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Does that make a difference?
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Yes it does because the combiner protects the preamp from the strong UHF signals in the test that I suggested. The VHF input passes VHF signals but rejects UHF signals. The UHF input passes UHF signals and rejects VHF signals. Look at the UVSJ specs here:
http://www.hollandelectronics.com/ca...-Diplexers.pdf
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I would prefer to keep the db8e amplified as it does help a few problematic channels come in reliably.
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That would be a balancing act to provide a little more gain for UHF without overloading the preamp which would harm the reception of your weak signals. It has to do with the Dynamic Range which is the difference between your strongest signals and your weakest desired signals. When the preamp is overloaded by strong signals it produces spurious signals from IMD (Intermodulation Distortion) within the preamp that wipe out your weakest desired signals.
There is a limit to the Dynamic Range that your system can handle. When the Dynamic Range is too great you must resort to exotic (expensive) measures like custom filters and separate antennas for problem channels.
There is a technique that I use when without a preamp doesn't give enough gain and with a preamp gives too much gain. It is to insert an attenuator between the antenna and the input of the preamp to find the happy medium.