[Amps] reading and tuning

[Charles Harpole]

READING... It is rather difficult to get closer than 10% measuring your RF output due to meter variations at the ham finance level.  The Bird wattmeter is the silver standard, but the gold and platinum meters of other brands/models are more costly.  The Bird can be fitted with peak reading, a Bird mod, but it requires batteries inside the unit which die very fast if the peak function is left on and which are trouble to replace due to screwing the case open and closed..  Read the Bird claimed specs and see the latitude.
Other ham-grade wattmeters run in the 20% to 30% error margins.  The Elecraft Wattmeter I have reads 160 watts from my 200 watt radio into a 50 ohm dummy load, for example.  The Elecraft is a toy that lights up.  Many other brands run in the same league, but most do not light up.  I have never tested the Alpha meter and wish to hear user reports on it.  Also, I need information on the use of Ampere meters measuring RF output.
To get an approx. of RF out, use a straight key or switch to key your rig on CW mode.  That is "key down RF out."  Some folks switch to FM mode to output RF, but it is possible that that mode (transmitting at full output) does not output the same RF level as the CW test will give.  AM mode on most rigs nowdays outputs much less than full CW power.
Measuring RF out in SSB voice mode is even more difficult due to many variables, including meter inaccuracies (which are inherently greater in peak mode) and your voice characteristics which may not be graphic equalized for max out.  The "two tone test" provides two different audio tones to the rig which should give a good indication of SSB voice RF output because this kind of input is at a steady level (unlike voice) and also includes two voice audio freqs. to simulate voice keying.  
Note: please do not whistle or "aahhhh" or growl in the mic to do tests.  Not only does it sound stupid to your listeners, these audio freqs. are so unlike real voice as to give false peak readings.  Some claim a loud whistle into some mics actually destroy some mic funtion due to overload.
TUNING....  The best and simplest way to get RF from ur exciter to tune your amplifier is to use "CW key down RF out" mode.  That is, to key your exciter via a CW Morse key or a switch, adjust the exciter output to desired level (50 watts average usage), then un-key and turn on the amp.  Then, key the exciter again and tune your amp for correct match and output.  A Morse key allows you to un-key quickly if needed and many keys have a key-down-locking-switch on them for that application.
The problem with this "best" way is that many exciters must be manually switched to CW mode to get the above action which inserts more activity by the operator.  However, the new Yaesu 9000 line, for example, allows instant CW keying from the ssb voice mode... just close the key and the exciter is putting out RF with the added bonus of remaining on your SSB frequency (should you wish to work someone in two modes on the same freq.).  Some modern rigs allow this function, but they do not shift the xmit freq to match the SSB pre-existing freq. 
Interestingly, Alpha manuals say to tune for max out and say nothing about dipping the plate or the other old ways.  This is called "tuning for max smoke" meaning that one should not bother too much except to get max out (and WATCH THE GRID CURRENT to keep it low enuf).  This is probably good advice since "max out" should be also the best resonant point in matching the antenna via the pi net in the amp to the amp.
73, K4VUD



Charles Harpole
k4vud at hotmail.com   



> Date: Sun, 19 Sep 2010 21:27:51 -0400
> From: robrk at nidhog.net
> To: w7ry at inbox.com
> CC: amps at contesting.com
> Subject: Re: [Amps] HF AMP Issues questions
> 
> On 9/19/10 4:42 PM, Jim W7RY wrote:
> > BUT you can only see the real output power if you have a peak reading
> > wattmeter. If you have one, your good. If you don't you cannot read the
> > real power output of the amplifier.
> >
> > 73
> > Jim W7RY
> 
> 
> BUT you can if you have a straight key and any wattmeter (or an FM button on the 
> radio).
> 
> 
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