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Author Topic: Vertical antennas without radials  (Read 6557 times)
K2OWK
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Posts: 1048




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« on: January 31, 2011, 03:31:09 PM »

I have a technical question about a vertical antenna I used to use in the 1980s for ship to shore, ship to ship and shore to shore operation. The frequency of the commercial transmitter was 4460 MHZ, mode was LSB, power output was 75 watts PEP. The band was about 75 meters. The vertical antenna was about 6 feet in length and about 1/2" in diameter. It had a wound coil that went from about 1/4 the way up to the top (about 4 feet), because this was a custom antenna there was no provision for tuning. We could mount the antennas on base towers about 30 to 50 feet in height, on ships masts or on vehicles for land use. We never had to use radials and these antennas outperformed dipoles just about all the time. I am assuming that this was a top loaded 75 meter antenna. The reason I am asking this question is that I am looking to buy a vertical multiband antenna. I have do not have provision for installing radials. I find it hard to believe that there are no verticals that work well without radials. They sell a few that can work without radials, but all the instruction sheets for these antennas say they will work better with a ground radial system. The antenna we used in he 1980s performed no better with radials then without. As far as performance we were able to talk from base to base in excess of 100 miles, and of coarse much farther when communication with the ship. My question is why does no one seem to make a vertical antenna like the one we used in the 1980s that had such great performance? I am about to give up my antenna search and stick with my inverted "Vs" unless someone can come up with a modern antenna of the type I used in the 1980s. These vertical antennas they sell today seem to be a crap-shoot. They are expensive and I hate to spend money that I don't have on something that may or may not work.

Thanks for your time in looking at this post. I hope someone has some answers.

Regards,
73s
K2OWK (again)   

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N2EY
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Posts: 3877




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« Reply #1 on: January 31, 2011, 04:03:54 PM »

I have a technical question about a vertical antenna I used to use in the 1980s for ship to shore, ship to ship and shore to shore operation. The frequency of the commercial transmitter was 4460 MHZ, mode was LSB, power output was 75 watts PEP. The band was about 75 meters.

I think you mean 4.460 MHz.

The vertical antenna was about 6 feet in length and about 1/2" in diameter. It had a wound coil that went from about 1/4 the way up to the top (about 4 feet), because this was a custom antenna there was no provision for tuning. We could mount the antennas on base towers about 30 to 50 feet in height, on ships masts or on vehicles for land use. We never had to use radials and these antennas outperformed dipoles just about all the time. I am assuming that this was a top loaded 75 meter antenna. The reason I am asking this question is that I am looking to buy a vertical multiband antenna. I have do not have provision for installing radials. I find it hard to believe that there are no verticals that work well without radials. They sell a few that can work without radials, but all the instruction sheets for these antennas say they will work better with a ground radial system. The antenna we used in he 1980s performed no better with radials then without. As far as performance we were able to talk from base to base in excess of 100 miles, and of coarse much farther when communication with the ship. My question is why does no one seem to make a vertical antenna like the one we used in the 1980s that had such great performance? I am about to give up my antenna search and stick with my inverted "Vs" unless someone can come up with a modern antenna of the type I used in the 1980s. These vertical antennas they sell today seem to be a crap-shoot.

There are a couple of big differences between the antenna you describe and typical ham antennas.

When that antenna is on a tower, the tower acts as a counterpoise. Also, being on a tower raises it above nearby obstacles so it has a clear shot at the horizon.

When that antenna is on a vehicle, the metal of the vehicle acts as a counterpoise.

When that antenna is on a ship, the ship and the water act as a counterpoise.

In all cases you didn't need radials because there was an adequate counterpoise/ground system.

On top of that, the antenna is optimized for a single frequency, not a band nor multiple bands.

The 100 mile range you describe is typical ground-wave or line-of-sight. And since it was for maritime operation, it was on or near the seacoast, where things are usually quite flat, and the ground conductivity is very good.

Now, if you'd installed that antenna at ground level with no radials, in hill country away from the coastline, I suspect the performance wouldn't be so spectacular.

----

What you're encountering is the classic challenge of HF/MF amateur radio:

1) There are lots of bands, and some of them are quite wide.
2) The waves are big and so are the antennas
3) Typical homes aren't all that ham-radio-friendly.

73 de Jim, N2EY
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WX7G
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« Reply #2 on: January 31, 2011, 04:28:15 PM »

Are you looking for a vertical that does not require ground radials? Here are a few that cover down to 40 or 80 meters:

Hy-gain AV-640, 40-6 meters
Hy-gain DX-77A, 40-10 meters
Cushcraft R8, 40-6 meters
MFJ-1796, 40-2 meters
MFJ-1798, 80-2 meters
GAP Eagle DX, 40-10 meters
GAP Titan DX, 80-20 meters

A ground mounted vertical does not require a large counterpoise area. For example, a Hustler 6BTV vertical will work quite well with 20' ground mounted radials.


« Last Edit: January 31, 2011, 04:29:50 PM by WX7G » Logged
W0BTU
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« Reply #3 on: January 31, 2011, 06:03:21 PM »

Of all the physical laws that there are, none are more well-established than the fact that a bottom-fed vertical needs something to "push against" to be effective. Call that 'something' a counterpoise, radials, or whatever you want to; but to be effective, it's got to be there. Period.


