Jim, Garey,
Thanks for the quick advice guys. I appreciate it. I think I will give
the TR-7 a shot at this. If I find that I'm going too long between
contacts or somebody complains about my signal, I'll just turn up
the power. Like I said, this is just for fun. Unless I start really
doing well, then of course I will get serious. Usually what happens is,
I last a couple of hours and then I find myself in front of a football
game, or throwing a ball for the dogs until their tongue hangs out (or
mine does).
Thanks again,
Bob K6GGO
Bob -
First off, QRP SSB is 5W or 10W PEP. PEP is roughly equivalent to
twice 'carrier' power, so you would set for 5W carrier and then
modulate. A little tough to 'calibrate' without a PEP meter or a
scope. But as you say, you're not too concerned about the 'letter of
the law' here.
The C-Line is not well suited to QRP operation on SSB. I would start
out with the LOAD control at 0, which is a low as you'll get for input
power, especially on the low bands. Then dip the PLATE, and if you
whistle (or tone) into the mic, adjust the GAIN control for 5W
output. This will give you approximately 10W PEP on SSB as seen on a
scope. The WH-7 sees 5W quite easily on the low scale, certainly
close enough for this purpose. The down-side of this method is that
you are setting the output level by adjusting the mic GAIN, and at
very low levels the S/N ratio of the AF stages degrades somewhat. The
(suppressed) carrier also stays at max, so officially your carrier
suppression is also degraded. It would be possible to add some
capacitance on the output to allow a better match at the lower plate
impedance, essentially rotating the LOAD control below 0. The BEST
method would be to load the T-4XC to at least 40-50 W and hang a
resistive pad on the output to reduce output to 5W! :-) Seems kinda
silly though.......
I had some fun years ago by tuning up the T-4XB on CW, then switching
to UPPER SIDEBAND (the non-X position). I worked quite a few stations
including a VK6 before I bothered to measure the output. When I did,
I discovered that it was right at 600 mW. :-)
The TR-7 is considerably easier. I think you're correct about the
CARRIER control not affecting SSB. But you should be able to go to
SSB and adjust the MIC gain for 5W on a whistle or other steady tone.
You should then be close to 10W PEP, and can check with a scope.
Again, you're going to be in a poorer S/N ratio in the audio stages,
plus most of your power is going to be in the cross-over area of the
PA, reducing the 'purity of emissions' of your signal. So once more
it would be best to run 40-50 W output and use a resistive pad to
lower to the desired level.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Robert Fish wrote:
Hi Guys,
As some of you guys know, the ARRL sweepstakes phone contest starts
in a few hours. It looks like I am going to have to some time this
weekend to play radio.
This is, pretty much, an exclusively US and Canada contest. I usually
only compete in the CW contests if at all, but I was thinking it
might be fun to see how many multipliers
I can work with SSB QRP power (5 watts). The only rigs I have working
well right now are a TR-7 and a C-Line.
Which brings me to my question. (quicker than usual, I know). What is
the proper way to run lower SSB power with a T-4XC. I know I need to
keep the Plate circuit resonant no
matter what power I run, but do I lower the gain control until I
reach the desired power in the tune position or do I load the finals
lighter (more capacitance) with the load control until I get
my 5 watts. I want a clean, properly modulated 5 watt signal.
(obviously). In fact, now that I think about it, how do they want you
to measure it? It's not like you can just measure the carrier like CW
or AM.
I guess you just measure the peaks, except I don't have a power meter
that does that well (WH-7). I guess I could just look at the signal
on a scope and do the math. Same question for the TR-7, do I just
lower the mic gain until the peaks are 5 watts? I don't think the
carrier control affects SSB (at least it doesn't when I run PSK31
with the TR-7).
It's not that big a deal really, It's not like I am going to win the
contest. I might win my section, there was only one entry last year
from San Joaquin Valley. I am curious about the right way to run low
power SSB on these rigs, even though that isn't what they were
designed for.
Thanks in advance for your thoughts,
Bob K6GGO
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