[Elecraft] Re: [Elecraft]Noise generator was Spectrogram - Again

[Don Brown]

Hi

If you have built one of my noise generator kits and want a low level output
to drive your K2, you can tap off the signal right from the 2N3904 noise
source. Just connect a .01 UF cap to the junction of the 2.2K resistor and
the emitter of Q3. Connect the other end to the center pin of a BNC
connector and ground the outside of the BNC. Now you have a high level
(about 2 volts) for troubleshooting and signal injection and a low level
output for alignment that will not overdrive the front end of the radio. You
can use the low level signal to pre-align the receiver and get all of the
tweaks peaked up before doing the final transmitter alignment. Connect the
low level out to the antenna connector and peak each coil or capacitor for
maximum noise on each band. You can use this signal for spectrogram also.

In fact I should not explain this as it will reduce my sales of the noise
generator kits but that is OK. The 2n3904 transistor will make enough noise
to drive spectrogram by itself the amplifiers are really not needed. So if
you need a noise source for spectrogram just build this circuit. Connect the
base of a 2n3904 (or 2n2222) to the negative side of a 9 volt battery (this
will be ground). Connect a 2.2K ohm resistor to the emitter and the other
end of the resistor to the plus side of the battery. Connect a .01 UF cap to
the emitter and resistor junction and connect the other end of the cap to
the center pin of a BNC connector with the outside of the BNC grounded. The
collector is not connected. This circuit uses the emitter base junction as a
zener diode noise source and capacitively couples the noise to the antenna
connector of the K2. The noise level will only be a few milivolts but that
is plenty to drive the K2 for Spectrogram.


Don Brown
KD5NDB

If you still want a noise generator kit they are $15 check or money order to

Don Brown
19132 Falls Creek Drive
Flint, Texas 75762


----- Original Message -----
From: "Tom Hammond N�SS" <n0ss@earthlink.net>
To: "JAKidz" <jakidz@pullman.com>; <elecraft@mailman.qth.net>
Sent: Wednesday, December 11, 2002 9:06 AM
Subject: Re: [Elecraft] Spectrogram - Again


> John, K7JG, wrote:
>
> >I was having a lot of trouble aligning my K2's crystal filters even
though
> >I was using the N0SS noise generator and Spectrogram. Starting from the
K2
> >manual settings for the filters, lots of peaks of variable heights were
> >appearing everywhere across the spectrum no matter the filter settings
even
> >though the radio seemed to be working. After a lot of fiddling, two
things
> >became apparent. I was setting both the N0SS noise generator and the K2
AF
> >gain too high. Using the output pot to set the noise generator just above
> >receiver noise on my headphones and then setting the K2 AF gain to
minimum
> >and increasing it slowly, the desired shapes began appearing. I'm
guessing
> >my computer's soundcard was clipping even at moderate audio levels and
the
> >FFT processing of the resulting "squared" waves in Spectrogram resulted
in
> >all those interesting peaks.
>
> John makes an EXCELLENT point here... especially with regard to the use of
> the AF GAIN on the K2.
>
> While an output level pot on the noise generator may be a worthwhile
> addition for many (the generator DOES have quite a bit of output), the
MOST
> important control when performing a CAL FIL alignment using noise (from
ANY
> source) and Spectrogram is to NOT overdrive the input to your sound card.
> Overdriving the sound card input WILL (almost guaranteed) result in a
bunch
> of spurious artifacts appearing on the Spectrogram display.
>
> Use of the 60dB scale, and adjusting your AF gain to the point that the
> peak signal level displayed on the screen doesn't exceed 40dB should work
> well. Adjusting the AF Gain to produce a 30dB trace may work even better.
>
> When using Spectrogram, NOTE that there is a slider bar along the RIGHT
> edge of the Spectrogram screen. This slider should be run to the top end
of
> its range before you begin establishing an AF Gain level setting.
>
> Thanks for the reminder, John.
>
> 73,
>
> Tom Hammond   N0SS
>
> _______________________________________________
> Elecraft mailing list: Elecraft@mailman.qth.net
> You must be a list member to post to the list.
> Postings must be plain text (no HTML or attachments).
> See: http://mailman.qth.net/mailman/listinfo/elecraft
> Elecraft Web Page: http://www.elecraft.com
>