It wouldn't suprise me if the VSWR wasn't terrible since you'd be operating
the antenna at an odd multiple of its original design frequency. However,
the elevation pattern will likely be a mess. In other words, it may look
just dandy on the Sitemaster, but under-perform by a whole lot out in the
far field.
A 1/2 wavelength dipole has a free space pattern which has one major lobe at
90 degrees perpendicular to the element, so, with the dipole oriented
vertically, the major lobe sits right on the horizon. A 3/2 wavelength
dipole, which is what you'd have if you took a dipole cut for VHF but used
it on UHF at 3X its design frequency, has two equal major lobes, one about
42 degrees above the horizon and one about 42 degrees below the horizon if
memory serves. There is also a third, minor lobe at the horizon. So,
unless you want to talk to worms or martians, the 3/2 wave dipole probably
isn't going to give you the elevation pattern you're looking for. Of
course, when you stack multiple elements, the fields from each element
interact, so it's hard to say what it will really look like for a multi-bay
antenna without modeling it, but I wouldn't expect it to be pretty...
--- Jeff WN3A
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Doug Bade
> Sent: Sunday, March 22, 2009 4:37 PM
> To: [email protected]
> Subject: RE: [Repeater-Builder] Decibel dipole array sweeps
>
> Jeff;
> What is your thoughts on the radiation launch angle in this
> case if beam tilt does not suffer/gain ???
>
> I have a case in point of a wideband 406-470 uhf sinclair dipole
> 310C4.. on VHF as the elements are larger than vhf needs ??? in other
> words using it on both vhf and uhf assuming reasonable vswr....
>
> Doug
>
> At 04:17 PM 3/22/2009, you wrote:
>
> >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:
> >
> <mailto:Repeater-Builder%40yahoogroups.com>repeater-buil...@ya
> hoogroups.com <mailto:Repeater-Builder%40yahoogroups.com>
> > > [mailto:[email protected]
> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Doug Bade
> > > Sent: Sunday, March 22, 2009 4:10 PM
> > > To:
> >
> <mailto:Repeater-Builder%40yahoogroups.com>repeater-buil...@ya
> hoogroups.com <mailto:Repeater-Builder%40yahoogroups.com>
> > > 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>
> > > <http://www.broadsci.com/Antenna
> <http://www.broadsci.com/Antenna> >
> > > ><http://www.broadsci.com/Antenna
> <http://www.broadsci.com/Antenna>
> >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
> > >
> > >
> > >
> >
> >
>
>
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
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>
>
