G4HUP
Reference Locking the SDR-IQ and SDR-14 receivers
Thanks to the interest and efforts of Wolfgang, DJ3QD, there is now a DFS solution for locking your
SDR-I4 to a 10MHz reference. The SDR uses an internal 66.667MHz clock for
the ADC - this can be synthesised using a DFS - see the Iss 2
Filters and Version pages for details.
Click here for an article explaining the principles and the modifications required.
Complete kits are available for the 66.667MHz DFS version, including the crystals for the final filter
- see SDRDFS. Kits and information are also available for the squarer needed for
correctly driving the SDR-IQ - see here.
The connection of the signal into the SDR-IQ and SDR-14 are relatively easy - but please note that it is not a 'no intervention'
solution! You must go inside and make some small changes, as detailed below, and once you have done this the SDR
will require an external 66.667MHz input to operate.
See also the implementation by K9IQY
Modifying the RFSpace SDR products for External LO input
These instructions are courtesy of RFSpace, manufacturers of the SDR-IQ and SDR-14:
SDR-14
- 1. Solder a cable on location W2. This cable is where the 66 MHz signal comes in.
- 2. Short pin 1 of the G1 oscillator to ground. The pin is marked with a circle on the part and a triangle on the
board. (This disables the oscillator) You can also remove the oscillator if you like.
- 3. The required level is about 1.5 to 3.3 volts. You should be able to drive a sinewave or squarewave into it.
The clock is clamped to about 0.4 volts with diode D3. Any signal above that should work fine. There is also a 1:4
transformer that will increase the voltage so it does not need a lot of signal into it.
SDR-IQ
- 1. Short out the position labelled R36 to disable the internal osc.
- 2. Short out the position labelled R37 to connect J6 to the clock input
- 3. 66.667MHz square wave signal needs to be connected to J6
- 4. Use a gate (eg 74AC04) to provide a squared signal from sinewave output - note that the gate package must be
powered from a 3V3 supply, as the output connects directly into the DDS chip of the SDR-IQ. See here
for an interface example provided by VK3HZ.
Note that if you have any concerns about whether performing this modification may affect any warranty on your SDR-IQ or SDR-14,
please address your questions to RFSpace - not to me!
Page Created 7 Jun 09
Page Last Updated 17 Mar 12