Case in point: on another forum, someone just shared his experience after he added a bunch of ground radials to his inverted-L. It was a WOW! experience for him. Sure, he made some contacts without the radials. But what a difference it made in the amount of RF that radiated into space and the amount of DX he worked afterward.


If we make the statement that adding a counterpoise to a λ/4 vertical (for example) is not really necessary, then we might as well say that opening the blinds won't make the room any brighter. Sure, maybe we can see our way around, but when we let the sun in, life is so much better.

Or someone could say that we don't really need tires on a car. Sure, with enough ground clearance we can drive around on the rims, but isn't the car much more fun to drive with the rubber attached?

Take the radials off your 1/4λ ground plane and let us know what happens. :-)
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K2OWK
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« Reply #4 on: January 31, 2011, 06:57:07 PM »

Good information, Thank you, The frequency is 4.460 MHZ, thanks for catching that. I Guess as far as antennas are concerned you pay your money and take your chances.

73s
K2OWK
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AD6KA
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Posts: 2236




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« Reply #5 on: January 31, 2011, 07:36:05 PM »

Quote
I Guess as far as antennas are concerned you pay your money and take your chances.

Um, not really. Study antenna theory and talk to experienced hams
so that you can see through certain advertising hype...for starters.

Regarding "No Radial Verticals", Butternut has a couple decent treatments.
Of course, as a manufacturer of verticals, they have an agenda, but
the math they use looks right to me. (Re efficiency vs # & length of radials)

Beginners Primer:
http://www.bencher.com/pdfs/00815ZZV.pdf

Dirty Little Secrets I:
http://www.bencher.com/pdfs/00363ZZV.pdf

More Tech Notes here:
http://www.bencher.com/pdf_download.html#tech_notes
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WB6BYU
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Posts: 13126




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« Reply #6 on: January 31, 2011, 08:49:41 PM »

Is it possible that your memory of the antenna is a bit hazy?  The typical marine antennas were
lloaded whips as you suggest, but designed to be resonant somewhat above the band of operation
and tuned with a manually-adjusted matching network in the transmitter (typically with different
settings for each frequency, allowing an antenna to be used from 2.0 to 4.5 MHz or so even
though the SWR bandwidth on any one setting was pretty narrow.)  When installed on a tower
or mast these were typically connected to the transmitter with a SINGLE WIRE lead, often using
the tower as the bottom section of the antenna.  At least this was the standard mobile antenna
configuration of the era. 

They still were heavily dependent on a ground connection (which was attached to the RIG,
not at the antenna).  This would be superstructure of the boat (and the ocean, which makes
an excellent ground system.)  Same with a car. For use in a fixed station you'd still want some
sort of ground radials for good efficiency, though many of them were operated without it. 
Ground wave coverage on 80m is strongly dependent on transmitter power and ground conditions
due to the propagation mode:  with regular dirt 50 miles is about the limit, even running a kW. 
But the attenuation over salt water is much less, and much longer distances are possible, even
with an inefficient antenna if the station is near the water.


You CAN build a vertical antenna that doesn't require ground radials, but it must be configured
as a dipole (or half wave vertical) rather than a monopole.  That means that, for the same
physical height, the shortening effect is twice as great.  For example, an 80m vertical antenna
that is 25' tall is somewhat under half size when fed against ground, but closer to 20% of full size
if it is made ground-independent (where full size is around 125').  That makes a big difference,
as the losses go up quickly and SWR bandwidth shrinks with shortening much beyond 60%.
The commercial antennas that work in this mode (like the R8) are basically an off-center fed
dipole with traps and loading coils.  In fact, you do NOT want to connect additional ground
radial wires to such antennas as it will mess up the tuning.
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VA7CPC
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« Reply #7 on: January 31, 2011, 11:42:19 PM »

For an example of a small-footprint vertical antenna that needs no ground system (because it's a vertical _dipole_), look at the Force 12 "Sigma" series:

http://www.texasantennas.com/index.php?option=com_content&view=article&id=93&Itemid=55

I

                    Charles
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K3GM
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Posts: 1776




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« Reply #8 on: February 01, 2011, 05:13:00 AM »

.........They still were heavily dependent on a ground connection (which was attached to the RIG,
not at the antenna).  This would be superstructure of the boat (and the ocean, which makes
an excellent ground system.)..............

As a teenager, I often tinkered and tweaked the HF radio gear aka. ship to shore of my grandfather's large wooden fishing boat.  As 'BYU described, there was only one wire leading to the base of the fiberglass antenna. The gound system consisted of a wide, flat, copper foil strip leading from the back of the transmitter, down to the bilge and connecting to 2 large copper plates (approx. 3'x3') on either side of the keel.  I remember receiving a healthy jolt from one of those plates after I accidentally touched it while working on the bottom when it was in drydock for bottom paint.
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W0BTU
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« Reply #9 on: February 01, 2011, 10:38:23 AM »

...often using
the tower as the bottom section of the antenna.
You CAN build a vertical antenna that doesn't require ground radials, but it must be configured
as a dipole (or half wave vertical) rather than a monopole.

Absolutely! To do otherwise lowers efficiency.
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WA3SKN
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Posts: 5457




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« Reply #10 on: February 01, 2011, 01:50:19 PM »

I think the reason you fondly remember the antenna so much is that is was the 1980's, and you had much different propagation back then!
Things should be getting better soon.

-Mike.
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