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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