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WANTED 14.333MHz XTAL

Submitted by richard-g8jvm on Sat, 11/29/2008 - 14:49.

Hi All,

Playing catch in the the shack, building all the kits I had for a while.

I need a 14.333Mhz xtal HC49, pref low profile/SMD for a softrock-lite for use on a ICOM with a 10.75 MHz IF.

As it being used after a roofing filter it needs to be somewhere close to center frequency,

digi-key have 14.3359MHz as a stock item, good price less than $1 and $25 p+p.

That would give a center freq of 10.7519 MHz, maybe pull it 5 KHz lower, but not sure if its too far out of the passband of the roofing filter. I can sample at 96KHz.

Comments on that please

73 Richard G8JVM

richard-g8jvm's blog
1880 reads

One would not want the LO

Submitted by cecil.bayona on Sun, 12/07/2008 - 14:46.

One would not want the LO frequency of the SoftRock to be within the passband of the radio.

Around the LO frequency there is a spike and other possible artifacts, you would want the LO frequency to be at least 10KHz away from the IF frequency possibly a little more.

A few things to note;

The LO operates several KHz lower than the crystal frequency, the reason being that the Softrock has a lot of capacitance across the crystal which pulls it 2KHz to 5KHz lower in frequency.
The SoftRock can be tuned to receive at the LO frequency and up to plus or minus 1/2 the sampling rate of the sound card. So if you have a sound card sampling at 48KHz you can receive signals plus or minus 24KHz away from the LO frequency.

So there is no need and it's actually undesirable to have the LO frequency be within your IF band pass.

What is the bandwidth of your filter, and what is the sampling rate of your sound card? Then I can be more specific about possible crystal frequencies.

Mouser has this crystal at 14.4756MHz , and a 14.69MHz that might work depending on your filter bandwidth and sound card sampling rate. The 14.69MHz crystal will work well if you have a sound card capable of 96KHz sampling rate.

One more item, unless your radio has a buffered IF output out the back of the radio, I suggest that you put a small board with a buffer such as an emiter follower or a source follower using a FET inside the radio, then a small coax back to the SoftRock. The reason being that either the cable or the softrock filter unless isolated can detune your IF stage and mess up the radio's performance.

Cecil

K5NWA

www.softrockradio.com www.qrpradio.com