Re: IA QRP-10 RX Specs

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From: Jim Kortge, K8IQY (jokortge@prodigy.net)
Date: Sun Dec 31 2000 - 18:31:34 CST


At 11:30 AM 12/31/00 -0700, you wrote:
>I just check the NorCal page for the latest on the IA QRP-10 building
>project. There Jim Kortge, K8IQY reports the following RX specs:
>
> MDS -130 dBm (That's less than 0.1 micro volt
>folks)
>
> Filter Bandwidth 230 Hz (Missed the design bogie by 20 Hz)
>
> Minimum Opposite
> Sideband Rejection 62 dB (Very good for a 3 pole filter)
>
> IF Rejection 110 dB (Excellent for any rig)
>
> Image Rejection 70 dB (Very good for a simple superhet design)
>
> Rx Current Draw 35 milliamps (VXO and receive strip combined)
>
>
>OK, we're talkin' 10m. Layout, lead length...etc have strong influence
>on performance. Things get "jiggy" at 28MHz ;-) What construction
>practices/techniques/layout...etc. Have the greatest effect, so as to
>reproduce these excellent specs?

Hi Rod,

Well here is my 2 cents worth on the subject. First, keep the
leads as short as possible, and don't run leads of caps, inductors.
and resistors parallel to each other. Ditto on the components; keep
them at 90 degrees to each other if at all possible. Same is true
for inductors that are on the input and output of amplifier stages,
or parts of input or output filters. Or offset them so that their
fields can't interact. Set drive levels to the minimum required
to drive the next stage adequately. Shield critical circuits
from each other, so they can't interact. And finally, build over
continuous ground planes when ever possible using Manhattan-style
construction or dead bug. These methods reduce circulating ground
currents which can cause all manifestations of instability.

The pads used in Manhattan-style construction also afford small
decoupling capacitances at each node, which in most cases should
enhance stability.

Overall, a good layout where the sigals flow from one section to
the next without doubling back adds to stability and low noise,
everything else being equal. That's why it is important when
starting the layout of some circuitry to "fiddle with it" on
paper before building the real thing. And one must not be in
so much of a hurry as to rule out tearing out a whole section
if you see a much better way of doing the layout after you have
70 or 80 percent of it built. I've done that many times, and
always was glad that I made the choice. Besides, most of the parts
are then already pre-bent, ready for reinstallation! :-)

There are probably other considerations that don't come to mind
at the moment, but that's my New Years eve brain dump on the subject.

72 and Happy New Year to all of the QRP-L gang. Year 2000 was
a blast! Many new projects and many new friends. Life is good!

Jim, K8IQY


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