As far as the picture of the GRE preamp, I still own mine, took a 9-volt battery or AC power supply and was made for a portable to go in between the radio and the rubber duck. They made a flat larger unit to sit on top of your radio and I have that one also, both in good shape. Very old.
I used them on UHF and 800 MHz, slight difference in the adjustment of the small dial. In some cases they actually improved reception but what they were doing was allowing more noise and interference in along with the signal. A better signal would outweigh that.
However, there's a reason I keep them in pristine condition after throwing away so much crap in the last 50 years. I wouldn't let these puppies go. Certain conditions, certain frequencies and different applications I actually saw Improvement and for a period of time of maybe months to years, until frequency changes, they stayed in my current set up of the time.
