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Old 23-Apr-2015, 1:50 AM   #7
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,725
Bill Naivar's Anti-ghosting Antennas Revisited

The links to Bill Naivar's Anti-Ghosting Antenna to minimize multipath reflections were blocked by my Norton Internet Security, but I was able to find enough images at Google to describe his experiments, while giving him credit for his images.

Bill's first anti-ghosting antenna was a Winegard PR-9014 UHF antenna in a screened enclosure. See Attachments 1-3.

He used a spectrum analyzer to view the shape of the digital signal to look for signs of multipath. This is not always a fool-proof method to detect multipath as Trip in VA found out. It is possible to have a good looking trace, even when there is a serious multipath problem. This is because the reflections can fill in the dips in the trace. The analyzer records amplitude during the trace, but doesn't account for time differences between the original signal and the reflections according to Dr. O. Bendov in his paper DTV Coverage and Service Prediction, Measurement and Performance Indices.

See Attachment 4 for the bad looking ragged spectrum analyzer trace by Bill, BEFORE using the anti-ghosting antenna. Attachment 5 is the good looking spectrum analyzer trace, using the Winegard PR-9014 anti-ghosting antenna.

Chattanooga: Trouble getting OTA Signal post 25 post 26

Bill's second antenna was a double bowtie in a trash can which gave better results. Attachments 6-8.

Can you see the anti-ghosting antennas built by Bill Naivar of Georgia Tech in this photo?

I took a standard UHF bowtie antenna and mounted it to the bottom of the can. The metal bottom makes a great back reflector, the can provides the multipath shielding, and the U-bolt that came with the antenna mounts the whole thing on the pole. (I can even use the handles to tie guy wires to so that the wind doesn't move the can.) I mounted a F-81 barrel for the coax connection. And I even got 2 dBmV MORE signal level than my original design!

Attachment 9 is the spectrum analyzer trace for the double bowtie in the trash can.
Attached Images
File Type: jpg NaivarA-G Ant1_1.jpg (96.7 KB, 427 views)
File Type: jpg NaivarA-G Ant2_1.jpg (109.4 KB, 403 views)
File Type: jpg NaivarA-G Ant3_1.jpg (109.9 KB, 2483 views)
File Type: jpg NaivarA-G Ant4a_1.jpg (105.4 KB, 428 views)
File Type: jpg NaivarA-G Ant4b_1.jpg (111.4 KB, 400 views)
File Type: jpg NaivarA-G Ant5_1.jpg (170.3 KB, 913 views)
File Type: jpg NaivarA-G Ant6_1.jpg (178.9 KB, 428 views)
File Type: jpg NaivarA-G Ant7_1.jpg (128.5 KB, 893 views)
File Type: jpg NaivarA-G Ant8_1.jpg (115.9 KB, 423 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 3-May-2015 at 7:05 PM.
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