I have found the Apex DT502 to be very useful when trying to solve OTA antenna problems. It gives not only signal strength but also signal quality. It's a measurement bargain even without the coupon. But, the supply has dried up, so I wanted to try the Centronics ZAT502 HD because it has the the same tuner and dual signal bars. The Centronics is in short supply and I noticed that some Sony TVs have a diagnostics screen mentioned in the
pdf manual but no screen shots of it.
I went to a local store to look at the diagnostics screen in the menu of a KDL-26L5000 and then ordered a KDL-22L5000. (The KDL-xxM3000
manual also mentions a diagnostics screen.) The diagnostics screen looks like this:
Now that I have all three units I am able to make a comparison using them, a SLM (signal level meter), and a 4-way splitter. My previous tests were done in my car to get away from the street traffic in front of my antenna at home that causes the readings to vary (but the signals stay locked when they are strong) and I was able to drive to strong and weak signal areas. I couldn't work that out because having the 22-inch TV in the car was a big logistical problem. I stayed at home, ran the tests at night with light traffic, and used preamps to vary the signal levels. I also rigged up a mic, amp, and speaker to listen for the traffic to ignore readings when cars were passing by.
The first test used two preamps; a CM7777 near the antenna and a RS 15-1115 inline preamp (one of my better RS purchases) before the attenuator to find out where the signal meters maxed out:
antenna-> 7777-> 50 ft coax-> CM power inserter-> RS amp-> attenuator-> 4-way splitter:
Code:
Attn Apex Centronics Sony SLM Equiv
dB Q S Q S S Er SNR dBmV dBm
0 100 87 100 89 79 0 25 +18.5 -30.3
3 100 86 100 89 79 0 25 +15.0 -33.8
6 100 86 100 89 79 0 25 +11.9 -36.9
9 100 86 100 88 79 0 25 +8.8 -40.0
12 100 85 100 88 79 0 25 +5.9 -42.9
15 100 85 100 88 79 0 25 +3.1 -45.7
18 100 83 100 87 79 0 25 0.0 -48.8
21 100 79 100 85 79 0 25 -3.5 -52.3
"Q" is quality, "S" is strength.
Sony IF-AGC figures not listed because in all cases they were the same as strength.
The RS preamp was removed, leaving only the 7777 (my normal setup):
Code:
Attn Apex Centronics Sony SLM Equiv
dB Q S Q S S Er SNR dBmV dBm
0 100 84 100 88 79 0 25 +3.0 -45.8
3 100 81 100 87 79 0 25 -0.8 -49.6
6 100 78 100 84 79 0 25 -3.9 -52.7
9 100 73 100 80 78 0 25 -7.0 -55.8
12 100 69 100 76 76 0 25 -10.0 -58.8
15 100 66 100 71 74 0 25 -12.9 -61.7
18 100 62 100 67 71 0 25 -15.7 -64.5
21 100 58 100 63 69 0 25 -18.6 -67.4
24 100 54 100 59 66 0 25 -21.6 -70.4
27 100 49 100 54 62 0 24 -25.4 -74.2
30 100 45 100 50 59 0 23 -28.2 -77.0
33 100 38 100 45 55 0 21 -32.0 -80.8
The 7777 was removed (to simulate weak signals) leaving only the coax between the antenna and the attenuator:
Code:
Attn Apex Centronics Sony SLM Equiv
dB Q S Q S S Er SNR dBmV dBm
0 100 55 100 58 66 0 24 -22.0 -70.8
3 100 49 100 53 62 0 24 -25.9 -74.7
6 100 45 100 49 58 0 22 -29.0 -77.8
The RS preamp was inserted between the splitter and the SLM because the meter was near the bottom of scale, and I repeated the test just above. The preamp noise figure does not affect the tuners because it isn't in line with them:
Code:
Attn Apex Centronics Sony SLM+amp dBmV corr Equiv
dB Q S Q S S Er SNR dBmV for amp dBm
0 100 54 100 58 66 0 25 -6.1 -22.1 -70.9
3 100 49 100 53 62 0 24 -9.3 -25.3 -74.1
6 100 44 100 49 58 0 23 -12.1 -28.1 -76.9
9 100 38 100 44 55 0 21 -14.9 -30.9 -79.7
12 77 27 65 38 55 0 18 -18.1 -34.1 -82.9
15 26V 0 20V 27 55 0 16 -21.2 -37.2 -86.0
18 dropout dropout 55 3099V 13F -24.3 -40.3 -89.1
A "V" after a figure means that it varies; the Sony errors are updated about once every second. An "F" after the SNR means that the display is frozen at that value. Adding even more attenuation makes the Sony screen go black and say "no signal." At least 15.5 to 16 dB SNR is needed to maintain lock.
When aiming or comparing antennas using the signal strength meter you must keep it below the max value (where your meter doesn't go any higher) by using an attenuator. In my case, that would mean keeping it well below 86 for the Apex, 89 for the Centronics, and 79 for the Sony.
Attachment No. 1 shows a Sony "frozen screen" at 13 dB SNR.
Attachment No. 2 is the RS preamp specs.
Attachment No. 3 is the RS preamp diagram. RS used to print diagrams in the manual,
but they don't anymore. I think that's a mistake, because showing the diagram encourages experimentation, which means more sales. Looking at the diagram, you can see how the RF signal and the DC power are combined on the coax using capacitors and chokes (inductors). Capacitors pass RF but block DC; chokes pass DC but block RF.
Incredible. I hope you aren't really a dr and just play one on the internet. I know exactly what a splitter is and what it does. I've only used them professionally for 27+ years. Nobody here that I am aware of, including myself, has ever denied the fact that combining 5+5=10 on the output. The whole point is that a 
, "Get Along", you GOT to be kidding ! 
