Universal spectrum analyzer antenna

This stuff looks interesting:

We're probably going to buy one to do first-cut EMI testing. We'll have to get out of the city and do free-field stuff out in the boonies... the local EMI fields are insane.

John

Sure. A few inches of wire :-)

Depends what you mean by "non-linear". If you mean that the sensitivity and directionality are going to vary with frequency, then yes, they will.

If you just want to pick up _something_ at all frequencies, and don't care very much about sensitivity and pattern variations, and are working mostly with strong signals, then almost anything will do... a random wire will probably work well enough.

If you have more stringent requirements, then you'll have to say what they are.

Several relatively-broadband types of antennas which might be applicable, could include a bowtie dipole, a conical monopole over a ground plane, a discone, a random long-wire or V or rhombic, a conical spiral, or an end-fire helix.

My old HP spectrum analyzer can see all sort of stuff, with a simple whip or rubber duck antenna stuck into its BNC port.

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"Mark Condon"

** You asking about EMC testing or something else ??

Questions with NO context are impossible to answer.

** Broadband receiving antennas never have " flat " gain - but this rarely matters.

The average combined VHF-UHF TV antenna covers the range from 50 to 700MHz with fairly similar gain at all frequencies - the UHF end may well have more gain and hence more directivity too.

** From 500kHz to 3GHz - quite a few.

Now, if you are only interested in EMC testing - it's a different ball game.

.... Phil

You're sure you're not just looking to take your cabin as a business expense? :-)

Just kidding...

"John Larkin"

** Hey, that is pretty funny you know:

" Sorry Mr FCC inspector - we could not conduct satisfactory EMC tests for our new product cos there is just far too much damn ** INTERFERENCE ** round here !! "

... Phil

The closest you''ll come to is a discone antenna, they have astoundingly broad bandwidths but at the cost of low gain & no directionality. Even at that you won't find one that covers more than half the range you're looking for.

H.

No, but I could sure do EMI testing there. There's a cell site on Alder Hill nearby, but a few spectral lines are managable. Just switch the DUT on and off to tell which is which.

I'm paying AMT, so most deductions, things like mortgage interest, don't help.

John

In the US, most FCC compliance testing is done open-field, so the test sites tend to be in rural areas. And, unlike CE testing, people usually don't self-certify. If we get an antenna, we'd just use it for first-cut testing, to see if we're in the ballpark. We'd still go to a certified cal lab for the official tests.

John

"John Larkin = f****it"

** The boy is about as sharp as a bowling ball.

Yawnnnnnnnnnnnnnnn....

.... Phil

We do all our testing at a lab with a 10M chamber. That part of compliance testing is relatively cheap. Where we spend the money is in AC line and communications interface tests. They take forever and the meter keeps running.

A sniffer is probably more useful than a calibrated antenna.

Anyone say "bi-conic"?

Without wishing to appear rude, your query suggests that your experience is not in keeping with normal users of spectrum analysers.

I suggest that you should start off by shoving a couple of feet of hook-up wire into the input socket and see how you get on.

Yes, as you suggest, this will be "non-linear" over the range. I put that in quotes because "non-linear" had another meaning which does not apply here.

"Operating over 150 MHz to 6 GHz, fractal antennas deliver excellent omnidirectional coverage in a compact form factor."

Their price points are a tad steep but the information on how to roll your own is out there.

Mark L. Fergerson

On a sunny day (Thu, 25 Feb 2010 13:48:27 +1100) it happened "Phil Allison" wrote in :

That has always been so, I had a big organisation send somebody to do acceptance test on some power supply system I designed. It was tested with big wirewound load resistors. The guy complained about modulated RF on the output. Disconnecting my stuff showed the wirewounds were tuned to the local AM station, and the modulation was still there: Music.

A possible lower-cost alternative:

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EMI test labs use spectrum analyzers and antennas!

EMI antennas usually come with a calibration graph so you can convert the spectrum analyzer's dBm numbers into field strength. A couple of feet of hookup wire won't be quite so accurate.

John

I doubt it. It's been over a decade since I had a pre-compliance lab, but I needed at least two antennas and a third would be needed to get all the way down to AM. I was only interested in something like 50MHz to 6GHz.

Yagis are reasonably flat across their range, but it really doesn't matter. Compliance antennas are calibrated (that's what you're paying the big bux for).

Depends on what you mean by "broadcast frequency range". You could try looking at a supplier's catalog (Agilent or Tek) to see what's offered. Here's one antenna that's calibrated from 26MHz to 2GHz: