RF Cascade Workbook for Excel
RF & Electronics Symbols for Visio
RF & Electronics Symbols for Office
RF & Electronics Stencils for Visio
RF Workbench
T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads
Espresso Engineering Workbook™
Smith Chart™ for Excel
|
|
Measuring a Transmitter´s output Impedance components - RF Cafe
Forums
|
Laser
|
Post subject: Measuring a Transmitter´s output Impedance components
Posted: Wed Dec 05, 2007 11:14 pm
|
|
|
Lieutenant |
|
Joined: Wed Dec 05, 2007
10:09 pm Posts: 2 |
Hi everyone. I was asked to develop a linear
amplifier for an RC transmitter (35MHz). This
transmitter uses a simple telescopic antenna, and
now I will have to design the amplifier and adapt
it´s output to a 50ohm transmission line and antenna.
So far so good, but then, as I started to analyze
the problem, things started to complicate a little.
In order to adapt the amplifier´s input to the
transmitter´s output, I need to know the transmitter´s
output impedance components (resistive and reactive
parts). The resistive part should be something
much lower then 50ohm, which is the typical impedance
of short whip antennas (antennas bellow resonance).
I also know that short whip antennas present
a natural capacitive reactance, and to counteract
this, the transmitter has an inductive reactance
part on it´s output to balance with the capacitive
reactance of the antenna. This is called Conjugate
Matching and in order to adapt my amplifier´s input,
I also need to know the magnitude of this inductive
reactance. Now, my question is: How do I
measure these values without using high priced equipment,
like network analyzers? Are there any techniques
to do this, with an outside test setup made of variable
capacitors, inductors and resistors and then measuring
phase shifts, voltages and currents in some way
on this setup, with an oscilloscope, that will allow
us to calculate the resistive and reactive parts
of the transmitter´s output impedance? My intuition
tells me that this is possible, but how? I´ll
appreciate any help. Thanks
|
|
|
|
|
Feng |
Post subject: I gave you my suggestion in Circuit board.
Posted: Thu Dec 06, 2007 4:05 am
|
|
|
Captain |
|
Joined: Sun Mar 19, 2006
5:25 pm Posts: 23 Location: Burnaby
|
Hi Laser,
I gave you my suggestion in Circuit
board where you posted your question first. Hope
it is useful.
|
|
Posted 11/12/2012
|
Copyright: 1996 - 2024
Webmaster:
Kirt
Blattenberger,
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
|
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
|
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website: AirplanesAndRockets.com
My Daughter's Website: EquineKingdom
|
|
|
|