[50mhz] Antenna Modeling

Mon Jun 27 12:13:27 EDT 2011

Hi Carl,

I agree!  I have had some amazing EME contacts with small stations beaming out over 
arid plains, as well as out over the ocean.  I think the big thing to avoid is 
"ground clutter" (such as boulders, houses, rooftops, etc.) and uneven terrain.  I 
have also seen tri-band HF beams installed underneath the 6m yagi shield it from 
ground gain reflections, so an antenna by itself on the tower or mast is much more 
likely to get good ground gain.

Of course, more people (unless they are overlooking the ocean or some huge plain), 
often have less cluttered and uneven terrain in the immediate proximity of their 
antenna, compared the the more distant view of the antenna.  This seems to result in 
a second ground gain lobe actually being better than the "main" (or first lobe).  I 
have seen this repeatedly in EME skeds that I have run with horizon-only stations. 
As a result, I always make sure to run skeds with such stations so that we include 
the time when the moon is between 10 and 15 degrees elevation.

GL and VY 73, Lance

On 6/27/2011 3:41 PM, Carl wrote:
> I dont believe that the ground conductivity over land has much effect on the ground
> reflection gain. Yes there is some loss but as long as the obstructions are not
> present the gain should be decent.
>
> Im on top of a granite ridge in an area of about the lowest conductivity in the US
> and it doesnt doesnt appear to hurt me at all on any band from 160 to microwave. In
> fact its just the opposite.
>
> On a flat desert with a tall tower you likely have several nulls at elevation angles
> that would be helpful and this is where stacked antennas with selectable phasing can
> find the sweet spot. If OTOH the antenna is too low to start with that is something
> different.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
> To: <w7gj at q.com>; "Dan Schaaf" <dan-schaaf at att.net>
> Cc: <50mhz at mailman.qth.net>
> Sent: Monday, June 27, 2011 6:40 AM
> Subject: Re: [50mhz] Antenna Modeling
>
>
>> Dan, Lance, et al.,
>>
>> The other thing you have to take into consideration regarding ground gain
>> besides Height Above Average Terrain (HAAT) and the contours of that terrain
>> is the COMPOSITION of the terrain. Out here in the desert, the ground is
>> very dry, lossy, clay sand. Most RF energy from a transmitting antenna goes
>> into this sandy ground a few inches, warms it up a little, and is never seen
>> again. :-) But if you have earth with good conductivity, it will act more
>> like a mirror than like a sponge at 50 MHz -- and of course if you're lucky
>> enough to live right on the coast, you'll have terrific "ground" gain in the
>> directions where you're beaming out over salt water (though not necessarily
>> in other directions).
>>
>> Charts mapping ground conductivity across the US can be found in most ham
>> antenna publications and on many websites. You might not like what the
>> charts tell you, but the truth is out there. :-)
>>
>> Bill W5WVO
>> Rio Rancho, NM
>>
>>
>> -----Original Message----- From: Lance Collister, W7GJ
>> Sent: Sunday, June 26, 2011 20:55
>> To: Dan Schaaf
>> Cc: 50mhz at mailman.qth.net >> 50mhz
>> Subject: Re: [50mhz] Antenna Modeling
>>
>> Hi Dan,
>>
>> Yes, I am sorry I can't help you any more that that chart showing free space
>> dBD
>> gains of all the antennas. However, if you look at similar boom length 4
>> element
>> beams, you can certainly get an idea what the MAXIMUM possible gain is that
>> you are
>> could have from that antenna.
>>
>> One thing very few people consider when evaluating antennas is the GROUND
>> GAIN that
>> is afforded at the site where the antenna is installed. In the case of a
>> small
>> antenna like yours, the potential ground gain may be very significant -
>> maybe even
>> just as significant than the free space gain itself! If you stick the
>> antenna on a
>> TV rotor attached to the chimney in an urban development with houses and
>> rooftops all
>> around, there won't be much or any ground gain, and you might be very
>> unhappy with
>> the performance. However, somebody who puts it up on its own mast or tower
>> in a flat
>> field may be thrilled with how well it works. When you consider that the
>> ground gain
>> can be up to 6 dB (equivalent of stacking 4 yagis), you can appreciate how
>> big an
>> effect it can have. Of course, antenna manufacturers cannot control or
>> anticipate
>> the ground gain of every installation, which is why the more reputable ones
