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Author Topic: Antenna for 10m  (Read 4064 times)
KE2KB
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Posts: 651




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« on: May 31, 2011, 07:46:58 AM »

Hi;
Way back, maybe ten years ago I bought a Radio Shack HTX-100 10m radio. I hooked it up to a modified 102" CB antenna mounted to my car's bumper. I was never able to make many contacts with the rig, and wasn't receiving many signals either. I assumed that the radio was at fault, but today, ten years after the fact I had an epiphany... What is the normal polarization for 10m? Is it horizontal or vertical?

I had a 10m vertical antenna on my house more than 20 years ago, so I just assumed that was correct. But what are most 10m stations using?

That said, anyone operating the low bands from his/her car will use a vertical antenna. So that would tend to reduce the amount of signal received by the antenna, right? Then, on long distance propagation, the signals twist as they travel through the air, and bounce off the ionosphere, so maybe it doesn't make so much of a difference.

Before I order a book (an e-book preferably) on antenna and wave propagation, can someone fill me in on this? I know that I should already know it, but I haven't operated the low bands in over 20 years, and unfortunately, a lot of my knowledge has propagated out of my brain into the ether!

FW
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WB6BYU
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Posts: 17190




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« Reply #1 on: May 31, 2011, 08:57:24 AM »

Polarization is important (and cross-polarization a problem) when signals travel directly from one
antenna to the other.  This is typically the case for relatively local VHF work, and also applies
to ground wave propagation (which only works for vertical polarized waves.)

Once signals travel via the ionosphere the polarization gets skewed in transit, so you have no idea
what it will be at the far end of the path.  In fact this is one cause of fading:  slow polarization
rotation at the receiver even though the transmitting antenna stays the same.

So if you are talking to other stations out to perhaps 10 miles on 10m, polarization is important,
and you may have problems talking to stations with horizontal antennas.  But beyond that, it
doesn't make much difference.
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K2OWK
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Posts: 1273




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« Reply #2 on: May 31, 2011, 04:22:08 PM »

Hello, I use an inverted "V" on 10 meters. This takes care of both polarizations. It works for either. In the 1960s when the 10 meter band was open I to used a modified 102" SS whip on my car. I had a Heathkit tenner (Beton Harbor Lunch Box) with a 5 watt input. I worked all sorts of local and DX with this set up. The band in the 1960s was wide open so just about any antenna worked. The 10 meter band is starting to open  up again, and with the 10 meter inverted "V" I can talk to just about anyone I can hear. I have a Yaesu FT-450AT transceiver that puts out about 100 watts.

73s

K2OWK
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KE2KB
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Posts: 651




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« Reply #3 on: May 31, 2011, 05:16:43 PM »

Thanks for your help guys;
Maybe I can get an inverted V up between a couple of trees and my garage roof. Only problem would be the feed line. It would have to "hang" in mid-air between the feed point and the house. If I can get it up, I can "wake up" my HW-101, or maybe just use the HTX-100. With Field Day fast approaching, I've got the incentive to get something up...

FW
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WB6BYU
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Posts: 17190




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« Reply #4 on: May 31, 2011, 05:30:40 PM »

There really isn't that much vertically polarized radiation from an inverted vee, in spite of the
common mythology.  Unless you have significant common mode current on the feedline,
of course.

But once the signal reaches the ionosphere it is anyone's guess what the polarization will be
when it comes back to Earth.

Where polarization actually makes more of a difference is in the takeoff angle from your
antenna.  Horizontal polarization reflects off the ground out-of-phase, and the higher
the antenna the lower the angle of radiation.  Vertical polarized waves reflect in phase
(except at or below the pseudo-Brewster angle) and so for a low antenna vertical may
be a better choice than horizontal for DX.  But ground losses are often higher for verticals
near the ground, and the trade-offs depend on your soil characteristics.

If you can get a wire antenna up, great!  Things are still pretty quiet:  we're just coming
out of one of the lowest dips in the sunspot cycle, and even at the peak in a few years
we'll probably still be well below the historic levels of the 1959 - 1963 era, but there are
still occasional openings and they will tend to get better over the next several years.
Just string up a dipole wherever you can, and don't worry if it sags a bit one way or
the other.
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KI4AX
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Posts: 113




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« Reply #5 on: May 31, 2011, 07:38:28 PM »

In respect to 10m signals received through ionospheric propagation the polarization is not going to make much difference. The signal, by the time you receive it, will have gone through many changes in polarization. And on 10m noise is also not an issue like it is on the lower bands such as 40m and 80m. On those bands a horizontal receiving polarization helps to attenuate some of the noise that is present. In fact there are some "CB" antennas (verticals) out there that operate quite well on the 10m ham bands. I think a lot of the problems that you had with your mobile set up was a height problem. I have found that you have to get your antennas off the ground at least 15 or 20 feet for them to work with any satisfaction. There are always exceptions... mobiles that "talk skip" and those multi-band trapped verticals like the old 18ATV that are mounted right down on the ground. They work... but not very satisfactory. Also, an awful lot depends on the condition of the ionosphere. If there is no propagation you ain't going no where. At least in my opinion
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W7ETA
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Posts: 2527




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« Reply #6 on: June 01, 2011, 09:01:19 PM »

For many years, I used my CB gp type of antenna.

I couldn't afford a tower and tribander, so I had a CB antenna that I modified a little for use on 10 meters.  But, that was all towards the zenith of a sun spot cycle.  ten was hopping with USA and DX ops.

Best from Tucson
Bob
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VE3FMC
Member

Posts: 36




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« Reply #7 on: June 02, 2011, 06:28:24 PM »

For many years, I used my CB gp type of antenna.

I couldn't afford a tower and tribander, so I had a CB antenna that I modified a little for use on 10 meters.  But, that was all towards the zenith of a sun spot cycle.  ten was hopping with USA and DX ops.

Best from Tucson
Bob

My late Father was a ham and for years he had an old RS ground plane modified for 10 meters mounted on the roof of the old two story farm house.

That antenna worked great on 10 meters. I know have it stored away in my utility shed.

When 10 is open you can work a lot of stations with a simple vertical antenna. The A-99 comes to mind.
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