[ADTech]

You don't need more gain, you need more of a cleaner signal. Amplifying a "dirty" signal gains you nother. With only 35' of coax, adding the RCA preamp would, at most, improve the system noise margin by about 3-5 dB (Assumptions: 1 dB coax IL @ 200 MHz, RCA NF=3.1 dB @ 200 MHz, Tuner NF=~4-7 dB). Since his calculations suggest an excess of 50 dB margin before building envelope attenuation and antenna gain, the odds that a pre-amp is going to fix this are near zero. Skip the amp, identify the source of the problem and fix it.

You probably need to look at the hints I offered to see if any apply. Your existing antenna has plenty of gain and it is unlikely that the Techshield is attenuating your VHF (only) by 50 dB. Therefore, noise of some kind is likely and, since the issue abates at night time, something solar would lead my list.

A simple dipole outside *should* suffice in the absence of RFI.