Wideband antennae for Spec Analyzer

[Jim Jeffery]

I have just purchased a secondhand Advantest 3465, 100KHz to 8MHz
spectrum analyzer.

Well, that was expensive, so I can't really afford any factory-made
antennae at this time.

Can anyone please advise how I can make a wideband antenna, or limited
series of same, that will work within this range for monitoring of
environmental EMI?

Hopefully, a little more than just hanging a wire off the input. The
relevant specs are below.

**********

Measurement range: +30 dBm to avg. display noise level
Maximum safe input:
Avg. continuous power (input ATT = 10 dB): +30 dBm (1 W)
DC input: 0 V
Display range: 10 × 10 div
Log ;10, 5, 2, 1, 0.5/div
Linear; 10% of reference range/div
Reference level range:
Log; –105 dBm to +60 dBm (0.1 dB steps)
Linear; 1.25 µV to 223 V (approx. 1% of full–scale steps)
Input attenuator range: 0 to 70 dB (10 dB steps)

**********

Many thanks,

Jim Jeffery

 

[Martin Riddle]

I have just purchased a secondhand Advantest 3465, 100KHz to 8MHz
spectrum analyzer.

Well, that was expensive, so I can't really afford any factory-made
antennae at this time.

Can anyone please advise how I can make a wideband antenna, or limited
series of same, that will work within this range for monitoring of
environmental EMI?

Hopefully, a little more than just hanging a wire off the input. The
relevant specs are below.

**********

Measurement range: +30 dBm to avg. display noise level
Maximum safe input:
Avg. continuous power (input ATT = 10 dB): +30 dBm (1 W)
DC input: 0 V
Display range: 10 × 10 div
Log ;10, 5, 2, 1, 0.5/div
Linear; 10% of reference range/div
Reference level range:
Log; –105 dBm to +60 dBm (0.1 dB steps)
Linear; 1.25 µV to 223 V (approx. 1% of full–scale steps)
Input attenuator range: 0 to 70 dB (10 dB steps)

**********

Many thanks,

Jim Jeffery

I think you meant 8Ghz.

These spectran antennas look good.
<http://www.spectran.com/EMC_Test_Antenna.shtml#1>
The problem is you need a calibrated/flat response from the antenna.
I would rent, as Jim pointed out.


Cheers

 

[Jim Jeffery]

These spectran antennas look good.
<http://www.spectran.com/EMC_Test_Antenna.shtml#1>
The problem is you need a calibrated/flat response from the antenna.
I would rent, as Jim pointed out.

Here they show the internal configuration.

http://www.spectran.com/HyperLOG7000_en.shtml

Would this really be that difficult to approximate using some soldered
brass rod?

Jim Jeffery

 

[[email protected]]

I have just purchased a secondhand Advantest 3465, 100KHz to 8MHz
spectrum analyzer.
Really?

Well, that was expensive, so I can't really afford any factory-made
antennae at this time.

Can anyone please advise how I can make a wideband antenna, or limited
series of same, that will work within this range for monitoring of
environmental EMI?

Antennas are easy. Calibrating them is not. You're going to need more than
one for this range (assuming you meant 8GHz), though.

 

[Jim Jeffery]

A log-periodic antenna is your best bet. They are relatively easy to
make. Refer to these web pages for design info:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=21876
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=16289

Great links. How about some less rigous methods for those who may not
need calibration or directionality?

1. A number of concentric circles glued on a piece of perspex. Each
would have a gap so as not to be complete, and be oriented at 180
degress from the next one. Feed would be from one end of each, and
wired in series.

2. An array of a few dozen pieces of brass welding rod (different
lengths) with one end of each soldered to a copper base plate. Or
telescoping antennae if they need to be adjustable.

Worth a try or too simplistic?

Jim Jeffery

 

[Rich Grise]

OK, then the revised answer is to make a shielded loop to go up to 30
MHz. then a series of log-periodics from 30-100, 100-1000, and
1000-10G.

You *COULD* do 30-10G in one fell swoop, but the mechanicals get real
hairy.

There are "fractal" antennas, but the only thing I know about them is
that they're fractal.

Good Luck!
Rich

 

[Jim Jeffery]

Another option, somewhat similar to (2), is a biconical antenna...
http://en.wikipedia.org/wiki/Biconical_antenna has one description.

Can anyone elaborate upon the properties of this one ... tin foil
"butterfly" antenna.

http://en.wikipedia.org/wiki/File:2...ltra-low-cost_dvb-t_schmetterlingsantenne.jpg

If it is meant to be broadband, how are the attached LC components
determined?

Thanks,

Jim Jeffery

 

[axolotl]

I have just purchased a secondhand Advantest 3465, 100KHz to 8MHz
spectrum analyzer.

Well, that was expensive, so I can't really afford any factory-made
antennae at this time.

Can anyone please advise how I can make a wideband antenna, or limited
series of same, that will work within this range for monitoring of
environmental EMI?

You might want to look at Wilmar Robert's measurement antennas.

http://glendash.com/Archives/Roberts - FCC Antennas.pdf

Kevin Gallimore