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

[Eddy Avila]

I bought Don's board before I purchased my K2 and it has been indispensible 
in aligning the K2 filters using the Spectrograph software! I tried doing 
filter alignments by ear and it was a mess!!

Tnx agn Don for the noise generator kit.....been working great!

73...ed


>From: "Don Brown" <DolfinDon@msn.com>

>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).
>
>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 -----
>   From: Ron D'Eau Claire
>   To: elecraft@mailman.qth.net
>   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.
>
>   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.
>
>   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.
>
>   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.
>
>   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.
>
>   Ron AC7AC
>   K2 # 1289

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