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Author Topic: Capacity hats on whip antennas  (Read 8602 times)
W8JX
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« Reply #15 on: August 17, 2011, 05:53:04 PM »

John, I've been operating mobile longer than you've been licensed! If I thought it wasn't worth the effort, I wouldn't have dumped all that money in every mobile I ever had.

What ever makes you happy


I can assure you, that even .5 dB can make a tremendous difference. What you have to start looking at is signal to noise ratio, and not the absolute signal strength. If you understood receiver dynamics, you'd already know that.

I know more about dynamic that you likely but what is the point. Now we are down to .5db being a huge difference. Signal to noise ratio and chasing signal into mud pay off in some VHF and all of UHF where back ground noise is much less of a factor and noise figure of radio itself is a bigger issue.

If it makes you feel good to think that .5 db is a big difference have at it. (just like those that think LMR 400 on HF is a must have) I just chimed in because I did not want those newly considering doing HF mobile being led to believe than .5 or 1 db is a deal maker or breaker when it indeed is not.
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K0BG
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« Reply #16 on: August 18, 2011, 05:51:10 AM »

Tell me John, what do you use mobile?
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W8JX
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« Reply #17 on: August 18, 2011, 01:02:03 PM »

Tell me John, what do you use mobile?

I use a old TS-140 for local stuff and a 570 when traveling far. (I plan to setup another vehicle to support 480) I have very little money in current 140 that i got very cheap used ( I have owned 3 so far) so I have no reservations about leaving it in car/suv 24/7. I never use a tuner but rather match antenna well. As far as antennas, back in 80's when I started HF mobile I tried hustler resonators and related hardware but never really liked them. Around 90 I switched to HamStick type clones and they worked well for me. (actually wore a few out from fiber glass breaking down from flexing) Mostly do 20 and some 40, 17 and 15. Antenna is on a chain type bumper mount and they have quick disconnects so I can swap them. I have worked VK's on 40 from mobile in years past going to work in morning. If the antennas did not work well for me I would dump them but they work fine and also seem to get good signal reports from it. I also usually use a Heil BM-10 mic/headset because it lets me hear radio better but still hear background noise. Old 140 is not a bad kick around rig except for gas tube display is hard to read in bright light. My first one saw it get to 35 below over-nite in car in SD one time. Next morning when I powered up radio is took a few minutes to warmup before VFO would lock up and display work but then it worked fine. Tuff radio.
« Last Edit: August 18, 2011, 05:32:34 PM by W8JX » Logged

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G7DIE
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« Reply #18 on: August 21, 2011, 06:31:10 PM »

I use a rather large copper wire formed capacity hat on my High Sierra Sidekick screwdriver antenna, I use it with a stainless steel 5' rod and my none scientific tests on 40m consistently prove it's good for another S point, or 6dB.
It's not the most robust thing, good only for local driving up to around 40Mph, beyond that it just begins to distort, however close by the sea I've worked a healthy amount of DX with it, in fact using it on 80m allowed me to work the 4A4A DXpedition off the coast of Mexico with surprising ease, timing and technique having a lot to do with that too Wink
There's a picture of it's earlier iteration on the top right hand side of my QRZ page if you're interested.
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AC4RD
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« Reply #19 on: August 22, 2011, 04:22:13 AM »

There's a picture of it's earlier iteration on the top right hand side of my QRZ page if you're interested.

Great photos!  It looks like you really enjoy mobiling!   Do you run into problems with the roof mount for the HF antenna?
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W8JX
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« Reply #20 on: August 22, 2011, 07:05:04 AM »

 Do you run into problems with the roof mount for the HF antenna?

When I used to travel cross country a lot when I got in great plains area and rockies I used to use a custom made mag mount with several magnets (this was before you could buy them) and mount a hamstick on roof of my suburban. It worked really well up there and in area mentioned above there was very few overhead obstructions. Overall height was about 14 feet. I once took out a overhead florescent bulb in a motel check in area because I misjudged clearance.   
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G7DIE
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« Reply #21 on: August 23, 2011, 04:14:55 AM »

Great photos!  It looks like you really enjoy mobiling!   Do you run into problems with the roof mount for the HF antenna?

I don't get the same thrill operating from home that I do from the car, don't get me wrong I get a thrill every time my call is answered no matter where I am, but busting a pile up with 100W and a short vertical brings a BIG smile. When operating with large antennas I have a number of considerations, gas stations being one of them, the High Sierra with 6' whip will go under most gas station roofs when retracted, the home brew antennas would probably get damaged, it takes on the appearance of a dogem car Grin
The home brews bend quite a lot at 60Mph and over time it leads to electrical failure of the mount, but then I'd rather the mount fail than the antenna, I can replace the mount for a couple of bucks.
I drive 60 miles to work so I get plenty of time to operate mobile, when travelling the same road for any period of time one becomes acutely aware of the different terrain and the effect it has on performance, if I'm looking to work a station and conditions are marginal I'll quite often wait until I'm in a better location before I put out a call, this has paid off a number of times Wink
A big issue is maintenance, one has to stay on top of the condition of ones antenna, mount, coax and other connections, I regularly check and service the screwdriver, being exposed to motorway speeds on a daily basis take their toll.
The big benefit of going mobile, be that in the car or on foot, I can take the radio to where the best locations are, and fortunately for me those locations are either within walking distance or a 5 mile drive, very low noise and an exceptional take off over the sea, it doesn't get much better than that Smiley

HTH
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W8JI
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« Reply #22 on: September 01, 2011, 11:20:47 AM »

I don't believe anyone can justify the change in efficiency between brass, copper, or stainless in a capacitance hat. I think there is some misplaced or convoluted math involved.

