The Electronics Universe

Digital numbering systems,

in Digital electronics, one of the first things one needs to understand is the numbering systems used, so in this thread I will briefly explain a few of them,

one numbering system that we all should be familiar with is called decimal, I think we all know how the decimal numbering system works, but for reference and just to be thorough i'm going to cover it anyway,

Decimal:
in decimal a single digit can represent one of 10 possible values beginning with 0 and ending with 9, the first digit advances from 0 through 9 before the next digit advances, this is called base 10, or decimal, here is an example using 2 digits,

00
01
02
03
04
05
06
07
08
09
10

up next: Binary,

Discussion area for this thread is here: http://gokarters.com/smf/index.php?topic=2437.0

i finally figured it out, i just re did my linux, and after reinstalling photoshop i forgot to change my rulers and guides from metric to inches, so i was creating pics at 300 dots per centimeter rather that dots per inch, way too big, lol

i forget that every time i upgrade my linux, lol

it makes no sense to me, the red trace on the top looks like just a dirtier version of the green trace on the bottom, plus both scope pics look almost identical, i'm lost bro there should be alot more difference in the two signals, and all of em say 5.xxMhz, it makes no sense, looks like the VFO is all thats working in these pics,

i'm gonna get off this thing for a while and see who's on the radio, catch you tomorrow bro,

l8r

which DSO is it? i know you posted about it over at CBT but i don't remember,

with mine i had to format a USB stick to work with it, it had the wrong type of file system on it, i think it had to be formated with FAT32 to work with mine, tho i can't remember for sure, or maybe it was FAT 16, yup i believe that was it now that i think about it,

I know you hated that.  But like you d\said, got to eat.

ok, that signal is nasty looking. I post what I see on the Tek 2235 and the DSO
The first is the DSO. Sorry for the super imposed image of me taking the pic. I dont have the lap top out here do could not send file to it. And main pc too far away.

Second is the Tek.Set at 50 Mu per Div and .1 Ms per Div

well the one on the DSO looks clean enough to me, looks like i can see a little of the VFO fundumental riding on it, but it looks supressed enough, the other scope looks a little out of sync to me,

is that the output of the 1st mixer? looks like the freq says 25.something, can't make it out for sure,

and if it is, does the freq change with the VFO as it should?,

Now that makes sence to me.
The VFO signal is coupled via a 1pf cap while the 31 meg signal is couple via a 5pf cap.
I think I should try and repalce those caps. They could be causing the issue I am having. I will throw the scope on it tonight or in the morning. These caps are very old style (looks like a resistor) and since they are value my cap meter reads 56pf on them.

also i think it would be interesting to see what the 26.51Mhz signal from the 1st mixer looks like going into the second mixer with no signal going into the antenna jack, it think it should be a pretty clean 26.51Mhz sine wave, but i'm curious to see just how well the output tank on the 1st mixer suppresses the fundamentals,

quote from you on the other site

31.4 + .455 - 4.890 = 26.965
31.4 being the crystal, .455 the IF and 4.890 being the vfo.
So since I still do not get this, what should I see between C14 and C22. that is part that really gets me atm.

ok using the above example for channel one,

lets start at the 31.4Mhz crystal oscillator, and the VFO, and how they are mixed,

the signal from the 31.4Mhz crystal oscillator and the signal from the VFO are being mixed passively at the junction of C14 and C22, at that point there is a total of 4 signals present all at once, the two fundamentals which are:

1: the 31.4Mhz crystal oscillator signal,

2: the 4.89Mhz VFO signal, 

and two heterodyne frequencies which are:

3: the sum heterodyne at 31.4 + 4.89 = 36.29Mhz

4: the difference heterodyne at 31.4 - 4.89 = 26.51Mhz

now these heterodyne signals at this point are kind of like phantoms, and they don't really exist yet as distinguishable signals that can be seen on a scope or frequency counter, (i bet they would show up on a spectrum analyser though), but that will soon change after the signals passed through the 1st mixer, which is really not acting as a mixer in the conventional sense at all (because both fundamental signals are going into only one input), but is simply acting as an amplifier with a low Q or wide band tuned circuit on its output which is tuned to allow only the deference heterodyne frequency range to pass, therefore both the fundamental frequencies and the sum heterodyne are prevented from passing, and because of the flywheel or ringing effect of the tuned circuit at the output, what comes out is a real signal at the deference heterodyne frequency of the two fundamentals, which is 26.51Mhz,

now lets assume that there is a strong 26.965Mhz signal being injected into the antenna jack,

this 26.51Mhz signal from the 1st mixer is then mixed at the grid of the 2nd mixer with the incoming 26.965Mhz signal, and again two heterodyne frequencies are produced from those two fundamentals same as before, so we have two fundamental frequencies and two heterodyne frequencies at the input of the second mixer, and again at the output of the second mixer is another tuned circuit, this time a very hi Q or narrow band one, which is tuned to allow only the deference frequency of 455Khz to pass,

so here is the math:

31.4 - 4.89 = 26.51Mhz <--output from the 1st mixer

then

26.965 - 26.51 = .455Mhz or 455Khz  <--output from the 2nd mixer

i hope that helped,