Another Question

[J. M. Blackmon]

How about applying a stead tone for a short period of time and noting the power a second or two after applying it- this should give you a good indication of steady-state power capability as well as what you are putting out at peaks.  Also, what do you put out when tuning, in CW mode, for a few seconds?  This would be another indication of the general state of things.

Jeff, W8YI

w1id wrote:

> On Wednesday, January 10, 2001 at 08:52:36 PM, reds1964 wrote:
>
> > Hello All,
> >
> > I have a question about power output from an AM transmitter as read on a Heath HM-102 wattmeter. When I turn the transmitter on in the AM mode the wattmeter shows 10 watts with no modulation. With modulation the wattmeter kicks up to about 20-25 watts. This is supposedly a 100 watt transmitter. I am assuming that the HM-102 is a peak reading wattmeter,so is the 25 watts my actual output power,or is it some multiple thereof, or in other words, would my power output with 100% modulation actually be 100 watts,PEP? I forget how to figure PEP so maybe you guys and gals can remind me. On the CW mode I get about 50 watts,but I have normal plate current 250mA or a little less since that is the max value for the 6146's, drive level is entirely sufficient,even over sufficient as I have to lower it a bit most times, so why don't I get the full 100 watts? I am using a dummy load for testing, the dry variety. So,do I need new finals, does my wattmeter need adjusting, or do I need to stop!
>  asking stupid questions? By the way, the transmitter is the Knight T-150A. Hope this doesn't open another can of worms about this particular transmitter.
> > Any help would be greatly apprecitated.
> >
> > 73's
> > Carl
> >
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> I don't have my T-150a manual handy at the moment but it is a controlled-carrier screen modulated transmitter. I would normally expect the resting carrier to be at some low value without modulation. With modulation it would kick up to some higher value but much less than the CW output. I always question the calibration and accuracy of test and monitoring equipment. Even more so in the case of the HM-102 because it was obviously a kit and I don't know to what standard it was calibrated to. No disrespect intended to you or whoever built and calibrated it. I also have an HM-102 and I always take its readings with a grain of salt. The filter capacitor used in the meter is of some low value which won't show PEP (either 0.001 or 0.01uF). I believe it shows average. There was a popular article in QST many moons ago whereby the author modified his HM-102 to measure PEP with a couple of op-amps. I remember building it to verify that it really worked then discarded it because it require!
> d a pair of 9 volt batteries and I always seemed to forget to turn off the darn thing. I also believe the article was not clear as to the adjustment procedure. You had to adjust for zero and max as shown on the meter and this had to be repeated until little change was shown in the final setting. It was reminescent of alignment of a VFO or receiver LO. There was also a small amount of drift as there was no voltage regulation and I had to use carbon composition resistors tho breadboard the circuit. Finally replaced the capacitor in question with a 0.1uF to get a better indication of modulation percentage and that's the way it remains to this day. One more thing, I always find it very helpful to monitor modulated transmitter output with a scope. Controlled-carrier modulated transmitters can be tricky to adjust for best quality output but it's a breeze with a monitor scope.
>
> w1id
> e-mail: w1id at fcgnetworks.net
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