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Old 22-Aug-2016, 1:02 AM   #14
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,550
Quote:
Yup - it's the same powered amplifier that came with the omnidirectional antenna, which I left in place and am using it with the HDB4X. Seems to be getting better results with it than without.
Thanks for the amp info. What I'm concerned about is overload; there is such a thing as too much amplification.

WMOR has a Noise Margin of 58.0 dB for an antenna mounted in the clear. If you add the HDB4X antenna gain of 12 dB (they say max of 14.2 dB) you are up to 70.0 dB NM, which is on the edge of overload.



Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html

Looking at it using the signal power, WMOR is -32.8 dBm.

-32.8 dBm + 12 dB ant gain + 20 dB amp gain = -0.8 dBm, which is tuner overload even when allowing for the coax loss after the amp.

It might be even worse than that, because the 1byone website says 32 dB gain, but they don't state the conditions:
https://www.1byone.com/TV-Accessorie...nna/OUS00-0683

ATSC Recommended Practice:
Receiver Performance Guidelines


Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity


Quote:
A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm to –5 dBm for both the VHF and UHF bands.
5.2 Multi-Signal Overload

Quote:
The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm, will exist at the input of the receiver.
You have more than one high-level signal.

When you have partial overload, it is possible to receive your strongest signals, but the weaker signals (like NBC) become damaged by IMD (Intermodulation Distortion) which produces spurious signals which raise the noise floor and reduce the SNR of the weak signals to less than the minimum required 15 dB for reception. NBC is listed as 6.4 dB weaker than WMOR, but the difference is greater than that because your present antenna isn't very efficient for NBC.

The Winegard HD7694P antenna is 65 inches long, but the UHF corner reflector makes it look more massive.
http://www.winegard.com/kbase/uploads/HD7694P.pdf

I don't know the length the RCA ANT751, because RCA gives the box size, which isn't very helpful. If the RCA antenna is in the clear it SHOULD have enough gain, but the 7694 antenna has more gain if the signals are weakened by objects in the path.
Attached Images
File Type: jpg NMChartRev.jpg (72.9 KB, 10673 views)
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Last edited by rabbit73; 22-Aug-2016 at 1:54 AM.
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