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.=20
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
----- Original Message -----=20
From: Ron D'Eau Claire=20
To: [email protected]=20
Sent: Tuesday, July 08, 2003 10:48 PM
Subject: RE: A Question From a Dummy - Regarding : [Elecraft] Noise =
generator
The "noise generators" referred to here are actually "white" noise
generators. That is, they produce random noise that is uniform in =
amplitude
across a large portion of the RF spectrum. If you look at their output =
on a
spectrum analyzer, the display turns "white" with the broad-band RF =
"noise"
across the RF spectrum, which is what gives them their name.=20
Such a noise generator is useful for "peaking" the tuning of r-f =
amplifiers
in receivers and evaluating the bandpass characteristic of RF/I.F. =
stages.
In the case of the Elecraft rigs, it finds its greatest use with
"spectrogram" - a software spectrum analyzer that runs on a personal
computer - to adjust and observe the bandpass characteristic of the =
I.F.
amplifiers. If you tried to do that with a normal signal generator, =
you'd
have to sweep the frequency slowly across the bandpass and note the =
output
from your K2 every few Hz to plot the "curve" of the I.F. filters by =
hand.
The noise generator produces uniform RF at all of the frequencies of
interest at once, so you can see the whole bandpass at a glance.=20
A noise generator is handy but not at all essential for aligning a K2. =
There
is PLENTY of noise on the lower HF bands for this purpose. But using =
one has
some advantages: It eliminates the need to hook up an antenna to pick =
up
the noise. It avoids finding signals in the bandpass which can confuse
readings. And it ensures that the noise is uniform and broad.=20
Where a noise generator really becomes important is when you get above =
the
frequencies at which there is plenty of "atmospheric" noise. When the =
bands
are quiet, it can be hard to find enough atmospheric noise above 21 to =
30
MHz at times. Above 50 MHz, it becomes very rare to hear enough
"atmospheric" noise to align a receiver and a good "noise generator" =
is
essential.=20
And, don't forget, Elecraft is about to break loose with some =
transverter
kits for the 50 MHz and up range... <G>
Another way a noise generator is quite useful is in troubleshooting. =
You can
make up a test probe (with a d-c blocking capacitor to be sure you =
don't
short any d-c voltages) and touch it to the inputs of stages in the =
RF/I.F.
sections of a receiver to see if each stage is working. By comparing =
the
loudness of the noise in the speaker when it is injected at each =
stage, you
can get a rough idea of whether or not the stage has gain. If you =
start at
the product detector and work toward the antenna touching the probe to =
the
input of each stage a 'dead' stage is obvious because suddenly the =
noise
will disappear or the level will be much lower than it was.=20
Ron AC7AC
K2 # 1289
--- StripMime Report -- processed MIME parts ---
multipart/alternative
text/plain (text body -- kept)
text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed. To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html ---