++++++++++++++++++++++++++++++++++++++ Date: Fri, 4 May 2001 17:02:15 -0400 From: "Don Wilhelm" Subject: Re: [Elecraft] RF Adjustment (long explaination) Joe, I believe the answer to your questions is yes, maybe, all or none! Now that I have been purposely confusing, let me explain: You should believe none of your meters with great precision unless they have been calibrated against a known accuracy standard. If you have not done so, take any readings that you may see with a grain of salt, and size that grain of salt to be +/- 20% of what you are reading unless you know that a tighter tolerance is valid. So what does that mean for your specific question - well, the K2 does not spec the accuracy of the power output display and until proven otherwise, a display of 5 watts out can actually be anywhere between 4 watts and 6 watts. BTW - for the K2 this is the average power - which for CW or PSK31 idle tone is the same as RMS power (not the same for SSBs irregular voice patterns though) - to determine what your external meter is reading, you must know the specs for your particular meter. Please don't stop at the K2 - because your external power meter can have the same inaccuracy, and at the 5 watt level it could be off by as much as 1 watt in its indication too. So what if the K2 is reading 1 watt lower than the actual power out (the K2 power out is really 6 watts) and your external meter is reading on the opposite side of the tolerance, and is looking at the 6 watts from your K2 and displaying 7.2 watts. This situation is termed cumulative error. I have used extremes as an example, and most of the time things are not really as far out as I have mentioned. In fact the more common is for the tolerances of several meters tolerances is to narrow the actual error by averaging rather than going to the extremes I stated. Unfortunately with digital displays, we have an inate tendency to believe the number that is displayed is the real thing. This seemed to be better understood when all we had was analog meters - folks seemed to better grasp the concept of errors in the readings - with an analog display one always has to preface any reading with 'about'. An additional truth is that even digital displays may be in error by +/- 1 count in the last digit displayed, and any meter that is speced properly will state that in its statements relating to accuracy. I have not really answered the question of which is right, for without additional calibration information, there is no right answer. If you can obtain a claibrated DVM and RF probe (combination calibrated together) or a calibrated oscilliscope, you can read the actual RF voltage being fed into a (calibrated) 50 ohm load, calculate the power and by that means determine which meter is correct (if either). Until then, you will just have to make an assumption and go from there. 73, Don Wilhelm -Chapel Hill, NC W3FPR home page: http://www.qsl.net/w3fpr/ QRP-L # 485 K2 SN 0020 mailto: w3fpr at arrl.net - ----- Original Message ----- From: "Joe Wittmer" > > Where should I be reading the RF power - at the K2 or the tuner? > > And, if I adjust the power level on the K2 to 5 watts and reflected power is > zero. Why am I transmitting more than what I have set on the K2 power > adjustment? +++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 04 May 2001 21:06:59 -0400 From: Charles Greene Subject: Re: [Elecraft] RF Adjustment At 02:29 PM 5/4/2001 -0500, Joe Wittmer wrote: >Hi Group, > >After performing the ALC modification to my SSB adapter, I no longer saw >abrupt changes to my forward power on the meter (MFJ 949E). Before the >modification I would see peaks ranging from 5 to 8 watts as I transmitted a >singal on PSK. On RTTY, I saw minor fluctuations to the forward power, but >still some fluctuation. > >Now that I have performed the mod. There is more of a continuous transmitted >forward power. It is a little above 5 watts when I transmit. Now reading >Ron's post to my IMD question... I question my operation practices... > >Where should I be reading the RF power - at the K2 or the tuner? Which tuner? KAT2? How are you reading the power? >And, if I adjust the power level on the K2 to 5 watts and reflected power is >zero. Why am I transmitting more than what I have set on the K2 power >adjustment? As Ron said, you should adjust your power level control to something over 5 watts (try 6.5) then adjust your audio drive until you get 5 watts peak on an idle signal. If you use a program that has Tune, put it in tune and adjust the drive until you get 5 watts. When you transmit text, the power varies up and down a bit, but this is normal. If you have a "real" peak reading SWR/power meter, your power on idle will read 5 watts. If you have an average power meter or some of them that say peak but aren't, your power will read 2.5 watts on idle. It will increase as you type text. I have a Daiwa SWR/Power meter that says peak but it isn't. I also have an Autec WM1 that says peak and it is. 73 Chas, W1CG +++++++++++++++++++++++++++++++++++++++++++++++