How to prototype HF RF circuits
Andrew W. Hull
I am designing some low power rf circuits to operate
in the 27 MHz ISM bands. What type of prototyping
material is useful at these frequencies? Will a simple
bread board work? I recall various caveats regarding
their performance at higher frequencies due to stray
capacitance. Are there general lay out rules to follow,
as well?
Where is a good place to buy such things?
I apologize for the lack of knowledge on these things. Any
enlightenment that you can provide will be appreciated!
Michael Covington
: I am designing some low power rf circuits to operate
: in the 27 MHz ISM bands. What type of prototyping
: material is useful at these frequencies? Will a simple
: bread board work? I recall various caveats regarding
: their performance at higher frequencies due to stray
: capacitance. Are there general lay out rules to follow,
: as well?
Actually, rule number one is to build circuits that won't be much
affected by stray capacitance :)
Seriously, some circuit designers are much better at this than others.
27 MHz is not all that hard to work with; almost all modern components
are small enough to work well. Using a solderless breadboard is
pushing it; it _might_ work (I have done such things), but normally,
you should build your prototypes on perfboard. Even Radio Shack has
some perfboards with useful copper patterns already etched on them (holes,
stripes, etc.).
--
< Michael A. Covington, Assc Rsch Scientist, Artificial Intelligence Center >
< The University of Georgia, Athens, GA 30602-7415 USA mcov...@ai.uga.edu >
< Unless specifically indicated, I am not speaking for the University. > <><
For information about any U.Ga. graduate program, email gra...@uga.cc.uga.edu.
Jerry Gaffke
: in the 27 MHz ISM bands. What type of prototyping
: material is useful at these frequencies? Will a simple
Maintaining a solid ground reference across the entire circuit can
critical.
A popular technique in amateur radio circles is to solder parts down
to an unetched circuit board, using the circuit board as a ground plane.
Parts that have no ground pins get suspended in mid air between other
parts. The results (electrical, not visual :-) are often better than
carefully laid out and etched circuit boards.
Glue chips upside down first (dead-bug style). If small parts need
additional mechanical support, use high value resistors between that
point and the ground plane (at least a factor of 10 greater than the
impedance of the circuit). Place things reasonably close together.
Avoid placing the input side of an amplifier next to the output side (or
next to a later stage) or you may see oscillations due to feedback.
This is especially true if the amplifier gain is high.
jerryg Jerry Gaffke Portland Oregon, USA KE7ER
C.M. Hicks
>I am designing some low power rf circuits to operate
>in the 27 MHz ISM bands. What type of prototyping
27MHz - that's practically dc :-)
>material is useful at these frequencies? Will a simple
>bread board work? I recall various caveats regarding
No, a conventional breadboard will be a disaster! The best way I have
found is to get a piece of copper-clad board and use it as a ground
plane. Solder earthy ends of components direct to the copper and leave
other connections dangling in mid-air. You can also glue components
(such as DIP's, TO92 packages etc.) to the board (upside-down, so the
legs point upwards) with cyanoacrylate. This helps keep the whole
thing stable. The main layout rule is to keep connections absolutely
as short as possible.
This technique is workable up to UHF (500Mhz ish) frequencies, though
the thought involved with getting something to work seems to rise
exponentially with frequency!
Christopher
--
=====================================================
Christopher Hicks http://www.eng.cam.ac.uk/~cmh
c...@eng.cam.ac.uk Voice: (+44) 223 332767
=====================================================
SMaas
(Andrew W. Hull) writes:
>I am designing some low power rf circuits to operate
>in the 27 MHz ISM bands. What type of prototyping
>material is useful at these frequencies? Will a simple
>bread board work? I recall various caveats regarding
>their performance at higher frequencies due to stray
>capacitance. Are there general lay out rules to follow,
>as well?
27 MHz is not high enough in frequency to be really critical. I suggest
you use perfboard and clips--perforated board, in which you stick little
terminals. This is a good way to go for just about anything in this
frequency range.
Use copper tape for the grounds.
S. M.
Reid J Mullen
Try building your prototype as a spider wed in the air. -keep
leads short. Works well for me, give it a try
Reid rjms...@pitt.edu
Erik Sorgatz
Please, someone put this in the FAQ!!
ARRL Press - The Radio Amateur's Handbook ($20US)
available at most amateur radio stores.
