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@ifwtech.co.uk>
To: "'Jim Thomson'" <jim.thom@telus.net>, amps@contesting.com, "'Benedikt
Sveinsson'" <benedikt@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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|