QDX External Clock Reference Interface

User’s Guide Version 2.1b

Please note: These interface boards are only compatible with QDX hardware versions 4 and later.

The QDX digital transceiver from QRP Labs is a brilliant little radio.

For most uses, just plug it in and it works. But some digital modes require a bit more frequency stability than the internal TCXO can deliver. For these applications we provide a modification kit that lets you connect an external precision reference clock (typically provided by a GPS Disciplined Oscillator) to the QDX, bypassing the internal 25 MHz oscillator.

There are two options: If you already have a stable 25 MHz source, the Direct Interface Board provides a SMA connector and transient protection:

Direct Interface Board

Or, if you have a 10 MHz (or 5 MHz) source, the Multiplier Board will convert that input to the 25 MHz required by the QDX. This board contains a PLL chip and is powered from the QDX internal voltage regulator:

Multiplier Board

Installing either of these boards require a bit of soldering work, to remove a capacitor on the QDX board and attach wires from the interface board to the QDX. We provide a replacement for the QDX rear panel with a hole for the SMA jack on the interface board:

Or you can drill a new hole in the existing panel.

These boards are provided as “kits”, which include the Direct or Multiplier board and the replacement QDX Back Panel. Each kit also contains the twisted-pair wires that are used to connect the interface board to the QDX. You will need to cut, strip, and solder these wires to the board and the QDX (see the User’s Guide).

The price for the Direct kit is $20 ea plus shipping.

The Multiplier kits will cost $30 ea plus shipping.

I can fit two kits per padded envelope, and the U.S. First Class postage within the USA is $5 per envelope. International postage will be $20, or possibly more.

These prices are subject to change. Payment via PayPal (see the Turn Island Systems home page for the link.)