Keith KD1E wrote: I'm still wondering how hard it would be to hook that LDG meter up to the K2 to give me a real analog S-meter!
One of the things I've noticed about the K2's AGC is that it doesn't seem to boost gain as high as my 830s. In other words, it will allow background noise to remain in the background. I need to spend some more time under the cans with both rigs to get a better long-term feel for them. ---------------------------------- The K2, like many modern receivers, has very limited "RF gain control" range compared to receivers of years ago that had multiple I.F and R.F amplifier stages active on all bands. In the K2, the only stage controlled by the AGC or the RF gain control is the I.F. amplifier. Like many modern receivers, the K2's front end or "RF" gain is manually controlled by switching a preamp or an attenuator in or out. That gives you another 24 dB control over the total gain, but that's not controlled by either the RF gain control or the AGC. The K2 uses an MC1350 I.C. It has a maximum gain control range of perhaps 60 dB. Now, in rigs like the K2 with their excellent dynamic range that's enough when it's coupled with manual control of the front end gain but, as you noticed, it's not enough to silence the receiver when it's turned all the way down, particularly if you have the preamplifier switched on. I agree with your lusting for a real meter on the K2! I've considered doing exactly that many times. It should be straightforward to do. The MC1350 uses an analog d-c voltage to control its gain. The voltage runs, typically, from +5 to +7 vdc to vary the gain of the MC1350 over its range. That voltage is applied to pin 5 of the I.C. There are times when an S-meter with good resolution is handy for more than just having fun watching it jump around. Comparative signal reports, for example. But it takes a meter than can be read with some accuracy. An S-meter, even if it's not calibrated to any particular standard, coupled with a step attenuator like the Elecraft AT1 at the receiver antenna input can provide very useful checks. When the other station makes a change, you note the change in the "S-meter" reading, then switch attenuation in or out to bring the meter reading back to the original level. Then you know the exact effect of the change in decibels. Once you know the difference in dB the signal has changed, it's easy to equate that to the change in "apparent power". For example, if a change raises the level of a signal such that you have to switch in 4 dB on the AT1 to bring the S-meter back to the same reading, you know that the change had the same effect as if the other station had raised his transmitter power 2.5 times, say from 5 to 12.5 watts or from 100 to 250 watts. That procedure works equally well for helping someone else understand the effects of change at their station or for doing A/B comparisons of two antennas at your own station while listening to signals on the air. Recognizing that a lot of folks don't like poking at calculators, the AT1 manual even includes a look-up table where you simple find the dB of attenuation changed and next to it is the value to either multiply or divide the original value by to see the change in watts, volts or amperes. A suitable interface using a simple op-amp circuit to prevent loading the AGC line in the K2, coupled with an adjustable offset to zero the meter with the maximum gain voltage applied to the MC1350 should drive just about any meter movement you can think of One of these days I'll get around to it. In the meantime, I'll continue to do it the "hard way" and carefully adjust the K2 so I'm certain it is not overloaded, turn the AGC OFF so the audio output accurately follows any change in signal level, and monitor the audio output at the headphone or speaker jack. But that loses all the "pizzazz" of the big S-meter! Ron AC7AC -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Darwin, Keith Sent: Monday, October 16, 2006 12:13 PM To: elecraft@mailman.qth.net Subject: RE: [Elecraft] Re: When do you use fast AGC? -----Original Message----- Still, top o' the line receivers like the K2 feature I.F. AGC that is far more versatile than the receivers with those huge S-meters. And maybe the piddlin' little bargraph puts the real value of an "S" reading in perspective <G>. Ron AC7AC -------------------------- Yea, I have 2 rigs, the K2 and the TS-830s. I'm not sure which I like better but for now I've been on the 830 most of the time. After last night's QSOs in which I was just struggling to copy signals, I'm about ready to switch back to the K2 for a while. Bar-graph S-meters, yuck! I hear you about putting the real value of an "S" reading in perspective, but I still want to watch that meter move! I'm still wondering how hard it would be to hook that LDG meter up to the K2 to give me a real analog S-meter! One of the things I've noticed about the K2's AGC is that it doesn't seem to boost gain as high as my 830s. In other words, it will allow background noise to remain in the background. I need to spend some more time under the cans with both rigs to get a better long-term feel for them. - Keith KD1E - - K2 5411 - _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. 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