Tuesday, 26 March 2013

The Elecraft K3 as an IF for 472kHz

After a few days playing with my new PICAXE 20M2 project board I thought I'd put it on one side and go back to the 475kHz transverter project to try something I had meant to try previously.

I use an Elecraft K3 as my 630m band IF transceiver.

By putting the Elecraft K3 CONFIG:KXV3 to TEST it is possible to 'bypass' the normal restrictions on K3 coverage ( to some extent). It is then possible to tune the K3 to 10.472 kHz to 10.479kHz and then downconvert to 475kHz +/- by mixing with 10.000MHz. This can be either the shack 10MHz standard or alternatively a suitable crystal oscillator.

I found that by just replacing the 3.2MHz crystal in the original oscillator (G3XBM 472kHz transmit converter) with a good quality parallel mode 10MHz crystal the oscillator and buffer would go directly on 10MHz and could be netted onto 10.000000MHz quite readily!
In due course I will tap off the 10MHz shack standard instead of using the crystal for rock solid 472kHz operation. LO output power seems to be similar to the original arrangement ( to be checked again)

As the K3 produces up to about -12dBm of clean output at 10.475MHz, this is a good match to the transverter SAM1 mixer IF input without requiring further attenuation of the IF transmit signal. And in test mode the K3 power setting still works allowing a 10dB or so adjustment range.

Using my SMG signal generator I checked the K3 sensitivity at 10.475MHz and although less sensitive than at 10.1MHz, it is still capable of better than -120dBm MDS. This should be adequate for use with the 10dB gain of the transverter receive side.

Now to complete the transmit chain.


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