Hi everyone, I just wanted to share my experiences tuning my recently converted Drake downconverter. I failed to hear Dove after doing the IF and Crystal mod. Several people have mentioned that the mod doesn't have the exact offset expected, so I suspected that I was listening too far from the actual frequency. Combined with the doppler and the narrow beamwidth of the Conifer 21 dish, I was probably just tackling too much at once. So, I set about to try to determine the actual offset without having a steady 2.4 GHz signal source at my disposal. As a bit of background, the Drake converter has a crystal which is multiplied X256 and subtracted from the recieved frequency to obtain the output, otherwise known as the intermediate frequency (IF). The mod attempts to do the following: 2400-(8.8125*256) = 144 MHz. I hooked up my frequency counter to a 10X high impedance probe (to avoid loading the oscillator circuit and changing its frequency) and probed around the crystal, attempting to find the crystal's fundamental frequency. At the little chip cap closest to the trimmer cap, I found a solid signal at 8.8133 MHz. This is the cap to the right of the trimmer if the unit is oriented so the N connecter is facing away from you. Running the numbers (2400-F/256) showed that the 2400 MHz comes out as 143.795 MHz, similar to the frequency tested in the Feb '98 QST article. Allowing for doppler, this means that Dove will come out on 144.016 +/- .050, so for a good portion of the pass the signal is out of the band, and my radio won't go out of band! The QST article says to adjust the trimmer and bring it onto frequency, but I could not get enough range to bring it to the desired 8.8125 MHz. Careful tuning did allow approximately 8.81265 , bringing Dove just barely into the 2M band at the lowest extreme of the doppler shift. To be honest, my main counter has not been recently calibrated and I have not yet heard Dove, so there is possibly some error in the measurements. Nevertheless, I did get similar readings on two different counters so I have reasonable confidence in the results. With a 256 multification factor, it doesn't take much change to cause a big change in the operation of the converter! If you are doing the mod and your 2M rig won't go below 2M, I'd recommend testing the actual frequency of the LO crystal and adjust as necessary. If you don't have a frequency counter, you can probably hear it on a general coverage receiver (with the Drake's cover removed). I haven't tried this yet, but have on other crystal oscillators, so it should work. If yours is lower than expected, try tuning the crystal trimmer for the lowest oscillation frequency possible (to move the signal up in the 2M band). Those who haven't yet purchased the crystal for this conversion might want to consider a slightly lower crystal frequency. After all, P3D and the current satellites don't occupy even 1.5 MHz of the band, so if you adjusted the frequency so that 2400 MHz came out on 145 MHz instead of 144, you'd stay more centered in the 2M band and would never encounter this situation. Bleedthrough from strong terrestial 2M signals may be more of a problem, however. So what's next? I may attempt to add more capacitance (or inductance) to pull the crystal closer to the desired 8.8125 MHz frequency, but it is usable as is. I'll let you know how this goes if I attempt it. I'd be interested in hearing any comments or experiences of others doing this modification. How much adjustment did you get from the trimmer cap? Were you able to get the converter aligned so that 2.4 converts to 144 MHz? Any comments on adding more capacitance? 73, John Oppen, KJ6HZ Obligatory disclaimer: These are simply the results of my testing. Your results may vary. Do not attempt this if you are not comfortable probing around inside RF circuitry with test equipment. If you let the smoke out, you're on your own!