>From: "Jochen Siegenthaler" <Jochen.Siegenthaler@...> >Reply-To: LPFM_Radio@... >To: <LPFM_Radio@...> >Subject: [LPFM] RE:STUB CUT... >Date: Tue, 15 Mar 2005 10:20:35 +1300 > >Hi, > >A 'stub' is a short, stubby, piece of coax cable, which you can easily assemble yourself. > >It's basically a measured length of coax, with a short circuit or open circuit at one end, and joins to your main cable with a T connector. > >The measured length is based on the frequency of the signal you wish to remove (filter out). the length is normally a 1/4 wavelength. Because when the signal has traveled down the stub, and been reflected by the short or open cct, it has then travelled exactly ½ wavelength, and cancels itself out. > >The stub becomes a tuned filter to remove the unwanted frequency, without impacting on your normal operating frequency. > >It has no impact on your operating frequency, as normally the frequency you want to remove is 2x (2nd harmonic) or 3x (3rd harmonic) of your operating frequency - ie: so far away that the filter charteristics of the stub don't impact on your operating frequency at all. > >So if you operated on 107.5MHz, your second harmonic would be 215 MHz, which is within the ch9 TV channel. >215MHz has a wavelength of 1.39m (300 / f MHz = wavelength in m) >1/4 wavelength = 349mm (1.39m / 4) >You also have to take the velocity factor of the coax cable into account, so then multiply the length by the VF, which for RG213 is around 0.66. > >So if you used RG213 your stub would be around 349mm x 0.66 = 230mm long. > >Now that is all from memory - so someone please correct me if my memory is rusty :-) > >It is normal practive to fit stub filters - we do it on our high-power broadcast sites as an effective means of reducing harmonic products whenever necessary. > >Happy stub building :-) > >Jochen > > >>> radiopegasus@... 15/03/05 >>> > > >Please could our technical whizzes..morning Jochen...tell me what a STUB CUT ia...where do I purchase... or can it be easily assembled. >Thanks to Jochen.. Im aware of a cavity filter.. >Regards Davewihamsteve" <kiwisteve@...> > > >Reply-To: LPFM_Radio@... > >To: LPFM_Radio@... > >Subject: [LPFM] TV Interference > >Date: Mon, 14 Mar 2005 19:35:57 -0000 > > > > > >Re Interference to TV from LPFM . > >I have experienced cases where the 88 end of the band causes > >interference to CH4 VHF  and the 107 end causes interference > >to CH9 VHF . This is normally the second harmonic of the LPFM > >transmitter.  Fit a stub cut for the freq you are on from RG213 coax > >cable and N connector, > >use an N type T connector to insert it in the feeder . Or if you have > >1 or 2 cavity filters they remove a considerable amount of second > >harmonic content . normally only  those combinations of > >channels at very > >close range and in areas of poor TV reception or if the TV owner has > >a faulty antenna , feeder or mast head amplifier . > > > >SteveJ > > > > > > > > > >Find the coolest online games at XtraMSN Games > >--------------------------------------------------------- >LPFM Website: http://au.groups.yahoo.com/group/LPFM_Radio > > >Yahoo! Groups Links >To visit your group on the web, go to: >http://au.groups.yahoo.com/group/LPFM_Radio/ >   To unsubscribe from this group, send an email to: >LPFM_Radio-unsubscribe@... >   Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. > > > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >CAUTION : This email message and attachments are confidential and >may contain legally privileged information or copyright material. If you >have received this email in error, please advise the sender immediately >by return email and then delete both messages and any attachments. >If you are not the intended recipient you are notified that any use, >distribution, amendment, copying or any action taken or omitted to be >taken in reliance of this message or attachments is prohibited. We do >not accept liability in connection with computer virus, data corruption, >delay, interruption, unauthorised access or unauthorised amendment. >Views expressed in this email may not be those of originating organisation >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ><<<< GWAVASIG >>>>