	Because of the noisy electrical environment in our home, I had to bring a long wire attic antenna signal down to the radio through a 100 foot 75 ohm coax cable. And then, because the cable was apparently a lousy impedance match to the long wire antenna, I didn't get a usable signal at the radio. So, I experimented with antenna amplifier circuits I found online that worked with the AM broadcast range, 0.5-30 MHz. Unfortunately, these all failed due to saturation caused by strong electrical interference. I then resorted to designing and making my own noise-tolerant antenna amplifier.
	My goal was to provide an amplifier of manually variable gain so that it could be adjusted to local signal strength requirements. Additionally, I wanted it to attenuate signals below 500 kHz and above 30 MHz, essentially the tuning range of my 3-band Zenith radio. Because the most significant noise in our home was of a low frequency, I designed the amplifier with a second order high pass filter to strongly attenuate low frequency noise below 500 kHz. I further decided to use inductor coils in the high pass filter, thinking that shunting low frequencies on the long-wire antenna to ground would forcefully damp low frequency oscillations on the antenna. I added a first order, capacitive, low pass filter to attenuate noise above 30 MHz. The circuit features a high impedance input for a long-wire antenna and a low impedance output for a 75 (or 50) ohm coax cable. Each amplifier stage utilizes bias resistors to forcefully center the bias voltage between the upper and lower limits. This minimizes the risk of saturation due to strong input signals or noise.
	I used the freely available LTspice circuit simulator to perform test simulations the circuit design. This excellent simulator can be downloaded from https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html. I used KiCad to design the printed circuit board (PCB). Many Linux distributions include this software in their repositories. Alternately, and for other operating systems, it can be downloaded from http://kicad-pcb.org/. Most components are of a
generic nature and can be sourced from many places. The gain control RV1 is a Bourns 3296 Trimming Potentiometer or equivalent.
	The LTspice folder contains the LTspice files, and the KiCad folder contains the KiCad files used to design the PCB.
	NOTE 1:	The LTspice model includes additional components simulating an antenna, external power supply and radio input. These include Rant, Vant, Vcc, L4, Rradio, and Cdcblock. L3 is optional and included only for powering through the coax cable.
	NOTE 2: For LTspice, open the file with a ".asc" extension.
	NOTE 3: For KiCad, open the file with a ".pro" extension.
	NOTE 4: The LTspice model includes potentiometer RV1 comprising R12 and R23. LTspice does not include a potentiometer. I used one from an LTspice forum (https://groups.yahoo.com/neo/groups/LTspice/files/%20Lib/Potentiometer/). I cannot find the potentiometer there anymore so I included it here in the "potentiometer" folder. See below for installation instructions.
	NOTE 5: I DON'T RECOMMEND a modern switching type adapter! Switching type adapters all produce very narrow spikes that don't bother most equipment. However, the Fourier transform of a tall spike includes a wide band of sinusoidal waveforms which apparently extend up into the RF band. Injecting these into the power bus creates unwanted noise. I recommend using an old-fashioned, heavy 12V transformer into a 9V IC regulator circuit to produce a quiet 9V. I have an RCA attic antenna with an RCA amplifier and that's seems to be exactly what RCA did. 

INSTALLING THE POTENTIOMETER
If running LTspiceXVII in Windows10:
If not using Onedrive...
1. Create subdirectory MyDevices: "My Documents"\LTspiceXVII\lib\sym\MyDevices
2. Copy Poti.asy to "My Documents"\LTspiceXVII\lib\sym\MyDevices\
3. Copy Poti.sub to "My Documents"\LTspiceXVII\lib\sub\
If using Onedrive, something like...
1. Create subdirectory MyDevices: OneDrive\"My Documents"\LTspiceXVII\lib\sym\MyDevices
2. Copy Poti.asy to OneDrive\"My Documents"\LTspiceXVII\lib\sym\MyDevices\
3. Copy Poti.sub to OneDrive\"My Documents"\LTspiceXVII\lib\sub\

If running LTspiceXVII in Linux using Wine (works well):
1. Create subdirectory MyDevices: /home/[your username]/Documents/LTspiceXVII/lib/sym/MyDevices
2. Copy Poti.asy to /home/[your username]/Documents/LTspiceXVII/lib/sym/MyDevices/
3. Copy Poti.sub to /home/[your username]/Documents/LTspiceXVII/lib/sub/

