A Question From a Dummy - Regarding : [Elecraft] Noise generator

[Ron D'Eau Claire]

Don's point about not overloading a stage when using a noise generator =
(or
any signal generator) is an excellent one.

Next to a noise generator, the next item that I'd recommend for the test
equipment bench would be a step attenuator calibrated in dB. These are
electrically quite simple devices that usually offer swtichable =
attenuation
levels of 1, 2, 3, 5 10 and perhaps two or three 20 dB sections. By =
putting
one in between your noise generator and the circuit under test, you can
reduce the level to prevent overload and you control the level over a =
wide
range in known 1 dB steps. The known steps can be very useful in
troubleshooting.

When troubleshooting, you connect an ac voltmeter to the audio output of
your rig to monitor the noise level. Then, when you move your injection =
from
the output of an amplifier to the input of an amplifier and see the =
audio
level increase, you switch in more attenuation to bring it back down to =
the
same level as it was before. With a calibrated attenuator, that tells =
you
exactly how much gain the stage has. For example, if you have to add 40 =
dB
of attenuation to bring the signal back to the same output, you know =
that
stage has 40 dB of gain!=20

Electrically, step attenuators are very simple devices using a switch =
and a
few resistors or each section. Mechanically, they can be a bit of a
challenge because it is very important to prevent "feed through" (what =
he
filter guru's like to call "blow by") around the attenuator that will =
ruin
its accuracy. For that reason the maximum step is usually 20 dB.=20

They aren't too common. I have built (and passed on to other hams) a =
number
of them over the years. I currently find myself attenuator-deprived =
again
and scoured the SeaTac hamfest but missed out on the few that were =
available
there.=20

MFJ is the only company that I now of who makes one for Ham use right =
now,
and it's a bit pricey (hint, hint...).=20

Ron AC7AC
K2 # 1289

-----Original Message-----
Hi

As many of you know I have been selling a noise generator kit for about =
2
years. I started kitting these when Tom Hammond indicated he was no =
longer
going to sell the boards. I made a few changes to the circuit and =
designed a
circuit board. I have sold around 200 of these at about my cost as a =
service
to Elecraft owners. I am glad Elecraft has picked up this product as =
they
are very handy around the shack. It sounds like the Elecraft version =
will be
better because of the flat output and it also has a 50 output impedance. =


The only thing I can add to Ron's info below is when using the noise
generator as a signal injector it will sometimes overwhelm the low level
stages of the radio and give a false indication. I have found an =
attenuator
on the output of the noise generator to help or in the case of my =
circuit
you can tap a low level noise source right off of the noise diode (add a
second BNC and connect a .01 UF between the center connector pin and the
junction of Q3 emitter and R1).=20

Be careful when using the noise source to pre align the receive filters.
Sometimes you can get a peak when doing the alignment but it is actually =
the
image frequency so the receiver works but the transmitter has no output.
This is common on the K1 with the 4 band module. You need to retune the
filters to the other peak and sometimes its hard to find. Just keep
twiddling you will find it.

I still have a few boards left (about 20) but I will not have any more =
after
these are gone the price is still $15 check or money order for the kit

order from

Don Brown
19132 Falls Creek Drive
Flint, Texas 75762

Thanks

Don