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33cm filter

You can click any thumbnail on this page for an enlarged picture

comb.jpg (46353 bytes)I needed a good 900 MHz filter for a clean signal source I was building for antenna testing. My source generates a comb with a tooth every 100 MHz, requiring some selectivity before amplifying to a useable power level.

 

goodsig.jpg (34689 bytes)This is the same spectral display after filtering. About 1db insertion loss.

 

 

noise.jpg (30937 bytes)

Reducing the input attenuation to examine the noise floor, there is at least 50db suppression of the unwanted signals.

 

Construction is similar to the other filters for 23 and 13cm. I used a Hammond 1590BB die-cast aluminum box (119 x 93 x 34 mm), 3" aluminum spacers cut from 1/4" rod stock, #6 and #8 hardware, and SMA connectors. The braid you see in the second picture was used as an RF gasket for the lid, to eliminate squirrelly behavior from the poor contact it makes without it. I made it from the shield removed from RG-174.

900-flxdone.jpg (99493 bytes)900-flxparts.jpg (101991 bytes)900-flxinside.jpg (408113 bytes)900-tune1.jpg (67556 bytes)900-tune2.jpg (56431 bytes)