Thread: Rca ant751
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Old 6-Jun-2017, 3:29 AM   #78
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,332
The Sadelco DislayMax 800 signal level meter makes 43 measurements across the channel and diplays the average of all readings. If one of the 43 measurements is below -20 dBmV, the meter says "Ur" for under range and doesn't give a reading. The scan covers about 5.3 MHz of the 6 MHz channel.

If the meter is switched to the single frequency mode, it will measure down to -35 dBmV at the center of the channel, but the correction for a digital signal is not added; +6.8 dB IIRC.

The screen on the meter actually shows a dark gray image on a dark green background and doesn't have much contrast. The image looks pretty good on a computer screen, but makes a muddy image on a print.

analog channel:

digital channel:

To make an image that has more contrast and room for notes, I set my digital camera for a B&W image, and then edit in Photo Gallery to increase the contrast.

Photo Gallery will only allow me to increase the contrast one time, AFAIK, so I use Lunapic to increase the contrast 4x more:

Attached Images
File Type: jpg DisplayMax800_43meas.jpg (90.3 KB, 1209 views)
File Type: jpg DisplayMaxImg5.jpg (34.6 KB, 1147 views)
File Type: jpg DisplayMaxImg1.jpg (92.7 KB, 1193 views)
File Type: jpg DisplayMaxImg2_1.jpg (149.0 KB, 1178 views)
File Type: jpg IMG_1010 (4).jpg (68.2 KB, 1176 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 6-Jun-2017 at 7:54 PM.
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