Filtering Out Alien Signals

This is the actual response of  1 of 2 Systems installed at WCAU-TV,
Philadelphia PA.   LNA Gain is 11.72 db, and the 
other markers are referenced to this level.
WORST CASE PCS is -63.16 db,
sharply increasing to beyond 140 db.

One little known fact you should know about cavity filters

There are two basic ways to filter out unwanted signals that are not on your frequency:

Use an external bandpass filter ahead of the receiver to:

1. Eliminate interference from signals 2 or more channels away
2. Eliminate signals 2 channels under your channel in single conversion receivers with 70 Mhz I.F.s
3. Reduce, but not totally eliminate adjacent channel interference higher than -40 dbm. (Place the filter ahead of the LNA, if used, for any signal greater than -40 dbm at the antenna)
4. Group Delay increases with narrow bandpass filters. A narrow filter can eliminate unwanted signals, but increase the bit-error-rate in a Digital System! 
   Call us for questions and special filters for Digital Systems:  1-888-828-8775

"Master Control says we're getting some phone conversations. Someone gotta PCS phone on??"

Surface Acoustical Wave (SAW) Filters that go inside the IF Amplifier of your receiver

Use our internal SAW filter in the I.F. stage to:

1. Get rid of adjacent channels. If the adjacent channel signal exceeds -40 dbm, an external bandpass filter should also be used. If it exceeds -30 dbm, the bandpass filter is a must, and has to be placed ahead of the LNA, if used)

Oops! One of those "masts" is really a PCS tower!

Think of bandpass filters as a hill.  Think of a Surface Acoustical Wave filter as a cliff. The skirts of an LC or cavity bandpass filter become steeper as the number of sections is increased (and the Group Delay at the band edges also increases).  Typically, the first and last stages of a filter are used for matching, and the remaining section(s) do the brunt of the filtering. The skirts fall off at about 6 db per octave per section. This means that if you have a 1 section filter that is 100 Mhz wide, if you go an octave (100 Mhz) away from the bandpass, the signal drops 6 db. if you have a 4 section filter, it drops 24 db, et.

A SAW filter is good for an additional 60 db selectivity (reduction of signal) on adjacent channels! The average receiver with an LC filter in the I.F., reduces adjacent channels typically 6-15 db. We cut our filters slightly higher than your highest audio subcarrier, so nothing is lost, and it never has to be retuned.

We do have some "off the shelf filters", but some filters are custom made according to your needs. This will save you both money and worry. We guarantee that the product we deliver will do the job. Think of us as your first and only choice when the equipment you order is a reflection of you.

When you can't afford to guess, need something that has to work the first time, will still be working after an electrical storm, and give many years of trouble-free service, WE ARE THE ONLY GAME IN TOWN, BECAUSE WE SET THE STANDARDS THAT OTHERS TRY TO IMITATE!

We are broadcast people who have worked at stations, not 9 to 5 weekday engineers, designing "cost effective" equipment. LLoyd personally has worked at tv stations as far back as 1975. He has also worked with Motorola in Communications, Antenna Design, Special Products, and Technical Operations. We speak your language.

Call LLoyd at: 1-888-828-8775, or Email with your request.

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