Referring to previous posts:
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Compare Several Preamplifiers OTA-DFW
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Compare Preamplifiers - Test Procedure & Configuration
As mentioned earlier, the two VHF channels in the DFW area are channels 8 and 9. Measurements of both channels were attempted during the channel scans. Because channel 9 signal strength is weaker than other channels in the scanned list, it could not be reliably decoded by some of the preamps without attenuator adjustment during the tests.
Below is a graph showing the averaged MER value for each of the 7 preamplifiers receiving channel 8. The values shown represent the average of 3 individual measurements. The range of MER for the preamps is nearly 3 dB. The AD PA-18 provided the highest MER (26.7 dB), with the new CM7778 second (26.6 dB).
The image below shows the output power level for each of the preamplifiers.
The highest output power is shown for the CM7777 versions:
- CM 7777 new (-54.6 dBm) and,
- CM 7777 old (-57.7 dBm)
Notably, the lower MER values for channel 8 originated in the preamplifiers with separate amplifier sections for VHF and UHF.
- TVPRAMP1R
- CM7778 old
- CM7777 old
- WG LNA200*
*The WG LNA-200 has separate amplifiers even though it doesn’t have dual inputs.
A plausible explanation for lower channel 8 MER values could be;
The VHF-only sections have higher noise figures & generally lower gain than the VHF-UHF combination or UHF-only sections (single or dual amplifier versions). Investigations into the hardware design tend support this. Some factors specific to VHF could make this design choice seem logical to a manufacturer.
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