Contains virtually everything known to man about
RF, circuits, theory and practice. Your school library
(you know...that building full o books??) probably has
at least one copy!
(sheesh! Don't you kids read books anymore??)
Breadboards work fine at hf, gets worse at 100MHz, there are
many general rules of thumb about such layouts - RTFM! You can
buy parts and such at any Rat Shack, swap meet, electronics
dealers...like, why not look in the Telephone Book under
"electronics - retail, wholesale, manufacturers, surplus, etc"
(ehhh....if you were in my class you'd have already FLUNKED!)
Need exact instructions??
05 REM ****how to hack electronics*****
10 rtfm Handbook
20 hack simple circuits
30 understand? (yes=goto 40) no=goto 10
40 rtfm Handbook
50 hack complex circuits
60 understand? (yes=goto 70) no=goto 40
70 dead yet? (yes=goto 90) no=(next Handbook)
80 goto 10
90 end
Yeah...I know...gotos are bad...and structured programmers are anal!
-Avatar-> (aka: Erik K. Sorgatz) KB6LUY +----------------------------+
TTI(e...@soldev.tti.com)or: sor...@avatar.tti.com *Government produces NOTHING!*
3100 Ocean Park Blvd. Santa Monica, CA 90405 +----------------------------+
(OPINIONS EXPRESSED DO NOT REFLECT THE VIEWS OF CITICORP OR ITS MANAGEMENT!)
Mycal
>
>Andrew W. Hull (hu...@platypus.csl.uiuc.edu) wrote:
>
>: I am designing some low power rf circuits to operate
>: in the 27 MHz ISM bands. What type of prototyping
>: material is useful at these frequencies? Will a simple
>: bread board work? I recall various caveats regarding
>: their performance at higher frequencies due to stray
>: capacitance. Are there general lay out rules to follow,
>: as well?
>
>Actually, rule number one is to build circuits that won't be much
>affected by stray capacitance :)
>
>Seriously, some circuit designers are much better at this than others.
>
True, in the general case anything below 50MHz you can get away with alot.
Above 50MHz follow good design rules.
It has been said the reason why Intel came out with DX2 and the like was
that they didn't trust board designers to make anything that worked
reliably above 50MHz.
mycal
---------------------------------------------------------------------------
my...@netacsys.com
\ //
"..unfortunately we can't control the actions // \
of everyone." President Clinton 04/20/93 No Risk, No Rush
David B. Thomas
the parts on with the shortest leads possible. Works well into VHF, and it's
nice and fast to change your circuit.
David
--
fghit entyrop
Robert Everitt Heiss
> ARRL Press - The Radio Amateur's Handbook ($20US)
> available at most amateur radio stores.
For examples of prototype-style (rather than printed circuit) construction,
see also "Solid State Design" by Hayward and DeMaw. ARRL Press.
In general, the ARRL publications are excellent on technical subjects but
not recommended as references for engineering.
Erik Sorgatz
>
>For examples of prototype-style (rather than printed circuit) construction,
>see also "Solid State Design" by Hayward and DeMaw. ARRL Press.
>
>In general, the ARRL publications are excellent on technical subjects but
>not recommended as references for engineering.
Why? Most of the "engineering" texts I had to suffer thru spend 70% of their
pages devoted to mindbending mathematical models and damn little space in
pursuit of actual working circuits, with real part values and construction
notes! With all humble intent, why would one NOT recommend so practical a
book as the Handbook?? (I mean, unless you're teaching a class and YOU wrote
the book that the class will be using....;-) )
73!
Robert Everitt Heiss
>In article <1994Aug10.0...@zeus.aix.calpoly.edu> rhe...@harp.aix.calpoly.edu (Robert Everitt Heiss) writes:
>>
>>In general, the ARRL publications are excellent on technical subjects but
>>not recommended as references for engineering.
>
> Why? Most of the "engineering" texts I had to suffer thru spend 70% of their
>pages devoted to mindbending mathematical models and damn little space in
>pursuit of actual working circuits, with real part values and construction
>notes! With all humble intent, why would one NOT recommend so practical a
>book as the Handbook??
I DO recommend it. I initially learned electronics from the Handbook
and worked very successfully as a technician. Some fun projects were
built that were similar to proven handbook designs.
For engineers it's actually easier and more productive to learn two more
years of math and then the abstract textbooks, rather than trying to
memorize a vast encyclopedia of circuits and their design formulas.
--
Robert Heiss, ex-NB0J