+++++++++++++++++++ See also Low S-meter Sensitivity +++++++++++++++++++ Date: Mon, 10 Dec 2001 08:15:43 -0700 From: Gary L Surrency Subject: [Elecraft] Poor S-meter action Some K2's do have slightly low S-meter action. But first be sure there are no problems in the rig that might actually be reducing the RX sensitivity. Check T6, T7, toroid leads, wrong caps in the IF circuit, etc. Be sure the rig is properly aligned for both the band-pass filters and CAL FIL BFO settings. Check the TX output and T-R switch area too. I have found that the S-meter sensitivity can be improved by selecting a silicon diode for D1 on the control panel that has a little greater Vf , or forward voltage drop. Use your DMM diode test function to sort through any common silicon diode and pick 2 or 3 of them that have the *highest* voltage drop. Then try them in the control board. Be sure to reset the CAL S LO and CAL S HI values, since they will change slightly with the new diode. I installed gold IC socket pins so I could easily swap the diodes. The original 1N4148 had about 0.550Vf and the one I picked that gave me the S-meter response I wanted, was about 0.630Vf. Note that the diodes temp will affect this reading, so do this at room temp and allow time for the diode to cool if you handle it or when it is soldered. The BE junction of a typical NPN transistor is close to the ideal Vf, so you can also try a PN2222A or 2N3904, etc. if you cannot find an appropriate diode. Use the Base lead for the anode, the Emitter for the cathode, and fold the Collector out of the way or clip it off. Also, many K2's have LM2930T-8 8V regulators that are quite a bit on the high side of their output voltage spec. Some can be as high as 8.3 to 8.4 VDC. Although this will actually benefit most of the circuits that operate from this bus, it can elevate the no-signal or weak-signal AGC threshold voltage, so the AGC is slightly acitvated. If you notice a fairly large drop in RX hiss when you turn off the AGC (press PRE/ATT + AGC together), then you may want to decrease the value of R1 (also on the control board) from 51k to 33K. This has much the same effect as if you could turn the RF Gain a little further clockwise, and the RX sensitivity will be better than before on weak signals. These two "blueprinting mods" work together, and will in most cases result in a much more responsive S-meter and better weak-signal RX sensitivity. We wanted to avoid any kind of trimmer adjustment in the original AGC circuit, but component tolerances in some rigs require a little tweaking if you are looking for the absolute best operation. Elecraft Tech Support Gary Surrency AB7MY support at elecraft.com On Sat, 8 Dec 2001 14:21:38 -0000 "Paul Barlow" writes: > Dear Elecrafters, > > this mya seem a usual, or even a silly question. > > I'm a bit flummoxed about the K2 S meter readings. I can't decide > whether my > IF gain is OK, or whether the meter is just stingy. > > The whole thing is confused even more because I have recently moved > QTH, so > it may be that my new antenna is just not a good as the one in my > previous > QTH. > > For example on 80m I worked a local(ish) guy who gave me 589/599 > whilst the > meter only showed 559 for him. (5W both ways) > > Comparing the meter with the meter on my FT817, perhaps not a > scientific > test, signals that are showing s7/8 are showing s9+. This is "like" > to > "like" with preamp settings etc. > > I *know* s meters are a source of contention, perhaps a waste of > space etc. > etc. etc. but I'm concerend that my K2 is not 100%. > > The basics are: I can hear band noise when I connect a matched > antenna. To > give "like for like" meter readings on 40m I have to have the preamp > ON. > > There is plenty of audio from the internal speaker, I have the gain > control > at 9 o'clock. > > A bit of helpful advice would be appreciated. > > 72/73 > > Paul M0CDP GQRP 10289 Fists 5579 ++++++++++++++++++