[50mhz] Antenna Modeling

Mon Jun 27 06:40:22 EDT 2011

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
>>> ==================================
>>> ______________________________________________________________
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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)!
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