Yes... And Dave, If you haven't done so yet, you may have to run the formula that Jack describes in the QST article in order to get the VFO calibrated perfectly. We breadboarded this project every step of the way... adding one piece at a time once parts started arriving from China. When the DDS board arrived, we hooked it up to the Nano and tested the output. With a small antenna coupled to the DDS and a portable shortwave radio's antenna, we fired it up and looked for a carrier. With the VFO dialed up to 7.040, we found ?the carrier way off frequency. Of course, we weren't expecting perfection since this was the DDS right out of the box and the code directly from Farrukh's website. No modifications other than some customized splash screen elements were made to the code at this point.
We ran the formula for calculating the Tuning Constant and made the correction in the code. Once we did that, problem solved. Solid carrier on 7.040 and the 49-er is pretty much dead on frequency as well
Aaron - N2HTL
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Don't forget that the crystal on the DDS board may not be exact and you should expect some deviation. The article details how to correct for the "slop" you may find.
73,
Jack, W8TEE
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Thanks for the response Aaron.? I haven't had time to investigate what is happening yet and won't get a chance to do that until next week sometime as I'm getting ready for a short trip.? My DDS is off a couple hundred cycles, but I will correct that next week also.? I'll keep you posted on what I find.
Dave, W0DF
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Hi Dave.
I have to admit that I haven't but I certainly will now. When I fired up the DDS controlled 49-er for the first time, I checked it against my frequency counter to see what it was doing. I was quite pleased that the VFO was showing 7.100 and the frequency counter was showing the output on 7.099.4 or something to that effect. I made the test which the radio putting a signal out directly into my 40m dipole and not into a dummy load since it was such a quick test.
While I'm not sure testing for harmonics on a frequency counter is the best method, I can tell you that over the summer I built a two tube QRP crystal controlled 40m transmitter into a coffee can. When I fired that thing up for the first time, it was radiating harmonics STRONGER on 14.110 rather than on 7.110 - which is the crystal I had installed. Turns out the coil I was using was too small, the wrong diameter, and my tap was in the wrong spot. Once I corrected the coil, the radio operated where if was designed to.
My point is that the frequency counter caught it right away that the transmitter was way off and in danger of getting me in serious trouble.
Aaron - ?N2HTL
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Has anyone looked at the harmonics on their 49er.? I must admit that my testing method is primitive but looking at the 2nd and third harmonics on my K3/P3 panadapter, the 2nd and 3rd harmonics on mine are progressively stronger than the fundamental.? I have my 49er (Frog Sound) xcvr terminated in a 50 ohm dummy load sitting on the desk next to my K3 that is terminated in either another 50 ohm dummy load or a ground mounted vertical antenna that is roughly 30 feet or so from the K3.? In both cases, the harmonics on 20 and 15 meters are stronger that the 40 meter signal, somewhat stronger on 20 meters and much stronger on 15.? Has anyone else checked this?
Dave, W0DF
