To make some more weak signal tests I set up my SONY KDL22L5000 TV indoors to see what I would get from a scan:
CM4221 > 6 ft RG6 > CM7777 > 50 ft RG6 > CM4707 Power Supply > 3 ft RG6 to TV or SLM
The gain of the preamp and the loss of the coax gives a signal 21 dB stronger at the output of the CM4707 than at the antenna; I measured it so that I can calculate the signal strength at the output terminals of the antenna from measurements indoors.
I didn't use a splitter to feed the TV and signal level meter because I wanted max signal strength; I just substituted one for the other. When I am comparing the sensitivity of two tuners, then I use a 4-way splitter to feed the two tuners and my SLM to bring them to the cliff with an attenuator.
I first measured the strength of some signals with my 719E SLM to check the system. The 4221 was used for UHF and a folded dipole cut for CH13 for VHF:
Code:
Real Equiv
CH dBmV dBm
7 +1.5 -47.3
9 -5.0 -53.8
11 -10.0 -58.8
13 +4.0 -44.8
16 +21.5 -27.3
29 +11.5 -37.3
31 +11.5 -37.3
33 +12.1 -36.7
40 +14.2 -34.6
42 -25.0 -73.8 very unstable, antenna aimed in wrong direction
46 +2.3 -46.5
50 +3.5 -45.3
The noise floor measured about -10 dBmV (-59 dBm) on VHF-Low and about -20 to -25 dBmV (-69 to -74 dBm) on VHF-High, which doesn't leave quite enough margin for reliable reception of CH11. I need to improve my VHF-High antenna.
The tuner scan gives the channels in virtual number order:
Code:
Virtual Real Errors SNR Sony Signal Strength Out of Ant OTA Signal
CH CH dB Scale dBmV dBm dBm dBm **
2.1 20 0-6971 13-15 58-61 -26.5 -75.5 -96.5 -108.0
3.1 40 0 25 79 >-4.0 >-53.0 >-74.0 >-85.5
4.1 9 0 26 78 -7.0 -56.0 -77.0 -77.0 FD
6.1 25 0-3000 13-17 75 -11.3 -60.3 -81.3 -92.8 *
7.1 11 0-3000 13-15 67-68 -20.0 -69.0 -90.0 -90.0 FD
8.1 22 0 17-20 76 -10.0 -59.0 -80.0 -91.5 *
10.1 31 0 25 78 -7.0 -56.0 -77.0 -88.5
13.1 13 0 28 79 >-4.0 >-53.0 >-74.0 >-74.0 FD
15.1 16 0 25 79 >-4.0 >-53.0 >-74.0 >-85.5
21.1 7 0 31 79 >-4.0 >-53.0 >-74.0 >-74.0 FD
27.1 50 0 25 79 >-4.0 >-53.0 >-74.0 >-85.5
33.1 33 0 23 78 -7.0 -56.0 -77.0 -88.5
35.1 26 0 18-19 76 -10.0 -59.0 -80.0 -91.5 *
43.1 29 0 25 79 >-4.0 >-53.0 >-74.0 >-85.5
45.1 45 0 22-23 72 -14.5 -63.5 -84.5 -96.0
49.1 46 0 25-26 78 -7.0 -56.0 -77.0 -88.5
23.1 42 NA NA NA Not picked up by scan *
* Signal from rear of antenna
** FD Folded Dipole for VHF, 0 dB gain; CM4221 average gain 11.5 dB
Notice that some SNR numbers below 15 dB are given by the Sony TV.
The Sony signal strength scale doesn't go any higher than 79, no matter
how strong the signal. It's derived from the AGC, which has a much smaller control range than the dynamic range of the TV. See attachment No. 1, and notice that the calibration curve is maxed out at 79.
My newer Sony, a KDL32R400A, has a much greater range for the signal strength scale, with one dB steps. Excellent for antenna experiments, but I'm at a different location now. See attachment No. 2.
The TV did well with the real CH 20 and 45 weak signals. CH 20 is a Tropo signal that is not expected to be stable, CH 45 was very stable.
It also did well with CH 11, considering that the noise level was high on VHF-High which reduced the SNR. Some days CH 11 is stable, some days not, depending on the power line noise. A better antenna for CH 11 would improve the SNR.
See the tvfool chart in my previous post and compare the signal power (dBm) numbers at 5 ft with the OTA Signal dBm numbers in the above chart.