View Single Post
Old 20-Mar-2017, 3:15 PM   #13
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,550

Any research on quality of TV tuners out there for DX? Manufacturer X vs Y?
Unfortunately, there are no published comparisons of tuner performance.

When the converter boxes came out, they had the best tuners because they had to meet performance specs to qualify for the coupon program. Later, the tuners in the TVs were improved to the same level.

Lately, some of the tuners aren't as good for OTA because the manufacturers now think only in terms of cable use and streaming. Some "TVs" are even being sold without tuners and are called displays, what we used to call monitors.

I have found that Sony TVs have good tuners for OTA and they also have a diagnostics screen that gives relative signal strength, SNR, and uncorrected errors; very helpful for antenna work.

Here is the diagnostics screen for my KDL22L5000:

Bad signal with picture freeze, SNR below 15 dB, and uncorrected errors:

Good Signal:

Lately, I have been doing experiments with indoor antennas, which are the only option for some people. This is the diagnostics screen for my KDL32R400A. I have added notes and a picture of the antenna.

In order to test for tuner sensitivity, I hook up two tuners with a splitter and a variable attenuator. I then increase the attenuation to see which tuner drops out last, making it the winner. The test can be made with or without a preamp, as long as the attenuator is after the power inserter if a preamp is being used.

Ant > coax > variable attenuator > fixed attenuator > splitter > tuners

The value of the fixed attenuator depends upon the strength of the signal. I use a fairly strong stable signal for testing. Sometimes a 20 dB fixed, sometimes a fixed 10 dB, and sometimes both.

Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
click on 1 dB for other values; the up and down arrows are faint

The most recent tuner sensitivity test that I have done was to compare the CM7003 STB tuner with my Sony KDL32R400A that I had calibrated for signal strength with my signal level meter (SLM). But, you can make the test without knowing the absolute values for signal strength.

The ATT-1 knob has 3-3/4 turns, so I put a mark on the knob with an ultra fine point Sharpie to count the turns. Clockwise rotation increases the signal; minimum attenuation at full clockwise rotation. I started there, and rotated the knob counterclockwise to increase the attenuation for the test.

I used the WTKR CBS, RF 40, virtual 3.1 signal for the test. It wasn't as stable as an LOS signal that I usually use because of trees, but it was what was available for the test.

These are the readings:

Dropout was at about -85 dBm, where you would expect it to be.

Thermal Noise Floor -106 dBm + 15 dB SNR = -91 dBm
and then adding tuner Noise Figure:
-91 dBm + 6 dB Tuner NF = -85 dBm

The CM7003 tuner is about as sensitive as the Sony, which is good, but the 7003 remote control isn't very responsive. The aim is critical and sometimes it is necessary to push a button more than once. I bought a Sony RM-VLZ620 Learning Remote and taught it some of the basic buttons on the CM-7003 remote. The box is much more responsive to the Sony remote.

Original post for test:
Attached Images
File Type: jpg AD ATT-1plus20fixed.jpg (157.3 KB, 1350 views)
File Type: jpg CM7003test2.jpg (47.0 KB, 569 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 20-Mar-2017 at 8:44 PM.
rabbit73 is offline   Reply With Quote