The Radiokit just went out the door on its way to Doug. Hope it still
works when it arrives. It's been fun. I'll write a summary when I get a
chance to breathe again.
Mike K1MG
The Honorable Chuck Adams, K5FO, Esquire
Dallas, TX 75218
Most esteemed and exalted Judge:
Herewith is the debugging contest entry, submitted by your most humble
servant, K1MG. I entreat you to examine it carefully, it being the best
effort of KA5T and K1MG, and judge whether you deem our efforts worthy, and
hand down your decree for all QRP-Lers to follow.
A few notes about the results, if I may:
We have adjusted the tuning range for about 6.994 MHz to 7.140 MHz.
Although it could be tuned just a little higher, this is my personal
preference since I spend a lot of time down near 7.00001 MHz. I feel the
rig is stable enough to operate at the bottom end of the band as long as
you are careful to check the dial calibration.
The AGC loop oscillation is gone. The IF oscillation is gone, but to be
sure, the rig would have to be tested over a long time under a wide
temperature range. I have adjusted the IF gain so that it is completely
stable so far at my QTH, but being greedy, I kept it as high as I dared in
order to keep the receive sensitivity up. If the receiver does start to
get unstable, it will appear as a loud click in the headphones. The gain
can be reduced a bit more by turning the AGC threshold pot just a hair
counterclockwise as viewed from the front of the rig. Nice receiver. I
heard lots of fox hunters working N6WG.
In my opinion, the AGC hang time is excessive. I confirmed that it
operates exactly like the original design should, but my personal
preference is for a very short AGC time. If the rig were mine, I would
replace the AGC cap with a much smaller one. Especially annoying to me is
the fact that, since the AGC acts on the transmitted signal to keep the
sidetone volume reasonable, it takes a while to recover when switching to
receive, further aggravating the semi-QSK nature of the design. Also, the
transient associated with the relay switching on tends to overdrive the AGC
when the rig is first keyed, and the AGC takes too long to come back up.
This is just my personal criticism of the design; others my not find it
objectionable.
I have backed off the power output level of the transmitter just a bit,
favoring quality of signal over power. It puts out nearly 3.5 - 4 watts
into a dummy load, maybe a little less into other than 50 ohms. Three
watts is plenty for me, and I prefer the cleaner signal. The rig would be
capable of much more power with a redesign of the output circuit, which is
beyond the scope of this exercise and a dumb idea anyway.
Don't forget that the main tuning is backwards because of the subtractive
mixing scheme.
Please, oh please, don't plug the power supply into the antenna jack. I
would recommend that the new owner change the power plug to something other
than a phono jack. Also, the headphone jack is a mono jack. Stereo
headphones will only work in one ear. Please note that the rig requires
13.8 volts minimum. It was not designed to work on 12 volts, as the
internal 12 volt regulator goes out of regulation with less than 13.8v.
The center pin of the phono plug is positive.
There are a few minor spurs in the receiver, but they become unnoticeable
when listening on a band with live signals.
Enjoy!
Mike K1MG
[
QRP-L Archive |
]
[
1993 |
1994 |
1995 |
1996 |
1997 |
1998 |
1999 |
2000
]