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BITX 40 - DDS right connection
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Hi Ashhar, i have two questions: 1. when connect ?DDS or External VFO do I need to desolder only the L4 coil and disconnect the tuning potentiometer? 2. I have replaced the six resistor to 220 values to try to reduce the drift, unfortunately it work good in rx but less in tx mode becuse the temperature increase ... now i go to move to dds, the uestion is: ?It is better to resolder the old resistors with 100 ohm vlues or i can continue to use the present values of 220?? Thanks for replay.? I do some QSO with success. Thank you again for the project. Giuseppe, IK8YFW |
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I think all you have to do (if you use the DDS tap) is to remove the VFO Tuning Pot from it's? 3-pin
connector (TUNING1) This removes the voltage to the Toroid / Varactor pair - no oscillation and no current will be used. I was happy to see that the DDS connection is placed before the buffer transistors (Q7, Q8, Q9), so there's a bit of gain for your AD9850 / Si570 / Si5351 / whatever you're using. Sadly, for me, it's the end of a long holiday, so I may not achieve the DDS VFO today. Mike Yancey, KM5Z Dallas, Texas |
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Thanks Mike.?
Today I done a fast test with my 9850 based dds, it work well but input signals was weak than the original vfo.? Then i think that the level of dds signal need to be buffered to work with passive diode mixer, or i need to desolder some components to prevent to drop dds signal to ground. We need to do more experiments...this is also the purpouse of the project. :-) Bye. |
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Mikele Martincic
i think that dds with ad9850 have only -6dbm ,you have put one small amplifier ;) 73 de 9a3xz
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Thank you for the AD9850 info!
Well, I had a little Arduino + an AdaFruit Si5351 already setup. I had been experimenting with a 10 Mhz based BFO / VFO combination, and the Si5351 will provide up to THREE (3) signals (a waste of ONE signal!). However, I changed the code, hardcoded the VFO to my (measured 11.998847 Mhz), and changed a couple of other things - and it WORKS! Insanely stable, of course. However, I'm not seeing much of a difference between 'Varactor / Pot' VFO and DDS VFO in incoming audio volume or quality. Of course, the Si5353 is a square-wave clock - not sure how much that brings. I see the CQ WW CW DX contest is still going on!! LOTS & LOTS of CW signals to hear. SSB is clear. I'm goin' with the DDS VFO, but I'll try the AD9850 - seems a waste of two 'clocks' to use the Si5351, and perhaps I can re-purpose it for something else down the line... Maybe I'll see a difference there, I dunno. Mike Y |
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Jack Purdum
The VFO we built for the Forty-9er (March, 2016, QST or see:?)?has buffered output if needed. Two sets of header pins? allow the user to pick off the drive they need. Farrukh charges $7 for a good quality PCB and he also has a kit with some of the parts for $15 (not including the AD9850 or the Nano). The software to drive the Nano is a free download. You can download the assembly manual I wrote for the article, which should give you a good feel for what's involved. 73, Jack, W8TEE From: "ik8yfw@... [BITX20]" To: BITX20@... Sent: Monday, November 28, 2016 1:27 AM Subject: [BITX20] Re: BITX 40 - DDS right connection
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Thanks Mike, this is a good news. I will try to use a small amplifier to output the 9850, mybe it will help a lot. I've used the 9850 with a ne602 based receiver with success. I think that a couple of 2n2222 will solve the problem.I Hope to test it in the next days or in the weekend.? 73 ik8yfw
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Mark W
开云体育This is the VFO I am building for my BitX 40. Just started it tonight. Mark K3MRK ? ? From: BITX20@... [mailto:BITX20@...]
Sent: Monday, November 28, 2016 9:20 AM To: BITX20@... Subject: Re: [BITX20] Re: BITX 40 - DDS right connection ? ? The VFO we built for the Forty-9er (March, 2016, QST or see:?)?has buffered output if needed. Two sets of header pins? ?
? allow the user to pick off the drive they need. Farrukh charges $7 for a good quality PCB and he also has a kit with some of the parts for $15 (not including the AD9850 or the Nano). The software to drive the Nano is a free download. You can download the assembly manual I wrote for the article, which should give you a good feel for what's involved. ? 73, Jack, W8TEE ? From: "ik8yfw@... [BITX20]" <BITX20@...> ? ? Thanks Mike, this is a good news. I will try to use a small amplifier to output the 9850, mybe it will help a lot. I've used the 9850 with a ne602 based receiver with success. I think that a couple of 2n2222 will solve the problem.I Hope to test it in the next days or in the weekend.? 73 ik8yfw ? |
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I made successfull QSO with dds vfo.
I add a 9850 based vfo plus a 2 x 2n2222 buffer amplifier to increase dds output signal. I connect the vfo to external input pin of bitx 40, before I removed L4 coil and C91 to avoid to send a lot of signal to ground. Now I have the same sensitivity that original VFO, but absolutely no drift. I Done 6 QSO with good reports. 73 ik8yfw. |