EMRFD Message Archive 8

Message Date From Subject
8 2006-07-11 11:46:55 kd5kxf Ferrite Core Experiments
The theme and content of EMRFD is wonderful, and the book has actually
got me building things "experimentally" instead of just playing
project songs of others "note for note". I have found ferrite cores
that are like giant ferrite beads that are used for data cables in our
local surplus electronics store 10 for a dollar. I would have never
tried this but the brief mention in the article about the R1 mentioned
using salvaged stuff from printer cables so I gave it a shot on a
mixer and lo and behold it mixes. It mixes well!!! I haven't checked
insertion loss with my O scope yet, I am using the myear test unit
right now. Does anyone know what material these things in printer
cables are? Is there any real way to determine material without lab
9 2006-07-11 20:14:01 Steven S. Coles Re: Toroids in Mixers (Tongue in Cheek—Sort Of)--Ferrite Core Expe

Coincidently, I built a passive mixer from 2 toroids and 4 diodes
Saturday. It's handy that toroids aren't required to be extremely
linear or efficient for up-converting a QRP CW transmitter. Often,
they're well superior to application requirements.

But how many mixings should we use? Let's start with 20 different
frequency crystals or DIP oscillators. That's 20 choices for the
first frequency leaving 19 for the second choice for 380 possible
combinations of which at least half are redundant (4 MHz + 8 MHz = 8
MHz + 4 MHz). (20 * 19)/2 = 190 frequency sums (I'm ignoring
differences). 18 unused crystals or oscillators remain. Mixing
again gives (190 * 18)/2 = 1710 frequencies. Mixing again gives
(1710 * 17)/2 = 14,535 frequencies.

Let's say all the mixing sums fall between 25 and 220 MHz. The USA
has 9.7 MHz of amateur radio frequencies within those 195 MHz.
14,525 * 9.7/195 = 723. We'd expect about 723 of the mixing sums to
fall within amateur radio bands. Considering that local oscillators
can be above or below the received signal, we'd have about twice as
many options of LOs.

Given a random set of crystals someone entirely allergic to PLLs
could transmit and receive on a good number of frequencies—ideally.

Actually few crystals acquired at random will be on integer 10 kHz
multiples. Anything for video abhors 10 kHz multiples. At the
other extreme are the too even crystals. The too even frequency
crystals produce redundant frequencies such as 2 MHz + 8 MHz = 4 MHz
+ 6 MHz = 10 MHz. Anyway most of my crystal and oscillator
collection falls at one extreme or the other. Given all that,
randomly selecting 20 unique crystal frequencies from my junk box
and taking sums in 4s would very likely produce 70+ unique
frequencies inside amateur radio bands. That's still pretty good.

See you
10 2006-07-12 08:06:20 Stan Re: Ferrite Core Experiments -EMRFD as a design training tool
Michael welcome to the building/design club. HI One thing you
might enjoy and it really helps to understand someone's design is to
reverse engineer their circuits.

I usually start with the LC circuits and see if I can calculate the
impedances, etc and to understand why they decided what values to

LTSpice is available free on the web and you can use it to analyze
the audio stages and more. AADE has a real good filter design
program (again free) and you can 'what if' output circuits all day.
AADE also has an excellent LC meter you will want when you start
building your own designs.

Yes you will find sometimes others (all of us) make mistakes in
their calculations and you can improve the circuit with minor
changes. You will also find some just copy others circuits even the
mistakes. hi

You have the EMRFD book with disk, add the AADE filter program and
Linear Technology LTSpice and you will find you have the best RF
design tools an amateur radio op/designer could every want. The
other tool I use is DL5SWB's minirk11.exe (also free) which will
allow you easy calculation of toroid coils.

Two more books to add to your library would be an old 50s or 60s era
ARRL handbook for LC circuits and a modern ARRL handbook for
transistor circuits.

A low cost RF library with tools for about $100 and you can enter
the hobby of RF circuit design.

Cheers Stan ak0b