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From: Joerg on 1 Apr 2010 19:19
Wimpie wrote:
> On 1 abr, 19:15, Joerg <inva...(a)invalid.invalid> wrote:
>> Wimpie wrote:

[...]

>>> I give some courses on antennas. Many people don�t have a spectrum
>>> analyzer or measuring receiver, so in that case I do the practical
>>> exercises with a diode detector that they can build themselves for
>>> just some Euros. Of course I discuss the quadratic to linear output
>>> transition also. Up to some GHz a return loss bridge can also be build
>>> with SM devices (with more then reasonable directivity).
>>> I like to show "old methods" to show that you can also do good
>>> measurements with primitive means.
>> Good man. I wish they'd do the same at universities. I remember coming
>> to a client with my laptop and some kludgy homebrew wideband probes.
>> Boss wasn't in yet but I got started. By the time he came out of a
>> production meeting I had the EMI problem unearthed. "We rented an
>> Agilent analyzer for you, top of the line, it's in my office" ... "Ahm,
>> I don't think we'll need it anymore, found the problem with this
>> detector jig here". He was almost in tears because it must have cost
>> them almost $1000 for a week's rental.
>>
>
> Hello Joerg,
>
> Painfull for your Boss.
>
> Such situations sound very familiar to me. Sometimes they don�t
> believe an opinion or don't take you seriously when you don't show an
> (expensive) Agilent or Rohde & Schwarz cabinet with many push buttons.
> It doesn't matter what it is, it just has to look impressive....
>

It was a client so he was my boss only for one day :-)

With some clients the faith in expensive name-brand lab equipment has
been shaken. For example at one where I waltzed in armed with a laptop
and a piece of wire with a 3.5mm phono jack. We used one of their safety
transformers for audio line isolation and via the sound card found a
noise peak that a $10k Stanfrod Research analyzer was unable to see. At
first they wanted to discourage me. "But we've already looked with a
high-end audio analyzer". After unexpectedly seeing the peak on my
laptop screen some expletives slipped out ...

Finding the source of it was then only a matter of minutes.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Joel Koltner on 1 Apr 2010 20:15
"Joerg" <invalid(a)invalid.invalid> wrote in message
news:81knvhFqbuU1(a)mid.individual.net...
> We used one of their safety transformers for audio line isolation and via
> the sound card found a noise peak that a $10k Stanfrod Research analyzer was
> unable to see. At first they wanted to discourage me. "But we've already
> looked with a high-end audio analyzer". After unexpectedly seeing the peak
> on my laptop screen some expletives slipped out ...

So let's see... I can go into business selling $10k test equipment with so-so
performance or become a consultant and have to be successful using $10
improvised sensors and a laptop.

I know which business I'm going into!

:-)


From: Joerg on 1 Apr 2010 21:48
Joel Koltner wrote:
> "Joerg" <invalid(a)invalid.invalid> wrote in message
> news:81knvhFqbuU1(a)mid.individual.net...
>> We used one of their safety transformers for audio line isolation and
>> via the sound card found a noise peak that a $10k Stanfrod Research
>> analyzer was unable to see. At first they wanted to discourage me.
>> "But we've already looked with a high-end audio analyzer". After
>> unexpectedly seeing the peak on my laptop screen some expletives
>> slipped out ...
>
> So let's see... I can go into business selling $10k test equipment with
> so-so performance or become a consultant and have to be successful using
> $10 improvised sensors and a laptop.
>
> I know which business I'm going into!
>
> :-)
>

Correction: It was a snipped off cable with molded phono jack on there,
salvaged from an old stereo tower. So it was $0 :-)

Ok, the laptop is a ruggedized one, not so cheap.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Benj on 2 Apr 2010 00:50
On Mar 30, 1:11 pm, n...(a)puntnl.niks (Nico Coesel) wrote:
> Every now and then you find something new on your path...
>
> I'm working on a wireless device which is going to use a PCB trace as
> an antenna. The bitrate is quite high (approx 250kbit) and we decided
> to use the 433MHz band because it has little restrictions. The main
> problem is the antenna. I managed to put a  115mm (4530 mil) long
> trace (1/4 labda monopole) onto the 50mmx80mm (2" x 3.15") board to
> form an L shaped antenna. Its fed from a 50 Ohm transmission line
> which runs over a reasonable big ground plane (top and bottom stitched
> ). So far I was able to gather some info from applications notes and
> so on.

Whimpie is giving you the best advice here. If it were me since you
are feeding the antenna with what sounds like a tri-plate line, I'd
actually build an SWR detector right into the drive line! YOU can use
that to measure SWR and that lets you trim antenna length for minimum
SWR. As Whimpie notes, depending upon what is on the board, proximity
of ground planes etc. Impedance may be quite low. So some kind of
matching is needed. Also some tuning of the end of the antenna may be
needed to get some efficiency. In short because of the nature of the
geometry there is going to be a considerable amount of trial and error
here to get this to work best. While at these frequencies it's likely
you'll get something that "sort of" works regardless, I'd recommend
getting help from someone experienced in antenna design at these
frequencies.

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