[Amps] low pass filter fail

[peter chadwick]

Can you get 43 + 10log P dB attenuation (not exceeding 70dB) for each harmonic up to the 10th using stubs? (as required by ERC/REC 74-01)


vy 73


Peter G3RZP

========================================
 Message Received: Apr 29 2014, 11:14 AM
 From: "Ian White" <gm3sek at ifwtech.co.uk>
 To: "'Jim Thomson'" <jim.thom at telus.net>, amps at contesting.com, "'Benedikt Sveinsson'" <benedikt at ok.is>
 Cc: 
 Subject: Re: [Amps] low pass filter fail
 
 >
 >##  Do you really require a LP filter ?  
 
 Nope - you should only need to attenuate the harmonics of the driver
 signal, so a harmonic notch filter should be fine. (Any non-harmonically
 related spurious signals must be coming from the driver, and should be
 removed before the reach the PA.)
 
 >You could also use a .25 wave long
 >coax stub..with far end shorted.   You can also add additional stubs
 etc.
 >Paralleling caps is the real answer to your exploding cap problem.  2-4
 caps
 >in parallel  would be the ideal ticket.   Your typ 2m ant will only be
 resonant
 >on
 >its 3 and 5th harmonic.   You can make stubs that will kill odd
 harmonics if I
 >remember correctly. W2VJN has a good book on stubs.
 >
 
 A ready-made design is right here:
 <http://www.ifwtech.co.uk/g3sek/swxfiltr/swxfiltr.htm#2.>
 
 Trim the stubs to length in the usual way, and stretch/squeeze the
 inductor for minimum VSWR. The 5f stub causes a slight increases the
 minimum VSWR, but you probably do need that notch at 720MHz. A version
 made with RG142/RG400 ("Teflon RG58") handled 1.2kW with no problems. 
 
 
 73 from Ian GM3SEK
 
 
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