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@hotmail.com
> Date: Sun, 19 Sep 2010 21:27:51 -0400
> From: robrk@nidhog.net
> To: w7ry@inbox.com
> CC: amps@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).
>
>
> --
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|