[aprssig] Scaling APRS antenna

[nc8q]

----- Original Message ----- 
From: "Glenn Little WB4UIV" <glennmaillist at bellsouth.net>
To: <vk4tec at tech-software.net>; "TAPR APRS Mailing List"
<aprssig at lists.tapr.org>
Sent: Saturday, September 18, 2004 6:46 PM
Subject: RE: [aprssig] Scaling APRS antenna


> You can just change the element lengths, but, the pattern will not be as
> expected.
>
> If you can accept the SWR, just leave it as it is since you cannot change
> the spacing of the elements and get everything at the correct spacing.
>
> Without changing the spacing between the elements, even if you did get the
> element length correct, you would have unexpected lobes and less gain than
> advertised.

IMHO, not necessarily.  It might increase the gain.  It might increase the
bandwidth without decreasing the gain.  There was an article about a
certain commercial 11 element 2 meter antenna that worked better after
removing 3 specific elements.  Typically, antennas are advertised by the
number of elements and not by boom length.  It is boom length that
determines the (maximum) gain of a Yagi-Uda antenna.  As long as there
are the minimum number of  'necessary' elements, there will be maximum
forward gain.

 Does anyone remember the 2 and 20 meter Yagi-Uda antenna observations
of a Mr. Greenbaum(?) in the early 1970s?

HTH, Chuck

> Glenn
> WB4UIV
>
> At 05:48 PM 09/18/04, Andrew Rich wrote:
> >Thats the thing the elements and boom are stailness steel and welded.
> >
> >dough
> >
> >-----Original Message-----
> >From: Glenn Little WB4UIV [mailto:glennmaillist at bellsouth.net]
> >Sent: Sunday, 19 September 2004 5:17 AM
> >To: vk4tec at tech-software.net; TAPR APRS Mailing List
> >Subject: Re: [aprssig] Scaling APRS antenna
> >
> >
> >You will need to change the spacing as well as the element lengths.
> >
> >This web site has some data and pointers to other web sites:
> >
> >http://www.hamuniverse.com/antennas.html
> >
> >There is a pointer to technical info on Cushcraft antennas. Some of the
> >manuals give dimensions.
> >
> >Hope this helps
> >73
> >Glenn
> >WB4UIV
> >
> >
> >At 08:36 PM 09/17/04, you wrote:
> > >Hi,
> > >
> > >I picked up a beam stainless steel 400-420 MHz
> > >
> > >How can I work out how much to cut off to bring it up to 438 MHz ?
> > >
> > >Cheers