For a parallel-fed (aka binary-fed, corporate-fed, etc.) antenna, if all of
the elements are fed in-phase (i.e. the branches in the phasing harness are
all the same length), as it typical with most dipole arrays, there won't be
any uptilt/downtilt as you vary the transmitter frequency outside of the
design range a bit. No matter what the frequency of the carrier is, it's
always going to hit the elements in-phase, so there won't be any beamtilt.
This is constrast to an end-fed (series-fed) collinear, where you will get
UPTILT if transmitting at a frequency ABOVE the antenna's design range, and
DOWNTILT if transmitting at a frequency BELOW the antenna's design range.
--- Jeff WN3A
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Doug Bade
> Sent: Sunday, March 22, 2009 4:10 PM
> To: [email protected]
> Subject: Re: [Repeater-Builder] Decibel dipole array sweeps
>
> Jeff;
> This is very interesting findings especially in that using
> an antenna longer than your freq tends to exhibit down tilt... that
> 440 use of a 450 antenna seems to be working in the correct
> direction. I for one found it very interesting to read....
>
> It may be real interesting to see some of the amateur antennas tested
> too as multiband ones seem to rarely work very well on the upper
> bands compared to the lower bands of those I have seen....
>
> Doug
>
> At 02:32 PM 3/22/2009, you wrote:
>
> >I'm in the process of putting up a remote receiver for a 440
> ham repeater
> >using a Decibel DB413 dipole array cut for 450-470 MHz. Since
> >Decibel/Andrew stopped making the 440-450 MHz custom models,
> I've used the
> >usual 450-470 split antennas for receive sites, and they've
> performed well.
> >I swept the DB413, and it measured as I expected. While I had the
> >Sitemaster out, I grabbed a few other Decibel dipole arrays
> out of the
> >warehouse and swept them and prepared a little document.
> Since the topic of
> >using commercial-band antennas on amateur frequencies comes
> up fairly often,
> >I figured these measurements might be of some interest to
> list members.
> >
> >I tested these antennas with them mounted above ground
> level, and away from
> >nearby objects, with the Sitemaster connected right to the
> pigtail so what
> >you're seeing is the true return loss at the feedpoint. I'll
> continue to
> >test more antennas (not just DB dipole arrays) over time and
> continue to add
> >them to this document. I have gobs of sweeps of antennas,
> but unfortunately
> >many of them were swept at the bottom end of heliax runs
> rather than right
> >at the feedpoint. From now on I'll make it a point to sweep
> them on the
> >ground this way.
> >
> >The antennas I tested in this first batch are:
> >
> >DB413, 450-470 MHz
> >DB408D, 450-470 MHz
> >DB411, 450-470 MHz
> >DB411, 406-420 MHz
> >
> >Note that the DB408D is actually two DB404's on a common
> mast, each with its
> >own pigtail/feedpoint, so there are separate plots for the
> upper antenna and
> >lower antenna. Its performance wasn't what I expected. I
> have more of the
> >same model of antenna, I'll try to test one of the others
> the next time.
> >
> >The document can be found here:
> >
> ><<http://www.broadsci.com/Antenna
> <http://www.broadsci.com/Antenna>
> >http://www.broadsci.com/Antenna <http://www.broadsci.com/Antenna>
> >Sweeps r1.pdf>
> >
> >If anyone finds this useful please let me know, so I know
> whether or not
> >it's worth the time/effort to continue to test antennas and
> add them to the
> >doc.
> >
> >--- Jeff WN3A
> >
> >
>
>
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.0.238 / Virus Database: 270.11.3/1970 - Release
> Date: 03/21/09 17:58:00
>
>
>