>> will only
>> show the dBD FREE SPACE gain. It is a much more conservative number, but one
>> that
>> allows you to make intelligent comparisons between antennas.
>>
>> GL and VY 73, Lance
>>
>> On 6/26/2011 8:16 PM, Dan Schaaf wrote:
>>> Hi Lance
>>>
>>> Thanks. I had seen this chart before. However, my antenna is not listed
>>> and that is
>>> why I was hoping that someone could model it, and maybe even add it to the
>>> list.
>>>
>>> I would just love to know what I am working with in terms of real gain on
>>> this A504HB
>>> antenna so that in my next choice of antenna, I will know how much
>>> improvement I will
>>> get.
>>>
>>> Dan Schaaf
>>>
>>> ==================================
>>> K3ZXL www.k3zxl.com
>>> Cape Cod Instruments www.gnm-inc.com
>>> NOBSKA www.nobska.net
>>> ==================================
>>>
>>> ----- Original Message ----- From: "Lance Collister, W7GJ" <w7gj at q.com>
>>> To: "Dan Schaaf" <dan-schaaf at att.net>
>>> Cc: <50mhz at mailman.qth.net>
>>> Sent: Sunday, June 26, 2011 3:44 PM
>>> Subject: Re: [50mhz] Antenna Modeling
>>>
>>>
>>>> Hi Dan,
>>>>
>>>> Most claimed gain figures for 6m antennas are greatly inflated. You may
>>>> find this
>>>> comparison table of interest:
>>>>
>>>> http://www.bigskyspaces.com/w7gj/6mTable.htm
>>>>
>>>> GL and VY 73, Lance
>>>>
>>>> On 6/26/2011 11:49 AM, Dan Schaaf wrote:
>>>>> Hi All,
>>>>>
>>>>> I have a Diamond A504HB 4 element yagi for 6 meters.
>>>>> The manual says that it is 10.8 dbi gain.
>>>>> I am not sure what to believe because that seems pretty high for a 4
>>>>> element yagi
>>>>> with 10.66 ft length boom.
>>>>>
>>>>> Has anyone ever modeled this antenna? Or is there anyone here who is
>>>>> willing to
>>>>> model it? I have all of the construction details.
>>>>>
>>>>> I am in SW Florida and have worked as far as several JA stations with it
>>>>> but they
>>>>> were just above the noise. Last night JA6GCE was coming in and he was
>>>>> the
>>>>> strongest that I had ever heard a JA but still not moving the S meter.
>>>>>
>>>>> Now, I have to say that this yagi is on top of a 28 ft tower and so I
>>>>> know that I
>>>>> am height limited. But I am just curious of it's real gain compared to
>>>>> other
>>>>> antennas on the market.
>>>>>
>>>>> Dan Schaaf
>>>>>
>>>>> ==================================
>>>>> K3ZXL www.k3zxl.com
>>>>> Cape Cod Instruments www.gnm-inc.com
>>>>> NOBSKA www.nobska.net
>>>>> ==================================
>>>>> ______________________________________________________________
>>>>> 50mhz mailing list
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>>>>>
>>>>> This list hosted by: http://www.qsl.net
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>>>>
>>>>
>>>> --
>>>> Lance Collister, W7GJ
>>>> (ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ)
>>>> P.O. Box 73
>>>> Frenchtown, MT 59834-0073
>>>> USA
>>>> TEL: (406) 626-5728
>>>> QTH: DN27ub
>>>> URL: http://www.bigskyspaces.com/w7gj
>>>> Windows Messenger: W7GJ at hotmail.com
>>>> Skype: lanceW7GJ
>>>> 2m DXCC #11/6m DXCC #815
>>>>
>>>> Interested in 6m EME? Ask me about subscribing to the Magic Band EME
>>>> email group, or just fill in the request box at the bottom of my web
>>>> page (above)!
>>>
>>>
>>
>>
>> --
>> Lance Collister, W7GJ
>> (ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ)
>> P.O. Box 73
>> Frenchtown, MT 59834-0073
>> USA
>> TEL: (406) 626-5728
>> QTH: DN27ub
>> URL: http://www.bigskyspaces.com/w7gj
>> Windows Messenger: W7GJ at hotmail.com
>> Skype: lanceW7GJ
>> 2m DXCC #11/6m DXCC #815
>>
>> Interested in 6m EME? Ask me about subscribing to the Magic Band EME
>> email group, or just fill in the request box at the bottom of my web
>> page (above)!
>> ______________________________________________________________
>> 50mhz mailing list
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>>
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>> Please help support this email list: http://www.qsl.net/donate.html
>>
>>
>> ______________________________________________________________
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>
>

-- 
Lance Collister, W7GJ
(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ)
P.O. Box 73
Frenchtown, MT   59834-0073
USA
TEL: (406) 626-5728
QTH: DN27ub
URL: http://www.bigskyspaces.com/w7gj
Windows Messenger: W7GJ at hotmail.com
Skype: lanceW7GJ
2m DXCC #11/6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME
email group, or just fill in the request box at the bottom of my web
page (above)!