High Gain, Low Noise 2.4 GHz Receive Pre-Amplifier Modification

This will show you how to add a high gain (13 dB), low noise figure (1.3 dB) receive pre-amplifier to your Proxim Symphony for under $50.  The cost is reduced by using the existing components on the Symphony, such as the PIN diode switch, and just inserting the receive pre-amplifier.

Adaptation to wireless network cards other than the Symphony should be trivial


Most schematics are in their native Xcircuit PostScript format for ease of printing and modification.  To use PostScript under Window$, you'll need to install the Ghostscript & Ghostview packages.  Set Media to A2 for ease of v ewing.

  1. 2.4 GHz Receive Pre-Amplifier Schematic

Construction Notes

Start by reading the data sheet and evaluation kit notes for the Maxim MAX2641, you'll find out quickly that it's a tiny little 6-pin SOT23-6, 2.4 GHz ultra low noise amplifier IC.  If you are up to working with this device, go to Maxim's website and order a few free engineering samples.

You'll want to pick up some quality 1/32 inch, double-sided, 1 ounce copper clad FR-4 circuit board.  The Injectorall circuit board from Digi-Key is perfect.  Its part number is PC44-ND for 3 x 4.5 inches and costs $3.23.  You should also pick up the Toner Transfer System design paper by DynaArt, part number TTS-5-ND for a 5-sheet pack.  This will allow you to print the circuit board pattern, (PostScript version), out on a laser printer and then iron it onto the copper clad board.  This is probably the best, and cheapest, way to create your own printed circuit boards.

The next step is to make the circuit board for the amplifier.  You must use the board pattern Maxim provides!  This is because the delicate 50 ohm strip lines that are needed are a real pain to recreate on your own.  Here are some links to help with the fabrication of your own printed circuit board:

After your circuit board is etched, you should drill and solder all the ground vias.  Those are what connects the top copper plane to the bottom plane on two sided copper clad boards.  Do this by drilling a small hole where the marks are in the circuit pattern picture (the black dots in the above JPEG), then solder a piece of wire in the holes to connect the top and bottom planes.  Cut off any excess length of wire flush to the copper plane.  You can then start to solder in all the discrete components.  Install the small surface mount capacitors, then move to the larger components.  The very last thing to solder in will be the MAX2641 IC.  This is done to protect the IC from any extended handling.


You'll need to unsolder the large RF shield to get access to the insertion points.

[new-preamp-insert]  Where to insert the new pre-amplifier module

[sym-closeup-1a.jpg]  A picture

Operation Notes

The receive pre-amplifier will amplify all the signals it hears, so it's best if you insert a 2.45 GHz bandpass filter in the RF input line.  You can order bandpass filters from Digi-Key for about $20 each.  The 2-pole model is part number TKS2610CT-ND and the 3-pole model is TKS2618CT-ND.  The 3-pole model is the better of the two.  These particular filters (Toko) can not be used with DC voltages on their terminals!  This is because they are DC grounded.  You'll need to add a DC blocking capacitor in front of the bandpass filter to block the PIN diode bias voltage.  A 0603 style 22 pF capacitor will work fine.

If you need to power the pre-amplifier only during the receive cycle (not continuously on), view the following pictures to get the location to tap point this control voltage.


View some of the construction pictures.

+5 VDC Tap Point

You can tap the 5 volts here:

[sym_pic-3a]  Open solder pad for +5 VDC

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