Searching \ for '[PIC] COMPLETED: PIC-based SWR/wattmeter' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devices.htm?key=pic
Search entire site for: 'COMPLETED: PIC-based SWR/wattmeter'.

Exact match. Not showing close matches.
PICList Thread
'[PIC] COMPLETED: PIC-based SWR/wattmeter'
2008\06\04@153454 by Jason Hsu

picon face
Those of you who are amateur radio operators may be interested.

I have recently completed work on a PIC-based SWR/wattmeter for HF
radio transmissions.  The SWR and wattmeter displays both consist of
10 LED outputs apiece, from lower levels to higher levels.  My old
design used an LM3914 for the SWR display and an LM3915 for the
wattmeter display.  The LM3914-based SWR meter behaved in strange ways
(LEDs lighting up randomly) between transmissions, and no modification
I made could completely get rid of this behavior.

My PIC design gets rid of the SWR meter's erratic behavior by keeping
all 10 LEDs dark when the transmitted power is below a certain level
(200 mW).

Additionally, my SWR/wattmeter design is for both low power and high
power (200mW to 200W).  Most of the high power SWR meters don't work
at low power levels (due to the rectifier diode drop loss), and most
of the low power SWR meters out there can't handle high power levels.
My design uses large ferrite cores and metal oxide resistors in the
directional coupler to handle high power and log amplifiers to
compensate for the diode drop loss that reduces accuracy at low power
levels.

My report on the SWR/wattmeter is at http://www.jasonhsu.com/swrwatt.html
My Assembly language source code is at
http://www.jasonhsu.com/swrwatt-source_code.html

--
Jason Hsu
http://www.jasonhsu.com/swrwatt.html
www.jasonhsu.com/swrwatt-source_code.html
NOTE: I am seeking employment as an embedded electronics engineer.

2008\06\04@154519 by Dario Greggio

face picon face
Jason Hsu wrote:

> My report on the SWR/wattmeter is at http://www.jasonhsu.com/swrwatt.html
> My Assembly language source code is at
> http://www.jasonhsu.com/swrwatt-source_code.html


hmmm,
http://www.jasonhsu.com/swrwatt-source_code.txt

actually :)

thank you Jason!

--
Ciao, Dario -- ADPM Synthesis sas -- http://www.adpm.tk

2008\06\04@161253 by Jason Hsu

picon face
Thanks for the correction.

--
Jason Hsu
http://www.jasonhsu.com/swrwatt.html
www.jasonhsu.com/swrwatt-source_code.txt
NOTE: I am seeking employment as an embedded electronics engineer.

2008\06\04@174008 by David VanHorn

picon face
> Jason Hsu
> http://www.jasonhsu.com/swrwatt.html
> www.jasonhsu.com/swrwatt-source_code.txt
> NOTE: I am seeking employment as an embedded electronics engineer.


So noted.. Where are you?

2008\06\04@174226 by David VanHorn

picon face
> My PIC design gets rid of the SWR meter's erratic behavior by keeping
> all 10 LEDs dark when the transmitted power is below a certain level
> (200 mW).

It's not diodes, but maybe you would be interested in the LT5534 (Linear)
It's an RF level detector that's supposed to be linear over a 60dB range.
I have eval boards here, they are way too sensitive to be used in an
SWR meter (unless you want to run at the mW level) but that's what
attenuators are for.

2008\06\04@191657 by Jason Hsu

picon face
I am located in Cedar Rapids, Iowa.  I am open to relocation anywhere
in the continental USA with a preference for the Midwest (Chicago,
Twin Cities, etc.).

On 6/4/08, David VanHorn <spam_OUTmicrobrixTakeThisOuTspamgmail.com> wrote:
>> Jason Hsu
>> http://www.jasonhsu.com/swrwatt.html
>> www.jasonhsu.com/swrwatt-source_code.txt
>> NOTE: I am seeking employment as an embedded electronics engineer.
>
>
> So noted.. Where are you?
> -

2008\06\04@192323 by Jason Hsu

picon face
Unfortunately, the LT5534  is for much higher frequencies (50 MHz to 3
GHz instead of 1.8-30 MHz).  For those who can solder surface-mount
parts, the LT5534 would work for 6m, 2m, 1.25m, 70cm, 23cm, and the
bottom end of the microwave range.

On 6/4/08, David VanHorn <.....microbrixKILLspamspam@spam@gmail.com> wrote:
>
> It's not diodes, but maybe you would be interested in the LT5534 (Linear)
> It's an RF level detector that's supposed to be linear over a 60dB range.
> I have eval boards here, they are way too sensitive to be used in an
> SWR meter (unless you want to run at the mW level) but that's what
> attenuators are for.
> -

2008\06\04@200215 by Marcel

picon face
Jason Hsu wrote:
> I am located in Cedar Rapids, Iowa.  I am open to relocation anywhere
> in the continental USA with a preference for the Midwest (Chicago,
> Twin Cities, etc.).


Isn't Rockwell Collins located in Cedar Rapids?  They could be an
interesting match for you as you seem to be interested in radio and
embedded systems.

2008\06\06@234120 by Sean Breheny

face picon face
Hi Jason,

Nice job! I do have a question, though: it looks like, from your
schematics on that page, that you do not have any filter capacitor
after the initial passive rectifiers. In other words, you have a
low-frequency diode-drop-compensating op-amp circuit but the input of
that is fed from just a diode. Are you relying on the input
capacitance of the op-amp to smooth out the half-wave rectified RF
into DC?

Sean


On Wed, Jun 4, 2008 at 3:34 PM, Jason Hsu <jhsu802701spamKILLspamgmail.com> wrote:
{Quote hidden}

> -

2008\06\07@003633 by Jason Hsu

picon face
Yes, I'm relying on that parasitic input capacitance.  There is a
trade-off.  Using a high capacitance value would reduce the
responsiveness of the circuit, which may be a problem during voice
transmissions.  (Admittedly, I don't think this is likely to be
noticeable.)  Given that the LM324 has a unity gain bandwidth of only
1 MHz, I'm not concerned that stray RF would be amplified.  Also,
there are .01uF capacitors in the voltage divider outputs that feed
the microcontroller inputs.

If you are concerned about the lack of capacitors to ground in the
rectifiers, you could add .01uF or .1uF capacitors.

On 6/6/08, Sean Breheny <.....shb7KILLspamspam.....cornell.edu> wrote:
> Hi Jason,
>
> Nice job! I do have a question, though: it looks like, from your
> schematics on that page, that you do not have any filter capacitor
> after the initial passive rectifiers. In other words, you have a
> low-frequency diode-drop-compensating op-amp circuit but the input of
> that is fed from just a diode. Are you relying on the input
> capacitance of the op-amp to smooth out the half-wave rectified RF
> into DC?
>
--
Jason Hsu
http://www.jasonhsu.com/swrwatt.html
www.jasonhsu.com/swrwatt-source_code.txt
NOTE: I am seeking employment as an embedded electronics engineer.

2008\06\07@102437 by Marcel Duchamp

picon face
Jason Hsu wrote:
> Yes, I'm relying on that parasitic input capacitance.  There is a
> trade-off.  Using a high capacitance value would reduce the
> responsiveness of the circuit, which may be a problem during voice
> transmissions.  (Admittedly, I don't think this is likely to be
> noticeable.)  Given that the LM324 has a unity gain bandwidth of only
> 1 MHz, I'm not concerned that stray RF would be amplified.  Also,
> there are .01uF capacitors in the voltage divider outputs that feed
> the microcontroller inputs.
>
> If you are concerned about the lack of capacitors to ground in the
> rectifiers, you could add .01uF or .1uF capacitors.

With rf circuits, one source of problems is rf getting in where it does
not belong and making life difficult, or at least, interesting.  I had
an example of this last year with an instrumentation amp that, as you
say, did not have the bandwidth to amplify rf in the slightest.

The trouble came when an rf source got turned on in the system.  Enough
rf came in through the input pins of the INA to cause an offset of about
15% of fullscale.  The rf gets differentially rectified and results in
an offset voltage at DC that does indeed get amplified.

This circuit had a ceramic cap between the leads approximately 5mm away
from the chip for just this sort of thing.  But the rf still got in.
Solution was to solder another ceramic cap directly on the pins touching
the epoxy of the chip.  This cured the problem until we could find a
replacement chip that did not suffer the same effect.

None of this is to say that your particular circuit has this defect but
one must be careful here. It is not always ok to say "my amplifier
bandwidth is too low to be bothered by rf"... surprises always lurk.

2008\06\07@105451 by David VanHorn

picon face
> None of this is to say that your particular circuit has this defect but
> one must be careful here. It is not always ok to say "my amplifier
> bandwidth is too low to be bothered by rf"... surprises always lurk.


Rail-to-rail, precision, cmos opamps seem to work well.
I used one of these to solve a NASTY noise problem caused by locating
the amp within a half-inch of an antenna with a 900mHz 6W pulsed
transmitter.

2008\06\07@105633 by David VanHorn

picon face
On Wed, Jun 4, 2008 at 7:22 PM, Jason Hsu <EraseMEjhsu802701spam_OUTspamTakeThisOuTgmail.com> wrote:
> Unfortunately, the LT5534  is for much higher frequencies (50 MHz to 3
> GHz instead of 1.8-30 MHz).  For those who can solder surface-mount
> parts, the LT5534 would work for 6m, 2m, 1.25m, 70cm, 23cm, and the
> bottom end of the microwave range.

True.  I don't know that it won't "work" at lower frequencies, it
detects AM CB radio from 50' away quite nicely, but how linear it is
would be the question.

It's an amazing chip, lots of interesting information is available
from watching its output.

2008\06\08@191637 by Peter Todd

flavicon
face
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Sat, Jun 07, 2008 at 10:56:12AM -0400, David VanHorn wrote:
{Quote hidden}

I built a partially successful cell phone detector with one of those
chips. http://petertodd.org/tech/emf-detector/ has some oscilloscope
captures of it operating, I was very impressed that you could see the
timeslices used by GSM phones, and individual phones going on and off
the air.

- --
http://petertodd.org 'peter'[:-1]@petertodd.org
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQFITGdl3bMhDbI9xWQRAjPiAJ0XAHCl7MWy0NxmiSL2TPkYUwivAACfVq3g
tx+ARNxcrvke3/OpOv8Mrbw=
=YPHu
-----END PGP SIGNATURE-----

More... (looser matching)
- Last day of these posts
- In 2008 , 2009 only
- Today
- New search...