Topband: Monopole Radiation Patterns, takeoff angles etc

[ZR]

The BCB stations migrated from 1/2 and 5/8 wave antennas, diamond shaped 
towers, and mountain tops by the early to mid 30's as they started to 
understand how things worked...or didnt.

Carl
KM1H



----- Original Message ----- 
From: "Guy Olinger K2AV" <olinger at bellsouth.net>
To: "Richard Fry" <rfry at adams.net>
Cc: <topband at contesting.com>
Sent: Sunday, May 06, 2012 10:05 AM
Subject: Re: Topband: Monopole Radiation Patterns, takeoff angles etc


> Hi, Rich.
>
> I guess one could ask why bother with this mid-field analysis.  It IS
> TECHNICALLY TRUE what you say, no argument, but of little use since you
> don't get to keep it, UNLESS you can get it over salt water, or off a
> mountain top.  The far field code in the various programs is adding up the
> gains AND THE LOSSES and presenting you with the sum, rather than giving
> you the loss in one presentation, the gain in another and making YOU add
> them up in your head.  For myself I will stick with the convenience of
> letting the program do the subtracting.  You are talking about salary
> before taxes.  I can only spend take-home pay, and I can only make QSO's
> with the take-home pattern.  I don't see anything wrong with using the
> take-home takeoff angle as the item of conversation -- it's the one you 
> get
> to use.
>
> 73, Guy.
>
> On Sun, May 6, 2012 at 8:44 AM, Richard Fry <rfry at adams.net> wrote:
>
>> All vertical monopoles of 5/8-wavelength __and less__ radiate (launch)
>> their
>> maximum relative field (E/Emax) in the horizontal plane.  This is true no
>> matter what the loss in the r-f ground connection they use.
>>
>> A lossy ground connection will reduce the gain of the antenna system, but
>> it
>> will not change the relative fields they radiate.  IOW, their pattern
>> shapes
>> remain the same regardless of the loss in the ground connection, be that 
>> to
>> salt water, or dry sand.
>>
>> The link below leads to a plot of the radiation patterns and 
>> directivities
>> of
>> several monopoles.  These are the shapes of the radiation patterns 
>> leaving
>> the monopole as they exist at the beginning of the far field of the
>> radiator.
>>
>> These patterns were calculated for two ohms of loss in the r-f ground
>> connection - which is about the loss that 120 x 1/4-wave buried radials
>> provides even in poor soil.  If fewer/shorter radials are used, then loss
>> increases and the directivities (gains) of these patterns would be
>> reduced -- but the radiation pattern shapes would remain the same.
>>
>> Many amateur radio operators consider only the far-field pattern of a
>> monopole antenna as shown by NEC and in textbooks, without realizing that
>> this is not the shape of the radiation leaving the monopole.  It leads to
>> the concept of a "takeoff angle" where radiation apparently was maximum
>> from that monopole.
>>
>> However the elevation field radiated by a monopole always is maximum in 
>> the
>> horizontal plane, and always is less than that at the elevation of an
>> assumed takeoff angle.  A NEC analysis including the surface wave from 
>> the
>> monopole will show this.
>>
>> Some of that low-angle radiation can reach the ionosphere and produce
>> skywave service, even though according to a NEC far-field analysis, the
>> fields are approaching zero at those low angles.
>>
>> This doesn't mean that radiation at and near the "takeoff angle" does not
>> provide significant skywave service, but it does mean that significant
>> skywave service can be generated by radiation at much lower angles than
>> commonly believed.
>>
>> http://i62.photobucket.com/albums/h85/rfry-100/MWElPatComparison.jpg
>>
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
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