Thread: Rca ant751
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Old 5-Jan-2020, 3:02 PM   #110
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,633
Quote:
Originally Posted by MikeBear View Post
Well, the Menard's store has the internet page ad labeled as ANT752Z, and that's what I thought I was getting. However in the store, the box is labeled ANT752E.
I really hate what RCA is doing with that antenna. The original 751 was a good design, but they have messed with it so many times it's difficult to know what version will be in the box you buy. It was originally introduced at the 2009 CES. AVS forum member holl_ands was there and he took some photos of it. I added some notes:





The design was based on a patent by John Winegard that shows a 3/4 wave folded dipole which he called a "Tetrapole," 1/4 wave shorting stubs, and director pairs:





The 751 is a combo antenna that receives UHF and VHF-High signals. The problem with a combo antenna is that the UHF section receives UHF signals and the VHF section receives VHF signals AND UHF signals. The UHF signals from the VHF section will interfere with the UHF signals from the UHF section, so they must be removed before the two sections are combined in one feedline. The conventional way to combine a UHF antenna and a VHF antenna is to use a UVSJ (UHF-VHF Separator-Joiner) which keeps the signals separated.

A UVSJ contains a low-pass filter and a high-pass filter. The low-pass filter passes VHF signals and blocks the UHF signals. The high-pass filter passes the UHF signals and blocks the VHF signals. It is an efficient low-loss device.



The Winegard Tetrapole and 1/4 wave shorting stubs act as a substitute UVSJ. The 1/4 wave shorting stubs at the top of the Tetrapole remove the UHF signals coming from the VHF section and the Tetrapole combines the VHF signals and UHF signals at the feedpoint on the bottom of the Tetrapole. Any VHF signals received by the UHF section are ignored because the UHF section isn't very good at receiving VHF signals; they will be very weak.

The function of the shorting stubs is based on transmission line theory which says that the open end of a 1/4 wave stub that is not connected is a high impedance point which makes the other end that is connected is a very low impedance point which shorts out any signals at the resonant frequency of the stub. The 751 has 4 stubs formed by two strips that are fastened off center. This makes two pairs of stubs, one long pair for the low end of UHF and one short pair for the high end of UHF.
Attached Images
File Type: jpg RCA ANT751CES2009bL_2.jpg (104.9 KB, 748 views)
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Last edited by rabbit73; 5-Jan-2020 at 7:24 PM.
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