A wide band pre amp for SWL and Scanner use
VLF to beyond 1000 MHz using a
Mini Circuits monolithic amplifier...
Chris
Arthur Vk3JEG 2000
I've been mucking around
with broad band RF amps for SWL and Scanner use on and off for some years now. During
this time I found the Mini Circuits range of monolithic amplifiers to be an
excellent choice for this particular application. The following is a brief
description on how to construct a wide band pre amp using the MAR / MAV RF
chip. I have chosen devices with average gains of around 12 dB to help minimise
receiver overload problems. These being MAV-11and MAR-7, with the MAV having
the better noise figure (3dB) and 3rd order intercept point.
You will need
the following components
-
Mini circuits MAV-11 wide band device (Clarke & Seven, Syd or RF parts,
Melb).
- 2 x 1nF Surf Mnt type caps (0.25mm or 0.1inch
width), you could use small ceramics.
- 2 x PCB edge mount BNC (female) or SMA, plus patch
lead and connectors.
- Bias resistor 120 Ohm for 12 V or 130 Ohm for 13.5
V.
- LF-1250 Ferrite Bead from Jaycar (mount on the bias
resistors leg to MAV-11 pin 3)
The PCB is made from
standard double sided FR-4 (1.6mm or 0.0625"). Mount all of the non active
bits first, leave the MAV to last. A feed-through cap (value is not critical)
should be soldered through to the ground plane as shown on the PCB layout, not
the schematic. Use this to connect to your supply. I made a little open top box
from double sided PCB off cuts, the Amp PCB is the bottom, it's soldered 6mm up
there-by leaving room for the feed through and supply wires.
The MAV-11 has a dot on pin
3, this is the output pin, place the MAV in the PCB hole so that it sits flush.
The device ground pins are pushed through pre drilled 0.8mm holes each side of
the device hole, the pins are then soldered on the ground plane side.
Less Current,
greater bandwidth...
You can use other Mini
Circuits Monolithic amps with this layout such as the MAR-7... It has lower
current drain (22mA) for slightly better gain and 2000 MHz of band-width but
has a higher average noise figure of 5dB.
R bias for the MAR-3 = (V supp - 4.0) / 0.022
NOTE: The MAR has the index DOT on PIN 1
(input)
VK3CAE (Ex
VK3JEG)