it is feasible on 20 and above.
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K0BG
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« Reply #12 on: November 26, 2010, 09:46:30 AM »

Dan, K6MHE, wrote this article: http://k6mhe.com/files/mobile_vhf_ant.pdf

It sort of puts a damper on whether 5/8 wave antennas actually perform better than 1/4 waves. He correctly points out, that the position on the vehicle has more to do with the pattern than the length.
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W8JX
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« Reply #13 on: November 26, 2010, 10:35:30 AM »

Alan, while I have never used a 5/8 on HF, I have extensively used a 5/8 and a 5/8 over a 1/4 wave collinear on 2 meters mobile during many cross country trips in 90's. There is a noticeable improvement of 5/8 vs 1/4 and not only in xmit and recv strength but also in flutter because of increased capture area. Grant there was no sky bounce with it but still it was better. The collinear was a bit better yet on extreme fringe of coverage.
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W3LK
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« Reply #14 on: November 26, 2010, 12:50:30 PM »

Since I am obviously ignorant on the way my antenna works (as pointed out - politely - by my friends Smiley) I won't add anything further and therefore show that I know when to quit. Smiley
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