Jeff,
I find this interesting, especially with regard to the db408. Did you test the db408 with both db404's harnessed and working together? Brian, k5in ----- Original Message ----- From: Jeff DePolo To: Repeater-Builder@yahoogroups.com Sent: Sunday, March 22, 2009 1:17 PM Subject: RE: [Repeater-Builder] Decibel dipole array sweeps 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: Repeater-Builder@yahoogroups.com > [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Doug Bade > Sent: Sunday, March 22, 2009 4:10 PM > To: Repeater-Builder@yahoogroups.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> > >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 > > >
