Another trick with K & L Microwave filters is to take one of their tunable
bandpass filters, put a coaxial "T" on one connector, and leave the other
connector open, or short it. Run the composite signal through the "T", and tune
the filter to "pass" the undesired signal until you notch it out.
The undesired signal passes through the filter and reflects off the open or
short. There is sufficient delay and phase shift through the filter to get a
reflection 180 degrees out of phase, canceling the undesired signal.
The notch is reasonably narrow, though I'm sure not as narrow as with their
tunable notch filters.
Don Borowski
Schweitzer Engineering Labs
Pullman, WA
"Price, Ed" <[email protected]> on 09/10/2002 07:11:51 AM
Please respond to "Price, Ed" <[email protected]>
To: "'[email protected]'" <[email protected]>,
[email protected]
cc: (bcc: Don Borowski/SEL)
Subject: RE: FCC Testing 2.45 GHz Transmitter
>-----Original Message-----
>From: [email protected] [mailto:[email protected]]
>Sent: Tuesday, September 10, 2002 6:07 AM
>To: [email protected]
>Subject: FCC Testing 2.45 GHz Transmitter
>
>
>
>Consider a 1W frequency hopping, spread spectrum transmitter
>operating at
>2.45 GHz. The FCC released a Public Notice on acceptable test methods
>(Filing and Measurement Guidelines for Frequency Hopping
>Spread Spectrum
>Systems) where they "recommend" that the spurious radiated
>emissions in the
>restricted bands are to be measured with a high pass filter. There is a
>restricted band at 2483.5-2500 MHz. Given a 1W transmitter and
>a spurious
>limit of 500 uV/m at 3 m, it would seem that I need a very
>sharp high pass
>filter or a very good notch filter to measure in that band. Is this
>feasible?
>
>It would also seem that a notch filter or low pass filter is
>required for
>measuring spurious emissions in the restricted bands below
>2.45 GHz. There
>is a restricted band at 2310-2390 MHz. Again, is a filter feasible?
>
>I am aware of semi-custom filter suppliers, but are there any
>off-the-shelf
>filters available?
>
>Richard Woods
>Sensormatic Electronics
>Tyco International
>
Rich:
I use tunable band-reject filters from K & L Microwave,
http://www.klmicrowave.com/ , for the type of measurements you are
describing. Typically, their BR filters have a 5% wide rejection notch that
is about 50 dB "deep". The mechanical tuning is sensitive and "touchy". You
still may not get a steep enough slope for your frequencies, but it's the
best I can think of. I also have a couple of custom-made HP filters from K&W
Microwave, at http://www.kwmicrowave.com/ , which I use for one of our
product lines that has a 20 watt emitter at 226 MHz.
I also keep a selection of HP, BP & LP filters, which are flatter or have a
wider passband than the K&L BR filters. Whenever I'm in my local surplus
junk store, I sort through their bins of unmarked microwave hardware. If
it's a two-terminal device and has TNC or N connectors, I'll offer them a
buck or two. Just characterize it in a 50 ohm system, and you can eventually
build up a handy library of filters.
Regards,
Ed
Ed Price
[email protected]
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
Shake-Bake-Shock - Metrology - Reliability Analysis
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