From: Donald McElheran [mailto:[email protected]]
Sent: Monday, January 05, 2004 6:57 AM
To: [email protected]
Subject: Extending Pre- complince test set to 2GHZ.
Group:
I am currently face with extending my pre-compliance RF emissions test system
>from a 1GHz upper limit to 2 GHZ to address FCC requirements for clock speeds
beyond 100Mhz.
My existing system consists of two antennas a bicon for the lower 30 to 300
MHz band and a Log periodic rated for the 200 to the 1Ghz band.
I have review some options to specifically address the 1 to 2 GHz but it
appears to me that because of the limited dynamic range and cost involved it
may be wise to considering replacing both these existing antennas with a broad
band combi-antenna which could address the additional bandwidth requirements
and eliminate the need for multiple antenna.
I suspect that with the increasing trend to high and higher processor clock
speed I am not unique in this regard.
Could any one else who has had to address this issue share their experience?
Donald McElheran
Ross Video Ltd.
Don:
I suspect that your comment about "limited dynamic range" refers to the log
periodic antenna's relatively high antenna factor. When combined with your
analyzer's internal noise, this limits how "low" of a signal you can see.
Sometimes, this threshold is uncomfortably close to the specification limit.
Although I have a log periodic that covers the 300 MHz to 1 GHz range, I
rarely use it due to it's high antenna factors. Instead, I use a large horn
antenna, an Antenna Research Associates DRG-2020A. It actually allows me to
switch from my biconical at 200 MHz (where the biconical antenna factor is
starting to rapidly climb), and will let me continue to 2 GHz. OTOH, I switch
to another horn antenna, an EMCO 3115, at 1 GHz, since the 3115's antenna
factor between 1 GHz and 2 GHz is lower than the DRG-2020A's. The EMCO 3115
can be used all the way up to 18 GHz, and is a very good choice for the 1 GHz
to 5 GHz range.
These antennas may be driven with a couple of hundred watts of RF power,
should you want to do your own immunity testing at some point. Also, horns
have better rejection of off-axis signals than log periodics, so you might
have less problems with site reflections.
Ed
Ed Price
[email protected] WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
