[Elecraft] Noise gen

[Ron D'Eau Claire]

No pitfall that I can see, Steve.  The noise bridge should be FB!  All you
want is a noise source that is constant in level over the range of a few kHz
that is strong enough to see on your display. 

The kits are a great convenience. Convenience always cost a little extra
<G>. One time when I got frustrated by not having a an antenna at my
workbench that picked up enough noise, I built a noise generator completely
out of my junk box. I think all the parts new would be under US$10 new. Tom,
N0SS, published the layout on his website. It's at http://tinyurl.com/4qggr

I used a little plastic box I had picked up at "Tap Plastics" - a retail
plastic goody outlet that is all over the country, I think. The key is short
leads. It's strong enough that I have to replace the box. I dropped it down
the stairs onto the concrete shop floor and broke the case, but some tape
keeps it working FB <G>. Such point-to-point construction is really very,
very strong. 

And it puts out very useful noise levels for peaking circuits from a few
hundred kHz up through 440 MHz. 

Ron AC7AC



-----Original Message-----
Ron:

Your points are well taken.

Clearly a calibrated noise generator is overkill.

The problem with a 160/80m antenna is that one is not always conveniently 
accessible.

If a person did not wish to fork over the $40 or so for the Elecraft noise 
generator, it occurs to me that there is one other possibility. Lots of 
hams (including me) have a noise bridge (such as the MFJ-202), and it might 
be a good noise source for alignment. The load port could be terminated in 
either a short, an open, a 50 ohm fixed load, or practically anything else. 
All that would be necessary is being sure that the tunable impedances in 
the bridge are set such that they are well away from the impedance of the
load.

Does this approach present a pitfall that has not yet occurred to me?

73,

Steve
AA4AK




>Ordinary background QRN on 80 or 160 meters works FB too. Just avoid 
>any frequency where a signal falls within the bandpass. If the 
>background QRN is not loud enough for someone on 80 or 160 (lucky, 
>lucky you having THAT QTH!) just turn on the Preamp.
>
>I use a noise source only when I'm in the shop away from an antenna. 
>There's absolutely NOTHING about a noise generator in this application 
>that makes the alignment any more "perfect". The noise source is just a 
>convenience. At times when an antenna is not available it's a 
>convenience well worth having, but that's all it is.
>
>Ron AC7AC
>
>
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