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
>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
>
>