There isn't any possible way loss would even approach a measurable fraction of a dB, let alone a few dB, unless the hat was very large with long thin radial spokes. The problem is I^2 R. The problem is not the resistance change of materials alone.

73 Tom
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KC2KCF
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« Reply #23 on: September 02, 2011, 05:50:21 AM »

Aluminum is about as good a compromise as you're going to get. The permeability hovers around 2,

I assume you are referring to the relative magnetic permeability? Do you have a reference for this? I am very surprised by this value (typical values for aluminium alloys are more like 1.00002), but it's never too late too learn something new. At mu_r=2, it might be worth exploring aluminium powder cores for building RF inductors/transformers.
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K0BG
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« Reply #24 on: September 02, 2011, 07:18:30 AM »

Here is a bit of information on antenna conductors: http://vk1od.net/antenna/conductors/loss.htm

When I first corresponded with Owen about this subject, I too was skeptical. As a result, I purchased the necessary hardware so I could measure the field strength differences between one set up, and another. I cannot measure absolutes, obviously.

I measure field strength basically the same way Rudy Severns, N6LF, did for his series on radials. I use a Mini-VNA, made by Mini Radio Solutions. The receiving antenna is nothing more than a 8 foot piece of aluminum rod. The mobile antenna is a Scorpion 680. The interconnecting cables are RG6, and each one is 200 feet long.

The cap hat I use, is mounted atop a 4 foot long, 1/2 inch OD, 6160T6 aluminum rod. The hub is also 6160T6. There are three loops, made from 304 stainless steel, .125 x 72 inches. The effective diameter is about 5 feet. If I replace the 304 stainless rods, with 6160 aluminum rods, the measured difference is 1.2 dB on 80 meters. The difference .5 dB on 20 meters.

The biggest problem using aluminum rod for cap hat loops, is flex stress. Rods made with 6160T6 will last no more than 50 miles, as they sing like a banshee! They always break right at the hub. One made from 7075 aluminum will last about 500 miles. They too sing, but not nearly as loud. When they break, it is always about 6 inches from the hub. However, at $58 per piece (.125 x 72 inches), they're darn expensive! So, I use 304 stainless rod material which at this juncture, have lasted well over 5,000 miles. They cost just $2 each.
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W8JI
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« Reply #25 on: September 03, 2011, 12:52:10 PM »

I don't believe it for a single second in a good hat design,  even though things would be worse with some of the poorly designed hats I have seen.

1.) in a lossless ground 8 foot vertical of #16 with copper, changing the element from copper to stainless steel reduces FS from 4.34 dBi to 2.26 dB. This is with ALL current in one wire, not like a hat at all.
 
2.) In a hat, current at the tips is virtually zero and increases in a straight line to the hub. Each rib or radial in the hat would have a proportional fraction of the current, so losses go down dramatically as more ribs are added.

3.) The hat is at a lower current point, so has lower loss for the same applied power and conductor resistance as a single 8 foot long wire which would have triangular distribution.

4.) External losses would swamp out the overall loss from  the hat or any other additional loss. For example if I take the same 8 foot tall #16 copper wire and change it to a stainless wire, and add ground losses and loading coil losses, field strength becomes -6.11 dBi with copper and -6.34 dBi with stainless. (This is a far worse case than a real antenna hat, because ALL of the current and the current maximum is in a single longer conductor that is being changed).

It makes absolutely no sense at all to think changing a hat from stainless to copper would change field strength even 1 dB. The numbers just are not there to support that.

First, because a normal hat has multiple conductors in parallel. This divides the current and reduces losses.

Second, because the conductors carry less and less current towards the antenna's open end.

Third, because the hat conductors are very short ( a 160 meter dipole has much more conductor loss than a 10 meter dipole, and shows a change in materials much more because the 160 dipole is longer).

Fourth, ground losses and coil losses would "swamp out" or dilute any changes. The change cannot possibly be more than a single wire as a monopole!

VK1OD's data for dipoles would be far more exaggerated than would appear in a hat, or even a 1/4 wave Marconi, let alone a mobile system with all the ground losses.

73 Tom
« Last Edit: September 04, 2011, 06:09:01 AM by W8JI » Logged
HS0ZIB
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« Reply #26 on: September 10, 2011, 06:19:33 AM »

As an update, I've just received a 12 mb Hustler resonator, 22 inch mast and Hot-Rodz top hat from DX Engineering, so I'll experiment over the next few weeks with configurations.  Somewhere in the post is a Breedlove base mount and a 100 watt amp, so I've got lots to play with Smiley

Simon
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AC4RD
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« Reply #27 on: September 10, 2011, 02:58:22 PM »

As an update, I've just received a 12 mb Hustler resonator, 22 inch mast and Hot-Rodz top hat from DX Engineering, so I'll experiment over the next few weeks with configurations.  Somewhere in the post is a Breedlove base mount and a 100 watt amp, so I've got lots to play with Smiley

Simon

Just this morning I set up a new RM-12 for 15m, for my car--been having fun on 15 from the home and I'm hoping it will be fun for my daily commuting.   I certainly hope I hear you on 15 one of these days!   :-)
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HS0ZIB
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« Reply #28 on: September 12, 2011, 03:38:37 AM »

It's been monsoon rain for several days nonstop, so there is no way I am going to install this antenna right now! Hopefully by the weekend the weather will improve a bit - else I'll be growing webbed feet Smiley

Simon
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AD1E
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« Reply #29 on: October 21, 2011, 09:39:28 AM »

New guy in town and i am reading before setting up my Avalahce with my 857D and a HF antenna. 

I see several posts where you talk about wind resonance and the wire singing.  Has anyon tried to wrap/bond nylon fishing line around wire and hats to disrupt the air flow and eliminate the singing?

My 2003 Avalanche has a wrapped AM/FM antenna and there is no singing wih the OEM antenna at any speed. 
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