<div dir="auto"><div><div dir="auto">Já muita gente me perguntou como é que se achava o foco de uma antena parabólica off-set. Isso e mais algumas coisas, Hi...</div>Reenvio um documento escrito por alguém que dedicou toda a sua vida profissional, e não só, à RF. Está escrito em italiano mas deverá ser um problema entender. </div><div dir="auto">Eu uso dois métodos: os espelhos e o ruído solar.<br><div dir="auto"> </div><div dir="auto">73, Miguel</div><div dir="auto">CT1BYM </div><br><br><div class="gmail_quote" dir="auto"><div dir="ltr" class="gmail_attr">---------- Forwarded message ---------<br>De: <strong class="gmail_sendername" dir="auto">iz2ewv--- via Moon-net</strong> <span dir="auto"><<a href="mailto:moon-net@mailman.pe1itr.com">moon-net@mailman.pe1itr.com</a>></span><br>Date: sábado, 12/09/2020, 20:46<br>Subject: Re: [Moon-Net] Finding the focus point in a dish<br>To: <<a href="mailto:moon-net@mailman.pe1itr.com">moon-net@mailman.pe1itr.com</a>><br></div><br><br>
<div>
<p>Hello friends,</p>
<p>maybe you should find interesting the attached paper, done by a
OM friend of mine (Giovanni, IN3HOG) who leads a microwave contest
team and builds/maintain all the equipment (he worked all his life
long as a radio link engineer for the public Italian radio/TV
broadcasting company, RAI).</p>
<p>The scope of his paper is to describe his methods to check the
dish: how to find the irregularities in the reflector surface and
the exact focus point.</p>
<p>Unfortunately, the paper is written in Italian, but I think that
Google Translator or other similar tool should solve.</p>
<p>73 de Alberto, IZ2EWV.<br>
</p>
<div>Il 11/09/20 16:59, Gedas via Moon-net
ha scritto:<br>
</div>
<blockquote type="cite">
<p><font size="+1"><font face="Arial">Paul, I see the number 1
priority to be placing the feed in the correct position to
ensure it is being illuminated properly. Then after that I
adjust the feed for best RL. Interestingly enough I noticed
little difference in the RL of my feed pointing in open
space and then when mounted on my small off-set dish for
terrestrial work on 10 GHz.</font></font><br>
</p>
<pre cols="72">Gedas, W8BYA EN70JT
Gallery at <a href="http://w8bya.com" target="_blank" rel="noreferrer">http://w8bya.com</a>
Light travels faster than sound....
This is why some people appear bright until you hear them speak.</pre>
<div>On 9/10/2020 8:26 PM, Paul Andrews
via Moon-net wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hello Moon Folk,
<div><br>
</div>
<div>I am amazed at how the measured VSWR of a feed changes
when you put it into a dish. The feed in open space is
trying to couple all the transmitted energy into spare.
When the feed is placed in a dish, there are reflected
signals from the test instrument involved that phase add and
subtract in mysterious ways..</div>
<div><br>
</div>
<div>I'm now working with a new dish and a new feed. The
measured vswr can change significantly with small changes in
feed position in the dish.</div>
<div><br>
</div>
<div>Life would be simple if the dish focus was found when
vswr was minimum. Or, should the feed be placed at the
geometric focus point regardless of vswr? Is there a
predictable vswr event as the feed moves inside the focus
and then outside the focus. </div>
<div><br>
</div>
<div>I will begin to experiment with focus vs vswr but I hope
others have already blazed this trail and can provide some
hints to what I will find.</div>
<div><br>
</div>
<div>73 - Paul - W2HRO</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
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