In my last blog, I discussed the Ran Technology 4 Channel Oscillator board. This device can accept 4 Epson chips available from Digi-key which are programmed to a specific frequency. My previous blog has links and information on the board and chips.
However, the big issue was the issue of whether the oscillator board would be a good substitute for an actual fundamental crystal. That was the question, and the answer is yes and no.
Before I continue, let me just explain how to hook up the board. In the photo above you can see one chip installed. That chip is from Digi-Key and is programmed for 14.030 mhz. The board has DC power leads 8 to 15vdc is okay. The blue wires are you output from the board, and the black wire switches the oscillator on and off by grounding the chip. For example, my black wire runs from "Ch1" to Com. When connected, this causes the 14.030mhz to the output (the blue wires). In essence, you can plug in the blue wires where you would ordinarily plug in your actual crystal.
Yes, the oscillator board with a chip installed definitely produces an oscillation right on the design frequency. For example, I bought four chips. I tested only the 14.030 mhz chip, and this chip produced an output when subbed in for an actual crystal in a homebrew transmitter at exactly 14.030
So, yes, the board and chip do provide a precise oscillation frequency.
The no part is that you cannot "pull" the chip via changing the impedence in the circuit. What this means essentially, is that my test transmitter, which is a 5w or so crystal controlled transmitter CAN be varied in output frequency by about 15khz when using an air variable in the circuit (as it is designed). With the board in place of the crystal, there is no "pulling" of the chip to allow for frequency variation. The short answer is that if you want to sub the board for a crystal and then vary the frequency using an air variable capacitor (as is common in a lot of homebrew simple transmitters), this will not happen.
What does this mean for the QRP operator? Well, it isn't the end of the world. On the 20m band, you can and should call CQ on 14.060. This is the frequency where folks expect to hear QRP signals. In additions, there is no reason why you can't call or answer CQ's on other frequencies even if you are "stuck." For example, if you go to 14.020 or 14.028 or any round number, you probably will hear a CQ. Then you use your homebrew transmitter and make that QSO.
The other good part is that you can put in a 4 pole switch and quickly jump from say 14.020 to 14.028 to 14.030 to 14.060.
The lack of crystals and the cost of finding a new crystal makes the 4 channel board inexpensive and practical for many operators. Once you have the board, so the chips cost you $5 or so. That means you can transmit on a specific frequency for $5....and not have to wait and hope that you can find the correct crystal at your next hamfest.
Of course, other uses of these chip oscillators are practical and varied.
Bottom line: It's sad that you can't "pull" the frequencies of the programmed chips, but at $5 a chip, well that is not a bad deal to give me options for my homebrew transmitter.
73
Mark 4x1ks
1 comment:
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