output alignment #20m #40m #power
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Syd, the 20 meter filter almost always needs L3 to be one or two turns less than specified and expanded somewhat. You can verify this by expanding the turns on L3 fully and if the power is still increasing when fully expanded, then remove?one turn and continue. Don't remove more than 2 turns. L2 is usually as specified ?but compressed and L1 is usually as specified but expanded somewhat. The 40 meter filter almost always comes really close with the specified turns. So if your 40 meter one is not working right, ie. very low power and no changing, then you need to check the soldering and do a continuity test from the BNC connector center pin to the C29 end of L3 and fix any open connections you find. It's a good idea to do this check on both of them. Hope that helps .. 73 .. Ron On Wed, Oct 27, 2021 at 3:13 PM Syd via <nhuq1=[email protected]> wrote: I have two kits (20m & 40m) that need the band pass filters aligned. Hans's tutorial on aligning this section by compressing and decompressing the inductor turns to figure out how many turns to add or subtract from the coils was quite instructive, so I gave it a try on both kits.? I see the power on these kits was 1w and 0.5w so alignment is needed. When I compress the turns on L1 - L4 and measure the rf level for reference on the scope, resulting in the low power,? and then decompress? the turns I never see the output level change either way. On the 40m? unit I removed 5 turns on L1 and got no change in the output.? The 20m kit has less turns to monkey with and easier to compress, so? I'm mainly working on that one first.? Compressing and decompressing the turns on these coils shows no change in output level: very low. The? only thing that I can think of doing now is to go back and add 10 turns to the original 40m unit to see if I'm going in the right direction. |
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Syd, I just finished a QCX+ (40M) build. I had to remove 7 turns from T1 to get the trimmer capacitor off the fully open position. The BPF (8.7) moved up as I removed turns. I did not bother going through the hole for this, I merely left about 1/4" of wire from the board and soldered the shortened winding to it. I then checked power output and found none, though an adjacent rig could hear it. It turns out L4 had a bad solder connection, easily fixed with a few seconds of soldering iron heat and a dab of flux. I then had .7 watts, so I spread out L3 and got it up to 2.7 watts. That was my clue to remove a couple of turns. Between that and tweaking L1 and L2 (mostly L2) I got it up to roughly 4 watts @ 13.8V. That's less that I'd like, but one more watt would make almost no difference to a receiving station so I quit there.
I have since made a bunch of great contacts.? |
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Syd, one time out of over 60 repairs of QCX rigs: Classic, Plus and Mini, I found an issue with a 20 meter version that was doing this same thing. In that case the two middle capacitors (390 pf) were both labeled 390 (39 pF) instead of 391 (390 pF). BUT... very interestingly, one of them measured 39 pF as expected but the other one measured 390 pF. So I replaced the one that was only 39 pF and the problem was corrected. This is probably so rare as to not be the case with you but worth looking at. You should be seeing some good variations in output with all the adjustments you've made. The most dramatic change should be with adjustments of L3 and the least dramatic with L1 as you are matching the filter input impedance (L3 end) to the final transistors and the filter output (L1 end) to your 50 ohm dummy load. Since you have good continuity through the toroids, I think you should?take a closer look at the 4 capacitors at this point. Good luck ... Ron On Sat, Oct 30, 2021 at 2:09 PM Syd via <nhuq1=[email protected]> wrote: So far I have removed 2 turns on L1, expanded and compressed the windings before and after the change, and see no output change on the scope. So I added 4 turns back on the coil and tried expanding and compressing the windings again: still no change on the PP on the scope! So I went to L3 and tried the same procedure. Expanding and compressing the turns with the original turns and with 2 turns removed and then 4 turns added still got no change on the scope.? Since I do see a sine wave the filter must be doing something.? No matter which coil I fool around with, L1 - L3, expanding and compressing the windings either in the original number of turns, or when I remove 2 turns, or when I then add in 4 turns, I always get the same PP on the scope!? The continuity from C29 to the rf output is OK:? 0 ohms. So either the filter is way out of specs (the number of turns is OK according to the table) or I'm not adjusting the number of turns by enough windings to get to where the filter can operate properly.? Assuming the caps, C25 - C28 are the correct value I need advice on which coil to focus on and how many turns I should add or subtract from the coil to try to get in range for proper operation.? Obviously 2 turns is not enough.? It's quite hard to read the cap values after being installed on the board, so just to make sure they are the correct value I'll probably go to DigiKey and order some replacement caps just to eliminate them being the problem. Any ideas as to which coil is the most important to fool around with first and how much should I add or remove the turns? |
Ronald Taylor
K9NUD-Steve
Julian N4JO