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Old 19-Jun-2015, 10:09 PM   #4
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,719
Quote:
I could also use some help with how to avoid signal overload with respect to using a high-gain system for both the remote stations as well as the powerful local channels.
Yeah, that's one of the problems.

CBOT-DT is your strongest signal with a Noise Margin of 64.5 dB, even before adding the 7698 antenna average UHF gain of 13 dB.



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

You will need an antenna like the 7698, 91XG, or DB8E for WNPI and a preamp which would be overloaded by your local signals. The dynamic range between CBOT and WNPI is 68.6 dB. To this you must add 16 dB for the SNR needed by WNPI to get the required SFDR (Spurious-Free Dynamic Range) of 84.6 dB. This will not work because the strong local signals will create spurious signals in the preamp itself from IMD (Intermodulation Distortion) that will probably wipe out the weak signals including WNPI.



Another problem with WNPI is that it is a 2Edge signal from terrain obstructions that interfere with the signal path. The curvature of the earth starts to interfere with signals at about 70 miles.

Yet another problem is that WNPI has adjacent channel interference from CICO-DT on real channel 24, which is 62.9 dB stronger.

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010

5.4.2 Adjacent Channel Rejection
The receiver should meet or exceed the thresholds given in Table 5.2 for rejection of first adjacent-channel interference at the desired signal levels shown above the columns therein.



62.9 dB is much greater than 33 dB.

The only way I can see for you to have a chance of receiving WNPI is with two separate antenna systems, one for your local channels, and one for WNPI. You could have an A/B switch for antennas or have a separate tuner for one antenna, with its output connected to the A/V input of the TV and other antenna would connect to the antenna jack of the TV.

The WNPI antenna system would need a single channel bandpass filter for real channel 23 from Tin Lee:
http://www.tinlee.com/bandpass_filters.php?active=3#CF7

You can call them to talk with an engineer and email your TVFOOL report.

Ant > CH23 BP Filter > Preamp > coax > Power Inserter > TV

Just for fun, you could try it before ordering the expensive custom filter, to see what you can get.

In theory, it is possible to use one antenna with RF relays to remotely switch in or out the preamp and filter, but that would be a custom job.

I wonder if you could stream over the internet what you want from PBS, either directly or with a Slingbox from a remote location in the US.
https://en.wikipedia.org/wiki/Slingbox
http://www.slingbox.com/
Help with NFL football games please!
http://forum.tvfool.com/showthread.php?t=14835
Attached Images
File Type: jpg NMChartC.jpg (71.3 KB, 921 views)
File Type: jpg SFDRdiagramJ2 (2).jpg (103.6 KB, 944 views)
File Type: jpg AdjacentChannelThresholds.jpg (59.0 KB, 3788 views)
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Last edited by rabbit73; 20-Jun-2015 at 12:01 AM.
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